THE RELATIONSHIP BETWEEN CRYSTALLOGRAPHIC TEXTURE AND SALT-WATER CRACKING SUSCEPTIBILITY IN TI-6AL-4V

Stress corrosion cracking (SCC) and low-frequency corrosion fatigue we re investigated for the alpha + beta alloy Ti-6A1-4V in 3.5% aqueous s alt solution. Both coarse lamellar and nominally equiaxed microstructu res with distinctly different textures were developed by thermomechani cal processing. Despite their inherent SCC sensitivity, lamellar micro structures have K-ISCC values equal to or greater than those of equiax ed microstructures, owing to the superior fracture toughness. The rela tive SCC sensitivity, K-ISCC/K-IQ, correlates well with the relative i ntensity of basal poles parallel to the tensile axis, suggesting that brittle fracture, rather than slip on basal or near-basal planes, is r esponsible for enhanced cracking. When the relative basal pole intensi ty parallel to the loading axis is significantly less than unity, K-IS CC is equal to K-IQ and corrosion fatigue crack growth is frequency in dependent. Otherwise, K-ISCC can be as low as one-half of K-IQ, and th e ''typical'' frequency dependence involving ''cyclic SCC'' is observe d. 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.