Microstructure evolution of titanium alloy under direct pulse current electromagnetic forming

Abstract

Titanium alloy has high deformation resistance and low electrical conductivity, so it is difficult to form by traditional electromagnetic forming (TEMF) at room temperature. Direct pulse current electromagnetic forming (DPCEMF) simultaneously combines electromagnetic forming and pulse current heating. This study investigates the microstructure evolution and deformation mechanism of titanium alloy sheet during DPCEMF through the microscopic characterization. Results show that the β phase volume fraction of DPCEMF-0.3 enhanced 262.5 % compared with that of TEMF-0.3. The KAM distribution of DPCEMF-0.3 is uniform and average KAM value is obviously smaller compared to the TEMF-0.3, which is indicated that the dislocation density decreases in DPCEMF. And the average Schmidt factor value of DPCEMF-0.3 specimen is larger than the TEMF-0.3, indicating a more favorable slip system activating in the DPCEMF. Although the electromagnetic field and high strain rate deformation could accelerate phase transition during the DPCEMF, the most important factor that promoted the phase transition was the electric pulse and thermal effects. The drift electrons of pulse current can push dislocations when the high density pulse current passes through the DPCEMF specimen, reduce the dislocation density, and enhance dislocation mobility. At the same time, the dynamic recrystallization inhibited directional grain growth, resulting in a large reduction in texture strength and a diffused orientation. The deformation mechanism of DPCEMF is dislocation plane-slip. The main softening mechanisms of DPCEMF are electropulsing thermal effect and dynamic recrystallization.