Title of Invention

"A PROCESS FOR PREPARATION OF IRON BASE TITANIUM CARBIDE METAL-MATRIX COMPOSITES"

Abstract

A process for preparation of iron based titanium carbide metal-matrix composite which are directly castable into near net shape products comprising the steps of pre-bakirig of the reactant powders preferably at 100-250°C for 2-6 hours, for moisture removal, wherein the reactant powder taken are 43 to 74.5% Iron Oxide (Fe203), 0.5 to 15% titanium dioxide (Tioa), 20 to 60% aluminium (Al), 0.1 to 10% Carbon (C ), and flux additives as herein described, preparing thermite charge mix by mixing of the reactant powders, compacting the thermite charge mixing, ignition of the charge mix for formation of Fe-TiC metal-matrix composites,casting the liquid Fe-TiC product into near net shape products.

Full Text

FIELD OF INVENTION This invention relates to a process for preparation of iron base titanium carbide metal matrix composites with improved combination of properties, including wear and erosion resistance, seawater corrosion resistance and high temperature oxidation resistance. PRIOR ART Titanium carbide (TiC) metal-matrix composites are well recognized for their resistance to wear and corrosion and resistance to softening at high temperature. Principal uses of TiC composites are in cutting, machining and wear resistance applications. Different sintered composites with varying percentages of TiC reinforcement in different materices (tool steels/stainless steels/alloy steels/Nickel/Cobalt) are known. These are produced by traditional powder metallurgical techniques which require hot isostatic processing (HIP) and vacuum sintering techniques. Besides, there are other methods for producing TiC composites which includes arc inetling, thermal spraying, liquid-base casting technology and carbo-thermic reduction. According to one of the process known in the art, (U.S. patent 3,977,837), sintered steel-bonded titanium carbide is prepared by using powder metallurgy methods. A drawback of the process is that it requires liquid phase sintering under non-oxidising conditions, such as in a vacuum. Another drawback of the process is that it requires a high temperature furnace to operate at 1450°C for the liquid phase sintering. According to another process known in the art (U.S. patent 5,574,954), erosion-resistant titanium carbide composite is made by two stage sintering and hot isostatic compression. A drawback of the above process is that it utilises titanium carbide granules as such and the matrix is also made of high chrome tool steel. Another drawback of this process is that it requires sintering furnace operating at 1450°C under vacuum. Yet another drawback of this process is that it requires expensive equipment for hot isostatic pressing at 1350°C and in argon atmosphere. Another process of making solid particle erosion resistant titanium carbide is disclosed in the U.S. patent 4,615,734 and U.S. patent 4,704,336. It utilises pre-alloyed high chromium iron powder as matrix material and angular titanium carbide particles as the feed material which are mechanically blended and then consolidated at high temperature by hot isostatic pressing or deposited as a layer by plasma spraying. Sintered powder metal products having titanium carbide additives are also disclosed in U.S. patent 4,194,910. This patent discloses titanium carbide particles which are pre-alloyed by liquid phase sintering with iron and nickel base metals, and the resulting alloy is then dispersed through a base matrix, such as a steel matrix. Another U.S. patent 3,715,792 discloses another sintered powder having 45% TiC by volume in a high chromium alloy matrix. The major disadvantage of the above conventional process of making TiC metal-matrix composites is that expensive pure metal powder and titanium carbide powder are used as feed materials Another drawback of this process is the necessity of external hear energy source to maintain high reaction temperatures above 1000oC. Yet another drawback of this process is that it requires long processing cycles ranging from hours to days. Still another drawback of this process is the requirement of expensive equipment for hot isostatic pressing and vacuum sintering. Titanium carbide has been used with a steel matrix to provide tool steel coating. The steel in the matrix of such a coating invariably has a martensitic metallurgical structure and can be applied, for example. h\ plasma spraying a relatively thin