Thermal Oxidation Effects on Sub-Surface Microstructure and ‎Mechanical ‎Properties of Cast and Forged α/β Titanium Alloys ‎

Document Type : Original Article

Authors

1 Faculty of Engineering, Dept. of Mining, Petroleum and Metallurgical Engineering‎

2 Central Metallurgical R&D Institute

3 Faculty of Engineering, Cairo University

Abstract

Ti-6Al-7Nb (Ti67) alloy has recently been developed to replace the commercial Ti6Al4V (Ti64) ‎biometallic alloy because of ‎the reported toxicity of the elemental vanadium. Thermal oxidation is an ‎important processing method applied to improve ‎the hardness and wear properties of such titanium ‎alloys. Since the developed alloy, Ti67, contains Nb as beta phase ‎stabilizing element instead of V in ‎case of Ti64, it is expected to behave differently upon processing by thermal oxidation. In ‎addition, this ‎behavior may be influenced by the processing method. Therefore, it is of interest to investigate the ‎influence of ‎thermal oxidation on the surface properties of Ti67 alloy in its forged and cast conditions ‎and compare the results to the ‎commonly used Ti64 alloy. It was observed that the thickness of alpha ‎case formed in Ti64 after oxidation at (1173 K-1373 ‎K) (900-1100 oC) was greater than in Ti67. In ‎addition, the equiaxed microstructure of the forged samples showed a thicker ‎alpha case than the ‎widmanstätten microstructure of the cast samples for the two alloys. Both forged and cast Ti64 showed ‎‎significant improvement in dry sliding wear resistance after thermal oxidation at (1173 K-1373 K) (900 ‎‎°C and 1100 °C), ‎while alloy Ti67 showed less improvement despite the improved surface hardness‎.‎

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