Strength evaluation of α and β phases by nanoindentation in Ti–15Mo alloys with Fe and Al addition

Abstract

The strengths of the α precipitate and the β matrix were evaluated by nanohardness in the Ti−15Mo−1Fe and Ti−15Mo−3Al alloys and compared to those of the Ti−15Mo alloy. The α phases with similar size (a long axis of a few micrometres and a short axis of a few hundred nanometres), distribution and volume fraction were obtained in three alloys by adjusting the aging temperature. Analyses by SEM-EDS confirmed that Fe and Mo were enriched in the β phase and depleted in the α phase, while Al was enriched in the α phase and depleted in the β phase. Tensile tests were carried out, and the tensile strength was shown to be higher in the Ti−15Mo−1Fe and Ti−15Mo−3Al alloys than in the Ti−15Mo alloy. The nanohardness measurements indicated that the α phase was softer than the β phase in both Ti−15Mo−1Fe and Ti−15Mo alloys, while it was harder in the Ti−15Mo−3Al alloy. The increased tensile strength was mainly caused by the strength of the Fe enriched β phase in the Ti−15Mo−1Fe alloy and by the strength of the Al enriched α phase in the Ti−15Mo−3Al alloy.