Texture evolution and deformation - induced amorphization in high pressure torsion of W

Abstract

Severe plastic deformation is a convenient method to prepare amorphous materials directly. To study the mechanism and critical conditions of deformation-induced amorphization, high pressure torsion (HPT) experiments of 1, 2, 5 and 10 turns subjected to sintered W were performed under 823 K at 1.5 GPa. The microstructures of sintered and HPT-processed W were observed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). In HPT, the angle between the (110) crystal plane of grains and the tangential direction decreased with more turns of HPT and the Schmid factor value of the texture with (110) was the biggest during HPT. It is implied that the slip systems in {110} were the easiest to be activated. Therefore, the number of dislocations in (110) crystal plane was the largest. Likewise, the dislocations on the grain boundaries increased with more turns of HPT. It is concluded that the grains with (110) orientation were more likely to transform into the amorphous structure and grain boundaries were the first area to occur deformation-induced amorphization. Deformation-induced amorphization mainly depends on three factors: temperature, local dislocation density and grain size. The critical local dislocation density is ∼6 × 1016 m−2 and the critical grain size is ∼62.4 nm for W in HPT under 823 K.