Effect of microtexture on fatigue cracking in Ti–6Al–4V

Fatigue cracking in forged bar, unidirectionally rolled (UD) and cross-rolled (XR) plate product forms of Ti–6Al–4V subjected to high cycle fatigue with a stress ratio R = 0.3 was studied by examination of crack tips using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The bar and the UD materials were composed of macrozones 50–70 μm in width whereas the bands identified in the XR product were only a few grains thick (∼20 μm). The fatigue fracture surfaces observed were related to the macrozones in the underlying microstructure. EBSD analysis of the crack tips showed that cracks arrested when confronted by grains badly oriented for prismatic {101¯0}〈112¯0〉 slip in both the bar and the XR materials. TEM foils were obtained from both the forward crack tip plastic zone and from the plastic wake, which showed that 〈c+a〉 slip operated in grains badly oriented for prismatic slip.