Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials

YH Chang and WJ Lu and J Guenole and LT Stephenson and A Szczpaniak and P Kontis and AK Ackerman and FF Dear and I Mouton and XK Zhong and SY Zhang and D Dye and CH Liebscher and D Ponge and S Korte-Kerzel and D Raabe and B Gault, NATURE COMMUNICATIONS, 10, 942 (2019).

DOI: 10.1038/s41467-019-08752-7

Hydrogen pick-up leading to hydride formation is often observed in commercially pure Ti (CP-Ti) and Ti-based alloys prepared for microscopic observation by conventional methods, such as electro- polishing and room temperature focused ion beam (FIB) milling. Here, we demonstrate that cryogenic FIB milling can effectively prevent undesired hydrogen pick-up. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, in wt.%) were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage reaching -135 degrees C. Transmission electron microscopy (TEM), selected area electron diffraction, and scanning TEM indicated no hydride formation in cryo- milled CP-Ti lamellae. Atom probe tomography further demonstrated that cryo-FIB significantly reduces hydrogen levels within the Ti6246 matrix compared with conventional methods. Supported by molecular dynamics simulations, we show that significantly lowering the thermal activation for H diffusion inhibits undesired environmental hydrogen pick-up during preparation and prevents pre-charged hydrogen from diffusing out of the sample, allowing for hydrogen embrittlement mechanisms of Ti-based alloys to be investigated at the nanoscale.

Return to Publications page