Microstructure and corrosion resistance of Ti-Ni/steel composite materials

Ti-Ni composite sub-micron powders with different compositions were prepared by vacuum melting and atomization technology. These powders, after being mixed with a solution of phenolic resin and alcohol, were applied on the mold cavity wall, by which a casting-infiltration layer was introduced on the surface of ZG45 steel via reactions between the powders and molten steel under the heat released by solidification. The effects of the powders' composition and pouring temperature on the corrosion resistance of the casting-infiltration layer were studied. An optimal casting-infiltration layer with a thickness of similar to 7 mm was obtained by infiltrating the Ti-Ni composite powders containing 35wt.% Ti to ZG45 steel pouring at 1,650 degrees C. The casting-infiltration layer has a good metallurgic bonding with the matrix, and is mainly composed of Fe2Ti phase and continuous gamma-(Fe, Ni) solid solution. In the corrosive H2SO4 solution, the corrosion potential of the casting-infiltration layer is lower than the matrix, tending to form a passivation film, which lowers the dissolution rate especially when the potential rises to 0.50 V. After dipping in the 10wt.% NaCl solution for 480 h, a lot of corrosion holes appear in the ZG45 steel matrix, while there are no obvious traces of corrosion on the casting-infiltration layer.