Fatigue Failure Modes of the Grain Size Transition Zone in a Dual Microstructure Disk

Abstract

Mechanical property requirements vary with location in nickelbased superalloy disks. In order to maximize the associated mechanical properties, heat treatment methods have been developed for producing tailored grain microstructures. In this study, fatigue failure modes of a grain size transition zone in a dual microstructure disk were evaluated. A specialized heat treatment method was applied to produce varying grain microstructure in the bore to rim portions of a powder metallurgy processed nickel-based superalloy disk. The transition in grain size was concentrated in a zone of the disk web, between the bore and rim. Specimens were extracted parallel and transversely across this transition zone, and multiple fatigue tests were performed at 427 C and 704 C. Grain size distributions were characterized in the specimens, and related to operative failure initiation modes. Mean fatigue life decreased with increasing maximum grain size, going out through the transition zone. The scatter in limited tests of replicates was comparable for failures of uniform gage specimens in all transition zone locations examined.

Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy

“…This suggests that this distribution is in a growth phase, leading to an increased number density of precipitates. The apparent absence of coarsening during this period differs from previous studies of precipitate evolution in other superalloys [21][22][23] and could be a consequence of the low lattice misfit, and associated strain energy, between the γ and γ′ phases providing a minimal driving force for this process. A constant lattice misfit has previously been observed in a similar alloy on aging up to 12 hours and linked to a constant secondary γ′ precipitate size.…”

Implementation and verification of a microstructure-based capability for modeling microcrack nucleation in LSHR at room temperature

“…The powder metallurgy disk alloy LSHR is a nickel-based superalloy noted for its exceptional tensile strength and creep resistance [24] at high temperatures and versatile processing characteristics attributed to a low γ solvus. It was developed by NASA at Glenn Research Center and is targeted for use in the hot zones of gas turbine engines.…”

Emergence and Progression of Abnormal Grain Growth in Minimally Strained Nickel-200

“…AGG is of significance because, like many other grain-scale and sub-grain-scale features such as freckles [1,2], precipitates [2], or dendrite arm spacing [3], AGG has been shown to have a significant effect on properties across many material systems under various loading conditions [4][5][6][7]. The exact mechanisms underpinning the occurrence of AGG are still unclear and remain a subject of much interest and research.…”