Title of Invention

"AM IMPROVED PROCESS FOR THE PREPARATION OF ALUMINIUM-RUTILE COMPOSITE THROUGH A SPRAY FORMING TECHNIQUE"

Abstract

An improved process for the preparation of aluminium-rutile composite through spray forming technique, the said process comprising the steps of: (i) melting of aluminium at a temperature ranging between 750 to 800°C, (ii) adding magnesium to the above said molten aluminium, in a ratio ranging between 1:200 to 1:50 by wt. to enhance the wettability of aluminium reinforced with rutile (Ti02) particles, (iii) degassing the resultant alloy by known method, followed by keeping it into a graphite crucible and allowing it to flow through an atomizer, (iv) superheating the rutile particles of size ranging between 85 to 115 microns, at a temperature ranging between 750 to 800°C and keeping into the inner concentric tube of the spray forming setup and allowing it to flow thorough the above said atomizer, (v) incorporating the above said rutile particles to the degassed resultant alloy obtained in step (iii), in a volumetric ratio ranging between 2 to 12 vol% and spray depositing the desired aluminium-rutile composite prepared on a rotating substrate.

Full Text

Field of the invention This invention relates to an improved process for the preparation of aluminium-rutile composite through spray forming technique. The invention particularly relates for the fabrication of Al based metal matrix composite using a novel spray forming process. Background of the invention The present invention is a simple design and low cost fabrication of Al based metal matrix composite having a wide range of applications in defense, aerospace and other engineering sectors. The composite that is produced in the present invention may be used either directly or after processing by conventional thermo-mechanical treatments such as rolling, extrusion and age hardening. The composites that are fabricated by the present invention may also be extended to use as a near net shape casting. Also, the variation in quantity of adding the reinforcing materials to the matrix is not restricted. In addition, ceramic particles such as SiC, AI2O3, TiN can be dispersed in the Al matrix as reinforcing materials by this new method. The thermo-mechanical treatment of the as sprayed composite improves the mechanical and tribological properties. The thermo-mechanically treated Al-rutile composite can be mainly used as a wear resistant material. In hitherto known processes for the fabrication of Al-rutile (TiO2) composite: Al based metal matrix composites have been synthesized by using this powder metallurgy route. Reference may be made to S.J.Hong, P.w.Kao: Mater. Sci. Eng. A, 119, 1989, Vol. 1-2, pp.153-159 wherein the addition of second phase particles has no limitation. •Using this process, as good as 50:50 compositions of composites could be easily prepared. It is also easy to apply various coatings on the particles to be milled or mixed to make the composites. Finer sized particles up to range of nano size can also be prepared. The process is more flexible for making large number of components in small size. In addition, intricate shaped components can also be made. In .conventional the industrial importance of the liquid phase has resulted in enormous research and development of several innovative technologies. From the voluminous work, it is found that in the liquid phase techniques, the reinforcing elements are either infiltrated or injected into the liquid metal. Mixing, in-situ growth and spray forming techniques are also used to prepare the MMCs. Many Al based metal matrix composites are being fabricated by using liquid metallurgy vortex technique. The process has been considered as a low-cost and easy handling process. The addition of second phase particles is easy and does not require complicated systems. A resistance type furnace is also more suitable for processing of these composites. Temperature and oxidation control are easily maintained. The casting in any type of mould is easy and does not require big handling equipment. This process controls quantity and quality of the composites. In the infiltration technique, the liquid metals are infiltrated into the ceramic preform to yield the composites. Reference may be made to S.Y.Oh, J.A.Cornie and K.C.Russell: Metall. Trans. 1989, Vol. 20A, p. 527, wherein the infiltration techniques is used to drive a liquid metal into the interstices of the preform. The force is essential to overcome the capillary and viscous drag between the reinforcing solids and moving liquids. Several types of infiltration techniques that are reported in literature include pressure less infiltration [reference may be made to Y.Gao, J.Jia, R.E.Loehman and K.G.Ewsuk,: J.Mater. Res. 1995, Vol. 10(5), p.1216], pressure infiltration [reference may be made to S.G.Warrier and R.Y.Lin : Scr. Metall. Mater. 1992, Vol. 27(8), p.1015], vacuum infiltration [C.G.Goetzel and A.J.Shaler,: J. Metals 1964, Vol. 16(11), p. 901] and reactive infiltration [A.E.W.Jarfors, L.Svendsen, M.Wallinder and F.Fredrikson : Metall. Trans. 