Dissimilar Joining of Nickel Aluminide Intermetallic Compound with Spheroidal Graphite Cast Iron by Using Combustion Synthesis

Nickel aluminide based intermetallic compounds were combustion synthesized from a powder mixture of elemental Al, Ni, and Si and were simultaneously bonded with spheroidal graphite cast iron substrate (FCD). Addition of Si to the elemental mixture of Al and Ni was confirmed to be effective both to the densification of combustion synthesized intermetallic compounds and to the joining between compounds and FCD. When the composition of precursor was Ni-69at%Al-9at%Si (Al/Si is the ratio of the eutectic composition), Al3Ni and Al6Ni3Si were mainly combustion synthesized. In the interface between compounds and FCD, reaction layers were formed to the thickness of 10 µm and the constituent phases were identified as Al7Fe2Si, FeAl3 respectively. In the four point bending test of the dissimilar joints prepared by heating at 973 K for 300 s, the brittle fracture did not occurred around the joint interface but mainly in the inside of nickel aluminide coating. The interface of reaction layers with 10 µm were chemically well bonded. The sample with Ni-69at%Al-9at%Si coating exhibited highest bonding strength of about 56 MPa because of the smallest void ratio of the obtained compounds.