Title of Invention

PREPARATION OF METAL-CERAMIC FRICTION COMPOSITES

Abstract

A process for preparation of metal-ceramic friction composites is disclosed which involves a pressure sintering method to sinter and bond the friction material to a steel backing frame to form a friction composite for use in high kinetic energy frictional engagements. The friction composites are in two types of compositions, copper and iron base; with two types of steel backing frames, cup type and flat plate type. A two step process involving loose sintering of the friction material followed by pressure sintering is used for copper base composites with cup type frame. A process involving a multi-layer compaction of the friction composite followed by pressure sintering of composite-backing frame assemblies involving simultaneous heating and pressure application by "pulling" action is used for iron base composites with a flat type frame. The friction composites possess good resistance to thermal gradients, stability of frictional properties and high wear life in service.

Full Text

The present invention relates to new process for the preparation of novel sintered metal-ceramic friction materials. The invention further discloses process for the use of these materials in applications involving frictional engagements that result in dissipation of high kinetic energies and also produce high temperatures and thermal gradients. Metal-ceramic friction material composites exhibiting (i) strong and thermally stable metallurgical bond between the friction materials and the supporting back plate, (ii) reduction in noise and judder during high energy frictional engagements in service and (ill) demonstrating high wear - life. The effort is to achieve structures in the resultant friction material that have structural stability, cracking and chipping resistance in the face of steep thermal gradients and loads imposed during service and in particular when subjected to continuous high kinetic energy dissipation applications. The copper and iron based friction material composites are intended for use in applications such as brake pads or liners in brakes of aircraft, high speed trains and heavy commercial vehicles(HCV). The applications of these friction composites also include transmission of high speed / torque in gear boxes and transmission clutch units of HCVs, ships, helicopters and battle tanks. Prior Art Various investigators in the past have attempted to achieve materials and processes to for frictional engagements and applications. A brief review will illustrate earlier attempts. U S Patent No. 3,946,192 describes a process of electrical resistance sintering and braze bonding of a number of small copper base metallic friction material elements on to a steel backing plate pre coated with brazing metal/alloys of copper/tin/nickel using two opposed electrodes and passage of electric cuaent for a short duration. This process could involve at least three heating/pressing steps instead of a much-desired single pressure sintering process. The brazed bonds done by resistance brazing for a short duration as described in this cannot withstand arduous service conditions of very high torque loads and thermal gradients in high-energy frictional situations such as aircraft braking. The patent does not address the case of feasibility of this process of bonding for larger friction material elements and when low thermal conductivity friction material composites of iron base, possessing a large volume fraction of ceramics, are to be bonded. The patent also does not address the issues of friction and wear rate of the friction m.aterial disc and the finer issues such as the structural /thermal stability of the friction material and ability for noise/judder damping which are critical in most applications. ^ U.S. Patent Nos. 3.528,807 and 3,761,256 also deal with brazing bonds where a material is located between a preformed friction material and the bottom of a retainer cup. Although the braze bond can work well in a cup type of design, the cost of the brazing material is high and furthermore this process is again limited to copper base friction materials in a cup type design. US Patent No. 4,050,620 describes a method of making a brake friction pad which includes the steps of placing a copper base sintered friction material into a retainer cup, heating the friction material and the retainer cup to a temperature of 1400 to 1650^ in an inert atmosphere, and striking the friction material with a single blow of a compressive force between 7000 and 20,000 psi force. This single blow is claimed to increase the density of the friction material and establish a metallurgical bond between the friction material arid the retainer cup. This patent is limited to bonding in copper based cup type friction material elements and does not address bonding in iron base friction materials and flat plate type of configurations. A typical mechanical bond of copper based friction material in retaining cup is disclosed in U.S. Patent No. 2,784,105 where the sintered friction material is held in a retainer cup by crimping the sides of the cup against the friction material. Although the bonding on the sidewalls is good, the friction material with the cup bottom is not sufficiently strong and is mostly limited to welded screen. The integrity of the friction material with the bottom of the cup depends on the strength of the spot welds with the cup bottom. The U.S. Patent No. 4,311,524 uses copper, tin, zinc sulphide, pyroceramic, graphite and lead etc. mixed in iron powder, formed by pressure under 294 MPa, then sintered at 1030.degree. C. for three hours under protected atmosphere of 1.96 Mpa. It describes the above composition and the powder metallurgy process of preparation for a specific application condition of operation under liquid lubrication and moderate frictional performance modes. The patent claims a superior wear resistance of the resulting friction material under liquid lubrication conditions but does not indicate the wear performance of the material under dry operating conditions. Moreover, the patent is only limited only to a specific composition of an iron base friction material and does not cover other compositional ranges and copper base materials. The issues related to the nature of bonding and noise damping are also not investigated. U S Patent No. 4,415,363 also describes the formulation and preparation of a sintered iron base friction material. It discloses a specific formulation with iron-tin alloy as the matrix and equal portion mix of graphite - coke incorporated to impart a constant wear upto 300° C and a predictable linear wear between 300 and 500° C. The patent is specific in nature as it describes only an iron base friction material and also does not address the issue of use of a back plate and it"s bonding with the friction material. U S Patent No. 4,456,578 relates to the method and apparatus for producing a friction element for a disc brake. This patent also describes a method of electrical resistance sintering and bonding of essentially a number of copper based friction materials to an electrically conducting back plate. The method applies specifically to disc brakes used in motorcycles and cars and does not address the problems related to continuous high kinetic energy dissipation applications. U.S. Patent No. 4,871,394 uses copper powder mixed with silicon dioxide (or alumina), graphite, lead, tin and zinc, pressed to form green bodies of density 2.9.about.3.1 g/cm.sup.3, with a core plate pinched by two green bodies, and sintered for 1 hour at 650.degree. C. under 0.52 MPa protected in non-oxidizing atmosphere. This patent also is limited to a specific copper base composition suitable for operation only under oil lubrication. The aspects of bond strength and wear resistance have not been addressed. U S Patent No. 5,5&5,266 describes bonding a friction material brake lining element to a metallic backing plate element. This patent deals with organic resin bonded friction materials and does not address the issues of metal-ceramic sintered friction materials. US patent no. 6,139,673 also deals with bonding of an organic resin based friction material with a metallic back plate. U S Patent No. 5,824,923 covers frictional and physical properties of composite copper alloy powder sintered friction material and therefore is limited in scope as it does not include iron base materials and also does not qualify the aspects of bonding of the friction material to a backing plate. U S Patent No. 5,925,837 covers manufacturing method and products of metallic friction materials and includes processes of (i) preparing powder materials, (ii) mixing copper as a base, proper proportion of iron powder or steel wool, aluminum powder, zinc or tin or lead powder, graphite powder and alumina or silicon dioxide powder, (iii) pressing mixed materials into green bodies under 375 to 625 MPa at room temperature, (iv) pre-heat treating the green bodies in an air furnace with temperature raised to 100 to SOO.degree. C. for 1 to 3 hours, (v) sintering the green bodies into test samples under 350 to 750 MPa for 24 to 60 hours to gain sintered friction materials having an oxidized layer of less than 1 mm thick, (vi) processing and grinding the sintered test samples with grinders to remove the oxidized layer, (vii) washing the outer surface of the sintered test samples ground into