The mechanism of compression-induced variant selection in [0001]-textured titanium alloys: A combined experimental and molecular dynamics simulation study

The microstructural evolution of [0001]-rich textured titanium alloy under hot compression and subsequent cooling is investigated, with the variant selection mechanism elucidated through a combined approach of experimental analysis and molecular dynamicssimulations. During the BCC -> HCP phase transformation upon cooling, the pattern has been established between precipitated martensitic alpha' phase variants and their micro- structural properties, such as lattice spacing, stress and orientation. For the [0001]-textured Ti-6Al-4V alloy subjected to hot compression and cooling, EBSD results show the preferred [0001] texture is 45 degrees away from compression direction, while the preferred [1120] texture aligns approximately 0 degrees, 45 degrees or 90 degrees from compression direction. A series of schematic transformation processes are presented to explain the deformation behavior of alpha-Ti simulated under high-strain conditions with compression along various crystal directions of [0001], [1120] and [1010] respectively. During cooling, variant selection mechanism consistently favors the HCP variant with smallest (001)beta ->(1120)alpha contraction and highest Schmid factor for {0001}(1120) slip. Notable twinning formations, such as {1011}, {1012}, {1013} twins, are observed and identified by their misorientation angles around 60 degrees, and 90 degrees respectively. Shockley partial dislocations are observed at location of HCP stacking faults while dense 1/3<100> Hirth dislocations are extending along basal planes in parallel with grain boundary between adjacent HCP grain. The findings of this work underscore the significant influence of mechanical loading on alpha-Ti, potentially offering an innovative approach to tailor microstructure through controlled thermomechanical processing.