Fatigue crack initiation and short crack growth in nickel-base turbine disc alloys--the effects of microstructure and operating parameters

摘要

An assessment of the effects of microstructure and operating parameters on both crack initiation and propagation of short fatigue cracks is presented. The assessment was carried out on RR1000, U720Li and microstructural variants of U720Li. Fatigue tests were carried out at room temperature (20 Hz sinusoidal cycling) and at 650 deg C (1-1-1-1 trapezoidal cycling). Comparisons of the performance of the different microstructures revealed that initiation occurred predominantly at pores at both temperatures. At room temperature, stage I crack growth predominated and the presence of large primary gamma' precipitates on the grain boundaries, larger grains and larger coherent gamma' sizes gave improved fatigue crack growth resistance, whereas at 650 deg C, larger grains gave the most significant performance benefits.