finished products. Products according to the invention has friction coefficient within the standard value, low wear loss and good heat stability. This patent does not address the issues of a strong, thermally stable inferfacial bonding with a backing plate and material integrity at elevated service temperatures. Further it is limited to essentially copper based friction materials. U S Patent No. 6,004,370A sintered friction material especially suitable for use in a braking system has a matrix of a copper-system metal such as copper, tin, nickel and aluminum, and contains a specific additive, graphite and potassium titanate as friction conditioners. The specific additive consists of at least one material selected from a group consisting of zirconium oxide, silica, dolomite, orthoclase and magnesium oxide. The specific additive, the graphite and the potassium titanate are preferably blended in volume ratios of 1 to 15%, 10 to 50% and 5 to 30% respectively. The fonri of the potassium titanate is at least one of whiskery, platy and spherical forms and preferably plate-like or spherical. The sintered friction material has good abrasion resistance, low abrasion of the counterpart, a high friction coefficient, excellent material strength, good chattering resistance, and good squealing resistance. Although this patent addresses the problem of judder reduction and material integrity, is limited to sintered copper based friction materials and does not cover the aspects of bonding with a backing plate or cup. U S Patent No. 6,143,051 describes a friction material comprising a sintered mass of iron in which graphite particles are dispersed, which sintered mass is formed from between 13 and 22 vol. % of iron fibers, between 13 and 22 vol. % of iron particles having a particle size of 10-400 ^.m, between 40 and 70 vol. % of graphite particles having a particle size of 25-3000 jam, and between 10 and 15 vol. % of a metallic binder having a melting point of 800-1140.degree. C, and a method of preparing such a friction / material, wherein a mixture of these components is compressed at a pressure of at least 100 MPa so as to form a compact having a desired form and size, and where the compact thus formed is sintered at a temperature between 800 and 1140.degree. C. for a period of time which is sufficiently long for achieving concretion of iron fibers, iron particles and metallic binder. This patent describes development of a specific iron based friction material with good a thermal material integrity. However interfacial bonding of the material with a back plate is not attempted. Summary of the Invention The invention disclosed here is related to novel process of manufacture of metal-ceramic friction materials involving copper / iron base metal-ceramic friction composites applicable to cup type and flat plate type designs and intended for a variety of applications. These applications include frictional engagements that result in dis"sipation of high kinetic energies and also produce high temperatures and thennal gradients. It also discloses a range of formulations appropriate for this process. This invention overcomes the limitations and drawbacks of earlier work done through successful development of process for the preparation and compounding of sintered metal-ceramic friction material composites that result in good, strong and thermally stable metallurgical bond between the friction material and the supporting back plate, reduction in noise and judder during high energy frictional engagements in service, achievement of a high wear - life of the resultant friction material when subjected to continuous high kinetic energy dissipation applications. It further achieves a metallurgical structure in the resultant friction material that demonstrates a superior structural stability, cracking and chipping resistance in the face of steep thermal gradients and loads imposed during service. The main object of this invention is to provide process for manufacture of sintered metal-ceramic friction composites that ensures a good interfacial metallurgical bonding between composite friction material and supporting backing member that withstands severe thermal and torque loads which obviates the drawbacks of eariier inventions as detailed in the prior art. Another object of the present invention is to provide process for manufacture of sintered metal-ceramic fridion composites with thermal integrity to achieve reduction or elimination of material breakaway and chipping due to thermal abuse during service. Yet another object of the present invention is to provide process of manufacture of friction composites for improved frictional service wear life Still another object of the present Invention is to provide formulations for sintered metal-ceramic friction material composites with features that reduce excessive noise and judder during bral Thus according to the process of this invention the manufacture of sintered metal-ceramic friction material composites broadly comprise of the following steps : (i) Selection of the appropriate materials in their particle size ranges. (ii) Dry and wet mixing of metal and ceramic powders (ill) Shearing/forming of alloy steel back plate or cup (iv) Spot welding of thin perforated metallic mesh/grid on to bottom of cup in cup design (v) Nickel/copper plating/coating on the back plate /cup (vi) Diffusion treatment of the coated layer, if necessary (vii) Loose or bulk jDre-sintering of metal-ceramic mix into coated cups (in case of copper based compositions using cup type backing), (viii) Single or multi layer compaction of the metal-ceramic friction material mix with or without adhesive / cushioning layers or compaction of cup-composite loose sintered units (for copper based composites with cup type design) (ix) Pressure sintering of the assembled compact and coated back plate using a variable load hydraulic "pull type" hydrogen atmosphere pressure sintering process or pressure sintering using a static dead weight ( for copper base composites with cup type design) (x) Post sintering heat treatment, coining /sizing and finishing One of the embodiments of the invention the supporting back plate is flat segmental plate type or circular annular disc type or cup type. In another embodiment of the Invention loose sintering/bulk sintering of friction composite powder mix contained in copper coated backing cup is a process step prior to compaction for copper base friction materials in a cup type design to enhance bonding. In yet another embodiment of the invention Hydrogen atmosphere pressure sintering using variable hydraulic "pull type" loading and static dead weight type loading is employed. in another embodiment of the invention a rapid suiphamate nickel-plating process is introduced for building up thick stress free nickel coating on steel upto 0.15 mm thickness possessing good adhesion power. Detailed description of the Invention The process details are as follows: (A) Preparation of iron or copper base friction material mix (i) Mixing of metallic powders such as iron, copper, tin, lead, zinc, antimony, molybdenum, nickel, silicon, ferroalloys etc., of specified particle size ranges in-dry state in a roller type pot mill for 1-6 hrs (ii) Wet mixing of ceramic ingredients (i.e., friction additives/friction stabilisers) such as Silicon Carbide/Nitride, Silica, Aluminosilicates, Barium/Calcium Sulphate etc in alcohol medium in a pasty consistency for 1-4 hrs followed by drying at 60 -100 °C. (iii) Mixing of metallic mix and dried ceramic mix in a blender for 1-4 hours followed by adding of solid lubricants/friction modifiers/ anti-seizure additives such as natural /synthetic graphite. Ferrous Sulphide, H-Boron Nitride, steel wool fibres etc., and further mixing for 2-8 hours The final metal-ceramic friction composite mix composition is as follows : metallic ingredients : 45- 70% by weight ceramic ingredients : 10-30 % by weight solid lubricants/modifiers : 10-30% by weight (B) Preparation of the alloy steel back plate/cup/contalner Two types of alloy steel for backing plates are used in the manufacture of copper and iron base friction materials, v.i.z.. (a-Type) low to medium plain carbon steel back plates with a hardness of 170 HV maximum to aid forming into cups, forming embossments and other shaped projections and (b-Type) medium carbon HSLA steel back plates with a final hardness up to 550 HV with high hardenability and thermal curling resistance and used as backing for high -energy-high temperature friction material compositions. Processing of "a" type back plates involves the following steps • Receiving the raw materials as continuous strip coils in cold rolled and bright annealed condition (thickness from 1.0 to 2.5 mm) • Blanking and piercing to segmental shape with a central hole • Cup drawing, multiple embossment fonning, shaped rivet seat forming • Degreasing, cleaning and blasting with fine sand to make active surface/ increase surface area OR Spot welding of perforated metal blank/mesh/grid on bottom of cup in cup design for copper based composites ^ • Nickel or copper plating/coating from cyanide/acid/sulphamate bath to a thickness of 10 - 30 microns • Diffusion treatment in hydrogen atmosphere furnace at 800-850 °C for 1-3 hours (applicable only to nickel plating/coating) • Ductility and adhesion test of plating by bend test of the nickel/copper coated back plate/cup by 90 ° minimum Processino