Effect of grain size on the yield stress and microscopic mechanism of a near-α titanium alloy during non-superplastic hot deformation

Abstract

In this paper, the effect of grain size on the yield stress of a near-α TA15 titanium alloy during the non-superplastic hot deformation was modelled, and the microscopic mechanism was analyzed through the crystal plastic finite element simulation. The effect of grain size on the yield stress changes from the refinement strengthening to refinement softening with the increase in temperature. To model this transformative effect, the grain boundary region is separated to consider the deformation mechanism of grain boundary sliding, and a concise relationship was obtained with a max prediction error of 3.7%. The distribution of microscopic strain is determined by the critical grain size Dc, when the strength of grain boundary regions is equal to α phase. When the grain size is greater than Dc, there are two high strain regions in the α phase, which are the intragranular deformation band caused by the prismatic slipping and the deformation band near grain boundaries caused by the multiple slipping. The continuous and discontinuous dynamic recrystallization appears simultaneously. When the grain size is less than Dc, the strain in the α phase is concentrated near the grain boundary due to the stimulant grain boundary sliding, and the discontinuous dynamic recrystallization is promoted.