| TiAl alloys is considered to be the potential high-temperature alloy material in current alloy areas with highly oxidation resistance and mechanical properties at high-temperature conditions,which has been widely used in the field of aerospace and automotive sector.At present,the application of TiAl alloys has been carried out in Chinese industry,but the properties of TiAl alloys lead to the processing difficulties at room temperature.Considering of the difficulties of alloys processing,the high Nb-TiAl alloys were prepared by metal injection moulding process(MIM process),and the deblinding and sintering process were studied,the main research conclusions of this thesis include:1).The solvent debinding were done and found that: At the same time interval for degreasing,the higher rate of removal for the binder can be got when the samples are at the higher degreasing temperature;At the same temperature conditions for degreasing,the higher rate of the removal for binder can be obtained when taking longer degreasing time;Under the same degreasing conditions(degreasing temperature and degreasing time are the same),the less defects can be got at the solvent degreasing process with the thinner blank sample and the higher the binder removal rate;The binder removal rate also got higher by using the larger surface area volume ratio of sample.The solvent degreasing is affected by several factors,such as the degreasing temperature,degreasing time,and specimen shape etc.According to the comparative analysis of above conclusions,the optimum degreasing conditions of solvent degreasing of high Nb-TiAl alloy powder injection molding process are as below: Use a single solution trichlorethylene as degreasing solution for 12 hours degreasing time at 70 ℃.2).The optimum process of the thermal degreasing process was determined by studying the characteristics of binder used in injection molding and DSC test: the temperature rising for 60 mins from 0 ℃ to 120℃;the temperature rising for 180 mins from 120 ℃ to 300℃;the temperature rising for 240 mins from 300 ℃ to 450℃,and then hold for 60 mins at 450℃;the temperature rising for 90 mins from 450 ℃ to 620℃,and then hold for 60 mins at 620℃;the temperature rising for 60 mins from 620℃ to 850℃,and then hold for 60 mins at 850℃;The researches show that the binder has been almost completely removed after hot degreasing.And at the same thermal degreasing conditions,the rate of final degreasing can be higher with the larger the surface area to volume ratio of specimen;After the pre-sintering of heat degreasing,TiAl3 compound has occurred in the blanks,and provided conditions for the further densification sintering.3).The optimum sintering process of high Nb-Ti Al alloys using MIM was determined after comparing the shrinkage of the sample,sintered density,flexural strength,hardness and bending fracture morphology at different sintering temperature,they are: carried out the thermal degreasing process under 850 ℃,and when the temperature are higher than 850 ℃,the final high temperature sintering after pre-sintered began,and then,taking 120 mins to get the temperature from 850 ℃ to 1480 ℃,and hold 120 min at a maximum temperature of 1480 ℃,then cooled to room temperature with the furnace.The samples sintered at this temperature have the uniform tissue composition,small lamellar structure gap,fine grain,homogeneous distribution between Nb and B elements,and Nb single substance was more thorough and diffusion in the matrix,and in this sintering temperature the C elements was granular and uniform distributed. |
