Formation of Ni Aluminide Containing Hf by Simultaneous Electrodeposition of Al and Hf and Cyclic-Oxidation Resistance

Abstract

A Ni aluminide layer containing Hf was formed on a Ni specimen by the simultaneous electrodeposition of Al and Hf using a molten-salt bath. Al and Hf were only slightly electrodeposited and an electrodeposited layer was not formed when the simultaneous electrodeposition of Al and Hf was tried using molten NaCl-KCl containing 3.5 mol%AlF3 and 3.5 mol%HfF4. On the other hand, an electrodeposited layer consisting of Ni2Al3 and NiAl3 layers, for which the Al3Hf particles were formed on the surface region, was formed, when the simultaneous electrodeposition of Al and Hf was carried out using the molten NaCl-KCl containing 3.5 mol% AlF3 and 0.05 mol% HfF4. The cyclic-oxidation resistance of the Ni specimens covered by the Ni aluminide layer containing the Al3Hf particles was evaluated in air at 1423 K. The sample covered with the Ni aluminide containing the Al3Hf particles, which was formed using the melt containing 3.5 mol%AlF3 and 0.05 mol%HfF4, showed a high cyclic-oxidation resistance. On this sample after the oxidation test, an adhesive scale having a spiked shape, which consisted of Al2O3 as the outer layer and HfO2 as the inner layer, was formed.