of "b" type back plates • Receiving raw material as straight strip lengths or plates in hot rolled and spheroidise annealed condition (thickness from 2.0 to 5.0 mm) • Blanking and piercing to segmental shape with multiple, precise rivet holes or machining to back plates /discs • Acid pickling and blasting with cast iron grits to make surface active/ increase surface roughness /area • Nickel-plating from sulphamate bath to a thickness of 60 to 150 microns. Cyanide copper plating of 20 -35 microns on annular discs • Diffusion treatment in hydrogen atmosphere furnace at 900-950 °C for 2-3 hours • Adhesion test of plating by metallography of the nickel/copper coated back plate or by abrasion tests/peel tests (C) Loose sintering of copper based friction composites involving cup shaped backing container In case of copper base friction composites, particularly of higher final thickness, an additional sintering step is carried out prior to compaction on loose mass of friction powder mix contained in the copper plated and spot welded formed cup-mesh assembly. A measured quantity of mix from step (A) is poured Into the backing cup. Since the volume of loose powder will be quite high the vertical cup wall is extended all round by wrapping it with a stainless steel sheet welded canister. Several such assemblies are arranged in Inconnel / Nimonic alloy boats and loose sintering of the powder mix in the cups is carried out in a hydrogen atmosphere continuous type of furnace at a temperature between 700 to 900 "C for 1-3 hours. The reusable canisters are then stripped off the loose sintered cup-assemblies and these are then subjected to compaction in the next operation. (D) Preparation of single or multi layer friction material compacts {]) For iron base fiiction cx>mposites: • Cold die compaction of the friction material element comprising of one or more layers, such as adhesive/cushion layer (0.5 to 2.0mm thick) of pure sponge iron powder and friction material layer (2.0 - 5.0 mm thick) of iron base friction material mix prepared as per para A above • Compaction is carried out in a die using a hydraulic press at pressures from 440 to 590 MPa and dwell times at pressure from 20 - 40 seconds. The compact is segmental in shape and about 0.5 to 1 mm undersize all round from the profile of the corresponding back plate. The friction material top face of the compact is flat but the bottom pure sponge iron face has technological projections to facilitate precise location of the compact on the back plate when they are assembled together. ,/• • In case of a formed cup type steel backing the above two layers are directly compacted in to the nickel plated cup housed in the die. f/7j For copper based friction composites: Formed cup type design of bacl For thin friction material elements (up to approximately 3 mm friction material layer) friction composite powder mix is directly cold compacted into the cup housed in the compaction die using a hydraulic press at pressures of 310 to 460 MPa and dwell time at pressure from 10 to 25 seconds. For thicker friction material thickness loose sintered friction material - cup assembly is cold compacted in a die at pressures between 235 to 385 MPa and dwell time at pressure between 5 to 10 second Flat plate design of back plate either in segment stiape or annular disc shape Friction material compact is made separately as in the case of iron base composites. However only single layer cold die compaction of the friction material mix is carried out at pressures of 310 to 460 MPa and 10-25 seconds dwell time (E) Pressure sintering of friction material back plate assemblies "Pressure sintering" is achieved by the following methods: (i) Applying a static dead weight load on the powder compact - back plate/cup assembly at high temperature in a reducing atmosphere furnace (ii) Applying pressure by two opposing electrodes and heating by passing current through the assembly as done in resistance sintering (iii) Variable hydraulic or pneumatic compressive or "pushing" pressure application on the assembly at high temperature in a reducing atmosphere furnace (iv) Variable hydraulic or pneumatic tensile or "pulling" pressure application on the assembly at high temperature in a reducing atmosDhere furnace (v) By hot pressing in a die by hydraulic press and heating the die and part by induction heating/cartridge resistance heating. Iron base flat plate type and cup type of configurations as well as copper base flat plate type and disc type configurations have been subjected to method (iv), whereas copper base cup type configurations have been subjected to method (i) (a) For iron based friction composites This comprises of the following steps : (i) Assembly of the friction material compact on the back plates with the pure iron layer facing the nickel-plated back plate surface and its technological projections housed in the respective holes in the back plate, (in case of cup type design this step is not required) (ii) Stacking of the friction material - back plate assemblies into vertical stacks(1) with appropriate high temperature ceramic paper separators and preparing three vertical stacks. In case of back plates with projections additional inconnel / nimonic alloy fixture plates with necessary clearances/holes to house these projections are used. Three vertical stacks are made with about 30 to 60 friction material - back plate assemblies per stack. These stacks are placed, 120 ° apart from each other, on a circular graphite cushion block placed on the pressure sintering furnace refractory base. The height of the vertical stacks shall be equal. On top of the stacks one more graphite cushion block is placed. A pressure plate made of nimonic alloy is placed on top of the graphite cushion block. A water-cooled central circular pull rod enters the furnace base from the bottom and passes through central holes in the top and bottom graphite cushion blocks and the pressure plate and projects beyond the top of the pressure plate. This projected length has an undercut groove all round and this receives two steel split rings which help lock the pressure plate against the pull rod. After the pressure plate is locked, the hydraulic pressure on the stacks is gradually increased till the set value. For pressure sintering of iron based friction materials a hydraulic load con-esponding to a pressure of about 2.5 to 3.5 Mpa is applied. The pressure is kept at about 1.5 Mpa initially. An inconnel bell shaped furnace muffle is then lowered on to the base to cover the charge and the base. Hydrogen gas is then introduced into the muffle and then the heating hood of the furnace is lowered to sun-ound the muffle and the heating is started. Pressure sintering is carried out in the following steps : Temperature Range Soaking time Pressure H2 gas flow rate (°C) (Minutes) (Mpa) (NmVhr) 400 to 550 30-45 1.5-2.0 0.5-1.0 750 to 900 15-25 2.0-2.5 0.2-0.3 950to1050 120-180 2.5-3.5 0.2-0.3 (final temp) In case of cup type designs in iron based friction composites the hydraulic pressure is restricted between 1.5 and 2.0 Mpa in order to prevent cup wall defonnation. The other parameters are however the same as above. (b) In case of copper based friction composites (i) For cup type designs that have undergone pre-sintering and pre-bonding by loose sintering prior to compaction Pressure sintering is carried out in the above set up in a similar way but instead of using a variable and positive hydraulic load during pressure sintering a static dead weight load is applied on the stacks of cup shaped friction material compact assemblies which is equivalent to a pressure of 0.2 to 0.4 Mpa. Heating during sintering is carried out in two steps as follows : Temperature Range Soaking time Pressure H2 gas flow rate (°C) (Minutes) (Mpa) (Nm%r) 400 to 550 30-45 0.2-0.4 0.6-1.0 750 to 900 120-240 0.2-0.4 0.2-0.3 (Final temp) (ii) For fiat plate design of back plate either in segment shape or annular disc shape Normal hydraulic "pulling type" pressure sintering under higher and variable sintering pressure, similar to the iron based friction composites, is employed. However the steps of sintering and temperatures employed are similar to the above as follows: Temperature Range Soaking time Pressure H2 gas flow rate (°C) (Minutes) (Mpa) (Nm%r) 400 to 550 30-^5 0.7-1.0 0.5-1.0 760 to 900 120-240 1.5-2.0 0.2-0.3 (F) Post sintering heat treatment, coining and sizing and finishing This comprises of the following steps: (i) Post sintering heat treatment : In the case of the sintered and bonded friction material elements/segments which comprise of a "b" t^e back plate of a medium carbon-high strength steel, tempering heat treatment operation of the friction material elements is carried out at 350 - 500 °C for about 1-2 hours. No heat treatment is required for friction material elements backed by "a" type low carbon steel back plate. (ii) The friction material elements are then coined and sized to remove distortion and impart final density to the friction material in a hydraulic .press under flat dies at a pressure of 235 to 465 l\/IPa"for dwell time from 5 to 10 seconds (iii) Finally the coined elements are machined marginally to their required final dimensionsAhickness Examples A few non limiting examples are used to illustrate the invention. Example-1 ; Manufacture of a copper based cup type friction composite element A copper based friction material composite of the following composition ; 4.5%Tin powcler( Copper +Tin powder (metallic mix) are treated for 1 hour in a pot mill. Mullite powder is added to pot mil) and run for Ihour. Synthetic graphite powder is then added and run for another 1 hour A 1.3 mm thick 0.2% plain carbon steel sheet used as a backing member was formed in the shape of a segmental cup of top area of 30 sq cm with a wall height of about 5 mm. A,jnesh / grid blanked out from a perforated steel sheet of 0.3 mm thickness was spot welded at 4 places at the inside bottom of the steel cup. The assembly was copper plated from a cyanide bath to a copper coating thickness of approximately 20 microns. Measured quantity of the above powder mix was poured into the copper plated cup as obtained above after wrapping the cup wall all round with a stainless steel canister to increase the height of the cup to receive the extra volume of powder. The powder was lightly rammed in to this assembly. 