Artifacts from FIB milling can be of great concerns. Aside from commonly known defects (e.g., Ga ion implantation, re-deposition, specimen temperature increase, surface amorphization, etc.), FIB milling can even result in phase transformation in some metal alloys. One will have to be certain that the FIB prepared TEM specimen is a true representation of the bulk material.
Limited study has shown normal incident Ga ion beam milling can transform FCC (austenite) to BCC structure in some stainless steels. This can be detrimental when residual austenite need to be analyzed.
The susceptibility of austenite transformation to BCC is studied using EBSD on commercial stainless steels. When irradiated by normal incidence even with low dose, surface of SS304 and SS316 were completely transformed from austenite to BCC structure (ferrite or martensite). However, irradiation from high glancing angle does not result in any such transformation of relatively unstable austenite structure in SS304.