Realizing wear-resistant Cr2O3 coatings using finer feedstock: Role of diverse plasma spray torch configurations

Abstract

This study investigates the microstructural, mechanical, and tribological properties of Cr₂O₃ -based coatings deposited using finer feedstock with three different plasma spray torches: the traditional 9MB torch, the cascaded SinplexPro (SLX) torch, and the Axial III (AXL) torch. The specific objective is to achieve denser Cr₂O₃ microstructures; thereby, enhanced wear resistance and mechanical performance shall be realized. Detailed characterization and performance analysis, including X-ray diffraction (XRD), scanning electron microscopy (SEM), sliding wear tests, wear track profiling, coefficient of friction measurements, etc., were conducted to evaluate the influence of torch configuration on the resulting coatings. Phase analysis confirmed that the AXL coating displayed similar XRD peak intensities of all planes as that of feedstock, indicating that the axial spray coatings retained the structural characteristics of the original feedstock powder. SEM and wear studies revealed that the AXL coating, characterized by its dense microstructure and minimal porosity, exhibited superior hardness (12.1 GPa) and least specific wear rate (0.1 × 10⁻⁶ mm³/N-m). In contrast, 9MB and SLX coatings showed relatively higher porosity, lower hardness, and increased wear rate. The study demonstrates the critical impact of torch design towards achieving dense coating structures and highlights the combination of fine-sized feedstock fed in axial injection mode, eventually producing coatings with enhanced wear resistance and mechanical properties.