18 such assemblies were an^anged in an Inconnel boat and subjected to loose sintering in a laboratory type hydrogen atmosphere pusher type continuous furnace at 750 °C for a total soaking period of 1 hour. The loose sintered assemblies were then compacted in a shaped die using a.hydraulic press at a load of 100 tons and dwell time of 15 seconds. The 18 compacts were then arranged in three vertical stacks of 6 compacts each, separated by alumina paper separators, and these stacks placed 120° apart from each other on a pressure sintering furnace base. A circular 300 mm diameter graphite cushion block was placed on top of the stacks and then a tungsten alloy dead weight of the same diameter and weighing 300 kgs was placed on top. Pressure sintering in hydrogen atmosphere was carried out following the cycle given below; Temperature CO 450 800 Soaking time H2 gas flow rate (Minutes) (Nm""/hr) 30 0.5-1.0 210 0.2-0.3 The sintered compacts were then coined using a hydraulic press in a shaped die at 80 tons load for 5 seconds to final density and finally surface ground to a thickness of 4.5 mm. The friction elements thus made were then subjected to hardness tests, bend test and microstructural analysis for assessment of bond quality, friction test in a chase type machine to assess fiction and wear properties and finally to a thermal cycling test involving repeated cycles (50 cycles) of heating of the element to 500°C followed by air blast cooling and then observing for cracks in the friction material and bond failure by bend test and microstructural test. The results are as follows : Test carried out Results /Observations Hardness on friction surface ( HB 5 ) Bend test on unused friction element over a 15 mm dia roller type mandrel by 90° bend and then further bending upto 120° Microstructural examination 90-105 The friction material found to bend along with the backing cup up to 90° bend. On further bending the friction material started to break away (normal) but left a layer of adhering friction material firmly stfcking on to the cup bottom and side walls(evidence of good bonding) The element was sectioned across its thickness and polished to observe the microstructure of the friction material and the bonding interface at 50 X magnification. A friction material strnrfiire nomDrisino of uniformly distributed graphite (g) and Friction and wear test (On 2 opposed friction element segments acting against a rotating steel disc mating member on a run -down test) Thermal cycling (500 °C, 50 times ) mullite(m) phases in a copper base matrix (Cu) observed. Also observed is a sound interfacial bonding across the friction material(1) and cup bottom (3) through an intermediate steel mesh{2). This is shown in figure 1 A. Figure 1B shows the good bonding achieved between friction material(l) and cup side vertical wall(4) 100 continuous braking stops carried out using a fixed inertial mass of 3.5 kgfmsec^ and rubbing speed of 30 m/sec. Brake pressure applied : 40kgf/sq.cm Results : Average stopping time : 7 seconds Coeff. Of friction ; 0.36 Average brake torque : 158 kgfm Max temp achieved : 272 °C in the 44"*" stop thereafter more or less constant Wear in 100 stops :0.13mm (1.5 gms by weight) . Appearance : uniform shiny bluish black layer formation on the friction surface as observed after 100 stops. No chipping or cracking noticed. Smooth brake engagements without any judder/noise/vibration After every thermal cycle the friction surface observed visually for cracks. No cracks found even after 50"*" cycle. The friction element was subjected to fluorescent penetrant test and microstmctural analysis across the bonded interface. No cracks or discontinuities observed in penetrant test indicating good structural integrity of friction material against thennal gradient. MicrostruiCture did not reveal any bond line discontinuity indicating no deterioration of bond during thermal cycling. Example-2: Manufacture of a copper based annular disc type friction composite element A copper based friction material composite of the following composition 35 gms of Lead powder( Copper + iron + lead powder (metallic mix) are treated for 4 hours in a 10 litre capacity double cone blender. Calcined Silica grains are added to the blender and run for Ihour. Natural, flaky graphite powder is then added and run for another 1 hour. A 5mm thick, medium carbon ( 0.35% C) alloy steel plate ( Cr-Mo-V steel ) was machined out in the shape of an annular disc of dimensions : OD = 180 mm and ID = 150 mm to be used as a backing member. Quantity 5 nos. of these machined discs were copper plated from a cyanide bath to a copper coating thickness of approximately 35 microns. Measured quantity of the above powder mix ( 90 gms ) was poured into a die cavity assembled on a 250 Ton hydraulic press. The die was designed and manufactured in a shape and size so as to produce annular compacts of 180 mm OD and 150 mm ID. Accordingly the die cavity ID was maintained at 180*°^ mm con^esponding to the OD of the compact and the ID of the compact was formed by a core block of 150"°"" mm dia, centrally housed in the die cavity. The powder mix was filled up in the annular space between the core block and the die wall to a fill height of approximately 5 mm. The excess powder was leveled off the top surface of the die with a straight edge. The leveled off powder mix in the die cavity was then compacted by bringing the top punch of the tool attached to the moving top platen of a 250 Ton capacity hydraulic press. Compaction was carried out at a load of 240 tons and dwell time of 15 seconds. Ten compacts made. Two compacts were taken each time and assembled on either side of the copper plated steel annular disc. Five such assemblies were prepared and were then arranged in one single vertical disc stack. The stack was then placed centrally on a pressure sintering furnace base. Each of the five disc assemblies were separated from / one another by alumina paper separators of the same annular shape and size. Pressure sintering of the stack of discs was carried out in a hydrogen atmosphere "pull type" hydraulic pressure sintering set up. Pressure sintering in hydrogen atmosphere was carried out following the cycle given below : Temperature Range (°C) Soaking time Pressure H2 gas flow rate (Minutes) (Mpa) (Nm%r) 500 850 40 180 1.0 2.0 0.5-1.0 0.2-0.3 The sintered compacts were then coined using a hydraulic press in a shaped die at 150 tons load for 5 seconds to final density and finally surface ground to a thickness of 8mm with equal thickness of sintered friction material lining on either side of the back plate within a tolerance of ± 0.10 mm. The friction material discs thus made were then subjected to hardness tests, bend test and microstructural analysis for assessment of bond quality, friction test in a chase type machine to assess fiction and wear properties and finally to a thermal cycling test involving repeated cycles (50 cycles) of heating of the element to 500°C followed by air blast cooling and then observing for cracks in the friction material and bond failure by microstructural examination. The results are as follows ; Test carried out Results /Observations Hardness on: friction surface { HB 5) back plate ( HB 30) Bend test on 2 mutually opposite segments of approximately 70 mm circumferential length cut from the bottom¬most disc of the stack over a 15 mm dia roller 35 to 45 247 The friction material lining on the top face was observed. This found to bend along with the backing steel plate up to 90° bend. On further bending the friction material started to break away (normal) but left a layer of adhering friction material firmly sticking on to the steel backing plate (evidence of good bonding ) / type mandrel by 90° bend and then further bending upto 120° Microstructural examination Friction and wear test (On 2 opposed friction element segments of 70 mm length acting against a rotating steel disc mating member on a run -down test) Thennal cycling ( 500 °C, 50 times ) One sintered disc element was sectioned across Its thickness and polished to observe the microslructure of the friction material and the bonding interface at 50 X magnification. A friction material structure comprising of uniformly distributed graphite, lead, iron and silica particles in a copper base matrix observed. Also observed was a sound interfacial bonding across the friction material and steel backing disc. 100 continuous braking stops carried out using a .fixed