Fabrication of NiAl/Steel Cladding by Reactive Casting

Abstract

A novel joining process based on reactive casting is proposed. By pouring molten aluminum and nickel onto a steel block, molten nickel monoaluminide, NiAl, is exothermically synthesized, and is joined to the steel block when it solidifies on the steel block. Heat generated by an exothermic reaction, Ni1Al→NiAl+DH_p298, is transferred from the synthesized NiAl to the steel block, and the surface layer of the steel block is melted. The depth of the melted steel increases with both the preheating temperature of the steel block and the thickness of the synthesized NiAl. Iron from the melted steel dissolves in the molten NiAl, and an NiAl-base intermetallic compound, (Ni, Fe)Al, is produced. Cracks or other intermetallic phases such as NiAl₃ or FeAl are not formed at all at the joint interface between the (Ni, Fe)Al and the steel block. The synthesized (Ni, Fe)Al has an excellent resistance to corrosion and oxidation.