Abstract

MWAMBA, LA.; CORNISH, L.A.  and  VAN DER LINGEN, E.. Microstructural, mechanical, and oxidation property evolution of gamma-TiAl alloy with addition of precious metals. J. S. Afr. Inst. Min. Metall. [online]. 2012, vol.112, n.spe, pp.517-526. ISSN 2411-9717.

Titanium aluminide of composition Ti-47.5 at.% Al was prepared by melting titanium and aluminium of commercial purity with additions of precious metals of 0, 0.2, 1, 1.5 and 2 at.% content. The microstructure, hardness and oxidation properties were assessed. It was found that at 47.5 at.% Al, the microstructure of plain TiAl alloys was duplex, consisting of duplex lamellar grains and γ grains. The lamellar grains consisted of alternating lamellae of γ (TiAl) and α₂ (Ti^Al), with overall aluminium content in the range of 43-47 at.%. The γ grains had a aluminium content above 50 at.%. The addition of precious metals to the TiAl alloy resulted in the formation of a new phase, with a high precious metal content, occurring mostly in the γ phase, without any major change to the microstructure. Increasing the amount of precious metals resulted in an increase of the new phase amount, at the expense of the γ phase. The hardness of the different alloys was around 300HVi₀. Overall, the research has shown that addition of precious metals to TiAl resulted in a slight increase in hardness and a significant improvement of the oxidation resistance. This shows that alloying TiAl with precious metals, at the addition levels investigated, does not alter the mechanical properties very much, but improves oxidation resistance.

Keywords : Titanium aluminide; TiAl; precious metals; ternary alloys; microstructure; properties.

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