Abstract
(V,Mo)N is a recently developed material for wear-resistant coatings due to its high fracture toughness. This study aimed to evaluate the mechanical and tribological properties of single-phase (V,Mo)N coatings. Five sets of (V,Mo)N coatings with different N/metal ratios were deposited on AISI D2 steel substrates using direct current unbalanced magnetron sputtering (dc-UBMS) and high power pulsed magnetron sputtering (HPPMS). The controlling deposition parameters in the HPPMS process were duty cycle and nitrogen flow rate. After deposition, the structure and compositions of the specimens were characterized by X-ray diffraction (XRD) and electron probe microanalysis, respectively. The residual stress of the coatings was measured using the average X-ray strain method. The tribological properties were evaluated by wear test and impact fatigue test. The results showed that the coatings in this study have higher N/metal ratio and (200)-preferred orientation compared with those deposited solely on Si substrates in the previous studies. The hardness of the coatings increases from 19.6 to 26.3 GPa with decreasing N/metal ratio. Additionally, the coatings deposited by HPPMS on steel substrates possess lower residual stress than those by dc-UBMS, which may be due to the stress induced by the power cycle being relieved by plastic deformation of steel substrate. All (V,Mo)N coatings show a very low wear rate ranging from 1.1 x 10-7to 4.0 x 10- 7 mm 3 N-1 m- 1 at room temperature. As temperature increases to 500 degrees C and above, the wear resistance of the (V,Mo)N coatings significantly decreases, while low friction coefficients are maintained by the formation of self-lubricating V- and Mo-oxides. All coatings remain intact after 150 k impact fatigue test, even when the deformation depth is larger than the coating thickness, implying the remarkable toughness of the (V, Mo)N coatings. In contrast, the coatings deposited using dc-UBMS have the lowest impact fatigue resistance, which may be associated with their lower fracture toughness.