Ultrasonic fatigue of a single crystal Ni-base superalloy at 1000°C

An ultrasonic fatigue testing system capable of operating at temperatures up to 1000 degrees C has been developed and utilized to study the fatigue behavior of a single crystal superalloy (PWA 1484) at a temperature of 1000 degrees C and loading frequency of approximately 20kHz. The stress-life data generated from the ultrasonic testing system were comparable to those from conventional servo-hydraulic fatigue tests for similar single crystal alloys. Interior Ta-rich carbides were the major microstructural feature responsible for crack initiation in the alloy. Crack growth under ultrasonic loading frequency at 1000 degrees C for PWA 1484 occurred in a crystallographic manner on {111) octahedral slip planes, in contrast to the normal Mode-I growth mode typically observed for single crystal superalloys at high temperature (> 850 degrees C) with conventional servo-hydraulic loading frequencies (< 100Hz). (c) 2006 Elsevier B.V. All rights reserved.