Improvement of resistance of TiAl alloy against high temperature oxidation by electroplating in AlCl 3–NaCl–KCl–CrCl 2 molten salt

Abstract

For improvement of the oxidation resistance of a TiAl alloy under high temperature conditions, aluminum chromium alloys were electroplated on the TiAl alloy in an AlCl 3–NaCl–KCl molten salt containing CrCl 2 at 423 K. The deposit electroplated at −0.1 V vs. Al/Al 3+ consists of γ-Al 8Cr 5 single phase, including chromium content at 41 at.%. A mixture phase of γ-Al 8Cr 5 and Al is, however, formed at potential from −0.2 to −0.4 V. The oxidation resistance of the electrodeposit layer was evaluated by a high temperature oxidation test at 1173 K for 24 h. On the TiAl specimen covered with γ-Al 8Cr 5 which was deposited at −0.1 V, a uniform AlCr 2 layer was formed during the oxidation at 1173 K. The AlCr 2 layer was covered by a thin dense Al 2O 3. Both AlCr 2 and Al 2O 3 layers play a role of superior protection from the high temperature oxidation of the TiAl alloy; therefore, the plating of the γ-Al 8Cr 5 single layer deposited at −0.1 V reduced oxide thickness by 1/40 during the oxidation at 1173 K for 24 h from that on the TiAl without any plating.