Enhancing surface characteristics of TC4 alloy through powder-mixed near-dry EDM surface strengthening

This study significantly improved the microstructure and mechanical properties of the surface strengthening layer on TC4 titanium alloy by introducing composite powder working media of C + B4C and C + B4C + Al into near-dry EDM (PMND-EDM). Experimental results indicate that under the C + B4C condition, the reinforcement layer mainly forms phases such as TiC, TiB, Ti, Al3Ti and AlTi3; whereas after adding Al powder (C + B4C + Al), it promotes the reaction between the matrix and the medium, generating new reinforcing phases such as Al5Ti, Al3BC and B8C. The introduction of aluminum powder provides a molten environment, significantly reducing porosity and splatter droplets and decreasing the density and width of microcracks. Elemental distribution shows that B, C and Al elements are enriched in the transition zone at the edge of the discharge pit, while the central region is mainly composed of Ti. When processing with C + B4C + Al mixed powder at a peak current of 8.2 A, the microhardness of the reinforcement layer reaches approximately 1300 HV, which is more than four times the hardness of the matrix, attributed to the synergistic strengthening mechanism of multiple phases. Meanwhile, the material removal rate (MRR) is improved after adding Al powder. This work demonstrates the superior potential of multi-component powder design in tailoring surface integrity and mechanical properties of difficult-to-machine alloys.