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

• Published in: MATEC Web of Conferences Vol. 321; p. 6003
• Main Authors: Donchev, Alexander, Galetz, Mathias
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Les Ulis EDP Sciences 2020
• Subjects: aluminization; Aluminum oxide; Fluorination; fluorine effect; Hardness; Heat resistant alloys; High temperature; high temperature oxidation; Operating temperature; Oxygen enrichment; Solubility; Substrates; Thin films; titanium alloys; Titanium base alloys
• ISSN: 2261-236X; 2274-7214; 2261-236X
• DOI: 10.1051/matecconf/202032106003

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 Ti x Al y -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.