溶融塩化物での不均化反応を用いたチタン合金コーティング

Abstract

The dependence of Ti alloy coating by using a disproportionation reaction in molten chloride upon the coating conditions has been investigated. The corrosion resistance of the coated specimen was also examined. An equimolar NaCl-KCl mixture was melted in a quartz crucible under the atmosphere of high-purity Ar, and TiCl3 was added with Ti sponge into the mixture. Iron, carbon steel, Ni and stainless steel plates were immersed in the bath at 1100~1250 K for a scheduled period. After the immersion, the Fe plate was covered with a dense layer of Ti-Fe alloy of which thickness was more than 10 μm. The layer adhered to the surface, and mainly consisted of Fe2Ti. Carbon steel was covered with a similar Ti-Fe layer to that on the Fe plate, and carbides were not found. The surface of the Ni plate was fully covered with NiTi2, and a dense layer of Ni3Ti was formed under the NiTi2 layer. The Ti alloy layer on Ni was thicker than those on Fe and carbon steel under the same condition. A dense layer of a few μm, where Ti content was about 90 mass%, was observed on the surface of the stainless steel plate after the immersion. The thickness of the Ti alloy layer was in proportion to the square root of the immersion time, and its formation rate was not affected very much by the initial TiCl3 concentration. These results indicated that the formation rate of Ti alloy layer was mainly controlled by the diffusion of elements in the formed layer. The corrosion resistance of Fe and carbon steel against salt water was significantly improved by the Ti alloy coating on the surface.