Effect of Non-fully Recrystallized Grain Structures on the Fatigue Behavior of a Wrought γ-γ′ Ni-Base Superalloy

The effect of non-fully recrystallized (NFRX) microstructuresMicrostructure on the fatigueFatigue performance of γ-γ′ Ni-base superalloySuperalloys GH4065A was investigated by comparing the fatigueFatigue properties of specimens with a homogeneous fine-grained structure and a heterogeneous grain structure containing many NFRX regions. The fatigueFatigue life was characterized by performing strain-controlled fatigueFatigue tests at 500 ℃ with a maximum strain amplitude ∆εmax/2 ranging from 0.8% to 0.45%. In order to study the fatigueFatigue slip, crack initiationCrack initiation, and propagation behaviors associated with the NFRX structures, interrupted stress-controlled fatigueFatigue tests of dog-bone shape specimens were carried out at 400 ℃, employing two loading levels with the maximum stress amplitude ∆σmax above and below the yield strength, respectively. The NFRX grain structures were characterized and classified into two distinct types: unrecrystallized (URX) and partially recrystallized (PRX). Their effects on the slip band formation, crack initiationCrack initiation and propagation, and propagation were investigated and compared with that of the fully recrystallized (FRX) structure. The superior resistance of NFRX structures to the fatigueFatigue damage, particularly restricting slip-induced crack initiationCrack initiation and inclusion-induced crack propagationCrack propagation, makes the rest of the FRX regions accumulate most of the fatigueFatigue damage, resulting in unnoticeable variation in fatigueFatigue life.