Phase precipitation behavior and mechanical properties of multi-phase Nb–Ti–C and Nb–Ti–Al–C alloys

Abstract The microstructural evolution and mechanical behavior of Nb–35Ti–4C, Nb–35Ti–4C–15Al, Nb–25Ti–8C and Nb–25Ti–8C–15Al (at. %) alloys prepared using traditional arc-melting process were investigated. Nb–Ti–Al–C alloy consists of Nbss phase and eutectic phases of Nbss and (Nb, Ti)C in as-cast state. The addition of 8 at. % C leads to the generation of massive primary (Nb, Ti)C while the addition of 15 at.% Al results in the formation of Nb3Al phase. After heat treatment, secondary (Nb, Ti)C and secondary Nbss precipitate within Nbss and (Nb, Ti)C, respectively. Meanwhile, massive Nb3Al phase precipitates from parent Nbss in the alloy containing Al element. Both the precipitation of secondary Nbss and Nb3Al follows a strict orientation relationship with the parent phase. Mechanical properties of the as-cast and heat-treated specimens at room and evaluated temperatures are significantly increased by adopting C and Al elements, as more (Nb, Ti)C and Nb3Al acting as the strengthening phase are introduced. Whereas, the plasticity of the alloys decreases owing to the formation of massive brittle carbide and Nb3Al.