It has been shown that the mill annealed form of Ti-6A1-4V has improved fatigue resistance after it has been heat treated at 900°C for 10 minutes and water quenched, some of the increased fatique strength of this material may result from microstructural adjustments to deformation. The present study deals with the general microstructure of the material and specifically with that of the martensite before fatigue, at the fracture surface after fatigue and at distances away from the fracture surface. In addition, microstructural changes which are brought about by annealing this heat treated material at 500°C for 8 hours are discussed.
Thin foil specimens were prepared from bulk materials by spark cutting and planing. This was followed by electropolishing in a solution of 62.5% methanol, 31% butanol and 6.5% of 70% perchloric acid at 13.9 volts at -40°C. Fatigue testing was conducted at ±0.020 shear strain with a constant axial stress of 2.12 x 107 N/M2.