The relationship between crystallographic texture and salt water cracking susceptibility in Ti6Al4V

Stress corrosion cracking (SCC) and low-frequency corrosion fatigue were investigated for the α + β alloy Ti6Al4V in 3.5% aqueous salt solution. Both coarse lamellar and nominally equiaxed microstructures with distinctly different textures were developed by thermomechanical processing. Despite their inherent SCC sensitivity, lamellar microstructures have K_ISCC values equal to or greater than those of equiaxed microstructures, owing to the superior fracture toughness. The relative SCC sensitivity, K_ISCC/K_IQ, correlates well with the relative intensity of basal poles parallel to the tensile axis, suggesting that brittle fracture, rather than slip on basal or near-basal planes, is responsible for enhanced cracking. When the relative basal pole intensity parallel to the loading axis is significantly less than unity, K_ISCC is equal to K_IQ and corrosion fatigue crack growth is frequency independent. Otherwise, K_ISCC can be as low as one-half of K_IQ, and the "typical" frequency dependence involving "cyclic SCC" is observed. The relative basal pole intensity and, in turn, the elastic modulus can therefore be used to predict or prevent environmentally enhanced cracking in this type of alloy.