Influence of oxygen ingress on microstructure and phase formation during two-step oxidation surface hardening of TiZrNbHfTa high entropy alloy

Titelangaben

Dickes, Daniel ; Zhao, Yujun ; Baier, Felix ; Öztürk, Beyza ; Völkl, Rainer ; Li, Tong ; Galetz, Mathias C. ; Glatzel, Uwe:
Influence of oxygen ingress on microstructure and phase formation during two-step oxidation surface hardening of TiZrNbHfTa high entropy alloy.
In: Applied Physics Letters. Bd. 124 (2024) Heft 7 . - 071903.
ISSN 1077-3118
DOI der Verlagsversion: https://doi.org/10.1063/5.0190771

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Abstract

Aiming for an increased surface hardness and a better wear resistance of TiZrNbHfTa, we investigate a two-step process combining oxidation of rolled, ultrafine-grained, single-phase bcc TiZrNbHfTa in air at 550 °C with a vacuum heat treatment process at 1200 °C, including subsequent quenching. The first process step is associated with the formation of a surface oxide layer, a phase decomposition of the bulk, and oxygen ingress into the bulk, leading to an oxygen-enriched subsurface region containing internal oxides. The second process step is capable of restoring the single-phase nature of the bulk TiZrNbHfTa. At the same time, the presence of a compact surface oxide layer of 1–2 μm and an oxygen-enriched subsurface region underneath is preserved. The oxygen present in the subsurface region stabilizes a two-phase regime consisting of a Hf- and Zr-rich hcp phase and an Nb- and Ta-rich bcc phase, with the oxygen being interstitially dissolved predominantly in the hcp phase.