Hydrogen environment embrittlement in nickel-base superalloy Alloy 617

Hydrogen environment embrittlement (HEE) in a nickel-base superalloy, INCONEL (R) Alloy 617, was scrutinized using a notch tensile test in a 99 MPa hydrogen atmosphere to determine the function of grain boundary carbides. The fracture surface ratio of the intergranular surface increased monotonically with increasing grain boundary coverage, which is defined as the ratio between the length of the grain boundary covered with carbide and the total length of the grain boundary. Strain distribution analysis clarified that more strain locally accumulated near the grain boundary covered with grain boundary carbide compared to the uncovered one. The suggested mechanism of HEE in the alloy is that a large amount of plastic strain near the grain boundary covered with grain boundary carbide triggers crack formation at the interface between the matrix and the grain boundary carbide, followed by crack growth along the grain boundary, ultimately leading to fracture.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.