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

• Published in: Nature communications 2019-02, Vol.10 (1), p.942-942, Article 942
• Main Authors: Chang, Yanhong, Lu, Wenjun, Guénolé, Julien, Stephenson, Leigh T., Szczpaniak, Agnieszka, Kontis, Paraskevas, Ackerman, Abigail K., Dear, Felicity F., Mouton, Isabelle, Zhong, Xiankang, Zhang, Siyuan, Dye, David, Liebscher, Christian H., Ponge, Dirk, Korte-Kerzel, Sandra, Raabe, Dierk, Gault, Baptiste
• Format: Article
• Language: English
• Subjects: 119/118; 140/58; 147/135; 147/143; 147/28; 639/301/1023/1026; 639/301/930/328; 639/301/930/328/2082; Alloys; Cryogenic effects; Electron diffraction; Engineering Sciences; Humanities and Social Sciences; Hydrides; Hydrogen; Hydrogen embrittlement; Ion beams; Lamellae; Materials; Molecular dynamics; multidisciplinary; Science; Science (multidisciplinary); Titanium base alloys; Transmission electron microscopy; Xenon
• ISSN: 2041-1723; 2041-1723
• 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 °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. Hydrogen contamination in metals during sample preparation for high-resolution microscopy remains a challenge, especially when hydrogen itself is being investigated. Here, the authors show that using cryogenic milling significantly reduces hydrogen pick-up during sample preparation of titanium and titanium alloys.