1993, Vol .24A, p. 2577]. In the pressure infiltration process, a premixed suspension of reinforcing particulates in liquids is solidified under a high hydraulic pressure. The application of high pressure to a solidifying body alters the melting point of the metal that increases the under cooling and results in numerous nucleation and in fine-grained structure. The high pressure also increases the cooling rate, eliminate solidification shrinkages, gas porosities and interfacial micro-voids and the process in general is referred as the squeeze casting. In conventional spray forming consisting of simple step, which includes atomization of liquid metal or composite into fine droplets and immediate deposition on a stationery or moving substrate to produce dense preform in one single step. This process is particularly useful for the synthesis of many engineering materials and composites. It is difficult to prepare such metals /materials and composites by other conventional processes. High cooling rates associated with the process that help in refining grains and minimize both the micro and macro-segregation. The turbulent fluid flow condition produced during deposition helps in the fragmentation of dendrites to yield equi-axed grains, which is known to exhibit better mechanical properties than the former. In conventional squeeze casting process mainly applied when the near net shaped castings are to be developed and the product of casting or ingot doesn't have porosity, shrinkage and other casting defects. All the hitherto known process has the disadvantages as mentioned below: In powder metallurgy route, the elemental powders are generally taken for mixing and attrition that makes the process expensive. The process also requires densification, which is carried out by cold isostatic pressing or hot isostatic pressing and makes the process time consuming and expensive. Also, this process cannot be used for large sized components. In the liquid metallurgy vortex route, size and size distribution of reinforcing particles restricts the process limitations. Also, long holding timings at higher temperatures may lead to generation of other intermetallic phases that deteriorates the , mechanical and chemical properties. In addition, due to poor wettability of reinforcing materials/particles with liquid Al restricts the usage of all reinforcing materials for the fabrication of Al based metal matrix composites. The grain size obtained through this process is comparatively larger than any other processes. In many infiltration processes, the processing steps involved are many and makes the process more complicated. High meting temperatures and high pressures are required and make the process expensive. High-pressure hydraulic presses and heavy-duty equipment are needed for processing of composites by this method. In conventional spray forming process, the porosity levels of the prepared materials or composites are high as compared to all other processes. Moreover, the injection of secondary particles requires special design of the nozzles and injection system. In homogeneity of the dispersion of the secondary phase in the metal matrix is a problem. Special care must be given to avoid this problem. Suring the process, loss of -large amount of reinforcing particles causes the production cost high. In addition, the porosity and non-uniform distribution of second phase particles requires secondary processing. This makes the process more complicated and expensive. Squeeze casting route is certainly beneficial for the fabrication of Al-rutile composite. However, the processing parameters are more precious and invariably the processing cost increases. Highly skilled technical personnel have to be involved for processing the composites using this process. Melting and, pressing has to be carried out separately in this process. The process of present invention provides an improved spray forming process for the preparation of aluminium-rutile metal matrix composite. In the present invention, ' the rutile sand that is abundantly available is just preheated and simultaneously spray deposited on a stable and/or a rotating substrate. The macro and microstructural observations showed a uniform distribution of TiO2 particles and a clean interface was observed in the spray formed composite, Macrostructural observations revealed fine equiaxed grains of Al in as spray formed alloys and composites in comparison to the columnar structure in as cast alloy and stir cast composites. Objectives of the invention The main objective of the present invention is to provide a process for "preparation of aluminum - rutile composite through a spray forming technique, which obviates the drawbacks as detailed above. Another object of the present invention is to provide an improved process for the preparation of aluminium-rutile composite using rutile as raw material for reinforcing that is abundantly available in nature and thereby reduces the cost of product. Yet another object of the present invention is to provide an improved process for the preparation of aluminium-rutile metal matrix composite wherein addition of reinforcing rutile particles in volume fraction has no limitation. Summary of the invention Accordingly, the present invention provides an improved process for the preparation of aluminium-rutile composite through spray forming technique, the said process comprising the steps of: i. melting of aluminium at a temperature ranging between 750 to 800°C, ii. adding magnesium to the above said molten aluminium, in a ratio ranging between 