Influence of Microstructure on Ultrasonic Backscattering Noise in Beta Forged Ti‐6246

Abstract

In order to evaluate the detectability of defects, ultrasonic backscattering noise in forged Ti-6246 was investigated. An axisymmetric forging was employed at the temperature above the transus. After solution and aging heat treatment, microstructural observation and ultrasonic measurements at frequencies of 5, 10 and 15 MHz were carried out. After the hot forging, flattened grains formed. The mean distance between grain boundaries decreased with increasing reduction. Taking into account results of computer simulation regarding ultrasonic scattering, it was concluded that the noise initially increased with increasing strain due to a morphological change of grains, whereas the noise inversely decreased if the mean distance between grain boundaries was sufficiently smaller than the ultrasonic wavelength. These findings are applicable to the prediction of the noise level with the initial gain size and forging strain.