Effect of microstructure on tensile properties and fracture behavior of intermetallic Ti_2AlNb alloys

The tensile properties and fracture behaviors of Ti 22Al 27Nb and Ti 22Al 20Nb 7Ta alloys were investigated in the temperature range of 25～800?℃. Three typical microstructures were obtained by different thermomechanical processing techniques. The results indicate that the duplex microstructure has an optimum combination of tensile yield strength and ductility both at room and elevated temperatures. Adding Ta to Ti 2AlNb alloy can improve the yield strength, especially at high temperature while retain a good ductility. The study on crack initiation and propagation in deformed microstructure of Ti 2AlNb alloys indicates that microstructure has important effect on the tensile fracture mechanism of the alloys. The cracks initiate within primary O/α 2 grains along O/B 2 boundaries or O phase laths in B 2 matrix, and propagate along primary B 2 grain boundaries for the duplex microstructure. The fracture mode is transgranular with ductile dimples for the duplex and the equiaxed microstructures, but intergranular for the lath microstructure.