Effect of cryogenic and electropulsing coupling treatment on microstructure and mechanical properties of Ti6Al4V alloy

This study systematically investigated the effects of cryogenic and electropulsing coupling treatment (CET) at −196 °C for different durations (8h, 16h, and 24h) on the microstructure and mechanical properties of rolled Ti6Al4V alloy. The results indicate that after 16 h of cryogenic and electropulsing coupling treatment, the microstructure inside the alloy is influenced by both the electron wind and the cold-shrinkage internal stress, resulting in a reduction in dislocation density. Under the effect of electron wind force, the internal colony of the alloy shows vertical arrangement with significant directionality. The cryogenic field and pulsed electric field promote the internal generation of nanoscale precipitate phases within the initial α phase, resulting in dislocation entanglement. After the cryogenic and electropulsing coupling treatment, the grain size of the alloy decreases, and the liquid nitrogen environment effectively mitigates the thermal effects associated with electropulsing, preventing grain coarsening and significantly reducing the thermal effect values, which subsequently leads to the formation of smaller-sized grains after recrystallization. The combined effects of electron wind and internal cold shrinkage stress result in a preferential orientation of the alloy's texture, with grains of the (102) crystal plane deviating towards the (002) and (101) crystal planes. After 16 h of electric field cryogenic coupling treatment, the tensile strength of the samples reached 830.3 MPa, and the elongation was 11.23 %, representing increases of 5.8 % and 16.7 %, respectively, compared to the untreated samples. The morphology of the fracture surface displays large and deep dimples, achieving a simultaneous enhancement of both strength and toughness.