Effects of Environment on Cracking in Titanium Alloys

Abstract

The laboratory conditions under which hot-salt cracking can occur in titanium alloys are reviewed and orders of merit among the alloys established. The large differences among alloys give promise of new alloys immune to the phenomenon. Hot-salt cracking is a case of classical stress corrosion. Alloy research and development disclose a system of titanium alloys that is immune to hot-salt cracking. One promising composition, Ti-2Al-4Zr-4Mo, is shown to have excellent combinations of mechanical properties. The fracture toughness of commercial titanium alloys in salt water is also examined. In the presence of fatigue cracks actively extending under applied loads, salt water can have the effect of reducing the crack propagation resistance of several titanium alloys. Because salt water has no effects on titanium alloys in the absence of cracks, its environmental effect is not classical stress corrosion. The problem can be largely eliminated in Ti-8Al-1Mo-1V sheet by creating microstructures consisting of a continuous matrix of transformed beta.