The effect of cooling conditions on Ti 6%Al 4%V microstructure observed using high-temperature in-situ scanning electron microscopy

Abstract

This study focuses on continuous imaging of microstructural changes in Ti 6% Al 4% V when cooling from the β transus of ~ 995 °C or above. A range of microstructures were obtained by accessing different cooling rates. With cooling rates of 0.1–0.5 °C/s, lamellar microstructures were observed, which initiate in a colony microstructure below temperatures of ~ 930 °C. When the lamellar microstructure began forming at grain boundaries, cooling was interrupted to further observe the kinetics in the system. Lamellae changed in projected length from 40 µm to ~ 160–320 µm over three minutes at ~ 930 °C, within the α + β mixed phase. On further time at temperature, the lengthening of lamellae stagnated. With further cooling at 0.1 °C/s, lamellae grew in projected width, while the projected length remained the same. In addition, a surface topography formed at elevated temperatures (around 800 °C), evolved during the α to β heating transition, and persisted upon cooling.