Friction and wear behavior of chromium carbide coatings

Abstract

Chromium carbides, tungsten carbide and chromium oxide have been tested and evaluated as coatings to protect high temperature gas-cooled reactor (HTGR) steam generator and other HTGR components from adhesion, galling associated with sliding wear or from fretting. Tests were performed in commercially pure helium and in helium doped with various gaseous impurities (H 2, H 2O, CH 4, CO) to stimulate the primary coolant of an HTGR. Several types of chromium carbide coatings including Cr 3C 2, Cr 7C 3 and Cr 23C 6 were tested for wear resistance and resistance to long-term spalling. Tungsten carbide and chromium oxide coatings were tested in sliding wear tests. Cr 23C 6-NiCr coatings showed the best performance (from 400 to 816 °C) whether they were applied by detonation gun or plasma gun spraying methods. The presence of the Cr 23C 6-NiCr coatings did not affect the creep rupture properties of alloy 800H substrates at temperatures up to 760 °C. Low-cycle fatigue life of similar specimens at 593 °C was reduced by 10% – 20% when tested in the 1% – 0.6% strain range.