NanoSIMS analysis of hydrogen and deuterium in metallic alloys: Artefacts and best practice

Hydrogen embrittlement can cause catastrophic failure of high strength alloys, yet determining localised hydrogen in the microstructure is analytically challenging. NanoSIMS is one of the few techniques that can map hydrogen and deuterium in metal samples at microstructurally relevant length scales. Therefore it is essential to understand the artefacts and determine the optimum methodology for its reliable detection. An experimental methodology/protocol for NanoSIMS analysis of deuterium (as a proxy for hydrogen) has been established uncovering unreported artefacts and a new approach is presented to minimise these artefacts in mapping hydrogen and deuterium in alloys. This method was used to map deuterium distributions in electrochemically charged austenitic stainless steel and precipitation hardened nickel-based alloys. Residual deuterium contamination was detected in the analysis chamber as a result of deuterium outgassing from the samples, and the impact of this deuterium contamination was assessed by a series of NanoSIMS experiments. A new analysis protocol was developed that involves mapping deuterium in the passive oxide layer thus mitigating beam damage effects that may prevent the detection of localised deuterium signals when the surface is highly deuterated.