Effect of <i>β</i> lath arrangement on activation of <a> slips in single-colony lamellar structures of Ti-6Al-4V alloy

Abstract

Micro-tensile tests using single-colony specimens of Ti-6Al-4V alloy with a fine lamellar microstructure were employed in the temperature range between 298 and 423 K to understand the effects of geometrical orientation of β lath on <a> slip behaviour. The critical resolved shear stress (CRSS) for the basal slips was lower than that of the prismatic slips, in addition, the temperature dependence of the slip behaviour was greater in the basal slips than the prismatic slips. In the case of single α phase excluding β lath, the CRSS and temperature dependence are independent of the slip modes. In the lamellar microstructure, however, the basal slip propagates simultaneously through all the lamellar layers (divider type) and the prismatic slip propagates sequentially from one layer to another (arrester type). Therefore, considering that dislocation motion is restricted through the pinning and pile-up mechanisms in divider and arrester orientations, respectively, the CRSS and temperature dependence in the basal and prismatic slips can be explained by the geometrical orientation of β lath included in lamellae. This finding suggests that the geometric configuration of β lath dominates the <a> slip in single-colony lamellar structure of the Ti-6Al-4V alloy.