layer over the metal substrate. U.S. patenr 5,194,237 and U.S. patent 4,806,394, disclose TiC based composite materials produced by the process of arc melting or thermal spraying. A coating or weldment including titanium carbide particles dispersed through a high chromium alloy matrix and deposited by plasma transferred arc application is also known. A drawback of the above processes is that these requires rapid heatim: of the starting materials that contain titanium, other metals and carbon either by expensive arc melting or thermal spraying equipment. According to another liquid metallurgy process known, iron-TiC composites are produced by in-situ TiC precipitation in liquid iron alloys. According to another known similar process Fe-TiC composites were produced by external TiC powder additions in liquid iron alloys. A drawback of the above processes is that these require expensive equipment for melting of iron alloys and other raw materials and maintaining this liquid iron bath during external TiC powder additions. Another process stated in the art is carbo-thermic reduction of ihnenite and rutile ores. The disadvantage of this process is that it requires an expensive plasma smelting equipment. According to yet another process known in the art U.S. patent 5,393,358 abrasion resistant steel is made by conventional steel making process where the titanium carbide is precipitated during the solidification stage or during hot rolling or tempering. A disadvantage of this process is that it requires a melting furnace for making the steel. Another disadvantage is the energy required for melting the steel. Yet another disadvantage of this process is that it requires processing time of few hours. Still another disadvantage of the process is that as it requires large amount of Ti dissolved in the steel for precipitation of TiC, it is prone to accelerated oxidation of the surface region during further hot rolling or heat treatment. This limits the rolling to lower temperatures, which degrades the hot-workability and makes the rolling difficult and lowers productivity. Yet another method known in the art as per U.S. patent 4,161,512 uses self-propagating high temperature synthesis (SHS) for preparing titanium carbide. However, this does not deal with the problem of making a composite material with fine-sized TiC crystals, distributed uniformly in a metal matrix. The above method has a drawback that it uses SHS only to produce TiC powder and secondary processing like powder metallurgy route is required for making a composite therefrom. Another disadvantage of this process is that it uses costly elemental powder. Still another disadvantage is that the product phase requires further crushing and grinding, even to get TiC powders. OBJECTS OF PRESENT INVENTION The primary object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites based on simple alumino-thermic self-propagating high-temperature synthesis (SHS) Reactions. Another object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites havinti superior combination of properties, including wear and erosion resistance. seawater corrosion resistance and high temperature oxidation resistance Still another object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites which is energy efficient process as it does not require external heat source as the process itself is exothermic as compared to some known processes which require prolonged heating at temperatures above 1000°C. Further object of the present invention is to propose a process lor preparation of iron base titanium carbide metal matrix composites which does not require any costly processing equipments like vacuum furnace, hot isostatic press, plasma spraying equipment or a melting furnace etc Yet further object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites which does not require costly and highly purified elemental powders or TiC powders as the feed material. Still further object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites having a cleaner particle/metal interface compared with conventional metal-ceramic composite materials made by, for example, powder metallurgical techniques using separate metal and ceramic powders, because the reinforcing particles are fonned in-situ. Even further object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites which does not require long processing time of hours and days. Even still further object of the present invention is to propose a process for