Influence of microtexture on ultrasonic reflection in Ti-6Al-4V alloy hot-forged in α+β region

Abstract

Morphological change in regions with microtexture, i.e., macrozones, in Ti-6Al-4V alloy after hot-forging in α+β phase region was analyzed using SEM/EBSD technique, and then the correlation with ultrasonic reflection was investigated. Starting material had colony-type microstructure consisting of lamellar-α with the same crystallographic orientation. Forging (cogging and upsetting) was conducted in α+β phase region to produce a cylindrical material with smaller cross section, followed by air cooling. Thus, resulting microstructure consisted of granular-α. To estimate local change in elastic modulus within the materials, we analyzed crystallographic orientations of α-phase using SEM/EBSD in terms of an inclination angle of c-axis. The regions having the nearly common crystallographic orientations of α-phase were found. Shapes of such regions with microtexture were elongated along the axial direction, which formed quasi-periodic variation of the inclination angle, i.e., elastic modulus, of α-phase along the radial direction of the forged material. Ultrasonic measurement was conducted at a frequency of 5 MHz along the radial direction and the axial direction. Relationship between the morphology of regions having microtexture and the amplitude of backscattered noises was evaluated. It was considered that the quasi-periodicity of the inclination angle correlated with the amplitude of backscattered noises in ultrasonic measurement.