Texture Evolution of Hot Rolled Titanium Alloys

Abstract

Ti-6Al-4V alloys have been the most widely used dual-phase titanium in past decades with a high strength-to-weight ratio and excellent corrosion resistance. This material developed strong transverse textures and large macrozones during hot rolling and highly depends on the temperature and strain. These pronounced textures and macrozone can detrimentally affect material performance and impact fatigue life. Previous investigations into the hot rolling texture of Ti-6Al-4V have either presented incomplete two-phase textures or lacked a comprehensive exploration of rolling conditions. Furthermore, modelling has struggled to accurately predict texture evolution due to the intricate interaction between the alpha and beta phases at elevated temperatures. Therefore, thorough investigations are required to shed light on the factors influencing texture evolution. In this work, the texture evolution during high-temperature rolling of two Ti-6Al-4V alloys from different manufacturers was investigated, aiming to establish a comprehensive and detailed database of alpha and beta texture evolution in dual-phase titanium under different hot rolling conditions. The effect of temperature (825 degree Celsius to 1020 degree Celsius), strain (50% to 93%), starting microstructure (fully equiaxed and lamellar) and reheating time on texture in both the alpha and beta phases were thoroughly examined with EBSD and synchrotron X-ray diffraction. During hot rolling, the 0002//TD transverse texture is dominant in the alpha-phase texture and strengthened with strain increase. The separation of the primary and secondary alpha demonstrates a stronger 0002//TD in the primary alpha, indicating its development through deformation. The overall alpha texture was weakened when the rolling temperature was approaching the beta transus temperature as more beta was involved in the deformation and the subsequent phase transformation during cooling tends to randomize the alpha texture. However, the 0002//TD alignment was strengthened at lower temperatures up to 895 degree Celsius followed by a weakening at higher temperatures. While the 0002//ND and 0002//RD alignments were strengthened with a higher fraction of the secondary alpha phase. The reconstructed EBSD data and the synchrotron diffraction both reveal the rotated cube, alpha fibre and gamma fibre texture developed in the beta phase but remained weak until approached beta-transus temperature and reached the highest intensity when deformed above beta-transus. A coupling between the 0002//TD and the rotated cube was captured by synchrotron diffraction but was difficult to see through EBSD. Moreover, a notable strengthening of the rotated cube texture was found at 975 degree Celsius and attributed to recrystallization. To further investigate the recrystallization and texture development during the annealing after hot rolling, a Ti64 sample sectioned from a pre-rolled material was scanned with an in-situ high-temperature SEM. The findings indicate that recrystallization occurs in both alpha and beta phases with distinct contributions to texture evolution. While the alpha texture remained relatively unchanged following recrystallization, the beta phase exhibited new orientations that significantly enhanced its texture. These findings significantly advance our understanding of the intricate texture evolution during hot rolling and annealing of Ti-6Al-4V and suggest that recrystallization can be a key effect on the beta phase texture evolution that needs to be considered. The comprehensive dataset provided herein contributes to refining texture models and explains the texture evolution mechanism in titanium during hot deformation.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philip Prangnell (Supervisor) & Joao Quinta Da Fonseca (Supervisor)