ROOM-TEMPERATURE STRAINS IN CR2O3 SCALES FORMED AT ELEVATED-TEMPERATURES ON NI-25 WT-PERCENT CR AND Y-DOPED AND AL-DOPED NI-25WT-PERCENT CR

Ni-25wt%Cr, Ni-25wt%Cr-1wt%Al and Ni-25wt%Cr-0.2wt%Y alloys were oxidized at 1000-degrees-C in O2 to form similar thicknesses of Cr2O3 scales. After cooling to ambient temperatures, the residual strains in these oxide films were measured using X-ray diffraction, and qualitative indications of the interfacial strength were obtained using a micro-identation technique. Compressive elastic strains of the order of 0.4% were measured on the Y- and the Al-doped alloys. This value agees well with calculated thermal strains which arose from cooling. Only 0.1% compressive elastic strains were observed for the undoped Ni-25Cr alloy. Localized scale buckling and separation from the substrate is believed to have allowed relaxation of the strain in this case. The Y- and the Al-doped alloys on the other hand, have extremely strong scale/alloy interfaces, and therefore were able to retain higher strain levels.