Formation of Ni aluminide surface layer containing La by molten-salt electrodeposition and cyclic-oxidation resistance

In order to improve the cyclic-oxidation resistance of Ni, the coating of a Ni aluminide containing La on the Ni was carried out by the electrodeposition of Al and La in a molten salt. The electrodepositions of Al and La were conducted using a potentiostatic polarization method at 1023 K in an equimolar NaCl-KCl melt containing 3.5 mol%AlF3 and that containing 4 mol% La2O3 and 24 mol%NH4Cl, respectively. Observation and analysis of the cross-section of the specimen after polarization showed that a deposit layer consisting of a thick inner Ni aluminide layer and a thin outer layer containing a large amount of La was formed on the Ni specimen. The cyclic-oxidation resistance of the specimen coated with the deposit layer having the layer containing La as an outer layer was higher than those of the untreated Ni specimen and the specimen coated with deposit layer without La. The scale formed on the specimen coated with the deposit layer without La after the oxidation test was thick and consisted of NiO, whereas the scale formed on the specimen coated with the deposit layer having the layer containing La was extremely thin, and consisted of alpha-Al2O3.