inertial mass of 3.5 kgfm"sec^ and rubbing speed of 30 m/sec." Brake pressure applied : 40 kgf/sq.cm Results : Average stopping time : 6 seconds Coeff. Offriction:0.38 Average brake torque : 174 kgfm Max temp achieved : 256 °C in the 69"^ stop thereafter more or less constant Wear in 100 stops : 0.08 mm Appearance : unifonn shiny bluish black layer formation on the friction surface as observed after 100 stops. No chipping or cracking noticed. Smooth brake engagements without any judder/noise/vibration After every thermal cycle the friction surface observed visually for cracks. No cracks found even after 50**^ cycle. The friction element was subjected to fluorescent. penetrant test and microstructural analysis across the bonded interface. No cracks or discontinuities observed in penetrant test indicating good structural integrity of friction material against thermal gradient. Microstructure did not reveal any bond line discontinuity indicating no deterioration of bond during thermal cycling. Example 3: Manufacture of an iron based flat plate type friction composite element An iron based friction material composite of the following composition ; 12% electrolytic copper powder( Sponge iron + Copper (metallic mix) was treated in a pot mill for 1 hour. A ceramic mix consisting of BaS04+ SiC + alcohol was treated to achieve a pasty consistency. This was then dried at 65-75 deg C for around one hour.. The dried ceramic mix was added to the metallic mix and run for Ihour in pot mill. Natural graphite and H-BN powder were then added and run in the pot mill for another 2 hours. A 2.5 mm thick Ni-Cr-Mo HSLA steel used as a backing member was blanked to the shape of a fiat segment of planar area of 22 sq cm. The plate was nickel plated from a sulphamate bath to a coating thickness of approximately 60 microns all over. Diffusion treatment of the nickel coated back plate was carried out in hydrogen atmosphere for 1 hour at 850 deg C. 18 nos of double layer compacts with the above iron base friction composite powder mix and pure sponge iron powder ( of size - 100 BS# for the intermediate layer )were then compacted in a shaped die using a hydraulic press at a load of 120 tons and dwell time of 30 seconds. Total compact thickness: 5 mm. Intermediate sponge iron layer thickness : 1 mm approximately. Two technological pear shaped projections, 20 mm apart, on the sponge iron side to facilitate locating the friction element precisely in the corresponding back plate holes, were also a feature of the compact. The 18 compacts were then pressure sintered in a hydrogen atmosphere hydraulic "pulling type" pressure sintering set up. Pressure sintering is carried out in the following steps : Temperature Range (X) 550 850 1040 (final temp) Soaking time Hydraulic H2gas Pressure flow rate (Minutes) (Mpa) (Nm%r) 30 1.5 1.0 20 2.0 0.2 180 2.5 0.2 After pressure sintering the heating hood was lifted off and the charge allowed to cool in the muffle to room temperature ( Test carried out Results /Observations Hardness on: friction surface(HBlO) back plate (HB 10) Bend test on unused friction element over a 20 mm dia roller type mandrel by 90° bend Microstructural examination 120-138 320 The friction material found to bend along with the backing plate up to about 45 - 50° bend. On further bending the friction material started to break away ( normal ) but left a layer of adhering friction material fimily sticking on to the cup bottom (evidence of good bonding ) The element was sectioned across its thickness and polished to observe the microstructure of the friction material and the bonding interface at a magnification of 100X. A friction material structure comprising of uniformly distributed graphite (g), copper (Cu) and SiC(s) phases in a pearlitic iron base matrix (Fe) observed. Also observed is a sound interfacial bonding / Friction and wear test (On 2 opposed friction element segments acting against a rotating steel disc mating member on a run -down test) Thermal cycling (600 °C, 50 times) /• across the friction materiai(1), sponge iron layer{2), mcke\ coated layer(3) and bacl 100 continuous braiding stops carried out using a fixed inertial mass of 3.6 kgfmsec^ and rubbing speed of 33 m/sec. Brake pressure applied : 45kgf/sq.cm Results : Average stopping time : 8 seconds Coeff. Of friction : 0.34 Average brake torque ; 176 kgfm i\/lax temp achieved : 298 °C in the 57*"" stop thereafter more or less constant. Wear in 100 stops: 0.08 mm (1.0 gm by weight) Appearance : unifomi shiny bluish black layer formation on the friction surface as observed after 100 stops. No chipping or cracking noticed. Smooth brake engagements without any judder/noise/vibration After every thermal cycle the friction surface observed visually for cracks. No cracks found even after 50"^ cycle. The friction element was subjected to fluorescent penetrant test and microstaictural analysis across the bonded interface. No cracks or discontinuities observed in penetrant test indicating good structural integrity of friction material against thermal gradient. Microstructure did not reveal any bond line discontinuity indicating no deterioration of bond during thermal cycling. Example 4: Manufacture of another iron based flat plate type friction composite element An iron based friction material composite of the following composition : 36 gms of carbonyl grade nickel powder ( powder (-100 + 250 BS mesh) and 1754 gms of reduced sponge iron powder (-100 BS#) was prepared by mixing as follows(total mix quantity 2 kg). Sponge iron powder + Nickel powder + LC Ferro-chrome + Fen^o- manganese + Ferro-tungsten + Ferro- phosphorus (metallic mix) was treated in a 10 litre capacity double cone blender for 2 hour. Silicon powder was then added to the blender and further mixing was carried out for 30 minutes. Flaky natural graphite were then added and the blender was run for another 1 hour. A 2.5 mm thick AISI 4340+Si HSLA steel used as a backing member was blanked to the shape of a flat segment of planar area of 30 sq cm. The plate was nickel plated from a sulphamate bath to a coating thickness of approximately 90 microns all over. Diffusion treatment of the nickel coated back plate was carried out in hydrogen atmosphere for 1 hour at 850 deg C. 18 nos of double layer compacts with the above iron base friction composite powder mix and pure sponge iron powder ( of size - 100 BS# for the intermediate layer )were then compacted in a shaped die using a hydraulic press at a load of 150 tons and dwell time of 35 seconds. Total compact thickness: 5 mm. Intermediate sponge iron layer thickness : 1 mm approximately. Two technological pear shaped projections, 25 mm apart, on the sponge iron side to facilitate locating the friction element precisely in the corresponding back plate holes, were also a feature of the compact. The 18 compacts were then pressure sintered in a hydrogen atmosphere hydraulic "pulling type" pressure sintering set up. Pressure sintering is carried out in the following steps : Temperature Range (°C) 550 850 1020 (final temp) Soaking time Hydraulic H2gas Pressure flow rate (Minutes) (Mpa) (NmVhr) 30 1.5 1.0 20 2.0 0.2 180 3.0 0.2 After pressure sintering the heating hppd was lifted off and the charge allowed to cool in the muffle to room temperature ( / The sintered friction elements were then heat treated at 500 deg C for 2 hours in a nitrogen atmosphere furnace to temper the backing plate and finally surface ground on both friction material as well as the back plate to maintain a thickness of about 2 mm on the back plate side and a total element thickness of 6.50 mm. The friction elements thus made were then subjected to hardness tests, ultrasonic test and microstructural analysis for assessment of bond quality, friction test in a chase type machine to assess fiction and wear properties and finally to a thermal cycling test involving repeated cycles ( 50 cycles ) of heating of the element to SOO^C followed by air blast cooling and then observing for cracks in the friction material by non-destructive penetrant tests and bond failure by microstructural test. The results are as follows : Test carried out Results /Observations Hardness on : friction surface(HBlO) back plate (HB 10) Ultrasonic testing Microstructural examination Friction and wear test (On 2 opposed friction 169- 185 465 All the friction elements were subjected to a contact ultrasonic testing using a 4 Mhz , 10 mm dia dual probe to assess the bond quality between the back plate 2.0 mm thick and the friction material layer ( ~ 4.5 mm thick ). All the pads passed the bond quality test when tested against a reference specimen with a known interfacial bond-line discontinuity. The element was sectioned across its thickness and polished to observe the microstructure of the friction material and the bonding interface at a magnification of 100X. A friction material stnjcture comprising of uniformly distributed graphite (g), and Si{s) phases in a peariitic iron base matrix (Fe) observed. Also observed is a sound interfacial bonding across the friction material(1), sponge iron layer(2), nickel coated layer(3) and back plate (4). The structure of the back plate is tempered martensite. This is shown in figure 3 100 continuous braking stops carried out using a fixed inertial mass of 3.5 kgfmsec^ and rubbing speed of 42 m/sec. / element segments acting against a rotating steel disc mating member on a run -down test) Thermal cycling (600 °C, 50 times ) Bral Coeff. Of friction: 0.32 Average brake torque : 159 kgfm Max temp achieved : 308 °C in the 74"^ stop thereafter more or less constant. Wear in 100 stops : 0.07 mm (1.0 gm by weight) Appearance : uniform shiny bluish black layer formation on the friction surface as observed after 100 stops. No chipping or cracking noticed. Smooth brake engagements without any judder/noise/vibration After every thermal cycle the friction surface observed visually for cracks. No cracks found even after 60"^ cycle. The friction element was subjected to fluorescent penetrant test and microstructural analysis across the bonded interface. No cracks or discontinuities observed in penetrant test indicating good structural integrity of friction material against themnal gradient. Microstructure did not reveal any bond line discontinuity indicating no deterioration of bond during thennal cycling. Scientific Explanation, Novelty and Inventive steps with respect to prior art The process for manufacture of iron base friction materials has the following improved features as compared with the prior art: (a) In case of iron base friction composites, a thick nickel coating is given on the back plate by electroplating from a sulphamate bath to a thickness of 50 to 150 microns on high strength back plates ( meant for high energy-high temperature capability friction material). The plating is stress free , has high strength and ductility and has very high adhesion power. This enables a very strong and sound metallurgical bond between the friction material and the back plate and retention of the bond at elevated service temperatures and steep thermal gradients encountered in high energy aircraft braking. The thickness of the plating and also the interfacial alloying with the friction material pure iron sponge layer on one side and the steel back plate on the other side ensures a gradual variation of thermal expansion from the friction material side to the back plate and this ensures retention of a good bonding and the bonding layer"s capability to withstand very high torque and shear loads at elevated temperatures during aircraft braking. The requirement of thickness of nickel plating on low carbon-lower strength and thinner back plates is lower, i.e., of the order of 10-30 microns, due to better ductility and lower thickness of the back plate. (b) The pure iron layer comprising of sponge iron powder which is juxtaposed between the friction material layer and the nickel plated layer and of a thickness from 0.5 to 2.0 mm is incorporated as a special feature by making a multi layer compact. The sponge iron layer very importantly acts as a cushion layer of good compressibility due to its high sponginess. This characteristic allows the effective damping of vibrations/judder/noise caused during braking. This layer also acts as a medium to further ensure good bonding between the friction material and the steel back plate through the intermediate nickel layer. The fineness of the sponge iron powder used and the high porosity of the Sponge iron layer offers a large suri"ace area for ensuring a good diffusion bonding of the back plate with the friction material. A portion of lower melting copper/tin, which are the ingredients of the friction material, also percolate to this sponge iron layer during pressure sintering by capillary action and are believed to enhance the noise/judder damping characteristics. This structure also prevents excessive cariDurisation of the back plate which could otherwise occur by diffusion of carbon from the friction material through the nickel layer. As an example the above unique functions of the multi layers in the friction material assembly is essential to meet the following demanding service conditions ; The kinetic energy of braking in a modem day high speed jet fighter of a large civilian transport or military aircraft is of the order of several millions of Joules( typically 15 -25 MJ) . This enormous quantum of energy when absorbed by the friction material elements of the brakes within a very short interval of 10 - 15 seconds after landing imposes very severe and steep thermal gradient of more than 5000°C per cm across the friction element section. This leads to a situation where the contacting surface of the friction material may be at a instantaneous temperature of 2000°C whereas the back plate may be closer to ambient temperature. This causes instantaneous and high thermal e)q3ansion on the friction material and at the same time the back plate resists this expansion and therefore the interfacidi layers will be subjected to enormous level of tensile stress which could lead to catastrophic bond failure during service. The sponge iron layer due to a large volume of porosity neutralises the expansion gradient to a large extent due to the pores acting as "stress sinks". The nickel coated layer also contributes to neutralising the thermal gradient due to a compositional gradient that exists across its thickness. The compositional gradient arises due to its alloying with some of the friction material ^ ingredients on one side and with the back plate elements on the other side. (c) The diffusion treatment of the nickel plated back plates earned out at temperatures between 800 to 950 ° C in hydrogen atmosphere ensures a sound metallurgical diffusion bonding of the nickel plated layer to the alloy steel back plate which is a prerequisite to the further bonding between the back plate and the friction material. The treatment also serves to ensure a complete stress free and ductile nickel coating with high adhesion power. (d) Loose sintering, on copper based friction composites with a cup type backing design, is carried out with the purpose of achieving a superior bonding between the friction material and the backing cup which is realised due to a much higher surface area offered at the bonding interface by a loose mass of powder when heated up to the sintering temperature compared to a fully compacted material. Further this bonding is also aided due to incipient melting of the low melting point metals such as tin/antimony etc which could easily percolate to the bonding interface in a highly porous mass of powder by strong capillary forces. In the same way during the process of loose sintering particle to particle bonding within the friction powder mass is also enhanced due to easy diffusion of atomic spedes through higher total surface area. This diffusion is aided by the incipient melting of the low melting elements which offer channels of liquid medium for easy transport of diffusing atoms. This also ensures that the friction material will have a higher inter-particle bonding to resist material chipping / break-away in the face of steep temperature gradients encountered during high energy frictional engagements. Loose sintering as a pre-sintering and bonding step is also necessitated in a cup type of design because during final pressure sintering only a small static dead weight load is applied on the friction composites in order to prevent defonnation of the cup walls during the process. (e) The three step pressure sintering carried out on iron based friction composites and the two step process applied to copper based composites achieve the following beneficial effects: (i) effective alloying between the various metallic species due to good diffusion under pressure , temperature and a reducing hydrogen atmosphere (ii) effective sintering and densification and good inter-particle bonding between metallic and ceramic constituents in the friction material due to thorough and uniform distribution of lower melting elements, under pressure and temperature, by capillary action (iii) effective carbon diffusion in the iron matrix leading to a more profuse peariitic structure Besides the high quality and thermally stable metallurgical bonding that is achieved, all the above also lead to the following beneficial properties/characteristics of the friction material (a) Enhanced, unifonn and more predictable dynamic friction and torque characteristics of the friction material during brake application (b) Enhanced wear-life of the friction material (c) Enhanced resistance to thermal degradation, chipping and material break-away during high energy braking and therefore a higher capability to withstand steep " thermal gradients ^ Advantages of the Present Invention The advantages of the present invention are as follows : (i) A process is developed to ensure achievement of a good metallurgical bond at the interface between friction material and back plate that will withstand thermal and mechanical stress under high energy friction engagements, (ii) The friction composite formulations processes in the manner described in the invention give high wear life under repeated high- energy frictional engagements in actual service, (iii) The process ensures development of a friction material with good structural integrity of friction material against steep thermal and stress gradients in service, (iv) The process ensures development of a friction composite configuration that helps reduce/eliminate judder/noise during high energy frictional engagements, (v) The rapid sulphamate nickel plating process achieves the building up of thick, stress free, nickel coating on steel upto 0.15mm thickness possessing good adhesion power, (vi) The process for loose sintering/bulk sintering of friction composrte powder mix contained in copper