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

This study focuses on continuous imaging of microstructural changes in Ti 6% Al 4% V when cooling from the beta transus of similar to 995 degrees C or above. A range of microstructures were obtained by accessing different cooling rates. With cooling rates of 0.1-0.5 degrees C/s, lamellar microstructures were observed, which initiate in a colony microstructure below temperatures of similar to 930 degrees 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 mu m to similar to 160-320 mu m over three minutes at similar to 930 degrees C, within the alpha + beta mixed phase. On further time at temperature, the lengthening of lamellae stagnated. With further cooling at 0.1 degrees 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 degrees C), evolved during the alpha to beta heating transition, and persisted upon cooling.