電析法による Zr を含む Ni アルミナイド膜のコーティングとその耐サイクル酸化性

Abstract

The formation of a coating layer consisting of Ni aluminide containing Zr on a Ni-10 at%Cr-8 at%Al alloy substrate was attempted by the electrodeposition of Zr, Ni and Al. The cyclic oxidation resistance for the alloys covered with this coating was then evaluated. Ni was deposited by aqueous solution electrolysis. Zr and Al were deposited by molten salt electrolysis. For the sample treated with the Ni deposition, followed by the Al deposition, a layer consisting of Ni2Al3 was uniformly formed. On the other hand, for the sample treated with the Zr deposition, followed by the Ni and Al depositions, a Ni-Zr alloy layer and a Ni2Al3 layer were formed in that order from the substrate alloy. The cyclic oxidation test showed that for the untreated sample and the sample only with Ni and Al depositions, a mass reduction due to exfoliation of a scale took place during the initial oxidation period. For the sample treated with the Zr deposition for 0.03 and 0.24 ks, followed by the Ni and Al depositions, a mass reduction was observed during the course of the oxidation test. However, for the sample treated with the Zr deposition for 0.18 ks, no mass reduction was observed. The result of a cross-sectional observation for this sample treated with the Zr deposition for 0.18 ks after the 5-cycle oxidation test showed that the Ni-Zr alloy layer disappeared and a wedge-shaped α-Al2O3 scale was formed on the Ni aluminide layer. Consequently, it was considered that for this sample, the Zr in the Ni-Zr alloy layer diffused into the Ni aluminide layer, contributing to an improvement in the exfoliation resistance of the Al2O3 scale.