Mesoscale deformation mechanisms in relation with slip and grain boundary sliding in TA15 titanium alloy during tensile deformation

Abstract Revealing the mesoscale deformation mechanisms of titanium alloy with tri-modal microstructure is of great significance to improve its mechanical properties. In this work, the collective behavior and mechanisms of slip activities, slip transfer, and grain boundary sliding of tri-modal microstructure were investigated by the combination of quasi-in-situ tensile test, SEM, EBSD and quantitative slip trace analyses. It is found that the slip behavior presents different characteristics in the equiaxed α (αp) and lamellar α (αl) grains. Under a low level of deformation, almost all the slip deformation is governed by single basal and prismatic slips for both of αp and αl, despite small amount of -pyramidal slip exists in αl grains. As deformation proceeds, -pyramidal and -pyramidal slip systems with high Schmid factors were activated in quantities. Specially, certain coarse prismatic slip bands were produced across both of single and colony αl grains whose major axes tilting about 40 °–70 ° from the tensile axis. Slip transfer occurs at the boundaries of αp/αp and αl/β under the condition that there exists perfect alignment between two slip systems and high Schmid factors of outgoing slip system. The slip transfer across αl/β boundary can be divided into two types: straight slip transfer and deflect slip transfer with a deviation angle of 5 °–12 °, depending on the alignment of slip planes of two slip systems. The grain boundary sliding along boundaries of αl/β and αp/β was captured by covering micro-grid on tensile sample. It is found that the crystallographic orientation and the geometrical orientation related to loading axis play great roles in the occurrence of grain boundary sliding.