Surface hardening of TiZrNbHfTa high entropy alloy via oxidation

D. Dickes, B. Öztürk, F. Baier, P. Berger, E.P. George, R. Völkl, M.C. Galetz, U. Glatzel

Corrosion Science 217 (2023), 111159, DOI: 10.1016/j.corsci.2023.111159

Dickes2023

Micrographs showing the microstructure of the as-cast, rolled, and rolled & annealed state before (a-c) and after 24h of oxidation in synthetic air at 600°C (d-e), including EPMA oxygen mappings indicating a surface-near oxygen-enriched zone (OEZ) and a non-oxygen-enriched substrate (g-i).
Reprinted from Corrosion Science, Copyright (2023), with permission from Elsevier.

We investigate the oxidation of TiZrNbHfTa high entropy alloy between 550 °C and 650 °C as a surface hardening method. Coarse-grained specimens with grain boundaries perpendicular to the surface exhibit catastrophic oxidation, while ultrafine-grained, cold-rolled specimens show a continuous mass gain and the formation of an adherent, µm-sized, vitreous oxide layer. Underneath, TiZrNbHfTa decomposes into a bcc- and an hcp-phase, while selective internal oxidation of hafnium and zirconium occurs upon oxygen inward diffusion. Oxygen concentration- and microhardness-depth profiles confirm an increase in oxygen concentration and hardness at the surface, raising the initial hardness by four times to 1522 ± 64 HV0.5.

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