Mechanism of self-protected structure formation in titanium alloy radiation rods during ultrasonic casting

During the ultrasonic casting, a self-protected structure (SPS) gradually forms on TC4 titanium radiation rod surfaces (TRRS). This structure effectively inhibits chemical corrosion of the TRRS, enhances the stability of ultrasonic transmission within the vibration system, and thereby extends the service life of the radiation rod. In this study, the effects of ultrasonic vibration, cavitation impact, and high-temperature environment on the microstructure of the TRRS were investigated, and the mechanism of SPS formation was elucidated. The relationship between ultrasonic stress amplitude and dislocation annihilation probability was analyzed to reveal the effect of ultrasonic vibration on dislocation evolution. The cavitation-induced microjet impact pressure on the TRRS was calculated using the water hammer pressure formula, and the stress distribution within two phases (α + β) of TC4 was determined by reference to the deformation behavior of duplex stainless steel. The contributions of various factors to the chemical corrosion resistance of the TRRS were verified through aluminum melt immersion corrosion experiments. The results show that ultrasonic vibration promotes dislocation annihilation, cavitation impact reduces β phase content due to the stress-shielding effect, and high-temperature environment accelerates grain growth by enhancing grain boundary migration. The combined effects of these three factors promote SPS formation, inhibit Ti atom diffusion and dissolution, and improve the chemical corrosion resistance of TRRS.