Microstructural Change of Beta Type Titanium Alloy by Intense Plastic Deformation
Usual static recrystallization treatment and a method to provide intense plastic deformation, ARB namely Accumulative Roll-Bonding, have been applied to two beta type titanium alloys, i.e. Ti-29Nb-13Ta-4.6Zr and Ti-15V-3Cr-3Sn-3Al. Microstructural change as well as work-hardening behavior was examined as a function of plastic strain. Both the work-hardening rate and the hardness at the initial as-hot-rolled state were smaller in the Ti-Nb-Ta-Zr alloy than in the Ti-V-Cr-Sn-Al alloy. Recrystallized grains of 14μm in size were obtained by the usual static recrystallization treatment, which was significantly smaller than that of the starting as-hot-rolled plate of 38μm. No significant change other than flattening and elongating of the original grains was found in the optical microscopic scale. It was revealed, however, from a TEM observation combined with selected area diffraction technique that geometric dynamic recrystallization occurred in the Ti-Nb-Ta-Zr alloy deformed at room temperature by a true strain of 5, resulting in an ultra-fine-grained microstructure where the grain size was roughly estimated to be about 100nm.
G. Itoh et al., "Microstructural Change of Beta Type Titanium Alloy by Intense Plastic Deformation ", Materials Science Forum, Vols. 503-504, pp. 705-710, 2006