In situ monitoring of phase transformation kinetics under rapid heating of Ti–6Al–4V titanium alloy

Abstract

The phase transformation kinetics of Ti–6Al–4V alloy was studied during rapid heating using in-situ high energy synchrotron diffraction and in-situ electrical resistivity measurement for heating rates varying from 0.03 to 200 °C.s−1. The application of Rietveld refinement to high energy synchrotron data tracked the mass fraction, mean lattice parameters and Full Width at Half Maximum (FWHM). For increasing heating rates, results evidenced a shift in the dissolution of α to β phase temperature range from 600 °C for 0.25C.s−1 to 960 °C for 200 °C.s−1. A Continuous Heating Transformation diagram (CHT) was constructed demonstrating the effect of high heating rate. The result also demonstrated a much narrower temperature transformation range at high temperature. FWHM showed a time-dependent decrease of the stress level and/or chemical heterogeneity in the β phase before the start of the α phase dissolution. The mean lattice parameter evolution of β phase suggested that the α phase dissolution kinetics was diffusion controlled despite a heating rate reached of 200 °C.s−1, leading to chemical heterogeneities in the β phase.