High Temperature Extruded Honeycomb Structure And Diffusion Bonding Of γ-TiAl Based Alloy

The Ti Al based alloy is one of the most promising high-temperature structrual material for the new generation of alloy,owing to its light weight along with heat resisting strength. Whereas, the current application of Ti Al based alloy is restricted by its difficulty in processing and low ductility at room temperature.To solve the current problems mentioned above, vaccum hot pressed sintering was adopted to produce bulk material of γ-Ti Al based alloy. The effect of sintering temperature on the quality of forming blank was studied;High-temperature compression simulation of sintered γ-Ti Al based alloy was analyzed in order to acquire the optimal hot deformation parameter; Experiment on extruded honeycomb structure was carried out, so that differences in microstructure and mechanical properties before and after extrusion were contrastively analyzed; The diffusion bonding technology of γ-Ti Al based alloy was investigated to uncover the effect of diffusion temperature and time on interface and strength of attachment joint; At last, the sound joint between honeycomb structure and covering was realized, and a hollow honeycomb structure was acquired.The study of hot pressing experiment on Ti-47Al-2Cr-1.8Nb-0.2W-0.15B(at%)pre-alloyed powder, at the temperature ranging from 1100℃ to 1300℃, shows that the sintered material are mainly composed of γ-Ti Al and α2-Ti3 Al phase. Its microstructure is mainly composed of equiaxial γ grain and α2/γ lamellar. Along with the rising up of temperature, lamellar structure and equiaxial grain extended, and the volume fracture of lamellar structure varied from 17.8% to 29.8%. In conclusion, the optimal sintering parameter is 1250℃ in temperature, 50 MPa in pressure, and 2 hours in the length of time.The experiment of hot deformation was conducted at the temperature ranging from 1050℃ to 1250℃, and 0.001s-1,0.01s-1,0.1s-1 was selected as the strain rate. The result illustrated that the dominant softening mechanism of sintered material were dynamic recovery and dynamic recrystallization. Material which were extruded at 1150℃ and 1200℃ have an obviously raised density and a fine and uniform microstructure. The whole deformation was a steady-state flow process. It indicates that the sintered γ-Ti Al based alloy has a relatively low yield-stress, which is favorable to hot working at a certain temperature.Based on the hot extruded characteristic of γ-Ti Al honeycomb structure at the temperature of 1150℃,1200℃,1250℃,the density of extruded honeycomb structure was elevated and the lamellar structure turned to be curved, which were regarded as the main reason for the improvement of comprehensive mechanical properties.The diffusion bonding research of γ-Ti Al based alloy was conducted at the temperature range of 900-1100℃. With the increase of temperature and holding time, an obvious decrease of porosity can be observed. The interface was replaced by an integrated microstructure,and a region of recrystallization was formed. In addition, the strength of joint increases as the temperature changes, and the joint strength can be reached at 329 MPa at the bonding parameter of 30 MPa in pressure, 1000℃ in temperature, and 1.5hours in the length of time.