Mechanisms of Recovering Low Cycle Fatigue Damage in Incoloy 901

摘要

The effect of thermal treatment and hot isostatic pressing (HIP) on eliminating low cycle fatigue (LCF) damage in the iron-nickel superalloy, Incoloy 901, was investigated. Testing was done in air at 500 deg F at a total strain range of 0.75%. The mechanisms of crack initiation and crack propagation in baseline specimens were determined and used as the basis of comparison for the rejuvenated specimens. Crack initiation in the baseline specimens was due to decohering of blocky grain boundary carbides. Pre-crack initiation damage consisted of extrusions and intrusions formed at persistent slip bands and partially decohered grain boundary carbides. A pre-rejuvenation damage level of 800 cycles (60% of crack initiation) was selected. Some specimens to be HIP processed were ceramic coated; the rest were left uncoated. Post-HIP testing revealed that LCF properties were adversely affected by surface microstructural damage caused by the HIP processing. Thermal rejuvenation, consisting of a standard solution treatment and double aging, was partially successful in recovering fatigue properties with a pre-rejuvenation damage level of 800 cycles. Initiation life was extended by 400 cycles and cycles to failure was extended by 600 cycles. This behavior is explained in terms of microstructural damage which is resistant to thermal treatment. (Author)