Effects of Ni foil thickness on the microstructure and tensile properties of reaction synthesized multilayer composites

The effects of Ni foil thickness on the microstructure and tensile properties of reaction synthesized multilayer composites have been systematically investigated. Multilayer composites have been fabricated by reaction annealing of their foil laminates consisting of 10 μm thick Al foils and 20, 50 and 80 μm thick Ni foils. Ni3Al multilayer composites prepared from 20 μm Ni foils were very brittle. Ni/Ni3Al multilayer composites prepared from 50 μm Ni foils exhibited significant work-hardening and behaved more like a ductile alloy, rather than a composite, with an ultimate tensile strength of 1050 MPa and elongations of >18%. The composites fabricated from 80 μm Ni foils, which contain Ni3Al precipitates, had a low yield strength and ultimate tensile strength (about 160 and 470 MPa, respectively), and had a very good capacity for plastic deformation (>34% elongation). The dislocations in Ni and Ni3Al layers can slide through the Ni3Al/Ni interfaces, with the result that the Ni and the Ni3Al layers in the composites can cooperatively deform during tensile testing. Delaminated interfaces containing Al2O3 inclusions further promote the capability of the Ni3Al layers for plastic deformation. As a result, the Ni/Ni3Al multilayer composites exhibit good tensile strengths and a high ductility. The existence of Ni3Al precipitates in the Ni layers inhibits cross-slip of dislocations, which results in dislocation networks in the Ni layers which have a preferred orientation.