Preparation of Ni-Aluminide Surface Layer Containing Hafnium by Molten-Salt Electrodeposition and Cyclic-Oxidation Resistance

Abstract

The preparation of a coating consisting of Ni aluminide containing a small amount of Hf was carried out by the electrodeposition of Ni using an aqueous solution and the electrodeposition of Hf and Al using a molten salt. Furthermore, in order to change the depth of the layer containing Hf in the coating, a four-step electrodeposition of Ni, Hf, Ni and Al was carried out, and the times of the first and third Ni electrodepositions were changed. As a result, coatings consisting of Ni aluminide, which contained different depths of the Hf-containig layer, were formed. The cyclic-oxidation resistance of these specimens was evaluated in air at 1423 K. For the specimen with a shallow Hf-containing layer in the coating, the specimen mass reduction due to spallation of the scale was observed, whereas for the specimen with a deep Hfcontaining layer, the specimen mass reduction was only slightly observed and a high-cyclic oxidation resistance was obtained. Among the specimens with a deep Hf-containing layer, the specimen prepared by Hf deposition for 0.6 ks showed the highest cyclic-oxidation resistance. For this specimen, the scale formed on the coating after the oxidation test consisted of Al 2 O 3 . This scale was adhesive, and locally entered the metal substrate.

Preparation of Ni-Al-Pt Coating on Ni-6 at%Cr Alloy by Electrodeposition Method and Cyclic-Oxidation Resistance

“…Furthermore, we showed that the coatings consisting of Ni aluminide (Ni 2 Al 3 ) were formed by the Al electrodeposition on the Ni plate or Ni film using a molten salt at 1023 K. 5,6) Though these coatings had a high oxidation resistance during the isothermal oxidation test, 5) they showed a mass loss due to spallation of a scale during a cyclic-oxidation test. 6) In order to improve a cyclic-oxidation resistance of the coating, we tried electrodeposition of Hf, 6,7) Zr 8) or Y 9) with Al using a molten salt at 1023 K. As a consequence, we succeeded in the preparation of a coating consisting of Ni aluminide containing small amounts of Hf, Zr or Y. Such coatings showed high cyclic-oxidation resistance in air at 1423 K.…”