Characterization and wear of oxides formed on CoCrMoSi alloy coatings

Abstract

CoCrMoSi alloys were developed for high-temperature use and their performance associated with the almost continuous Laves-phase network. The metallurgical stability of CoCrMoSi coatings exposed to high temperatures has been shown to be associated with the stability of the Laves phase. However, the successful development of coatings for high-temperature applications requires an understanding of their oxidation behavior and the role the oxide layer plays on their wear characteristics. The aim of the study was to assess the wear behavior of oxides formed on the surface of CoCrMoSi coatings. Exposure to 450°C and 750°C induced the formation of different oxides identified by Raman spectroscopy and X-ray diffraction. Abrasive wear tests were carried out with a rotating ball tester and low applied loads ranging from 0.2N to 0.45N. Confocal microscopy and scanning electron microscopy were used to characterize the wear scar. Exposure to 450°C induced the formation of Co3O4, Fe3O4 and Fe2O3 Their low adhesion to the coatings surface allows the removal of oxide particles that scratch the surface of coatings forming grooves. Exposure to 750°C resulted in a continuous Cr2O3 film, subsequent wear testing revealed rolling wear to be the predominant degradation mechanism. Comparison with as-deposited CoCrMoSi coatings wear results showed that the oxides formed at 450°C did not affect wear performance. In contrast, the continuous oxide film formed at 750°C has an increased wear resistance as is expected to postpone the on-set of wear in coatings.