Tribological behavior of duplex CrN/DLC and nano-multilayer DLC-W coatings on valve tappet under elevated temperature and varying load

In this work, the effect of increasing contact load and elevated temperature on the friction and wear rate of duplex CrN/DLC and nano-multilayer DLC-W deposited by hybrid Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition (PVD-PECVD) on valve tappet. The tribological behavior of the coatings were studied through reciprocating dry sliding experiments at temperatures between 25 and 250 °C, with 10 N step-increment from 5 to 50 N. The results presented revealed that the coefficient of friction of the duplex CrN/DLC coating was lowest at 150 °C and 20 N, while the nano-multilayer DLC-W coating was lowest at 25 °C and 50 N. The wear rate of the duplex CrN/DLC coating and the nano-multilayer DLC-W coating were the lowest at 25 °C. The wear rates for both coatings continued to increase with increasing temperature. •Tribological behavior of the coatings were investigated using reciprocating dry sliding tests between 25 – 250 °C and contact loads of 5 – 50 N.•An increase in the load from 5 N to 50 N resulted in a reduction in COF for both duplex CrN/DLC and nano-multilayer DLC-W coating at all temperatures.•Nevertheless, it was observed that the COF exhibited an upward trend across all load conditions as the temperature increased from 25 °C to 250 °C.•The specific wear rate during the sliding reciprocating tests exhibited a notable increase with the temperature increase from 25 °C to 250 °C.