Achieving recrystallization of prior β in Ti-6Al-4V alloy by electroshock

Fine grain strengthening is an important approach to improve mechanical properties in titanium alloys. The martensite (alpha ') of Ti-6Al-4V alloy generally shows fine acicular grain and has high strength. However, the grain size of martensite is influenced by the prior beta grain, thereby affecting the overall strength-plasticity combination of the alloy. Generally, the prior beta grains grow rapidly above beta-transus temperature (similar to 1000 degrees C). It is difficult to refine the prior beta grain through traditional heat treatment alone if it coarsened. In this work, we found that electroshock treatment could directly recrystallize the coarse prior beta grain in alpha+beta titanium alloy without plastic deformation process. EBSD and TEM analyses found that the prior beta grain size reduced from 44 mu m to 29 mu m and the remained textures had been eliminated after electroshock, therefore the tensile strength and elongation were simultaneously improved from 1196 MPa and 4.7 % to 1259 MPa and 10.4 %. The residual subgrain boundaries within prior beta grain, electric current-induced extra driving force and extremely high heating rate (10(6) degrees C/s) are the main reasons for the occurrence of recrystallization as well as no grain growth of prior beta. These findings may be used for repairing the mechanical properties of coarse overheated microstructure or eliminating the anisotropy of columnar grain that produced in additive manufactured alpha+beta titanium alloy without deformation processing.