The Effect of Pre-Oxidation Treatment on the High-Temperature Oxidation of Co–Re–Cr Model Alloys at Laboratory Air

Abstract

The aim of a pre-oxidation treatment at low oxygen partial pressure is to promote the formation of a Cr2O3 (or Al2O3) scale in such a way that the oxide layer can reliably prevent the contact of oxygen with the metallic substrate also at high oxygen partial pressure. In this study, the pre-oxidation treatment was applied to the two alloys Co–17Re–23Cr and Co–17Re–30Cr (at.%). Pre-oxidation of the Co–Re–xCr alloys was found to be non-protective for the metallic substrate at high oxygen partial pressure despite the formation of a Cr2O3 layer. Different kinds of Cr2O3 scale damage were observed depending on the Cr concentration. The Cr2O3 scale formed on the alloy Co–17Re–23Cr loses its protective properties as a result of cation transport by lattice and grain boundary diffusion, while the Cr2O3 scale formed on the alloy Co–17Re–30Cr degraded as a consequence of scale cracking. In addition, the effect of alloying with Si was investigated and found to be promising.