Hydrogen embrittlement (HE) of nickel base alloy UNS N07718 was studied by tensile testing at low strain rate (10-4 s-1) under hydrogen charging. Hydrogen-assisted cracking mechanisms were studied via the joint use of Electron BackScatter Diffraction (EBSD) analysis and orientation-optimized Electron Channeling Contrast (ECC) imaging. Both intergranular and transgranular cracking were observed when hydrogen was introduced. Embrittlement occurred by strong hydrogen-deformation interactions and several mechanisms were found to contribute to hydrogen-assisted cracking in this alloy. Transgranular cracking was caused by Hydrogen Enhanced Localized Plasticity (HELP)-assisted shear localization along slip planes. Intergranular cracking was more specifically categorized into three parts: grain boundary triple junction cracking, slip-localization on the grain boundaries and matrix/δ phase interface cracking. Observations on distinct metallurgical states of alloy UNS N07718, with different precipitation conditions for γ′′ phase and δ phase confirmed that the δ phase promotes HE by initializing micro-cracks.

Subject
Hydrogen induced cracking, Hydrogen embrittlement, Materials, Microstructure, Fracture surfaces, Tensile tests, Stress cracking, Hydrogen charging, Intergranular cracking, Slip, Grain boundary, Alloys, Hydrogen
Keywords:
UNS N07718, hydrogen embrittlement, tensile test, delta phase
© 2016 Association for Materials Protection and Performance (AMPP). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of AMPP. Positions and opinions advanced in this work are those of the author(s) and not necessarily those of AMPP. Responsibility for the content of the work lies solely with the author(s).
2016
Association for Materials Protection and Performance (AMPP)
You do not currently have access to this content.