Creep of uncoated and Cu–Cr coated NARloy–Z

Stress rupture creep tests were performed on uncoated and Cu–30vol.%Cr coated NARloy–Z copper alloy specimens exposed to air at 482–704°C. The results showed that creep failure in air of unprotected NARloy–Z was precipitated by brittle intergranular surface cracking produced by stress-accelerated grain boundary oxidation (SAGBO), which in turn caused early onset of tertiary creep. For the protected specimens, the Cu–Cr coating remained adherent throughout the tests and was effective in slowing down the rate of oxygen absorption, particularly at the higher temperatures, by formation of a continuous chromium oxide scale. As the result of reducing oxygen ingress, the coating prevented SAGBO initiated early creep failure, extended creep deformation and increased the creep rupture life of NARloy–Z over the entire 482–704°C test temperature range.