1:200 to 1:50 by wt. to enhance the wettability of aluminium reinforced with rutile (TiO2) particles, iii. degassing the resultant alloy by known method, followed by keeping it into a graphite crucible and allowing it to flow through an atomizer, iv. superheating the rutile particles of size ranging between 85 to 115 microns, at a temperature ranging between 750 to 800°C and keeping into the inner concentric tube of the spray forming setup and allowing it to flow thorough the above said atomizer, v. incorporating the above said rutile particles to the degassed resultant alloy obtained in step (iii), in a volumetric ratio ranging between 2 to 12 vol% and spray depositing the desired aluminium-rutile composite prepared on a rotating substrate. In an embodiment of the present invention about 0.5 wt% of hexachloroethane is used for degassing the molten aluminium alloy. In yet another embodiment the spray forming setup comprises a graphite crucible for containing molten metal, an inner concentric tube of diameter 6 to 10 mm, containing superheated rutile particles in such a way that mixture of rutile particles and molten metal flows through the atomizer by means of an inert gas pressure in the range of 10 to15 kgf and a rotating substrate placed below the atomizer nozzle, for the deposition of the said composite mixture. In yet another embodiment the rotation speed of the substrate used for spraying aluminium-rutile composite is in the range of 100-200rpm. In still another embodiment the substrate used for spraying aluminium-rutile composite is copper. Detailed description of the invention The procedure for melting of Al was similar to conventional meting practice, however the atomization setup used for synthesis of Al-rutile composite was different. The atomization unit consisits of two metallic tubes beng placed concentrically inside the confined type atomizer. The other tube was fitted to the atomizer, while the inner tube was suspeneded by fixing it on the steel frame with a screw and jack arrangemnt so that the tube can be concentrically moved to the desired position. The outer and inner tube sthat were used can be reused several times. In order to avaid the reaction problems, a boron nitride coating was given inside the tubes. This coating not only helps in minimizing the reaction problems but also useful avoid the srosion problems. The wettablity between coating material and liquid metal is very poor. In this new set up of spray forming, the advantage of having two separate tubes enables to vary the speed/flow of metal and particles separately. In oreder to achieve a fine droplets of composite , the melt was atomized using argon gas. The whole atomizing assembly was preheated to 500-600°C so that chocking could be avoided. The novelty of the present invention lies in obtaining a uniform distribution of Al-rutile composite. A new spray forming process has been adopted in which aluminium melt and rutile particles were passed through a set of concentric tubes and atomize the composite melt to disintegrate into fine droplets. These droplets together with dispersed powder were simultaneously deposited on a rotating copper substrate. A uniform distribution of rutile particles in the Al matrix with clean interface was observed in the Al-ruttie composite and the results obtained are superior to stir cast samples. The following examples are presented by way of illustration and should not be construed to limit the scope of the present invention. Example -1 The 1.0 Kg of commercial pure Al was cut into small pieces by a shear cutter. The Al pieces were cleaned with acetone to remove oil and greases. The cleaned Al pieces were placed in a 2kg capacity clay bonded graphite crucible and heated in an electric resistance furnace. In the molten Al, 20gm of Mg were added to make Al-(0.5-2.0) Mg alloy. Before addition of Mg, the Mg pieces were wrapped in Al foil. In order to remove the gases formed during melting, 1wt% hexachloroethane was added. Thorough stirring was done so as to remove the maximum removal of gases. The super heated molten Al at 800°C was poured into a preheated (150°C) crucible that was fixed just above the atomizer. Preheated rutile particles of 100g were charged through inconel tube that was fixed at the center of the graphite crucible. Argon gas of 'lOLAR-1 purity at 10Kgf/cm2 pressure was passed through the atomizing nozzle. The above steps were performed simultaneously. The atomized Al-rutile composite was allowed to deposit on a stationary circular copper plate. After completion of the deposition process, the substrate and composite are cooled with forced water. Example - 2 The 0.8 Kg of commercial pure Al was cut into small pieces by a shear cutter. The Al pieces were cleaned with acetone to remove oil and greases. The cleaned Al pieces were placed in a 2kg capacity clay bonded graphite crucible and heated in an electric resistance furnace. In the molten Al, 20gm of Mg was added to make Al-(0.5-2.0) Mg alloy. Before addition of Mg, the Mg pieces were wrapped in Al foil. In order to remove tfie gases formed during melting, 0.5wt% hexachloroethane was added. Thorough stirring was done so as to remove the maximum removal of gases. The super heated molten Al at 750°C was poured into a preheated (100°C) crucible that was fixed just above the