Improvement of Oxidation Resistance of TiAl Intermetallic Compound by Electrodeposition of Al Using Molten Salt As a Medium

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The intermetallic compound TiAl is currently of interest as a new heat-resisting material at high temperatures, because it has high specific strength and stiffness associated with low density. One of the major problems for the practical use of TiAl is poor oxidation resistance at high temperature. It is expected that the formation of a Ti aluminide surface layer containing a high concentration of aluminum leads to the formation of an Al^2O^3 improving the oxidation resistance of the TiAl substrate. In the present work, the electrodeposition of aluminum on TiAl was performed using a NaCl-KCl-AlF^3 molten salt at 1023 K. The formation of a Ti aluminide surface layer containing a high concentration of aluminum was tried by alloying of aluminum with TiAl during the electrodeposition. Furthermore, the high temperature oxidation resistance of the TiAl alloy, covered with a surface layer containing a high concentration of aluminum, was evaluated as compared with untreated TiAl. The obtained r … More esults were as follows:1. When nickel specimen was cathodically polarized in NaCl-KCl containing AlF^3, an increase in cathodic current was observed in the potential region lower than -1.2 V (vs. Ag/AgCl(0.1)). It was found out that in this potential region the cathodic reduction reaction of Al^<3+> occurred.2. When TiAl specimen was cathodically polarized at -1.3 ~ -1.6 V (vs. Ag/AgCl(0.1)) in NaCl-KCl comtaining AlF^<3+> a deposited material having stratified morphology was formed. This material consisted of TiAl^3 and uniformly covered the TiAl substrate.3. The results of the oxidation experiments at 1273 K showed the oxidation resistance for TiAl covered with the deposited layer was very high. In this case, the formation of a protective α-Al^2O^3 film was observed on the surface of the deposited layer.Consequently, it was found that the Ti aluminide surface layer containing a high concentration of aluminum was formed by the electrodeposition of aluminum on the TiAl substrate using the molten salt and the formation of this surface layer led to improvement of the oxidation resistance of the TiAl substrate. Less