Effect of temperature on friction and galling of laser processed Norem 02 and Stellite 21

Abstract

The Stellite family of Co-based alloys is known to offer superior performance in many demanding sliding contact applications. However, alternative materials with corresponding properties are searched for, e.g. due to the fact that wear and corrosion products of Co run the risk of activation in nuclear plant applications. Furthermore, due to the high price of Co, a competitive, less expensive alloy would be very welcome for use in many applications. The present investigation examines the frictional behaviour and galling resistance of the laser processed Fe-based alloy Norem 02 at temperatures ranging from room temperature (RT) to 250 °C. Friction and galling testing was performed by sliding two crossed test rods in a load-scanning test rig. The results are compared with those previously attained from laser processed Stellite 21, one of the best low friction, galling resistant Co-based alloys. At RT Norem 02 exhibited excellent sliding performance, comparable to that of Stellite 21, showing a low and stable friction coefficient at a level of 0.25, and no tendencies to gall. However, at temperatures of 150 °C or above, the friction coefficient raised to a level of 0.5–0.7 and massive galling was observed for Norem 02. Stellite 21, however, maintained its excellent friction performance at those temperatures. Consequently, laser processed Norem 02 might not be suitable as a candidate material to replace Stellite in valves and seals in the primary circuit of nuclear power plants, which usually operate at temperatures considerably higher than RT.