Influence Of Niobium Content On Microstructure And Mechanical Properties Of Ti-Nb-Ta-Zr Alloy

In comparison to the presently usedα+βtitanium alloysβtitanium alloys have many advantageous mechanical properties, such as improved wear resistance, high elasticity, excellent cold and hot formability.Some Ti–Nb-based alloys with non-toxic elements has been put into practical application. Study was made on the effect of Nb content on transformation strain of martensitic transformation in Ti–(15–35) at.% Nb alloys. It revealed that the martensitic transformation start temperature (MS) decreased significantly with increasing Nb content.This research mainly focus on the influence of niobium content on the microstructure and mechanical properties of Ti-Nb-Ta-Zr alloys. Also, experiments were made to discuss the effect of hot-forging deformation rate and solid-solution treatment procedure on microstructure and mechanical properties of Ti-Nb-Ta-Zr alloys. The results are:with less niobium the grain size ofβphase in Ti-xNb-3Zr-2Ta(x=35,31,27,23)(wt.%) alloys increased significantly and the Ti-xNb-3Zr-2Ta system were more likely to formα" phase and evenαphase. Ultimate Tensile Strength of Ti-xNb-3Zr-2Ta alloys improved as Nb content was decreased. The superelasticity range of the investigated alloys is Ti23Nb3Zr2Ta–Ti27Nb3Zr2Ta>Ti35Nb3Zr2Ta>Ti31Nb3Zr2Ta-Ti31Nb3Zr3Ta. Because Ti23Nb3Zr2Ta and Ti27Nb3Zr2Ta had higher yield strength, reversible martensite could be formed prior to permanent deformation. Ti31Nb3Zr2Ta and Ti31Nb3Zr3Ta had better shape memory property than Ti35Nb3Zr2Ta and Ti23Nb3Zr2Ta did. TEM observation found that dislocation density inαphase is much lower than that ofβphase. This explained that Ti23Nb3Zr2Ta withαprecipitation had high tensile strength.α" martensite in Ti-xNb-3Zr-2Ta (x=33,31,29,27,25)(wt.%) alloys could be formed during water quenching and decreasing Nb content intend to promote the formation ofα" martensite. Only littleα" phase could be found in air cooling group. This result revealed that microstructures of metastable Ti-xNb-3Zr-2Ta alloys were very sensible to cooling rate. Microhardness of Ti-xNb-3Zr-2Ta increased significantly as Nb content was decreased. Grain size of Ti-25Nb-3Zr-2Ta alloy increased proportionately with the decrease of deformation ratio. Elevated solid-solution treatment temperature led to grain coursing. This indicated that microstructures of metastable Ti-xNb-3Zr-2Ta alloys were also sensible to hot-deformation ratio and solidsolution treatment temperature.