Effect of Twinning on the Deformation Behavior of Textured Sheets of Pure Titanium in Uniaxial Tensile Test

Abstract

In this experiment, the uniaxial tensile tests were carried out in four differently textured sheets of pure titanium. The sheets have the texture, some of which show the quite different pole figures and some of which show the quite different relation of the orientation between neighboring grains in spite of showing the similar pole figure. The deformation behavior of these sheets, those were, for example, the anisotropy, that the deformation twinning occur or not, twin systems and ridging, were studied particularly by considering the effect of the orientational relation between neighboring grains and of the manner of the occurrence of the deformation twinning.The twin systems and the manner of the occurrence of the deformation twinning were classified in three types according to the texture and the stress condition.1. When the unevenness in the connection with the orientational relation between neighboring grains generate, the tensile or compressive deformation twinning due to the stress condition occurs.2. When the 〈0001〉 orientation of the grain is nearly the direction of the maximum principal stress, which is the tensile direction in this case, the tensile deformation twinning occurs.3. When the grain deforms to the 〈0001〉 direction in order to conform to the deformation of surrounding grains, the deformation twinning occurs.The stress-strain curves are influenced by the deformation twinning. On one hand, the yield strength as the 0.2% proof stress depends principally on the orientational relation between the tensile direction and the prismatic slip system of the preferred orientation deduced from the pole figures. On the other, the work hardening rate after yielding is influenced not only by such an orientational relation but also largely by the deformation twinning and the orientational relation between the tensile direction and the 〈0001〉 orientation of the twin, and furthermore by the orientational relation between the neighboring grains. Especially, when the 〈0001〉 orientation of the deformation twin is close to the direction of the maximum principal stress, which is the tensile direction in this experiment, the flow stress and thus the work hardening rate increase.