Fabrication process and mechanical properties of NiAl/Ni micro-laminated composites by reaction synthesis

Abstract

Fabrication process and mechanical properties of NiAl/Ni micro-laminated composites were investigated. NiAl/Ni micro-laminated composites have the possibility of combining the good ductility and toughness of metals with the higher elastic modulus, higher strength, and lower density of intermetallics. Toughening in these composites is derived from the rupture of the Ni phase that has bridged the cracks developed in the brittle NiAl phase. Thus micro-laminated composites are particularly attractive, because no physical mechanisms exist by which the cracks in the brittle phase can bypass the more ductile metal phase. NiAl/Ni intermetallic/metal micro-laminated composites were formed by a recently developed process in which SHS reaction was initiated at the interface between Ni and Al element foils. After the reaction, one of the metal foils was entirely consumed, resulting in NiAl/Ni micro-laminated composites. First objective of this paper is to characterize the microstructure evolution during processing, investigate how the reaction proceeds, and analyze the effect of processing parameters such as thickness and thickness ratio of element foils, diffusion bonding time, and pressure. Second objective is to characterize and analyze the elastic, tensile, and fracture behaviors of the micro-laminated composites which are designed to investigate the relationship between microstructure and mechanical property. The reaction mechanism and microstructure evolution during reaction synthesis have been investigated. The reaction between Ni and Al micro-foils started with a nucleation and growth of $NiAl_3$ followed by a diffusional growth of $Ni_2Al_3$ between Ni and NiAl3. By post-heat treatment with applied pressure, the reaction products were converted to NiAl and $Ni_3Al$ having better strength at high temperature. The hardness at the center of intermetallic is lower than other positions due to shrinkage cavity and becomes more uniform through the entire intermetalli...