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This study investigated the high temperature oxidation of Ni–Fe–Cr–Al porous metal. Two types of open porous metals with pore sizes of 30 and 40 PPI were used. For 24-h, the isothermal oxidation TGA tests were conducted at three different temperatures of 900, 1000, and 1100 °C. The oxidation resistance of porous metal decreased with decreasing pore size. Porous metals mainly created oxides such as Al2O3, Cr2O3, NiAl2O4, and NiCr2O4. The porous metal represented increasingly faster dwindling of Al and Cr content and easy progress to internal oxidation, comparing to the oxidation of bulk metal.

Electroless Ni–PTFE–P coatings have been successfully deposited on the surface of mild steel shaft from plating baths containing various concentrations of rare earth metal cerium (RE Ce). Surface morphology, Ce fraction, and thickness of the coatings were characterized by scanning electron microscope, inductively coupled plasma optical emission spectrometry, and reflection optical microscope, respectively. Salt spray test was used to determine the corrosion resistance of the coating. Results revealed that structure, compactness, and deposition rate of the Ni–PTFE–P coatings were increased significantly by addition of a small amount of RE Ce (10–20 ppm) to the plating bath. Electroless Ni–PTFE–P coating deposited from plating baths with 20 ppm Ce shows the highest corrosion resistance, owing to its high compactness and thickness. Deposition rate and corrosion resistance of the Ni–PTFE–P coating were deteriorated greatly as concentration of RE Ce in the plating baths exceeds 100 ppm.

Electroless Ni-P-Al 2 O 3 composite coatings have been synthesized on mild steel shafts using surfactant cetyltrimethyle ammonium bromide (CTAB) as dispersant. The effects of the surfactant on the alumina dispersion, weight fraction in coatings, and corrosion resistance of the composite coatings under salt spray test were investigated. Results showed that alumina dispersion was improved, whereas weight fraction was decreased, with the increasing concentration of the dispersant CTAB. The corrosion resistance ofthe composite coatings was found to increase with the increase in CTAB concentration up to a certain optimum of 20 mg/L, beyond which a decreasing trend of corrosion resistance was observed under salt spray test. Compared with Ni-P coating, all the Ni-P-Al 2 O 3 composite coatings showed improved corrosion-resistant properties.