Tailoring microstructure and tribological behavior of NiCr30WC coatings via MoS2@Ni content

Abstract

NiCr30WC-xMoS₂@Ni (x = 15, 25 and 35, wt., %) coatings were fabricated on 45 steel by laser cladding (LC). The effects of MoS₂@Ni content on the microstructure, phases and tribological behaviors at room temperature (25 °C) and elevated temperature (400 °C) were systematically investigated, and the wear mechanisms were also discussed in detail. The results show that the appropriate MoS₂@Ni content refines the microstructure and improves the uniformity of reinforcing and lubricating phases, which promotes the formations of Cr_xS_y, M₂₃C₆, Mo₂C and NiS and improves the overall lubricating effect. The NiCr30WC-25%MoS₂@Ni coating at 25 and 400 °C exhibits the best wear resistance, which is attributed to the fined microstructure and more favorable balance between the load support from hard phases and shear reduction from lubricating constituent. Its coefficient of friction (COF) and wear rate of NiCr30WC-25%MoS₂@Ni coating at 25 °C are 0.42 and 3.37 × 10⁻⁵ mm³ N⁻¹ m⁻¹, respectively; while those at 400 °C are reduced to 0.36 and 7.18 × 10⁻⁵ mm³ N⁻¹ m⁻¹, respectively. In contrast, the excessive MoS₂@Ni addition (35%) increases the fraction of soft lubricating phases and promotes the microstructural coarsening, which intensifies the plastic deformation and adhesive damage. The wear mechanism of NiCr30WC-15%MoS₂@Ni is dominated by abrasive wear, adhesive wear and third-body wear, and the NiCr30WC-25%MoS₂@Ni coating exhibits the mild abrasive wear and oxidative wear; whereas the NiCr30WC-35%MoS₂@Ni coating is governed by the combined action of adhesive wear, oxidative wear and abrasive wear.