Porosity-dependent cyclic-oxidation resistance at 850 °C of annealed Ni–Al-based coatings via electroplating

This study was focused on the cyclic-oxidation behaviors of porous Ni–Al-based coatings, and some alternative methods such as slow annealing and alloying with oxide additives to achieve better cyclic-oxidation resistance at intermediate temperatures. It was found that excellent cyclic-oxidation resistance at 850 °C could be obtained for the coatings even with low Al content when the initial porosity was less than 7%. When porosity was in the range of 7% to 11%, the coatings exhibited inferior resistance to cyclic oxidation in the initial stage, but improved resistance at the latter stage as pores are healed by diffusion. The formation of thin and close-packed oxide film on coating surfaces reduced the pore-healing rate in the coatings. Adding reactive oxides had little effect on oxidation resistance and pore healing under the current intermediated temperature of 850 °C and the relative short testing time (1000 h).