Composition Design Of TWIP Type Ti-Mo Alloys And Their Microstructures And Mechanical Properties

Titanium and titanium alloys have been widely used in the fields of aerospace,biomedical and marine engineering due to their low density,high specific strength,good biocompatibility and high corrosion resistance.However,traditional titanium alloys generally exhibit low plastic deformation ability and no significant work hardening behavior,which severely limits their further engineering application.Recently,β-type titanium alloys with twinning-induced plasticity(TWIP)effect have attracted wide attention due to their good ductility and remarkable work hardening behavior,while the low yield strength of this type alloys limits their application as the key structural components.The critical issue is to further enhance their yield strength by controlling alloy composition.Therefore,it is necessary to deeply understand the effect of alloying elements on deformation mode,and then more effectively develop β-type titanium alloys with a good strength-ductility combination by accurately controlling the deformation mode through composition design.In this paper,the effects of α phase stability element(Al),neutral element(Zr)and β phase stability element(Mo and Fe)on microstructures and mechanical properties in β-type Ti-Mo binary alloys were investigated.Based on the above research,the Ti-Mo-Fe-Zr and Ti-Mo-FeNb quaternary alloys were designed using the cluster-plus-glue-atom model,combined with delectron alloy design theory,Mo equivalency,e/a ratio and other empirical parameters.The microstructures and mechanical properties of above alloys were studied,and the microstructural evolution and deformation mode were further discussed.The results showed that the microstructures of Ti-Mo-Al alloys exhibited fine acicular α’’martensite in solution treatment condition and after compressive deformation.With increasing of Al content,the compressive yield strength of the alloys decreased slightly and the compressive curves occurred double yield phenomenon.Ti-Mo-Al alloys demonstrated relatively large uniform elongation,but the work hardening rate decreased rapidly after yielding.Ti-Mo-Zr alloys and Ti-Mo-Fe alloys changed from acicular α’’ martensite to large β grains after solution treatment with increasing of Zr and Mo content.These alloys exhibited relatively large uniform elongation and work hardening rate,which may be related to the plate-like features after compressive deformation.The Ti-Mo-Fe-Zr and Ti-Mo-Fe-Nb alloys exhibited single β phase after solution treatment,and the alloys exhibited high yield strength,large uniform elongation and good work hardening behavior.Stress induced α’’ martensite and{332}<113> twins formed in the Ti-7.81Mo-1.52Fe-4.95 Zr alloy after 5% tensile deformation,while {332}<113> twins and {112}<111> twins were observed in the Ti-7.62Mo-1.48Fe-9.83 Nb alloy.The high yield strength resulted from the solid-solution strengthening effect of alloying elements and ω phase dispersion strengthening effect,and the large uniform elongation and work hardening rate due to dynamic Hall-Petch effect caused by stress induced α’’martensite transformation,{332}<113> twinning and {112}<111> twinning.