preparation of iron base titanium carbide metal matrix composites which can be directly cast into near net shapes. Still yet another object of the present invention is to propose a process for preparation of fine and angular titanium carbide powders by simple leaching out of the matrix material. STATEMENT OF INVENTION According to this invention there is provided a process for preparation of iron based titanium carbide metal-matrix composite which are directly castable into near net shape products comprising the steps of : a) Pre-baking of the reactant powders preferably at 100-250°C for 2-6 hours, for moisture removal, wherein the reactant powder taken are 43 to 74.5% Iron Oxide (Fe203), 0.5 to 15% titanium dioxide (Tio2 ), 20 to 60% aluminium (Al), 0.1 to 10% Carbon (C ), and flux additives as herein described, b) preparing thermite charge mix by mixing of the reactant powders, c) compacting the thermite charge mix, d) ignition of the charge mix for formation of Fe-TiC metal-matrix composites, e) casting the liquid Fe-TiC product into near net shape products. The present invention provides one-step process to prepare iron base titanium carbide containing metal matrix composites by self-propagating high-temperature synthesis (SHS) utilizing exothermic heat during direct alumino-thermic reduction of less expensive oxides of iron and titanium. This technique features the advantage in terms of time and energy saving and elimination of expensive equipment for in-situ preparation of iron base titanium carbide metal matrix composites. This process comprises mixing of powder charge consisting of iron oxide and titanium dioxide blended with aluminium, carbon and flux additives, compaction of this powder charge mix in a suitable reaction vessel, spark ignition at one end of charge, propagation of self sustaining reaction front consuming entire powder mix releasing heat energy to produce molten pool of metal and slag phase and pouring this liquid metal to cast near net shapes of iron base titanium carbide metal matrix composites. The process can also be used for preparation of fine and angular titanium carbide powders by simple leaching out of the matrix material. DESCRIPTION OF FIGURES The present invention will now be illustrated with the help of accompanying figures. It is to be understood that the apparatus shown in Fig.1 is an illustrative type of set up showing one embodiment to illustrate the working of the invention and direct casting of the Fe-TiC composites into near net shape products. The apparatus shown in Fig.l is not intended to imply any limitation on the scope of the present invention. Such apparatus may be employed in different embodiments, employing the principles and Features of the present invention without departing from the scope of the present invention. In the accompanying figures:- FIG.1 is an experimental set up of one embodiment of the present invention, to produce directly cast rods of iron base titanium carbide composites. FIG.2 is a photograph of Fe-TiC cast rods obtained according to the present invention. FIG.3 is a cross sectional optical micrograph in polished condition showing angular titanium carbide particles, of one embodiment of the present invention. FIG.4 is a cross sectional optical micrograph in etched condition showing angular titanium carbide particles dispersed in ferrite matrix according to the present invention. kv DESCRIPTION OF THE PROCESS According to the present invention, Iron-based titanium-carbide metal matrix composite is prepared by the process comprising of the following steps:- (a) Pre-baking of reactant powders Commercial grade powders of Iron-oxide (Fe2Os), titanium dioxide (TiOa), Carbon (C) and Aluminium (AI) (which may be containing small amounts of impurities) and fluxing agent like cryolite (NaaAIFa) and/or calcium fluoride are separately subjected to pre-baking for moisture removal, in an oven at the temperature of 100-250°C, preferably at around 200°C for 2-6 hours, preferably for 4 hours. Iron Oxide powder is preferably of particle size of 1 to 15 micron, titanium oxide powder is preferably of particle size of 0.5 to 1.5 microns dia, carbon powder is preferably of particle size 1 to 40 microns dia, aluminium powder is preferably of particle size 1 to 40 microns, and calcium fluoride (CaF2) of cryolite powder preferably CaF2 is preferably of particle size 1 to 30 microns. (b) Preparation of thermite charge mix Pre-baked reaction powders of iron-oxide, titanium