Anisotropic behavior and micromechanisms of Ti60 alloy sheet

Abstract The mechanical anisotropy of near-α titanium alloys under high-temperature service conditions plays a critical role in determining their formability and structural reliability. In this study, a Ti60 rolled plate was selected as the research material, and the evolution of tensile anisotropy along the RD, TD, and DD was systematically investigated at room temperature and within the temperature range of 720-840°C. The results reveal that the anisotropy of yield strength in the Ti60 plate can be divided into three distinct stages. At room temperature, the yield strengths along the TD and RD are comparable and higher than that along the DD, following the order TD>RD>DD. In the intermediate temperature range of 720-780°C, the yield strengths along the RD and DD become comparable and are lower than that along the TD, maintaining the same ranking of TD>RD>DD. At 840°C, the yield strengths along the TD and RD become comparable, while the anisotropy exhibits a reversal, following the order DD>RD>TD. Based on texture data obtained from EBSD analysis, the distributions and average values of the Schmid factors for the primary slip systems along the three directions were calculated. Combined with the temperature-dependent variations in the critical resolved shear stress (CRSS) of different slip systems, a slip activity parameter was introduced to quantitatively elucidate the origins of mechanical anisotropy. The results indicate that at room temperature, plastic deformation is primarily governed by prismatic slip and basal slip, together with non-thermally activated path-controlled mechanisms, which collectively influence the anisotropic behavior of the titanium alloy. The ranking of slip activity, DD>RD>TD, provides a reasonable explanation for the observed yield strength anisotropy at room temperature. In the intermediate temperature range of 720-780°C, plastic deformation becomes increasingly dependent on thermally activated dislocation slip, and the yield strength exhibits a strong negative correlation with slip activity. Although the CRSS values of various slip systems decrease significantly, their rates of reduction differ, leading to the concurrent activation of multiple ⟨a⟩-type slip systems and resulting in the yield strength along the RD decreasing to a level comparable to that along the DD. When the temperature reaches 840°C, the dominant deformation mechanism undergoes a fundamental transition, shifting to grain boundary sliding-dominated deformation accompanied by the simultaneous activation of multiple dislocation slip systems, which ultimately leads to the reversal of yield strength anisotropy at 840°C.