Room temperature deformation and mechanisms of slip transmission in oriented single-colony crystals of an α/β titanium alloy

Primary creep at low homologous temperatures and low stresses has been widely reported in alpha/beta Ti alloys. Creep in these alloys is dependent on microstructure, with the colony microstructure showing the least creep resistance. There exists a Burgers orientation relationship between the alpha and the beta phase, which has been assumed to allow for easy slip transmission across the alpha/beta interfaces. Constant strain rate and creep tests were performed on single-colony crystals of a near-alpha alloy oriented for slip along different prismatic slip systems in the a phase. A distinct anisotropy in the deformation behavior of different colony crystals is found. The origin of this anisotropy is due to the relative misalignment of the slip systems between the alpha and the beta phases which results in the formation of residual dislocations during slip transmission. A simple model is presented based on the accumulation of residual dislocations at both the alpha/beta interface and the alpha matrix, which provides insight into the mechanism of slip transmission, strain hardening and primary creep of these colony structures. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.