Preparation of Ni Aluminide Surface Layer Containing Yttrium at Different Depth by Molten Salt Electrodeposition and Cyclic Oxidation Resistance

Attention has focused on a Ni aluminide containing a small amount of Y as a high-oxidation resistant material, and preparation of a coating consisting of this material was attempted by the molten salt electrodeposition which is a low-cost coating method. In the present study, the preparation of the coating consisting of this material was carried out by the electrodeposition of Ni using an aqueous solution as the electrolyte and the electrodeposition of Y and Al using a molten salt electrolyte. Furthermore, in order to change the depth of the region containing Y in the Ni aluminide layer, a three-step electrodeposition of Ni, Y and Ni was carried out, and the times of the first and third Ni electrodepositions were changed. As a result, surface layers consisting of Ni aluminide with a different depth of the region containing Y were formed. Furthermore, the cyclic oxidation resistance of these specimens was examined in air at 1423 K. As a result, for the specimen with a shallow Y-containing region in the Ni aluminide layer, the specimen mass reduction due to spalling of the scale was observed, whereas for the specimen with a deep Y-containing region, no specimen mass reduction was observed and a high-cyclic oxidation resistance was obtained. For the specimen with a deep Y-containing region, which showed the high-cyclic oxidation resistance, the scale formed on the coating after the oxidation test consisted of Al2O3 containing Y2O3, and this scale entered the metal substrate under the scale in the form of a wedge.