Wear resistance of coatings deposited by of high-speed arc spraying using Cr-B-Mn-Si system cored wires modified with Ti, V, Ni, Al, Nb

Анотація

Coatings obtained by high-velocity arc spraying (HV-AS) using cored wires (CW) are attracting increasing attention for the restoration of large and heavily loaded machine parts as a reliable and cost-effective alternative to hazardous hard chromium plating. However, coatings obtained by spraying of traditional CWs (Fe-Cr-B systems) usually exhibit insufficient wear resistance in abrasive wear tests due to severe matrix wear and carbide and boride ejection. The purpose of this study is to evaluate the effect of the complex addition of components such as Ti, V, Ni, Al, Nb to the charge of CWs of the basic system 90Cr10B2.5MnSi on the evolution of the structural and phase state of HV-AS coatings, their tribological characteristics during wear tests under conditions of fixed and unfixed abrasives, and the micromechanisms of wear that are realized in these cases. Eight CW compositions were created and used for HV-AS in an air flow in subsonic (0.6 MPa) and supersonic (1.2 MPa, Mach 2) deposition regimes. To assess the phase composition, structural state, and microhardness of the coatings, the X-ray diffraction method (with Rietveld enhancement and using Powder Cell 2.4), scanning electron microscopy (EVO 40XVP) with the INCA Energy system, and a PMT-3 microhardness tester were used. The wear resistance of the coatings was quantitatively determined in accordance with the requirements of the ASTM G65 standard. The coatings were tested in laboratory conditions by rubbing with a corundum disk Al₂O₃ (fixed abrasive) and a rubber wheel with sand supplied to the friction zone (non-fixed abrasive). Due to the supersonic spraying mode, self-propagating high-temperature synthesis reactions between B₄C and transition metals in the CW charges were initiated already during the flight of CW melt droplets to the substrate. The droplet temperature was increased to ~2500 K, which ensured complete dissolution of alloying elements. This contributed to the formation of high-density and hard coatings (with porosity of 2.5–4.0% and hardness of 800–1000 HV) containing 25 vol.% uniformly distributed complex borides (Fe,Cr)₂B. In tests with a fixed abrasive, all coatings demonstrated a twofold increase in wear resistance compared to hardened U12 tool steel (65 HRC). However, in tests with an unfixed abrasive, coatings sprayed with CW alloyed with Ti, V, Ni, and Al were destroyed due to matrix wear. While alloying CW with 3 wt.% Nb promoted the formation of an in situ nanocomposite structure with ultra-dispersed (10–30 nm) globular carbides/borides, which effectively reinforced and strengthened the tempered martensitic matrix. The coating with CW 200Cr10Nb3MoB showed an ultra-low mass loss of 0.02 g, which is 40% less than that of U12 steel.