Title of Invention

A PROCESS FOR MAKING DENSE CERAMIC COMPOSITES CONTAINING γ-AION, TiN AND YAG

Abstract

A process of making dense ceramic composites containing Aluminium nitride, γ-Al23O2?N5, titanium nitride and Y3Al5O12 by mixing by milling 92 to 96wt % A1N, 2 to 4 wt % ¥263 and 2 to 4wt % Ti02 powder in isopropanol medium, drying the mix and subjecting the dry mix so obtained to compaction and heat treatment by applying an isostatic pressure in the range of 100-300 MPa and then sintering the compacted powder under nitrogen gas at a pressure in the range of 1 to 50 psig over atmospheric pressure and a temperature in the range of 1700 to 1800°C for a period in the range of 1/2 to 1 h to obtain dense ceramic composite containing Aluminium nitride 40-60 vol. percent, y-Al23O27N5, 15-30 vol. percent, titanium nitride 5-20 Vol. Percent and Y3Al5O12 10-20 vol. percent.

Full Text

The present invention relates to a process of making dense ceramic composites containing AlN,γ-AlON, TiN and YAG . The present invention particularly relates to a process of making dense ceramic composites containing A1N, Al23O27N5,TiN and Y3Al5O12. The said composites may be used as wear parts, structural and electrical resistive components and refractories in a wide temperature range. The composite has sub micron size hard and elastic inclusion of TiN and YAG within a matrix of mainly A1N and A1ON. The present day method of making similar composites consisting of mixing the ingredients in acetone using Tungsten Carbide media and then hot pressing the powder at 1900°C at 30 MPa for 30 minutes reference for which may be made to "Mechanical Properties & Oxidation behavior of Al2O3-AlN-TiN composites." J. American Ceramic Society (75 (8) 2251 -2259,1992) wherein composites containing TiN, y-AlON and TiN, γ-AlON and Y3AlsOi2 have been prepared from a starting composition of A1N (0-50 wt.%) A12O3 (0-58 wt.%) and TiN 42 wt.%.) Properties of these composites prepared were : density 3.8-4.4, KIC-5.1 -6.25, MOR 370-550 MPa (3 point bending). A further reference may be made to D.SJPreera in "Nitrogen Containing Aluminium Titanate" J. of Material Science 26 (6) 1585-87,(1991) wherein a composite of Aluminium Titanate phase supposed to contain nitrogen along with A12O3 and TiN was prepared from a mixture of A1N, A12O3 and TiN by mixing ethanol,drying,compacting and then in firing under dynamic nitrogen atmosphere at 1470-1720°C. The main drawbacks of the above composites and the processes are 1. The required quantity of TiN is quite high to achieve high strength material which is expensive. 2. TiN a costly ingredient need to be added to the starting material before sintering. 3. Substantially high temperature (1900°C and above) and hot pressing was needed to sinter the material. The main object of the present invention is to provide a process for making dense ceramic composites containing A1N, γ-AlON, TiN and YAG which obviates the drawbacks as mentioned above. Another object of the present invention is to form TiN particle with a fine grain size (less than 1 (am) in-situ inside the matrix. Yet another object of the present invention is to provide a ceramic composite containing A1N and γ-AlON, the chemical formula of which is Al23O27N5 as the primary constituents and TiN and YAG the chemical formula of which is Y3Al5O12 as secondary phases made to form in-situ in the composites. Accordingly the present invention provides a process of making dense ceramic composites containing Aluminium nitride, γ-Al23O27N5 , titanium nitride and Y3Al5O12 which comprises mixing by milling 92 to 96wt % A1N, 2 to 4 wt % Y2O3 and 2 to 4wt % TiO2 powder in isopropanol medium, drying the mix and subjecting the dry mix so obtained to compaction and heat treatment by applying an isostatic pressure in the range of 100-300 MPa and then sintering the compacted powder under nitrogen gas at a pressure in the range of 1 to 50 psig over atmospheric pressure and a temperature in the range of 1700 to 1800°C for a period in the range of 1/2 to 1 h to obtain dense ceramic composite containing Aluminium nitride 40-60 vol. percent, γ- Al23O27N5 , 15-30 vol. percent, titanium nitride 5-20 Vol. Percent and Y3Al5O12 10-20 vol.percent. In an embodiment of the present invention A1N powder used may be of composition N: 15 to 33 wt %, C:0.1 to 0.5wt% and of surface area 3 m2/g. In another embodiment of the present invention Y2O3 powder used may be of 99.9% purity and of surface area 4 m2/g. In yet another embodiment of the present invention TiO2 powder used may be of purity 98% and of surface area 50 m2/g. In yet another embodiment of the present invention, the dry mix may be subjected to compaction and heat treatment by applying an isostatic pressure in the range of 100-300 MPa and then sintering the compacted powder under nitrogen gas at a pressure in the range of 1 to 50 psig over atmospheric pressure and a temperature in the range of 1700 to 1800°C for a period in the range of 1/2 to 1 h. In yet another embodiment of the present invention, the dry mix may be subjected to compaction and heat treatment by hot-pressing with an applied pressure in the range of 15-25 MPa under nitrogen atmosphere at temperature in the range of 1750°C to 1850°C using graphite die and punch. Detail of the process of making the composites is given below. 