Influence mechanism of current intensity on TiB equiaxed morphology and high-temperature mechanical properties of titanium matrix composites under ultrasound assistance

To overcome the strength-ductility trade-off caused by high-aspect-ratio TiB reinforcements, titanium matrix composites (TMCs) reinforced with 3 vol% TiB were fabricated via vacuum arc melting coupled with ultrasonic vibration, and the effects of current intensities of 0, 300, 350, and 400 A on the microstructure were systematically investigated. The objective was to characterize the microstructural evolution during ultrasonic-assisted solidification under varying current intensities and to elucidate the mechanism by which current intensity influences TiB morphology, thereby optimizing reinforcement morphology and enhancing high-temperature properties. The results indicate that the synergistic effect of the ultrasonic and electric fields effectively drives the mechanical fragmentation of primary acicular TiB into fine equiaxed particles, with the aspect ratio approaching unity at 400 A. The multiphysics theoretical model reveals that the elevated melt temperature reduces the flexural strength of TiB while mitigating the attenuation of ultrasonic cavitation impact pressure, thus triggering the fragmentation phenomenon. Furthermore, the equiaxation of TiB broadens the interfacial strain transition zone from 13 nm to 22 nm, relieving localized stress concentrations and promoting homogeneous dislocation slip. This microstructural transformation shifts the failure mode from premature interfacial debonding to ductile pull-out, enabling TiB to exert a significant load-bearing strengthening effect. Consequently, under the combined treatment of 400 A arc current and ultrasonic vibration, the TMCs achieve an exceptional strength–ductility synergy at 750 °C, with a tensile strength of 470.2 MPa and an elongation of 15.6%, reaching an advanced level of high-temperature mechanical properties in the field of TMCs.