Stress corrosion cracking of TC4 ELI alloy with equiaxed/Widmanstätten microstructures in simulated 1000 m deep-sea environment: A microstructure-electrochemistry-hydrogen synergistic mechanism

Titanium alloys are key structural materials for deep-sea engineering; however, the mechanism underlying their stress corrosion cracking behavior under deep-sea environment remains unclear. The stress corrosion cracking (SCC) characteristics of TC4 ELI alloy with equiaxed (EM) and Widmanstätten (WM) microstructures were investigated in a simulated 1000 m deep-sea environment (10 MPa, 4℃, 3.5% NaCl). Results show that EM, with high α-phase content (>50%) and pronounced microtexture, exhibits higher SCC susceptibility (K 1SCC =66.79 MPa·m⁰·⁵) and more distinct quasi-cleavage fractures than WM (K 1SCC =80.29 MPa·m⁰·⁵). A “microstructure-electrochemistry-hydrogen” synergistic mechanism is proposed: For EM, the continuous α/β network intensifies micro-galvanic corrosion, and microtexture bands accelerate pressure-driven hydrogen diffusion and enrichment at crack tips, thereby activating the Hydrogen-Enhanced Decohesion (HEDE) and Hydrogen-Enhanced Localized Plasticity (HELP) mechanisms. For WM, isolated α colonies, higher β-phase fraction, and stable passive film attenuate galvanic corrosion and hydrogen transport. This study provides a theoretical basis for the microstructure optimization of TC4 ELI alloy in deep-sea engineering components.