めっき法によるNi-Al-La合金膜のコーティングとその耐サイクル酸化性

抄録

  The formation of coating layer of a Ni aluminide containing La on a Ni-10 at%Cr-8 at%Al alloy substrate was tried by the electrodeposition of La, Ni and Al. The cyclic oxidation resistance for the alloys covered with the coating was then evaluated. Ni was deposited by aqueous solution electrolysis. La and Al were deposited by molten salt electrolysis. For the sample treated with the Ni and Al depositions, a layer consisting of Ni₂Al₃ was uniformly formed. On the other hand, for the sample treated with the La deposition for 0.6 ks, followed by the Ni and Al depositions, a Ni-rich layer and a Ni₂Al₃ layer were formed in that order from the substrate alloy. Further, when electrodeposition time of La became long to 1.2 and 1.8 ks, a La-rich layer, a Ni-rich 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 with Ni and Al depositions, the mass reduction due to exfoliation of a scale took place. However, for the sample treated with La deposition for 0.6 and 1.2 ks, followed by the Ni and Al depositions, mass reduction was not observed. For this sample after the cyclic oxidation test, a scale consisting of α-Al₂O₃ adhering to the substrate was formed. Consequently, it was found that a cyclic oxidation resistance of the alloy was improved by the La, Ni and Al electrodepositions.