A novel electropulsing treatment to improve the surface strength and repair the pore of additively manufactured Ti-6Al-4V alloy

The surface strength and pore content in electron beam melted (EBM) Ti-6Al-4V alloy play a key role in its tribological performance and fatigue life. In this study, a novel surface electropulsing treatment was applied to generate local phase transformation strengthening on the surface of EBM Ti-6Al-4V while simultaneously repairing the pores in the hardened zone. The surface microhardness was enhanced by 36 % from ∼260 HV0.2 to ∼355 HV0.2 when electropulsing treated for 120 ms, and keep the hardness with the prolongation of time to 240 ms. The thickness of the hardened surface increased from 1.3 mm to 1.7 mm with the increase in processing time. In addition, the hardened zone showed much fewer pores than the matrix. Mathematical simulation indicated that the high cooling rate in the treated zone was sufficient to result in a martensite transformation, and the compressive stress induced by thermal stress and electrode loading could cause deformation and furtherly improve the strength. More importantly, the combination of the large-scale compressive stress with the current crowding effect induced compression in the hardened zone is a benefit for repairing the pore. Predictably, this novel electropulsing treatment can be extended to other AM α + β Ti alloy systems and AM martensite steel systems for strengthening and pore repair.