Thermal expansion properties of laser melting deposited Ti-6.5Al-2Zr-1Mo-1V alloy during α + β zone annealing

Abstract

Thermal expansion properties of laser melting deposited Ti-6.5Al-2Zr-1Mo-1V alloy during α+β zone annealing have been investigated based on dilatometry. The texture of deposited Ti-6.5Al-2Zr-1Mo-1V alloy was analyzed by electron back-scattered diffraction (EBSD) and the evolution of microstructures during annealing was measured by optical microscope. The result showed that the expansion properties of deposited Ti-6.5Al-2Zr-1Mo-1V alloy were irreversible and anisotropic. After annealing at 960°C (Tβ-45°C) for 1h, a net-expansion was achieved in both laser scan direction and transvers direction while in the deposition direction, a net-contraction was gained. There was a selection of α variants happened in as-deposited Ti-6.5Al-2Zr-1Mo-1V alloy which was caused by the anisotropic internal stress during deposition. In the heating stage of annealing, the decrease of selected α variants led to a quick expansion in deposition direction and slow expansion in laser scan and transvers directions. In the cooling stage of annealing, the increase of selected α variants led to a quick contraction in deposition direction and slow contraction in laser scan and transvers directions. After α+β zone annealing, the volume fraction of selected α variants increased, leading to anisotropic net-expansion of the deposited alloy.