Effect of velocity and temperature on the dry sliding behavior of a SiC-Graphite composite against WC-CoCr and WC-FeCrAlY HVOF coatings

Abstract

Dry sliding tests on pin on disc testing equipment were conducted on a new and developing SiC-graphite composite material, for racing applications, against WC-CoCr and WC-FeCrAlY HVOF coated discs. The coated discs were paired with the composite material to observe the friction coefficient and wear behavior at elevated testing conditions for potential applications in high intensity aerospace and train braking systems. The testing conditions included one constant contact pressure of 0.5 MPa, two sliding velocities of 1.57 and 7 m/s, and two working temperatures at room temperature (RT) and 300 °C (HT). The COF and pin wear increased with increase in velocity at RT conditions. Conversely, the COF and pin wear decreased with increase in velocity at HT testing conditions. For both the testing conditions, tests with WC-FeCrAlY coated disc provided for higher COF and wear compared to the tests with WC-CoCr coated disc. The friction layers on the worn pin surfaces were made by elements originating from the pin and also transferred from the disc and their extension increased with increase in velocity and testing temperatures. The disc surfaces were characterized by mild abrasive wear, in particular at HT and high sliding speed. A basic analysis on contact temperature was conducted to understand the mechanism of formation of friction layer for various testing systems. For RT testing conditions, due to low contact temperature, pin wear as well as uncompact friction layer were observed. However, as the contact temperature increased for HT tests accompanied by high velocity, a well compact friction layer with reduced COF and wear were noted.