Mechanical properties and oxidation resistance of Mo-Si-B and Mo-Hf-Si-B coatings obtained by magnetron sputtering in DC and pulsed DC modes.

Mo-Si-B and Mo-Hf-Si-B coatings are deposited by magnetron sputtering in two regimes (direct and pulsed current) using composite ceramic cathodes. The structure of the coatings is investigated by XRD, SEM, EDS, and GDOES. Mechanical and tribological properties are measured by nanoindentation and tribological pin-on-disc testing. The short-term oxidation resistance of the coatings in the air is evaluated at 1500 °С. Results show that pulsed current deposition decreases the coating's growth rate and the grains size of coating's main constituent h-MoSi 2 phase while promoting the formation of MoB 2. The introduction of hafnium increased the coating's density and suppressed the formation of unwanted columnar structure. The highest hardness of 28 GPa, Young modulus of 366 GPa, and elastic recovery of 64% were achieved for the Mo-Si-B coating deposited at direct current. Optimal tribological performance, including a stable friction coefficient and low wear rate of 6.9х10−6 mm3/(Nm), was determined for Mo-Hf-Si-B coating also obtained using direct current. All coatings were oxidation-resistant at 1500 °С, but the Mo-Hf-Si-B composition demonstrated oxidation resistance superior to that of Mo-Si-B coatings because of the formation of two-layered HfO 2 /SiO 2 protective film. The thickness of the oxide layer was higher for the coatings deposited using pulsed current. Unlabelled Image • Hard Mo-Si-B and Mo-Hf-Si-B coatings obtained by magnetron sputtering in d.c. and pulsed modes • Mo-Si-B exhibit maximal hardness of 28 GPa and elastic recovery of 64%. • Mo-Hf-Si-B possess higher tribological properties and oxidation resistance. • Coatings withstand short-term oxidation at 1500 °C. • Oxidation is accompanied with formation of SiO 2 and HfO 2 /SiO 2 protective layers. [ABSTRACT FROM AUTHOR]