The tribological properties of short range ordered W-B-C protective coatings prepared by pulsed magnetron sputtering

In this study mid-frequency pulsed-DC magnetron sputtering was used to deposit W-B-C coatings. The effect of coating composition and the deposition parameters on the structure, mechanical and tribological properties of the coatings was investigated. The broad diffraction peaks in the X-ray diffractogram indicated the amorphous to nanocrystalline nature of the coatings. The hardness of the coatings ranged from 22.6 to 26.2 GPa. The coatings prepared at the elevated temperature of 500 degrees C exhibited greater hardness compared to the coatings prepared at the ambient temperature. The amount of W in the coatings was the main parameter influencing the friction coefficient with a higher W content leading to a higher friction coefficient. The coatings prepared at 500 degrees C showed lower wear in tribological measurements due to their higher hardness compared to the coatings prepared at ambient temperature. The friction coefficient decreased as the testing temperature increased beyond 500 degrees C. XRD analyses after the high temperature tests have shown that this decrease was due to the formation of W-O Magneli phases, which acted as a solid-state lubricant.