EBSD Study of Microstructural and Textural Changes of Hot-Rolled Ti–6Al–4V Sheet After Annealing at 800 °C

Abstract

In this paper, electron backscatter diffraction and various other characterization and analysis techniques including X-ray diffraction, electron channeling contrast imaging and energy-dispersive spectrometry were jointly employed to investigate microstructural and textural changes of a hot-rolled Ti–6Al–4V (TC4) sheet after annealing at 800 °C for 5 h. In addition, the hardness variation induced by the annealing treatment is rationalized based on revealed microstructural and textural characteristics. Results show that the TC4 sheet presents a typical dual-phase (α + β) microstructure, with α-Ti as the major phase and short-rod-shaped β-Ti (minority) uniformly distributed throughout the α matrix. Most of α grains correspond to the un-recrystallized structures with a typical rolling texture (c//TD and <11–20>//ND) and dense low angle boundaries (LABs). After the annealing, the stored energy in the as-received specimen is significantly reduced, along with greatly decreased LABs density. Also, the annealing allows recrystallization and grain growth to occur, leading to weakening of the initial texture. Furthermore, the water quenching immediately after the annealing triggers martensitic transformation, which makes the high-temperature β phases be transformed into submicron α plates. The hardness of the annealed specimen is 320.5 HV, lower than that (367.0 HV) of the as-received specimen, which could be attributed to reduced LABs, grain growth and weakened texture. Nevertheless, the hardening effect from the fine martensitic plates could help to suppress a drastic hardness drop.