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

Abstract

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 Al 2 O 3 containing Y 2 O 3 , and this scale entered the metal substrate under the scale in the form of a wedge.

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

“…On the contrary, Rommerskirchen 15) showed that for NiAl containing 0.39 mass% Y, the NiAlY alloys containing 30 and 29 mass% Y were deposited within the grains and along the grain boundaries, respectively. We also observed in a previous study 4) that for the Ni aluminide-coating specimen with the Y-containing layer, Y was deposited as the NiAlY alloy at the grain boundaries in the surface region of the Ni aluminide layer during the oxidation test. These results indicated that Y scarcely dissolved into the Ni aluminide.…”

“…1, and examined the cyclic-oxidation resistance of the Ni-10 at%Cr-8 at%Al alloy covered with these coatings. 4) As a result, we observed a high oxidation resistance when the Y-containing layer was formed in the vicinity of the center of the Ni aluminide layer ((b) and (c) processes). For the Ni aluminide-coatings with the Hfcontaining layer in the present study, however, when the Hfcontaining layer was formed in the vicinity of the center of the Ni aluminide layer, the cyclic-oxidation resistance was poor (Fig.…”

“…2,3) We already succeeded in the forming of Ni aluminide layer containing small amounts of Y by the stepwise electrodeposition of Y, Ni and Al on the Ni-base alloy and improved the cyclic-oxidation resistance of the Ni-base alloy. 4) In the present study, the forming of a Ni aluminide layer containing small amounts of Hf by the stepwise electrodeposition of Hf, Ni and Al on the Ni-10 at%Cr-8 at%Al alloy was attempted.…”

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.…”