coated backing cup as a process step prior to compaction for copper base friction materials in a cup type design enhances bonding, (vii) The process developed is applicable for a wide variety of fonnulations and designs of sintered copper and iron based friction composite elements. Besides the high quality and thermally stable metallurgical bonding that is achieved, all the above also lead to the following beneficial properties/characteristics of the friction material (d) Enhanced, uniform and more predictable dynamic friction and torque characteristics of the friction material during brake application. (e) Enhanced wear-life of the friction material. (f) Enhanced resistance to thermal degradation, chipping and material break-away during high energy braking and therefore a higher capability to withstand steep thermal gradients. ^ We Claim: ) A process for the preparation of metal-ceramic friction composites in copper or iron base material and bonded to cup type or flat plate type steel backing frames involving a method to sinter the composites and simultaneously bond the .composites on to the steel backing frames to form bonded friction composites mint for use in frictional applications involving kinetic energy dissipation or up to 8000 joules per sq cm. preparation of metal-ceramic friction composites as claimed in the metal-ceramic friction composite in copper base material formulation containing : ingredients: comprising a mix of powders such as antimony, molybdenum, iron and nickel of particle sizes 45 to "t5D microns with copper being the major ingredierrt" varying from 80 to 95 of the mix. 10-30 weight ceramic ingredients; comprising friction additives such as Silica, carbide or silicon nitride of particle size ranging from 60 to 10-30 Weight % ingredients : comprising of solid lubricants such as sulphide, hexagonal boron nitride; and anti- fibres; of particle size ranging from 50 to 600 microns A process preparation composites as claimed in claim 1 wherein in iron base material shall have formulation contain: 45-70 weight % of powders such as iron, copper, tin, antimony \silicon, ferrochromium, ferromanganese, of particle sizes ranging from 40 to 150 ingredient varying from 60 to 85% of the metallic mix. 4) A process for preparation of metal-ceramic friction composites in copper or iron base material as claimed in claim 1 wherein the steel backing plate frame of cup type design is made from low to medium plain carbon steels with a carbon content in the range of 0.15 to 0.6 %, hardness of 170 VPN maximum and a sheet thickness in the range of 0.8 and 2.0 mm. 5) A process for preparation of metal-ceramic friction composites in copper or iron base material as claimed in claim 1 wherein the steel backing frame of flat plate type design is in segmental shape or in annular ring/disc shape and is made from medium cariDon high strength low alloy steel material having a thickness in the range of 1.5 and 6 mm and a hardness in the range of 220 and 550 VPN possessing high hardenability and thermal curiing resistance. 6) A process for the preparation of metal-ceramic composites in copper base material with a cup type backing frame design as claimed in claims 1, 2 and 4 wherein the process comprises of forming of the cup, spot welding of a perforated metallic mesh to the cup, copper coating of the cup, mixing of copper base metal-ceramic friction composite powder formulation, loose/bulk pre-sintering of powder mix filled in the cup, compaction, pressure sintering and coining. 7) A process for the preparation of metal-ceramic friction composites in copper base materia) with a cup type backing frame design as claimed in claims 1, 4 and 6 wherein the forming of the cup is done by shearing of steel strips into blanks and simultaneous piercing of holes in the blanks using compound press tool followed by drawing of the blanks to cup shape and simultaneous forming of shaped embossments on the cup bottom using draw and form press tool. 8) A process for the preparation of metal-ceramic friction composites in copper base material with a cup type backing frame design as claimed in claims 1, 4 and 6 wherein spot welding of a perforated steel mesh of 0.3 - 0.5 mm thickness, shaped identical as that of the bottom of the cup, Is carried out at several places to the inner surface of the cup bottom for elements of more than 3 mm thickness layer of metal-ceramic friction composite material. 9) A process for the preparation of metal-ceramic friction composite in copper base material with a cup type backing frame design as claimed in claims 1, 4 and 6 wherein the copper coating process claimed is a cyanide copper plating process to obtain a coating thickness of 10 - 35 microns. 10) A process for the preparation of metal-ceramic friction composites in copper base material with a cup type backing frame design as claimed in claims 1,2 and 6 wherein the mixing of the copper base metal-ceramic friction composite material formulation is carried out in two steps with the first step being mixing of metallic powder ingredients for 1 - 6 hours followed by the second step of mixing of the metallic powder mix with ceramic friction additives for 1-4 hours and with friction modifier/ solid lubricant ingredients for a further 2-8 hours. 11) A process for the preparation of metal-ceramic friction composites ip copper base material with a cup type backing frame design as claimed in claims 1, 2, 4 and 6 wherein the loose/bulk pre-sintering of the metal-ceramic friction powder mix, contained in the copper coated cup type steel backing frame, is carried out in hydrogen atmosphere maintaining a hydrogen gas flow rate of 1.5 -2 Nm%r, at a temperature between 700 to 900 °C and for a soaking period of 1 - 3 hours. 12) A process for preparation of metal-ceramic friction composites in copper base materia! with a cup type backing frame design as claimed in claims 1, 2, 4 and 6 wherein the compaction step involves the direct cold compaction of the metal-ceramic friction composite powder mix into copper coated cup using a die in a hydraulic press at pressures of 310 - 460 MPa and dwell times at pressure between 10 and 25 seconds, for thicknesses of friction composite material layer up to 3 mm. 13) A process for preparation of metal-ceramic friction composites in copper base material with a cup type backing frame design as claimed in claims 1, 2, 4 and 6 wherein the compaction step alternatively involves the cold die compaction of loose pre-sintered metal-ceramic friction composite material, pre-bonded into a copper coated cup-mesh spot welded assembly, in a hydraulic press jat 235 to 385 MPa pressure and dwell times at pressure between 5 and 10 seconds, for thicknesses of friction composite material layer more than 3 mm. 14) A process for preparation of metal-ceramic friction composites in copper base material with a cup type backing frame design as claimed in claims 1, 2, 4 and 6 wherein the pressure sintering step is a hydrogen atmosphere sintering process of the metal-ceramic composite material compacted in cups, arranged^in vertical stacks, involving simultaneous hydraulic pressure application by a traction or "pulling" action and is carried out at a temperatures between 750 to 900 "C under 0.2 to 0.4 l\/lPa traction pressure for 2 - 4 hours of soaking time 15) A process for preparation of metal-ceramic friction composites in copper base material with a cup type backing frame design as claimed in claims 1,2, 4 and 6 wherein the coining step is carried out in close to form shaped dies in a hydraulic press at pressures between 235 to 465 MPa and dwell times of 5-10 seconds 16) A process for the preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1, 2 and 5 wherein the process comprises of fabrication of the flat plate type backing frame, copper coating of backing frame, mixing of copper base metal-ceramic friction composite powder formulation, compaction, assembly of powder compacts on backing frames, pressure sintering and coining. 17) A process for the preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1, 5, and 16 wherein the fabrication of the flat plate type backing frame is done by shearing of steel strips into blanks and simultaneous piercing of holes in the blanks using compound press tool for backing frames of segmental shape and by either press tool shearing or by machining from plate stock for flat plate type backing frames of annular ring / disc type shape. 18) A process for the preparation of metal-ceramic friction composite in copper base material with a flat plate type backing frame design as claimed in claims 1, 5 and 16 wherein the copper coating process claimed is a cyanide copper plating process to obtain a coating thickness of 10 - 35 microns. 19) A process for the preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1,2 and 16 wherein the mixing of the metal-ceramic friction composite material formulation is carried out in two steps with the first step being mixing of metallic powder ingredients for 1 - 6 hours followed by the second step of mixing of the metallic powder mix with ceramic friction additives for 1-4 hours and with friction modifier/ solid lubricant ingredients for a further 2-8 hours. 