STRUCTURE AND WEAR RESISTANCE OF PLASMA-SPRAYED COMPOSITE NiCrBSiC-TiCrC POWDER COATINGS

Abstract

Composite NTC20 and NTC40 powders based on the self-fluxing NiCrBSiC alloy with additions of 20 and 40 wt.% TiCrС were produced by conglomeration using an organic binder. Since the organic binder burns out in the plasma spraying process, components of the composite powders segregate, leading to the loss of a certain amount (up to 15–20 vol.%) of TiCrC particles. The plasma-sprayed NTC20 and NTC40 coatings show a heterophase lamellar structure, consisting of a nickel-base matrix in which fine grains of chromium borides and carborides (1–2 μm) and TiCrC particles (5–8 μm) are evenly distributed. Electron microprobe analysis revealed a higher content of oxides in the NTC20 and NTC40 coatings compared to the NiCrBSiC coating, which is associated with the oxidation of TiCrC particles in the plasma spraying process. The introduction of TiCrC additions into the self-fluxing NiCrBSiC alloy increases porosity of the plasma-sprayed NTC20 and NTC40 coatings (up to 8%) compared to the NiCrBSiC coating (5%). Wear tests of the plasma-sprayed NTC20 and NTC40 coatings were performed in dry sliding friction conditions using 65G steel as a counterface. For comparison, a plasma-sprayed coating consisting of the serial self-fluxing NiCrBSiC alloy was tested. Additions of 20 and 40 wt.% TiCrC particles to the self-fluxing NiCrBSiC alloy increase the wear resistance of the plasma-sprayed coatings by 2–2.3 times. As the sliding speed increases from 4 to 12 m/sec, the NiCrBSiC coating undergoes catastrophic wear (І » 60 μm/km), while the wear rate of the NTC20 and NTC40 coatings remains constant (І » 12–22 μm/km).