Influence of coarsened and rafted microstructures on the thermomechanical fatigue of a Ni-base superalloy

Abstract

a b s t r a c tThe aging of the microstructure of Ni-base superalloys during service is primarily characterized by coarsening and rafting of the c 0 precipitates. The influence of these different aged microstructures on thermomechanical fatigue (TMF) under either continuously cycled (CC) and creep-fatigue (CF) was investigated. Three different aged microstructures, generated through accelerated aging and pre-creep treatments, were studied: stress-free coarsened c 0 , rafted with orientation perpendicular to loading direction (N-raft), and rafted with orientation parallel to loading direction (P-raft). Under most conditions, the aged microstructures were less resistant to TMF than the virgin microstructure; however, there were exceptions. Both stress-free coarsened and N-raft microstructures resulted in a reduction in TMF life under both CC and CF conditions in comparison to the virgin material. P-raft microstructure also resulted in reduction in TMF life under CC conditions; however, an increase in life over that of the virgin material was observed under CF conditions. These differences are discussed and hypothesized to be related to the interactions of the dislocations in the c channels with c 0 precipitates.

A Study on Establishing a Microstructure-Related Hardness Model with Precipitate Segmentation Using Deep Learning Method

“…The strength of Ni 3 Al-based alloy is primarily derived from the coherent L1 2 -γ' precipitates, which are embedded in a face-centered cubic (fcc) γ-Ni matrix. The morphology and distribution of γ' precipitates have a significant impact on the mechanical properties and hardness of Ni-based superalloys [1][2][3][4][5]. As documented in numerous studies, γ' precipitates as a main microstructural characteristic of Ni-based superalloys are not stable at elevated temperatures [6][7][8][9].…”

A tensorial thermodynamic framework to account for theγ' rafting in nickel-based single crystal superalloys

“…However, recent studies under such high temperature/low stress conditions suggest that the N-type rafting mechanism is deleterious to the non-isothermal creep properties of MC2, CMSX-4 and MCNG alloys (Cormier et al , 2007, Cormier and Cailletaud , 2010b, Giraud et al , 2012, le Graverend et al , 2014a) while a P-type rafting leads to a decrease of the non-isothermal creep strain rate without affecting the creep life compared to a cuboidal microstructure (Giraud et al , 2012). It is also worth mentioning that a coarsened γ ′ microstructure at the beginning of mechanical tests also leads to a decrease in isothermal or non-isothermal creep properties (Shi et al , 2012, Steuer et al , 2014, as well as thermo-mechanical fatigue ones (Kirka et al, 2015). Since such kind of microstructural evolution (i.e.…”

“…It has already been proved in literature that this lamellar microstructure induces a decrease in high temperature properties compared to cuboidal structures (Fedelich et al , 2012a). In addition, N-type directional coarsening was demonstrated to be deleterious to strain-controlled low cycle fatigue (LCF) and out-of-phase thermo-mechanical fatigue (TMF) properties compared to cuboidal precipitates or P-type DC (Arrel et al , 2004, Epishin et al , 2005, Kirka et al, 2015 since it leads to a higher plastic flow, especially in the low temperature part of a TMF cycle. Furthermore, P-type DC is more creep resistant than N-type or even cuboidal γ ′ -morphologies, for at least the first percentages of creep deformation, since this microstructure provides efficient barrier to the glide/climb dislocation processes (Li et al , 2007, Mughrabi and.…”

Effects of Different Melting Technologies on the Purity of Superalloy GH4738

“…Superalloys, owing to their excellent high-temperature strengths and good resistance to oxidation, fatigue, and creep deformation [ 1 , 2 , 3 ], have emerged as materials for components that operate at high temperatures in the fields of aerospace and aviation engineering. These include turbine disks and blades, and combustion chambers in aerospace engines; thus, these alloys enjoy reputations as “cornerstones for advanced engines” [ 4 , 5 , 6 ].…”