Microstructure And Mechanical Properties Of Incremental Sintered TiAl Based Alloys

TiAl-based alloys have good oxidation resistance,low density and high temperature resistance,but the low room temperature plasticity and poor processing and formability still restrict the development of TiAl-based alloys.In this paper,spark plasma sintering process is used to fabricate Ti-43.63Al-1.2Mo-4.0Nb alloy and the structure and properties of obtained alloy under different process parameters are analyzed.Based on experimentai results,the optimal sintering parameters are obtained.Using the optimal sintering process parameters,the TiAl-based alloy with same composition of Ti-43.63Al-1.2Mo-4.0Nb was incrementally sintered with different sintering methods and sintering temperatures.Moreover,the incremental sintering experiment was carried out for TiAl-based alloys with different compositions of Ti-43.63Al-1.2Mo-4.0Nb and Ti-46.5Al-2.15Cr-1.90Nb-(B,Y,Mo).The above experiments contribute to determining the optimal sintering m ethod and the appropriate experimental condition for the incremental sintering of heterogeneous TiAl-based alloys.The main phase of Ti-43.63Al-1.2Mo-4.0Nb alloy powders prepared by gas atomization is B₂ phase,and the powders also contain a small amount of?₂ and?phases.The appearance of the powder is mostly spherical,and the cross section of the powder is dendritic microstructure.The eutectoid transformation temperature T _eof the alloy powders is about 1186?,and the?-phase transformation point T_?temperature is about 1314?.The loose-loading density and fluidity of the alloy powders were tested,and the loose-loading density was 2.75 g·cm^-3 and the fluidity was 38.20s·(50g)^-1.The ABAQUS software was used to numerically simulate the plastic deformation and densification behavior during the powder sintering process.Based on the results of the numerical simulation,the subsequent sintering temperature was set at temperature range of 950??1250?.The influence of different sintering temperature and holding time on the microstructure and properties of Ti-43.63Al-1.2Mo-4.0Nb alloy was studied.The experimental results show that when the sintering temperature is 1100?,the microstructure of the sintered a lloy is a three-phase homogenized structure of?₂,?,and B₂,and a small part of the microstructure that B₂ phase is the matrix with uniformly distributed?phase and?₂ phase particles.For this sintered alloy,the yield strength is 1062.41MPa,the frac ture strength is1726.81MPa,and the plastic strain is 0.28.At 1100?,the holding time is further optimized.It is determined that the optimal sintering parameters of Ti-43.63Al-1.2Mo-4.0Nb alloy are:1100?and holding for 9-12min,because the alloy sintered under these parameters has the best comprehensive performance at room temperature.The evolution of microstructure and properties of Ti-43.63Al-1.2Mo-4.0Nb alloy during sintering was analyzed.The strong?-phase stabilizing effect of Mo and Nb elements is confirmed,and it is found that the B₂-rich phase particles have a greater amount of deformation than the B₂-poor particles.The sintering temperature will change the density and microstructure of the sintered alloy and thus affect the compression performance.Meanwhile,the holding time only changes the density of the sintered alloy and is not able to change the microstructure of the sintered alloy.However,excessive heat preservation during sintering will coarsen the microstructure and adversely affect the compression performance.The ABAQUS software was used to numerically simulate the plastic deformation and densification behavior of the same TiAl-based alloy(Ti-43.63Al-1.2Mo-4.0Nb)during incremental sintering.It was found that the alloy powder compact has a relatively higher density when using the sintering method of"upper powder and lower block",rather than"upper block and lower block".Then,the incremental sintering experiments for TiAl-based alloys with the same composition and different compositions were carried out using different sintering methods and sintering temperatures.Through incremental sintering experiments of the same TiAl-based alloy,it is determined that the best sintering method for incremental sintering is:"upper powder and lower block"and rough connecting surface of the primary sintered block in this dissertation According to incremental sintering experiments of heterogeneous TiAl-based alloys,the optimal sintering temperature was determined to be 1100?in this dissertation.The active mechanism of current in the incremental sintering process is analyzed.The current density of the connection interface of the"upper powder and lower block"sintering method is greater than that of the"upper block and lower powder",le ading to better densification effect.From the perspective of the friction evaluated by the simulation results,the sintering method of"upper powder and lower block"is also better for densification.Therefore,it can be considered that the sintering me thod of"upper powder and lower block"is optimized due to the synergetic effect of these two factors in this dissertation.