Correlative NanoSIMS and electron microscopy methods for understanding deuterium distributions after fatigue testing of 304/304L stainless steel in deuterated water

Abstract

There is no single methodology that can map the distribution of hydrogen and relate it to specific crystallographic phases or defect structures. Here, we present a case study demonstrating two methodologies towards achieving this goal: Correlating nanoscale secondary ion mass spectrometry (NanoSIMS) deuterium maps with electron backscattered diffraction (EBSD) data ahead of crack tips in a 304 stainless steel sample fatigue tested in deuterated water, and secondly correlating NanoSIMS deuterium maps with (scanning) transmission electron microscopy ((S)TEM) data from focused ion beam (FIB) lift-out samples. Correlating NanoSIMS/EBSD images, we confirmed an association of deuterium with martensitic lath structures. Furthermore, we discovered localized enrichments of deuterium along the martensitic laths, with a higher associative preponderance to ε−martensite. Applying correlative NanoSIMS/(S)TEM imaging of the fracture surface, we found deuterium accumulation at the metal oxide interface. However, in the pre-crack region, the deuterium was clearly concentrated underneath the oxide layer.