CYCLIC DEFORMATION-BEHAVIOR OF HIGH-PURITY TITANIUM SINGLE-CRYSTALS -PART I - ORIENTATION DEPENDENCE OF STRESS-STRAIN RESPONSE

Randomly oriented single crystals of high-purity titanium were prepare d by strain annealing and were subjected to multiple-step fatigue test ing under strain-controlled conditions, in order to determine their cy clic stress-strain curves (CSSCs), These were found to fall into three groups, depending on orientation and the extent of slip and twinning, For those crystals oriented for single prismatic slip, a plateau was observed in the CSSCs, persistent slip bands (PSBs) occurred, and the plateau stress was 38 MPa. In a second group, oriented for prismatic s lip but for which cross-slip and twinning was favored, the plateau was suppressed and the flow stresses were higher. In a third group, conne cted with orientations on the borders of the unit triangle, extensive hardening occurred, the CSSCs were steep, and there were multiple case s of slip and twinning. The results are interpreted in terms of maps i n the stereographic projection recording the Schmid factors for the va rious deformation modes.