Study On Microstructure And Mechanical Properties Of Ti₂AlNb-based Alloy

Ti2AlNb-based alloy had an excellent mechanical properties for its better room temperature ductility,room temperature fracture toughness,the resistance to crack propagation,antioxidant capacity,a higher specific strength,creep resistance and so on.Therefore,Ti2AlNb-based alloy had a significant meaning on the application of aviation engines in China.The object of the study was Ti-22Al-24 Nb alloy,the effect of solid solution and aging heat treatment on changing rules and the mechanical property were studied.The plane strain fracture toughness of Ti-22Al-24 Nb alloy was tested,and the fracture toughness test was carried out,and the fracture form and fracture mechanism of the alloy were discussed.With the increase of Ti-22Al-24 Nb alloy solid solution time,the primary lath-shaped O phase and the equiax ?2 phrase turned to B2 matrix phase through the phase change reaction.At the same time,the volume fraction of B2 phase increased gradually,the undissolved ?2/O phase began to be equiaxial and began to grow.When the solution temperature was 1000?,partial recrystallization occurred in the B2 phase,and the grain increased gradually with the increase of the solid solution temperature.With the increase of the solid solution time,lath-shaped O phase started to dissolve into the matrix,then the equiaxial ?2 phase began to dissolve,but the undissolved ?2/O phase began to be equiaxial and began to grow,and B2 phase occurred recrystallization and grain growth.Aging time had a obvious effect on the content and the size of the phase in microstructure.With the increase of the aging time,when the time increased to 24 hours,parts of the grains began to grow,and the secondary ?2/O phase grew obviously,but the primary ?2 phase began to grow and to be equiaxial.With the increase of aging time,the changes of the grain's size were not obvious.The mechanical property at room temperature results of Ti-22Al-24 Nb alloy under different solid solution time showed: when the solid solution time was 30 min and 2h,the strength and the hardness of Ti-22Al-24 Nb alloy decreased,but its plasticity increased.But when the solid solution time increased to 3 hours,the plasticity of Ti-22Al-24 Nb alloy trended to decrease,but its strength and hardness trended to increase.Solid solution parameters of optimum mechanical properties of Ti-22Al-24 Nb alloy at room temperature were 1000?/2h/WC(water-cooling),its tensile strength,the yield strength,bickerers hardness,the elongation,the section shrinkage,elastic modulus were respectively 950 MPa,915MPa,344 HV,15.69%,42.28%,90 GPa.The effect ofsolid solution time on mechanical properties of Ti-22Al-24 Nb alloy at high temperature(600?)was demonstrated,and the result showed: The mechanical properties at high temperature were the same as those of room temperature,and the optimum mechanical property of Ti-22Al-24 Nb alloy at high temperature(600 ?)was 1000 /30min/WC(water cooling),the tensile strength,the yield strength and the elongation were respectively 965 MPa,917MPa,15.72%.After been treated with solid solution and aging process by 1000?/2h/WC(water-cooling)and 780?/20h/AC(air-cooling),on one side,Ti-22Al-24 Nb alloy normal mechanical property changed,its strength and hardness increased,but the ductility decreased to 3%.With the increase of the aging time,the alloy's strength and hardness increased further,but the changes of the ductility were not obvious;On the other side,Ti-22Al-24 Nb alloy high mechanical properties changed also,the increase of its strength was not obvious,but the increase of its ductility was obvious.With the increase of the aging time,the high temperature strength of Ti-22Al-24 Nb alloy increased further,but its ductility appeared to decrease.With the increase of solid solution time,Ti-22Al-24 Nb alloy plane fracture toughness trended to increase then to decrease,And the fracture toughness KIC had the maximum value of 51.6MPa.m1/2 when the solution time was 2h;with the increase of solid solution time,the amount of dimples in Ti-22Al-24 Nb alloy fracture morphology increased,but the size of the dimples became bigger,the color of the dimples became deeper.But when the solid solution time increased to 3h,the dimple number decreased greatly,and the alloy fracture was mainly intergranular brittle fracture.