Thermal stability and tribological properties of HiPIMS Cr2O3 coatings with varied pulse widths

Wear-resistant oxide coatings play an important role in protecting the surfaces of tools and components. The fabrication of hard oxides using advanced physical vapor deposition techniques has recently attracted considerable attention. In this work, Cr 2 O 3 coatings, with a Cr transition layer, were deposited by high-power impulse magnetron sputtering at different pulse widths, and their structure, thermal stability, and tribological properties were investigated. All Cr 2 O 3 coatings demonstrate columnar grain growth with a thermodynamically stable hexagonal structure. A pulse width of 70 μs at a constant frequency of 500 Hz yields a peak current of 500 A, resulting in a hardness of 27.2 GPa, which is superior to that achieved at 100 and 280 μs. Decreasing the pulse width to 35 μs at 1500 Hz gives rise to a maximum hardness of 29.3 GPa. The hardness of Cr 2 O 3 coatingsincreases upon annealing in air at 800 and 900 °C. Notable grain coarsening, along with increased porosity, leads to a decrease in hardness at 1000 and 1100 °C. The hardness at 1100 °C decreased by 3.5 to 4.7 GPa compared to that at 900 °C. The friction coefficients of the examined Cr 2 O 3 range from 0.32 to 0.36 at ambient temperature and diminish to 0.26 to 0.28 at 600 °C. At ambient temperature, Cr 2 O 3 coatings, including that deposited at a high pulse width of 280 μs, show outstanding wear resistance, with the specific wear rate below 2 × 10 −7 mm 3 /N∙m. Nonetheless, certain coatings exhibit severe localized wear at 600 °C, with cracking inside wear tracks. This reduced wear resistance is likely attributable to the inherent brittleness of Cr 2 O 3 and the inconsistency in deformation with the underlying Cr.