dioxide, carbon, aluminium and cryolite and/or CaF2 are mixed together. Titanium dioxide is taken in the weight percentage of 0.5 to 15% preferably in weight percentage of 2 to 12%; carbon is taken in the weight percentage of0.1 to 10%, preferably in weight % of 0.5 to 5%; Aluminium is taken in the weight percentage of 20 to 60%, preferably in the weight percentage of 23to 40%; and the remainder is iron oxide. Flux addition of CaF2 is preferred in the preferred range of 14-40% by weight of theoritically calculated amount of alumina slag. The amount of flux addition is based upon alumina slag phase that forms during alumino-thermic reduction of charge. However slag to metal ratio is in the broad range of 3:1 to l:1 , with preferred rage of 1.5:1 to 1:1. The mixture of reaction powders is thorouglily^mxedrto obtain homogenous mixture. The mixing is done either by hand-mixing or by using muller or rotary blender or by ball milling, preferably ball milling with care to avoid any impurities entering into reactant powder mix. The thoroughly mixed powder thus obtained is referred as thermite charge mix. (c) Compacting of thermite charge mix Homogenous mixture of reactant powders thus obtained by step (b) above, is compacted manually and shaped directly in a reaction vessel of any configuration which does not substantially take part in the reaction. Alternatively, reactant powders are compacted in a suitable die mould to form pellets. preferably under high pressure below lOMPa before charging into reaction vessel. Reaction vessel could preferably be a ceramic crucible or refractory lined vessel having high thermal and shock resistance. (d) Ignition of Compacted charge mix Fig 1 shows an illustrative set up of the apparatus using crucible 1 as reaction vessel which is aligned with due care to match its tap hole 2 with sprue basin 5 of the mould. The crucible 1 is placed over stand 3, below which cast iron mould assembly 4 is placed. One fourth of top-portion of crucible is left blank after compacting reaction powders. The reaction is initiated by igniting a magnesium sparkler wire 7 or/and by using electric spark.. Magensium wire is of about 2mm dia and 200mm length, and its one end is embedded into the charge mix (6) to a depth of about 5mm.The other end of wire is ignited using electric spark ignition and ignition is done preferably in open-air environment from the top-surface of the open end of reaction vessel. Once ignited, self-sustaining heat front moves automatically at high speed, liberating heat energy due to following alumino-thermic reduction reaction :- Fe2O3 + 3T1O2 + 3C + 6A1 => 2Fe + 3TiC + 3A1203 AH - f-)459cal where AH is the heat of reaction. Its negative sign indicates exothermic nature of reaction, releasing high heat energy during self propagation of this reaction, thereby "burning entire volume of thermite charge in a few seconds. The temperature of reaction mixture rises as high as theoretically calculated adiabitic temperature value of 3711°K. Reaction temperature can further be varied by addition of booster mixture the reaction powders, particularly by using sodium nitrate plus aluminium powder. The temperature generated is high enough to produce a liquid pool of Fe-TiC product phase 8 and alumina slag phase. Fi-TiC product phase being heavier, separates out at the bottom of the reaction vessel with a floating top-layer of light weight alumina as a slag phase. CaF2 addition in the processor charge mix 6 promotes better metal/slag separation with improved yield of Fe-TiC composite material around 90%. (e) Casting of liquid Fe-Tic At the end of the self-propagating high temperature synthesis (SHS) reaction, the heavy liquid phase 8 of Fe-TiC composite material, which collects at the bottom of crucible 1. starts flowing under gravity through bottom tap Iiole2 of crucible 1, directly into the mould cavity 9 to produce near net shape casting. The mould can be of any material which does not substantially react with the molten liquid. The complete filling of the mould cavity 9 produces two wire rods of Fe-TiC composite material. WORKING EXAMPLE 28 g TiO2 (1 micron mean particle diameter), 4 g Carbon (2 micron mean particle diameter), 51.2 g Cryolite (2 micron mean particle diameter), 128 g Aluminium (3 micron mean particle diameter) and 240 g Fe2O3 (2 micron mean particle diameter) dry fine reactants powders were intimately mixed in a ball mill using hardened steel balls. Reactant mixture was