Microstructure evolution of the rolled tungsten during the current-assisted annealing treatment

Abstract

Current-assisted annealing treatment (CAAT) is a promising method for adjusting the microstructure of metals. It was employed to heat treat the tungsten (W) with a rolling deformation of 90% to clarify its microstructure evolution under the action of current. The grain morphologies before and after heat treatment were observed by metallographic microscopy. Compared to traditional heat treatment, the CAATed W is easier to achieve full recrystallization with finer and more uniform grains. This indicates that the current increases the nucleation rate of recrystallization. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was applied to describe the increase rate of recrystallization fraction. It can be calculated that the apparent activation energy of recrystallization under current is only 352.9 kJ/mol. Combined with electron backscatter diffraction (EBSD) characterization, the rolled W prefers to align along the 〈100〉 // ND orientation with the prolonging of current action time. In essence, the acceleration of recrystallization and the tendency of grain orientation are both related to the atomic migration enhanced by current. The electric current can generate an additional driving force for atomic migration, especially in regions with high electrical resistivity, where this driving force becomes more pronounced, leading to intensified atomic migration.