Hetero-deformation induced stress and its microstructural morphology dependence in a near-alpha titanium alloy

Hetero-deformation induced (HDI) stress and the effect of microstructural morphology on it were investigated in a near-alpha titanium alloy featuring lamellar and equiaxed initial microstructures. The development of HDI stresses were confirmed in the two types of microstructures under tensile tests. While both microstructures exhibit comparable HDI stress magnitudes during initial tensile deformation, the equiaxed one demonstrates obviously enhanced HDI strain hardening compared to its lamellar counterpart as deformation progressed. Two factors are mainly responsible for the observed divergence in HDI stress evolution between the two microstructures. First and foremost is the surface-to-volume ratio of phase interface (sV), where the equiaxed structure shows significantly higher sV than its lamellar counterpart, which can offer more potential sites and better spatial interconnectivity of phase interfaces for GNDs development. The other factor is the microstructural size scale, in which the average layer thickness of the lamellar structure is considered being too small, as compared to the average grain diameter in the equiaxed one, to provide sufficient space for GND pileups to fully develop, which limits HDI strain hardening. This finding provides critical insights into microstructural design strategies for optimizing the development of HDI stress.