Deformation and Solid Solution Strengthening of Titanium-Aluminum Single Crystals.

Solid solution strengthening and deformation behavior of titanium-aluminum single crystals has been studied over the range of temperature 77-1100K and from 0 to 6.6 w/o Al. Crystal orientations have been chosen to promote prism slip, basal slip and c+a slip, and the temperature and composition dependence of the critical resolved shear stress (CRSS) for each of these slip systems has been determined. Although prism slip has the lowest CRSS of all the slip systems studied, both increasing temperature and Al concentration make the stresses for prism and basal slip converge. Deformation with a c+a slip vector is always more difficult to activate than either basal or prism slip with an a slip vector, and this resulted in fracture of crystals oriented for c+a slip by unstable shear, under certain conditions. In addition to the work on the deformation of Ti-Al crystals in compression, some studies were conducted on both creep and cyclic deformation (fatigue) of single crystals. The impact of these studies on understanding of deformation texture development and the use of textured titanium alloys in structures is briefly discussed. (Author)