Increasing the coefficient of sliding friction of NiCr at low loads by interstitial surface hardening

Low-temperature interstitial hardening of NiCr alloys by gas-phase carburizing and nitriding increases the coefficient of sliding friction (COF) at low loads by as much as 50%. While the substantial surface hardening provided by the very high concentrations of interstitial carbon or nitrogen tends to decrease the COF, the presence of these interstitial solutes also decreases the thickness of the air-formed surface oxide layer, which tends to increase the COF. The overall result is an increase in COF.