Study On The Shape Memory Effect And The Microstructure Of Ti-Nb High Temperature Alloy

The microstructure, martensitic transformation behavior, mechanical propertiesand shape memory effects of Ti-Nb alloys with Nb content16-20at.%were studied inthis paper. The influence of cold-rolled reduction and annealing temperature on themechanical properties and shape memory effects，and the martensite structure evolutionduring this process were also studied.The results show Ti-Nb alloys with Nb content16-20at.%were mainly martensiteat room temperature, trace of residual parent phase and fine dispersive distribution ωphase existed as well. Triangular and V-shaped is the major self-accommodationmorphology in Ti-Nb alloys. The martensite variants were {111} type twins.The martensitic transformation temperature of Ti-16Nb alloy is333℃, and themartensitic transition temperature decreases by40℃with a1at.%increase of Nbcontent.The plasticity of the Ti-Nb alloys is pretty good with elongation rate of40%, buttheir shape memory effects are poor with completed recoverable strain less than2%.Thermo-mechanical treatment can improve the mechanical properties of Ti-Nb alloy.With increasing annealing temperature, the elongation increases, the yield strength isreduced. The Ti-16Nb alloy which annealed at650℃after cold rolled can get100%shape recovery ratio with3%pre-strain.The microstructures of the cold-rolled Ti-Nb alloys are fiber-like with martensitelath warped. Martensite lath gradually restore straight after annealing at differenttemperature, and the martensite laths become smaller compared with the as-cast alloys.And the size of the martensite laths becomes smaller with increasing annealingtemperature. After annealing at650℃, fine sub-grains form via dislocationsrearrangement and in some regions recrystallization occurs.