Effect of environmental media on the growth rate of fatigue crack in TC4 titanium alloy: Seawater and air

The fatigue crack growth rate of TC4 alloy in seawater is significantly faster than that in air. In order to analyze the behind reasons, the crack propagation path are investigated by scanning electron microscopy in conjunction with electron backscattering diffraction. The results indicates that the complex ionic environment in seawater can diminish the resistance of the fatigue crack growth. Especially, the damage of the α/β interphase induced by hydrogen embrittlement and Cl- in the seawater accelerate the fatigue crack propagation along the phase interface, although the presence of α/β interphase can reduce the crack propagation rate in air.