Microstructure and microhardness of heat-treated Ti-6Al-2Sn-4Zr-6Mo alloy

Ti-6Al-2Sn-4Zr-6Moisa alpha + beta titanium alloy that combines the long-term strength at elevated temperature with the hardenability by heat-treatments. In this work the effect of conventional heat treatments on the microstructure is investigated, in relation with the hardness properties of the material, by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Energy Dispersion X-ray Spectroscopy (EDXS) and X-ray diffraction (XRD). According to the Rietveld method the quantitative phase analysis by XRD has been carried out, showing the evolution of the phases with the different heat treatments. Solution-treated samples exhibit a microstructure of alpha-phase crystals embedded in a matrix of retained-beta phase and/or alpha '' martensite, depending on solution treatment temperature; the alpha-phase amount depends on the solution-treatment temperature. The presence of the alpha '' martensite does not lead to a significant hardening of the material. The aging treatment induces the transformation of the retained-beta phase and the martensite in a very fine alpha + beta structure that hardens the alloy. The hardness is related to the amount of the fine (alpha + beta)-phase and a linear dependence on the beta-phase amount formed during the solution treatment can be identified. (C) 2013 Elsevier B. V. All rights reserved.