20) A process for preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1, 2, 5 and 16 wherein the compaction of the metal-ceramic composite powder mix is a cold die compaction process carried out in a hydraulic press at 310 to 460 MPa pressure and 10-25 seconds dwell time and applied to individual compacts of segmental or annular ring/disc shape 21) A process for preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1,2, 6 and 16 wherein the pressure sintering step is a hydrogen atmosphere sintering process of the metal-ceramic composite compact-back plate assemblies, arranged in vertical stacks, involving simultaneous hydraulic pressure application by traction or "pulling" action and is carried out at a temperatures between 750 to 900 °C under 1.5 to 2.0 MPa traction pressure for 2 - 4 hours of soaking time. r 22) A process for preparation of metal-ceramic friction composites in copper base material with a flat plate type backing frame design as claimed in claims 1, 2, 5 and 16 wherein the coining step Is candied out in a hydraulic press at pressures between 235 and 465 MPa and dwell times of 5-10 seconds using open flat dies. 23) A process for the preparation of metal-ceramic friction composites in iron base material with a cup type backing frame design as claimed in claims 1, 3 and 4 wherein the process comprises of forming of the cup, nickel coating of the cup, diffusion treatment of the nickel coated cup, mixing of the iron base metal-ceramic friction composite powder formulation, single or multilayer compaction of metal-ceramic friction composite formulation layer and other underiying metallic layers into the cup, pressure sintering and coining. 24) A process for the preparation of metal-ceramic friction composites in iron base material with a cup type backing frame design as claimed in claims 1, 4 & 23 wherein the cup type backing frame is made by shearing of steel Strips into blanks and simultaneous piercing of holes in the blanks using compound press tool followed by drawing of the blanks to cup shape and simultaneous forming of shaped embossments on the cup bottom using draw and form press tool. 25) A process for the preparation of metal-ceramic composites in iron base material with a cup type backing frame design as claimed in claims 1, 4 and 23 wherein the nickel coating process claimed is a rapid nickel plating process carried out in a sulphamate type plating bath for 1-2 hours to obtain a nickel coating of thickness 50 to 150 microns. 26) A process for the preparation of metal-ceramic composites in iron base material with a cup type backing frame design as claimed in claims 1, 4, and 23 wherein the diffusion treatment process of the nickel coated backing frame claimed is a heat treating process carried out in hydrogen atmosphere furnace at temperatures of 800 to 850 °C for 1 - 3 hours. y 27) A process for preparation of metal-ceramic friction composites in iron base material with a cup type backing frame design as claimed in claims 1, 3 and 23 . wherein the mixing of the metal-ceramic friction material formulation is carried out in three steps with the first step being dry mixing of the metallic powder ingredients for 1-6 hours, the second step being wet mixing of the ceramic ingredients in alcohol medium for 1-4 hours and drying the mix and the third step being dry mixing of metallic and ceramic mixes for 1-2 hours followed by addition of friction modifiers/solid lubricant ingredients and further mixing for 2-8 hours. 28) A process for the preparation of metal-ceramic friction composites in iron base material with a cup type backing frame design as claimed in claims 1,3,4 and 23 wherein the single / muiti layer compaction is a cold die compaction process, carried out in a hydraulic press at pressure between 440 and 590 MPa and dwell time at pressure from 20 -40 seconds, that directly compacts the metal-ceramic friction composite powder mix and underiying adhesive/cushion layer of pure sponge iron powder into the nickel coated cup housed in the compaction die and subsequently ejects the compact-backing cup assembly from the die as a single unit. 29) A process for the preparation of metai-ceramic friction composites in iron base material with a cup type backing frame design as claimed in claims 1,3,4 and 23 wherein the pressure sintering step claimed is a hydrogen atmosphere sintering process of the metal-ceramic composite compacted in cups, arranged in vertical stacks, involving simultaneous hydraulic pressure application by traction or /" "pulling" action carried out at temperatures of 950 to 1050°C under 1.5 to 2.0 IVlPa hydraulic traction pressure and 2-3 hours of soaking time. 30) A process for the preparation of metal-ceramic friction composites in iron base material with a cup type backing frame design as claimed In claims 1,3,4 and 23 wherein the coining step claimed Is carried out In a hydraulic press at pressures between 235 to 465 MPa for dwell times of 5 -10 seconds in close to form shaped dies. 31) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1,3 and 5 wherein the process comprises of fabrication of the flat plate type backing frame, nickel coating of the frame, diffusion treatment of the nickel coated backing frame, mixing of the iron base metal-ceramic friction composite powder formulation, single or multilayer compaction of metal-ceramic friction composite formulation layer and other underiying metallic layers, assembly of the compacts on coated backing frames, pressure sintering, heat treatment and coining. 32) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 5, and 31 wherein the fabrication of the flat plate type backing frame Is done by shearing of steel strips into blanks and simultaneous piercing of holes in the blanks using compound press tool for backing frames of segmental shape and by either press tool shearing or by machining from plate stock for flat plate type backing frames of annular ring / disc type shape. 33) A process for the preparation of metal-ceramic composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 5 and 31 wherein the nickel coating process claimed is a rapid nickel plating process carried out in a sulphamat? type plating bath for 1-2 hours to obtain a nickel coating of thickness 50 to 150 microns. 34) A process for the preparation of metal-ceramic composites in iron base material with a flat plate type backing frame design as claimed In claims 1, 5 and 31 wherein the diffusion treatment process of the nickel coated backing frame claimed is a heat treating process carried out in hydrogen atmosphere furnace at temperatures of 900 to 950 °C for 2 - 3 hours. 36) A process for preparation of metal-ceramic friction composites in iron base material with a flat type backing frame design as claimed in claims 1,3 and 31 wherein the mixing of the metal-ceramic friction material formulation is carried out in three steps with the first step being dry mixing of the metallic powder ingredients for 1-6 hours, the second step being wet mixing of the ceramic ingredients in alcohol medium for 1-4 hours and drying the mix and the third step being dry mixing of metallic and ceramic mixes for 1-2 hours followed by addition of friction modifiers/solid lubricant ingredients and further mixing for 2-8 hours. 36) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 3, 5 and 31 wherein the single / multi layer compaction is a cold die compaction process, earned out in a hydraulic press at pressure between 440 and 590 MPa and dwell time at pressure from 20 -40 seconds, applied to individual, shaped powder compacts comprising of either a single metal-ceramic friction composite layer or multi layers with additional adhesive/cushion layers of pure sponge iron. 37) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 3, 6 and 31 wherein the pressure sintering step claimed is a hydrogen atmosphere sintering process of the metal-ceramic composite compact - back plate assemblies, arranged in vertical stacks, involving simultaneous hydraulic pressure application by traction or "pulling" action carried out at temperatures of 950 to 1050°C under 2.5 to 3.5 MPa hydraulic traction pressure and 2-3 hours of soaking time. 38) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 3, 5 and 31 wherein the heat treatment step claimed is a tempering treatment carried out at temperatures between 350 to 500°C for 1-2 hours in order to obtain the desired final hardness of the backing frame wherever a high strength low alloy steel backing frame material is used. 39) A process for the preparation of metal-ceramic friction composites in iron base material with a flat plate type backing frame design as claimed in claims 1, 3, 5, and 31 wherein the coining step claimed is carried out in a hydraulic press at pressures between 235 to 465 MPa for dwell times of 5 -10 seconds under open 40) A process for the preparation of metal-ceramic composites in copper and iron base material bonded to steel backing frames as claimed in claims 1 to 39 for applications related to high kinetic energy frictional engagements including both energy dissipation and energy transmission involving high rubbing speeds (up to 80 m/sec) and high torque (up to 4500 Kgm) such as for braking and clutching applications in military/civilian aircraft, battle tanks, heavy vehicles and ships.

Documents:

33-mas-2002 abstract.pdf

33-mas-2002 claims.pdf

33-mas-2002 correspondecne others.pdf

33-mas-2002 correspondecne po.pdf

33-mas-2002 description (complete).pdf

33-mas-2002 drawings.pdf

33-mas-2002 form-1.pdf

33-mas-2002 form-13.pdf

33-mas-2002 form-19.pdf

33-mas-2002 form-26.pdf

33-mas-2002 form-3.pdf

33-mas-2002 form-5.pdf