manually compacted and shaped directly in a ceramic crucible 1. To initiate the exothermic reaction of thermite charge mix 6, in open-air environment, the magnesium sparkler wire 7 of about 2 mm diameter and 200 mm length was used and one end of it was inserted to about 5 mm depth at the center position of the compacted charge 6 in crucible 1. Other open end of this wire is ignited using electric spark. Molten liquid pool of Fe-TiC product phase 8 accumulated at the bottom of crucible 1 with a top layer of light weight alumina-cryolite (Al2O3-Na3AlF6) as a slag phase. Heavy Fe-TiC liquid phase 8 was discharged through bottom tap hole 2 of the crucible directly into a mould cavity 9. The complete filling of the mould cavity 9 produced two wire rods of Fe-TiC composite material Fig.2 is a photograph showing cast rods 10 of Fe-7 wt% TiC composite material prepared by this process. EVALUATION Chemical composition (given as percent by weight) of rods produced is 1.32% C, 6.04% Ti, and 10.78%A1, 1.88% Si, 0.04 Mn, 0.085% S. 0.014% P and remainder Fe. Fig. 3 is a cross sectional optical micrograph, in as polished condition, showing presence of angular titanium carbide particles 11. Particle size is in the range of 3-45 microns with average area traction of 10%, determined using image analysis system. Fig. 4 is cross sectional optical micrograph, in etched condition (using 10% Nital as etchant). showing presence of angular titanium carbide particles 11 dispersed in rernte matrix 12. Further evaluation by X-ray diffractometry (XRD) indicates essentially TiC phase. Dry sliding abrasive wear rate studies of Fe-TiC material carried out using pin-on-disc apparatus indicated very low wear rate in the range of 5-40 X 10-15 m3/Nm. Corrosion properties of this material, determined in natural seawater (salinity=27.9 g/litre, Ph=7.92) indicated low corrosion wear rate in the range of 3-5 mpy. High temperature oxidation resistance of Fe-TiC composite material determined by exposing to 1000 °C for 1 hour soaking period indicated practically no oxide scaling layer with low value of weight gain per unit area in the range of 20 -50 mg/cm2. WE CLAIM; 1. A process for preparation of iron based titanium carbide metal-matrix composite which are directly castable into near net shape products comprising the steps of : a) Pre-baking of the reactant powders preferably at 100-250°C for 2-6 hours, for moisture removal, wherein the reactant powder taken are 43 to 74.5% Iron Oxide (Fe20s), 0.5 to 15% titanium dioxide (Tio2 ), 20 to 60% aluminium (Al), 0.1 to 10% Carbon (C ), and flux additives as herein described, b) preparing thermite charge mix by mixing of the reactant powders, c) compacting the thermite charge mix, d) ignition of the charge mix for formation of Fe-TiC metal-matrix composites, e) casting the liquid Fe-TiC product into near net shape products. 2. A process as claimed in claim 1 wherein mixing proportions of the reactant powders is in the range of (in percent by weight) 2 to 12% of TiO2, 0.5 to 5% of carbon, 23 to 40% of aluminium and remainder iron-oxide. 3. A process as claimed in claim 1 wherein cryolite (Nas AlFe) and/or calcium fluoride commercial grade powders is added as a fluxing agent in the weight percent of 14 to 40%. 4. A process as claimed in claim 1 wherein the slag to metal weight is in the ratio 3:1 to 1:1, preferably in the range of 1.5:1 to 1:1. 5. A process as claimed in claim 1 wherein the said compaction mixture of reactant powders in a suitable die is preferably under high pressure below 10 Mpa. 6. A process as claimed in claim 1 wherein the charge mix temperature is varied by adding booster mixture, preferably by using sodium nitrate plus aluminium powder. 7. A process as claimed in claim 1 wherein the particle size of titanium oxide powder is preferably between 0.5 to 1.5 micron. 8. A process as claimed in claim 1 wherein particle size of carbon powder as well as aluminium is preferably between 1 to 40 microns. 9. A process for preparation of iron base titanium carbide metal-matrix composites substantially as herein described and illustrated.

Documents:

512-del-2000-abstract.pdf

512-del-2000-claims.pdf

512-DEL-2000-Correspondence-Others-(13-01-2010).pdf

512-del-2000-correspondence-others.pdf

512-del-2000-correspondence-po.pdf

512-del-2000-description (complete).pdf

512-del-2000-drawings.pdf

512-del-2000-form-1.pdf

512-DEL-2000-Form-15-(13-01-2010).pdf

512-del-2000-form-2.pdf

512-del-2000-gpa.pdf