1. 92 to 96 % AJN, 2 to 4 % Y2O3, and 2 to 4 % TiO2 powder is mixed in isopropanol by milling. 2. The mixture is dried in an oven. 3. The dry mix may be compacted and heat treated as follows : a: Dry mix is compacted under isostatic press in the range of 100-300 MPa and heated under nitrogen gas at a pressure in the range of 1 to 50 psig at a temperatures in the range of 1700 to 1800°C for a period in the range of ½ to 1 hour. b: Dry mix is hot pressed with an applied pressure in the range of 15-25 MPa under nitrogen atmosphere at a temperature ranging from 1750 to 1850°C using graphite die and punch. The novelty of the process of the present invention resides in preparing a dense ceramic composite containing A1N : 40-60 Vol. percent, γ-AlON ; 15-30 Vol. Percent, TiN : 5-20 Vol. Percent and YAG : 10-20 Vol.percent. The dense ceramic composites so obtained have improved thermal conductivity, chemical and wear resistance as compared to similar composites known in the art. The above novel features have been obtained by the inventive step of providing a mix consisting of 92 to 96 % AIM, 2 to 4 % Y2O3,and 2 to 4 % TiO2 powder, particularly TiO2 which results in formation of TiN submicron particle in the matrix of A1N and γ-AlON . Another inventive step resides in addition of Y2O3 to the ingredients to form YAG ( Y3Al5O12) in the final product and helps improved sintering of the composite. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example - 1 94 g A1N, 4g Y2O3 and 2g TiO2 powders are taken in a polypropelene jar. 1 00ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixes the ingredients thoroughly by rotating action for 24h . The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 5 g of the dried powder was then pressed to form green compacts of dia. 15mm and length 20mm by applying isostatic pressure. The compact was then heated in nitrogen atmosphere (30 psig over atmospheric pressure) after evacuation of the furnace thrice and held at 1800°C temperature for Ih. After that, the furnace was put off and the sample was cooled to room temperature. The chemical constituents of the composite have been identified by X-ray Diffraction studies and found to contain AlN,y-AlON,TiN and YAG. Properties of the specimen prepared was as follows : Densiry-3.22. Example -2 94 g AIM, 4g Y2O3 and 2g TiO2 powders are taken in a polypropelene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer which mixed the ingredients thoroughly by rotating action for 24h . The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 5 g of the dried powder was then pressed to form green compacts of dia. 15mm and length 20mm by applying isostatic pressure. The compact was then heated in nitrogen atmosphere (60 psig over atmospheric pressure) after evacuation of the heating furnace thrice and held at temperature 1800°C for Ih. After that the furnace was put off and the sample was cooled to room temperature. Properties of the specimen prepared was as follows : Density-3.30. Example -3 94 g A1N, 4g Y2O3 and 2g TiO2 powders are taken in a polypropylene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixed the ingredients thoroughly by rotating action for 24h . The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 5 g of the dried powder was then pressed to form green compacts of dia- 15mm and length 20mm by applying isostatic pressure. The compact was then heated in nitrogen atmosphere (90 psig over atmospheric pressure) after evacuation of the heating furnace thrice and held at temperature 1800°C for Ih. Aiter that the fornace was put off and the sample was cooled to room temperature. Properties of the. specimen prepared was as follows : Density-3.43, Young's Modulus- 363 GPa, Hardness-14.24 GPa and Fracture Toughness-4.3MPa m1/2Example -4 92 g A1N, 4g Y2O3 and 4g TiO2 powders are taken in a polypropelene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixed the ingredients thoroughly by rotating action for 24h . The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 5 g of the dried powder was then pressed to form green compacts of dia. 15mm and length 20mm by applying isostatic pressure. The compact was then heated in nitrogen atmosphere (50 psig over atmospheric pressure) after evacuation of the heating furnace thrice and held at temperature 1750°C for Ih. After that the furnace i was put off and the sample was cooled to room temperature. Properties of the specimen prepared was as follows : Density-3.62, Young's