Processing, structure and properties of metal-intermetallic layered composites

In this US Bureau of Mines study, metal-intermetallic laminar composites were produced by induction of a self-propagating, high-temperature synthesis (SHS) reaction at the interface between dissimilar metal foils. The reaction between Ni and Al foils produced a composite that consisted of alternating, well-bonded Ni and Ni2Al3 layers. The initial metallic foil thicknesses (composites were produced from various elemental foils ranging in thickness from 0.05 to 0.25 mm) only affected the volume fraction of the resultant Ni and Ni2Al3 layers and not the actual phases formed. The tensile behavior of these composites were found to be independent of the volume fraction of the layers present in the resultant metal-intermetallic laminar composites. In addition, the fracture behavior of the composites was similar from room temperature to 600 °C, with the Ni layers rupturing in a ductile manner after bridging many cracks in the Ni2Al3 layers. Heat treatment of the composite at 950 °C for 50 h resulted in a microstructure consisting of Ni and Ni2Al3 layers, but with a thick NiAl interphase layer. Heat treatment at 1150 °C resulted in a composite comprising Ni and Ni3Al layers. The microstructure and properties of similarly processed TiAl-based composites are discussed. The room-temperature tensile behavior of the TiAl composites was sensitive to the volume fraction of the resultant Ti and Al3Ti layers. The feasibility of the production of near-net-shaped metal-intermetallic layer composites by this technique was demonstrated.