Formation of Ni Aluminide Layer Containing La by Molten-Salt Electrodeposition and Cyclic-Oxidation Resistance

Abstract

In order to improve the cyclic-oxidation resistance of Ni and SUS304 steel, the coating of a Ni aluminide containing La on both samples were 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%La2O3-24 mol%NH4Cl, or 3.5 mol%LaF3. Observation and analysis of the cross-section of the specimen after polarization showed that a deposited layer consisting of a thick inner Ni aluminide layer and a thin outer layer containing a large amount of La was formed on both samples. The cyclic-oxidation resistance of the Ni specimen covered with the deposit layer having the La layer as the outer layer was higher than those of the untreated Ni specimen and the Ni specimen coated with the deposit layer without La. The stainless steel covered with the Ni aluminide showed a high cyclic-oxidation resistance in the atmosphere containing water vapor at 1273 K in comparison with untreated stainless steel, without depending on the existence of La in the deposited layer.