I'm glad to annonce that our work in collaboration with the Max Planck Institute for Iron Research and the Imperial College has been accepted today in Nature Communications: "Cryogenic focused ion beam milling of environmentally-sensitive materials: example of Ti and its alloys". Within this large experimental/numerical collaborative effort, I designed, performed and analyzed all the numerical investigations.
Cryogenic focused ion beam milling of environmentally-sensitive materials: example of Ti and its alloys
Y Chang, W Lu, J Guénolé, L Stephenson, A Szczpaniak, P Kontis, A Ackerman, F Dear, I Mouton, X Zhong, S Zhang, D Dye, C Liebscher, D Ponge, S Korte-Kerzel, D Raabe, B Gault
Accepted on January 15, 2019.
Abstract: Significant hydrogen pick-up, leading to possible hydride formation, is often observed in specimens for microscopic observation from commercially pure Ti (CP-Ti) and Ti-based alloys prepared by conventional methods, such as electro-polishing and room temperature focused ion beam (FIB) milling with gallium or xenon plasma. Here, we demonstrate an effective method to prevent undesired hydrogen pick-up – cryogenic FIB milling. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, all in wt.%) used in aerospace applications were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage going down to -135 °C. Microstructure characterization by transmission electron microscopy (TEM), selected area electron diffraction and scanning TEM indicated no hydride formation in the cryo-milled thin lamellae of CP-Ti. Compositional analysis by atom probe tomography further demonstrated that cryo-FIB significantly reduces the hydrogen level within the matrix of Ti6246 compared with conventional methods. The underlying mechanisms for H ingress are discussed, and supported by molecular dynamics (MD). We show that by significantly lowering the thermal activation for diffusion of H, the technique inhibits undesired hydrogen pick-up from the environment during preparation and prevents the pre-charged hydrogen from diffusing out of the sample, and hence allows us to investigate the hydrogen embrittlement mechanisms of Ti based alloys at the nanoscale.