Mechanism of crack propagation in hot salt stress corrosion of TC11 titanium alloy: Effects of chlorine and oxygen

This study investigates the hot salt stress corrosion cracking (HSSCC) behavior of TC11 titanium alloy at 500 °C using slow strain rate tensile (SSRT) testing, with emphasis on the influence of environmental factors on crack propagation. The results reveal that while corrosion damage facilitates crack initiation, the extent of crack growth is predominantly governed by the amount of deposited NaCl. Specimens pre-corroded with a low salt load exhibited lower HSSCC susceptibility than uncorroded specimens due to insufficient residual NaCl to sustain continuous crack propagation, whereas heavy salt deposition significantly enhanced susceptibility. Chlorine accelerates crack propagation in TC11 alloy via synergistic reactions among chlorine, oxygen, and hydrogen at the crack tip, where active chlorine promotes depassivation and slip-assisted fracture along stress-activated preferential slip planes. In chlorine-deficient environments, crack growth is controlled by passive-film rupture and repassivation, while oxygen diffusion–mediated activation of slip systems governs the subsequent crack path. These findings elucidate the mechanistic role of chlorine in controlling the HSSCC failure of TC11 titanium alloy and provide guidance for developing improved protection strategies in high-temperature hot salt environments.