Microstructure evolution in pure Ni and Invar-based Metallic-Intermetallic Laminate (MIL) composites

Metallic-Intermetallic Laminate composites of Ni/Al and Invar/Al were fabricated and investigated for the microstructure evolution, growth kinetics and microhardness distribution across the intermetallic/metal interfaces. A single-phase intermetallic layer, with parabolic growth kinetics, is shown in the pure Ni/Al reaction, while a complex multi-phase layer (eutectic and uniform layer) with mixed growth kinetic mechanisms is identified in the Invar/Al reaction by EDS and EBSD analysis. Primary growth and texture of the intermetallic phase in Invar-based MIL are analyzed with respect to their effects on the microhardness distribution across the metal/intermetallic layer. The intermetallic yield rate of the two different Ni-aluminide reactions are calculated and demonstrated to be reliable for predicting the final intermetallic layer thickness in Ni-based MIL composites.