Plastic deformation mechanism of Ti-Nb-Ta-Zr-O alloy at cryogenic temperatures

The deformation behavior and mechanism of Ti-36Nb-2Ta-3Zr-0.35O alloy at room and cryogenic temperatures (77 and 200K) were investigated. The microstructure near the fracture was observed with electron backscattered diffraction analysis (EBSD) and transmission electron microscopy (TEM). The results show that the plastic deformation behavior of the alloy is sensitive to test temperature and cold deformation history of the alloy. For the alloy without cold deformation, both tensile strength and ductility have a significant enhancement at cryogenic temperatures, mainly due to the occurrence of mechanical twinning. Moreover, with the decrease of the temperature, the density of mechanical twinning increases. For the alloy cold swaged by 85%, an increase in strength accompanied by a decrease in uniform elongation was found at cryogenic temperatures. The unique temperature dependence of the deformation behavior was due to the low stability of phase. At 200K, to phase precipitated in beta phase; while at 77K, an interesting transformation (beta phase to beta' phase) was observed.