atomizer. Pre heated rutile particles of 80g were charged through inconel tube that was fixed at the center of the graphite crucible. Argon gas of IOLAR-1 purity at 9Kgf/cm2 pressures was passed through the atomizing nozzle. The above steps were performed simultaneously. The atomized Al-rutile composite was allowed to deposit on a circular copper plate rotating at 30rpm. After completion of the deposition process, the substrate and composite are cooled with forced water. Example-3 The 1.2 Kg of commercial pure Al was cut into small pieces by a shear cutter. The al pieces were cleaned with acetone to remove oil and greases. The cleaned Al pieces were placed in 2 kg capacity clay bonded graphite crucible and heated in an electric resistance furnace. In the molten Al, 20gm of Mg was added to make Al-(0.5-2.0) Mg alloy. Before addition of Mg, the Mg pieces were wrapped in Al foil. In order to remove the gases formed during melting, 1.2wt% hexachloroethane was added. Thorough stirring was done so as to remove the maximum removal of gases. The super heated molten Al at 800°C was poured into a preheated (150°C) crucible that was fixed just above the atomizer. Pre heated rutile particles of 100g was charged through inconel tube tat was fixed at the center of the graphite crucible. Argon gas of IOLAR-1 purity at12-15kgf/cm2 pressure was passed thorough the atomizing nozzle. The steps above were performed simultaneously. The atomized Al-rutile composite was allowed to deposit on a circular copper plate rotating at 100rpm. After completion of the deposition process, the substrate and composite are cooled with forced water. The main advantages of the present invention are: The present invention uses the Inconel tube, which can withstand the thermal shock that required in the experimental conditions and not wettable with the molten AI-Mg alloy at 800°C. 1. The inconel tube can be used for repeated experiments. 2. Simultaneous deposition of rutile particles and atomized Al droplets on the copper substrate can be processed in a single operation. 3. Varying the Argon gas pressure during atomization can control the grain size of Al. 4. The addition of rutile particles in volume fraction can be varied from 2-20%. 5. As the process has a simultaneous operation and the incorporation of rutile particles through concentric inconel tube fixed at the center of the atomizer, the possibility of gas entrapment in the composite is negligible. 6. As the Al droplets and rutile particles are simultaneously depositing on the substrate, the distribution of rutile particles in the Al matrix is uniform. 7. Similarly, the loss of rutile particles during spray depositing on the copper substrate is minimum. 8. Standardization of height of atomizer from the copper substrate and rotational speed of copper substrate make the process more efficient. We claim 1. An improved process for the preparation of aluminium-rutile composite through spray forming technique, the said process comprising the steps of: (i) melting of aluminium at a temperature ranging between 750 to 800°C, (ii) adding magnesium to the above said molten aluminium, in a ratio ranging between 1:200 to 1:50 by wt. to enhance the wettability of aluminium reinforced with rutile (TiO2) particles, (iii) degassing the resultant alloy by known method, followed by keeping it into a graphite crucible and allowing it to flow through an atomizer, (iv) superheating the rutile particles of size ranging between 85 to 115 microns, at a temperature ranging between 750 to 800°C and keeping into the inner concentric tube of the spray forming setup and allowing it to flow thorough the above said atomizer, (v) incorporating the above said rutile particles to the degassed resultant alloy obtained in step (iii), in a volumetric ratio ranging between 2 to 12 vol% and spray depositing the desired aluminium-rutile composite prepared on a rotating substrate. 2. An improved process as claimed in claim 1, wherein in step (iii) 0.5 wt% of hexachloroethane is used for degassing the molten aluminium alloy. 3. A process as claimed in 1 wherein the spray forming setup of step (iii) comprises a graphite crucible for containing molten metal, an inner concentric tube of diameter 6 to 10 mm, containing superheated rutile particles so that mixture of rutile particles and molten metal flows through the atomizer by means of an inert gas pressure in the range of 10 to 15 kgf and a rotating substrate placed below the atomizer nozzle, for the deposition of the said composite mixture. 4. An improved process as claimed in claim 1, wherein the rotation speed of the substrate used for spraying aluminium-rutile composite is in the range of 100- 200 rpm. 5. An improved process as claimed in claim 1, wherein the substrate used for spraying aluminium-rutile composite is copper.

Documents:

2627-DEL-2005-Abstract-(02-03-2012).pdf

2627-del-2005-abstract.pdf

2627-DEL-2005-Claims-(02-03-2012).pdf

2627-del-2005-claims.pdf

2627-DEL-2005-Correspondence Others-(02-03-2012).pdf

2627-del-2005-correspondence-others.pdf

2627-del-2005-description (complete).pdf

2627-del-2005-drawings.pdf

2627-del-2005-form-1.pdf

2627-del-2005-form-18.pdf

2627-DEL-2005-Form-2-(02-03-2012).pdf

2627-del-2005-form-2.pdf

2627-DEL-2005-Form-3-(02-03-2012).pdf

2627-del-2005-form-3.pdf

2627-del-2005-form-5.pdf