On the compressive deformation behavior of new beta titanium alloys designed by d-electron method

Three beta titanium alloys in the Ti-Al-Mo-Cr-V system have been designed using the d-electron method with the aim of activating different combinations of deformation mechanisms. In this regard Ti-4Al-7Mo-3V-3Cr (Ti-4733), Ti-3Al-5Mo-7V-3Cr (Ti-3573) and Ti-3Al-8Mo-7V-3Cr (Ti-3873) alloys have been designed and compared with a commercial Ti-5Al-5Mo-5V-3Cr (Ti-5553) alloy. To evaluate the accuracy of the d-electron theoretical predictions, uniaxial compression tests were performed at room temperature. Different characterization methods including X-ray diffraction, electron backscatter diffraction, optical and transmission electron microscopy were used to investigate the microstructural evolution and deformation mechanisms. As a result of the modified deformation mechanisms, all the designed alloys showed enhanced compressive properties in comparison to the Ti-5553 alloy in beta single phase state. It was found that with increasing stability of the beta phase, the deformation mechanism of the new Ti-alloys gradually changes from slip + stress-induced martensitic transformation to slip + stress-induced martensitic transformation + mechanical twinning and finally to slip + mechanical twinning. The results showed that in the case of twinning the prediction by the d-electron method is consistent with experimental observations whereas regarding the stress-induced martensitic transformation this method should be used with considering an expanded martensite region on the lower portion of the d-electron phase stability map.