Suppressing the oxygen ingress into Ti-alloys by a one-step Al- plus F-treatment

Alexander Donchev,Mathias C Galetz

doi:10.1051/matecconf/202032106003

Alexander Donchev, Mathias C Galetz

Open Access

https://doi.org/10.1051/matecconf/202032106003

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Abstract

Oxygen ingress into technical Ti-alloys during high temperature exposure in oxygen containing environments leads to an enriched surface zone due to the high oxygen solubility in titanium. This affected zone is known as alpha case and is embrittled compared to the substrate material. Therefore, the operating temperature of these alloys is limited. An enrichment of Al in the surface zone of Ti-alloys leads to an improvement by the formation of intermetallic TixAly-phases with decreased oxygen solubility. This one-step Al-enrichment plus a F-treatment is proposed for the formation of a continuous stable alumina scale which prevents oxygen inward diffusion. In this paper the results of high temperature exposure tests in air of technical Ti-alloys are presented without any treatment and treated with Al-enrichment including fluorination. Post experimental investigations such as SEM reveal the formation of thin alumina layers on treated samples. Hardness measurements confirm that no embrittlement was observed for the treated samples while untreated specimens show increased hardness values in the subsurface zone corresponding with the oxygen inward diffusion profile.

Highlights

Titanium alloys are widely used as structural materials in several ambient temperature applications [1]
The rutile layer which is formed in the presence of oxygen protects the base material at lower temperatures but it loses its barrier properties due to an increased disorder of the TiO2-lattice [3]
This leads to a brittle subsurface zone, alphas case, which reduces the lifetime of Ti-components [5]

Summary

Introduction

Titanium alloys are widely used as structural materials in several ambient temperature applications [1]. The diffusion through this scale is easy and oxygen becomes enriched in the subsurface zone due to its high solubility in the a-Ti phase [4]. Results of high temperature oxidation tests show the positive effect of the one-step treatment.

Results

Conclusion