Atomic structure and elemental segregation behavior of creep defects in a Co-Al-W-based single crystal superalloys under high temperature and low stress

With the aim of understanding the effect of creep defects in the gamma' phase on the creep resistance, the atomic structure and elemental segregation behavior of stacking faults (SFs), three types of SF interactions and antiphase boundaries (APBs) in a Co-Al-W-based single-crystal superalloy crept at 1000 degrees C/137 MPa up to 1.0% strain were investigated. Both superlattice intrinsic and extrinsic stacking faults (SISF and SESF) were observed in the gamma' precipitates, and the interactions of such faults had different configurations. Both V- and T-like configurations can be composed of SISF-SISF, SISF-SESF and SESF-SESF interactions, while the X-like configuration was only observed to be composed by SISF-SISF interaction. The strengthening effect and mechanism of such SF interactions on the creep resistance are discussed based on their density and formation mechanism. W elemental segregation was present along the SISFs and SESFs. In contrast, only the gamma forming element Co was enriched near the leading partial dislocations (LPDs) of the SISFs/SESFs, stair-rod dislocations and APBs. The rate limiting step of the expansion of the SFs was estimated to be the drag effect induced by the Co diffusion. In addition, the local phase transformation from the L1(2) to A1 structure at the intersection of SFs was mainly attributed to the Co supersaturation and aided by wetting phenomenon from the APB. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.