Austenite stability under focused ion beam milling

Abstract

Artifacts from FIB milling can be of great concern. Aside from commonly known defects (e.g., Ga ion implantation, re-deposition, microstructure change due to specimen temperature increase, surface amorphization, etc.), FIB milling can even result in phase transformation in some metal alloys. Limited study has shown normal incident Ga ion beam milling which can transform austenite (FCC) to BCC structure in some stainless steels. This can be detrimental when austenite in stainless steels needs to be analyzed. However, one important question to answer is if milling in high glancing angle can result in such transformation. The susceptibility of austenite transformation to BCC structure is studied using EBSD on commercial stainless steels. When irradiated by normal incidence Ga ion beam, even with low dose, surface of SS304 and SS316 was transformed from austenite to BCC structure. However, irradiation from high glancing angle does not result in such transformation of relatively unstable austenite structure in SS304.