Effect of primary a phase on the fatigue crack path of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe near beta titanium alloy

The fatigue crack growth behaviour of laser melting deposited Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy was investigated. Deflective crack paths were observed in compact tension C(T) specimens under constant amplitude loading, which greatly extended their fatigue crack growth lives. Observations of metallographic microstructures and microscopic fracture morphology of C(T) specimens indicate that the deflection was caused by orderly distributed primary a phase (alpha(p)) laths in grains, especially in columnar grains. Further experiments with clamped single edge notch tension SENTC specimens showed that the deflective extent varies from global to local and even scarce with the gradual increase of the angle between the crack path and alpha(p) laths. SENITC results also indicate that the deflective effect of single acicular alpha(p) laths is stronger than that of crisscross one when comparing their range of influence.