Delayed Cracking Behavior of Titanium Alloy in Air
Akira Nozue, Toshihiro Uchimura, Tadatsune Okubo
Delayed cracking in air has been studied for three types of titanium alloys. Delayed cracking tests were carried out in air during sustained loading, and also in pure water, ethyl alcohol and vacuum in order to examine the effect of those environments on the delayed cracking. Compact specimens of 6mm thickness were cut from Ti-6Al-4V alloys annealed, and solution-treated and aged, Ti-5Al-4Mo-4Cr-2Sn-2Zr and Ti-15V-3Cr-3Sn-3Al alloys solution-treated and aged. In the Ti-6Al-4V alloy, the delayed cracking occurred markedly in specimens annealed in comparison with specimens solution-treated and aged. Its susceptibility increased from in vacuum, to in ethyl alcohol, air and pure water in the order described, and hence the delayed cracking in air might occur due to moisture and a very small amount of hydrogen retained in specimens. In addition, in-situ observation of the crack growth during loading revealed that the delayed crack extended mainly in alpha phases and was arrested by beta phases in the specimens annealed.