Formation of Ni aluminide coating layer having high oxidation resistance by the molten-salt electrodeposition

摘要

A Ni aluminide layer was formed on Ni substrate by electrodepositing Al in molten salt. The electrodeposition of Al was conducted using potentiostatic polarization method at constant potentials in an equimolar NaCl-KCl melt containing 3.5 mol AlF 3 at 1023 K. The deposited layer consisted of Ni 2Al 3. Nickel covered by the electrodeposited layer was more resistant than bare nickel to high temperature oxidation. Furthermore, the formation of a Ni aluminide layer containing Zr on a Ni substrate was attempted by the Zr deposition, followed by the Al deposition for the purpose of improvement of cyclic oxidation resistance. A layer consisting of Ni 2Al 3 and a Ni aluminide layer containing Zr on the Ni 2Al 3 layer were formed. Furthermore, when the Zr electrodeposition conditions were changed, the concentration of Zr in the Ni aluminide layer containing Zr, which was formed in the surface region, changed. The cyclic oxidation test showed that for the Ni sample with the Al deposition, the mass reduction due to scale exfoliation took place, whereas for the sample treated with a small deposit of Zr, followed by Al deposition, no mass reduction was observed. Furthermore, a synchronous electrodeposition of Al and Zr was attempted in order to decrease the number of electrodeposition. As a result, it was found that the synchronous electrodeposition of Al and Zr could be achieved by decreasing of ZrF4 content in the molten salt. The Ni aluminide layer formed by using the molten salt containing 3.5 mol AlF 3 and 0.05 mol ZrF4 contained a small amount of ZrAl 3 particles at the surface region and showed a high cyclic-oxidation resistance.