In-situ synchrotron diffraction study of the hot deformation behaviour in Ti-64Tuesday (05.11.2019) 14:40 - 15:00 Part of:
Alpha-beta Ti alloys often show pronounced softening during hot deformation. This softening is often attributed to globularisation of the α-phase, which is thought to occur by a kind of recrystallization mechanism, driven by deformation . However, recent detailed texture and microtexture studies have suggested that this behaviour might instead be due to dynamic phase transformation . The lack of a clear explanation is caused in part by the difficulty in interpreting the post-mortem microstructures in these alloy systems. On cooling, the β-phase transforms almost entirely into α, obscuring the deformed microstructure. Unfortunately, softening can only be seen at relatively high strain rates and large strains, making in-situ electron microscopy studies impractical. To avoid these difficulties, we used synchrotron diffraction to measure the internal strains, phase fraction and texture during hot tensile deformation of Ti-64 specimens. Using resistance heating and a fast acquisition rate (10 Hz), we were able to measure the microstructure evolution at a strain rate of about 0.1 /s at different temperatures and therefore different α/β phase contents. Our results showed direct evidence of dynamic phase transformation, during which the texture evolves by a kind of variant selection. Elastic strain measurements suggest that this variant selection is caused by the disappearance of highly stressed α variants during deformation. This finding has important consequences for understanding and controlling the microstructure development in dual-phase Ti alloys during thermomechanical processing.
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