Effect of carbide precipitation on Coffin–Manson relationship of a polycrystalline nickel‐based superalloy

Abstract

This study explores the dual‐slope Coffin–Manson (C–M) behavior of a polycrystalline nickel‐based superalloy, EA, used in turbine engine applications with an emphasis on discerning the micro‐mechanisms responsible for it. The motivation for distinguishing the micro‐mechanisms responsible for bi‐linear C–M behavior stemmed from the earlier evolved comprehensions that state that the fatigue life estimation based on the extrapolation of any single line gives inaccurate results. Transmission electron microscopy (TEM) investigations of fatigue fractured specimens at low strain amplitudes, Δε/2, revealed that dislocations are homogeneously distributed in the γ‐channels and occasionally form networks at γ/γ′ interface. Whereas deformation is heterogeneous at high Δε/2 owing to the complex dislocation reactions. Cr23C6 carbides are precipitated during the high Δε/2 fatigue tests, which act as obstacles for dislocations. The deformation heterogeneity resulting from the dislocation–γ′ precipitate interactions and the dislocation–M23C6 carbide interactions accounts for the dual‐slope C–M behavior.

Role of micro‐constituents on the fatigue deformation micro‐mechanisms of IN 713 C alloy

“…Recently, various modeling has been developed to evaluate the fatigue properties of polycrystalline nickel-based superalloys, and it was seen that the microstructure is one of the dominant factor influencing these properties. 5,[7][8][9][10][11][12] There is unpredictability in the literature concerning the exact influence of constituent microstructural variables, including γ 0 phase, MC carbides, and slip activities on crack formation and subsequent propagation in cast IN 713 C alloy. The microstructural complexities associated with IN 713 alloy modify the crack-initiation process and hence the related fatigue behavior.…”

“…Thus, the role of microstructure or constituent phases becomes the leading cause of crack initiation. Recently, various modeling has been developed to evaluate the fatigue properties of polycrystalline nickel‐based superalloys, and it was seen that the microstructure is one of the dominant factor influencing these properties 5,7–12 . There is unpredictability in the literature concerning the exact influence of constituent microstructural variables, including γ ′ phase, MC carbides, and slip activities on crack formation and subsequent propagation in cast IN 713 C alloy.…”