Morphology, phase composition and tribological properties of W–Co coatings formed by electrospark alloying of St3 steel

Abstract

Problem. For W–Co coatings on low-carbon structural steel, the influence of the combined variation of the discrete MODE and VIBRATION parameters during electrospark alloying on layer formation and the coordinated change in its structural and tribological characteristics has not been established. This complicates the selection of a mode that simultaneously provides coating density, strong adhesion to the substrate, and wear resistance. Aim. To identify the influence of electrospark alloying modes with W–Co electrodes on the structure and tribological properties of coatings on St3 steel. Methods. Coatings were deposited onto St3 steel specimens measuring 50×50×3 mm using electrodes composed of 85 % W and 15 % Co, produced by spark plasma sintering. On a UR-121 setup, five MODE and VIBRATION combinations were investigated with five passes and a processing time of 180 s. The structure and properties were evaluated using SEM, X-ray phase analysis, 3D profilometry, measurements of microhardness, porosity, and adhesion; tribological tests were carried out according to the ball-on-flat scheme. Results. Among the five studied modes, the optimal combination was MODE=2, VIBRATION=5, which formed the densest layer about 75 μm thick with a microhardness of 1520±45 HV, porosity not exceeding 1.5 %, and adhesion of 75 MPa. The α-Fe, W, Co, Fe–W, WO3, and WC phases were identified. At a load of 1 N, the mass wear intensity was 0.04–0.08 mg/(N·m), which is 2.5–4 times lower than that of uncoated St3 steel (0.15–0.20 mg/(N·m). Conclusions. The MODE=2, VIBRATION=5 mode provides the best combination of microhardness, low porosity, adhesion, and wear resistance among those studied and can be used as a basis for local restoration of worn surfaces of agricultural machinery parts.