Modulus- 406 GPa, Hardness-14.85 GPa and Fracture Toughness-5.27 MPa ml/2. Example -5 96 g A1N, 2g Y203 and 2g TiO2 powders are taken in a polypropelene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixed the ingredients thoroughly by rotating action for 24h. The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 80 g of the dried powder was then hot pressed by a graphite die-punch to form compacts of dia. 70mm and height 7mm by applying 250psi punch pressure in nitrogen atmosphere after evacuation of the heating furnace thrice and held at temperature 1750°C for 30 sec . After that the pressure was released and furnace was put off and the sample was cooled to room temperature. Properties of the specimen prepared was as follows : Density-3.26 Example - 6 96g A1N, 2g Y2O3 and 2g TiO2 powders are taken in a polypropelene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixed the ingredients; thoroughly by rotating action for 24h . The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 80 g of the dried powder was then hot pressed by a graphite die-punch to form compacts of dia. 70mm and height 7mm by applying 250psi punch pressure in nitrogen atmosphere after evacuation of the heating furnace thrice and held at temperature 1850°C for 60 sec . After that the pressure was released and furnace was put off and the sample was cooled to room temperature. Properties of the specimen prepared was as follows: Density-3.36gms/cc, Young's Modulus-350 GPa, Hardness-13.54 GPa and Fracture Toughness-4.09 MPam1/2. Example-7 92 g AIM, 4g Y2O3 and 4g TiO2 powders are taken in a polypropelene jar. 100ml isopropanol was poured inside the jar and the jar was then sealed and placed in a mechanical mixer that mixed the ingredients thoroughly by rotating action for24h. The slurry was then transferred to an enameled tray and dried in an oven for 2h. About 80 g of the dried powder was then hot pressed by a graphite die-punch to form compacts of dia. 70mm and height 7mm by applying 250psi punch pressure in nitrogen atmosphere after evacuation of the heating furnace thrice and held at temperature 1850°C for 60 sec . After that the pressure was released and furnace was put off and the sample was cooled to room temperature. Properties of the specimen was as follows: Density-3.6, Young's Modulus- 406 GPa, Hardness-13.38 GPa and Fracture Toughness-3.0 MPam½ The advantage of the invented process is that 1. No TiN is necessary to add to the raw material before processing. 2. Grain size of TiN formed is very small. 3. TiN grains reside on both intra as well as intergranular position of A1N matrix thus increasing the strength by crack surface roughening. 4. The composite matrix is mainly A1N so that higher thermal conductivity, chemical resistance and wear resistance of A1N is not reduced to a great extent by sacrificing too much to the brittle A1ON and TiN grains. 5. Substantial hardness as well as fracture toughness is achieved by the formation of less quantity of TiN phase in the ultimate product. Claim: 1. A process of making dense ceramic composites containing Aluminium nitride, γ-Al23O27N5, titanium nitride and Y3Al5O 12 which comprises mixing by milling 92 to 96wt % A1N, 2 to 4 wt % Y2O3 and 2 to 4wt % TiO2 powder in isopropanol medium, drying the mix and subjecting the dry mix so obtained to compaction and heat treatment by applying an isostatic pressure in the range of 100-300 MPa and then sintering the compacted powder under nitrogen gas at a pressure in the range of 1 to 50 psig over atmospheric pressure and a temperature in the range of 1700 to 1800°C for a period in the range of 1/2 to 1 h to obtain dense ceramic composite containing Aluminium nitride 40-60 vol. percent, γ- Al23O27N5, 15-30 vol. percent, titanium nitride 5-20 Vol. Percent and Y3Al5O 12 10-20 vol.percent. 2. A process as claimed in claim 1 wherein A1N powder contains Nitrogen in an amount 15 to 33 wt % and of surface area 3 m 2/g. 3. A process as claimed in claiml-2 wherein Y2O3 powder used is of purity of 99.9 % purity and of surface area 4 m2/g , 4. A process as claimed in claiml-3 wherein Ti02 powder used is of purity 98 % and of the surface area 50 m2/g. 5. A process as claimed in claim 1-4 wherein the dry mix is subjected to compaction and heat treatment by hot-pressing with an applied pressure in the range of 15-25 MPa preferably under nitrogen atmosphere at temperature in the range of 1750°C to 1850°C using graphite die and punch. 6. A process of making dense ceramic composites containing Aluminium nitride, γ-Al23O27N5, titanium nitride and Y3Al5O 12 substantially as herein described with reference to the examples.

Documents:

307-del-2001-abstract.pdf

307-del-2001-claims.pdf

307-del-2001-correspondence-others.pdf

307-del-2001-correspondence-po.pdf

307-del-2001-description (complete).pdf

307-del-2001-form-1.pdf

307-del-2001-form-18.pdf

307-del-2001-form-2.pdf