Effect of Intermetallic Volume Fraction on the Mechanical Properties of Intermetallic/Metal Micro-laminated Composites

The effects of intermetallic volume fraction on the mechanical properties of micro-laminated NiAl/Ni composites have been investigated. Two types of intermetallic/metal micro-laminated composites having various intermetallic volume fractions were fabricated through reaction synthesis using element foils. The difference of microstructure caused two types of micro-laminated composites had reverse dependence of tensile strength on intermetallic volume fraction. From the relationship between characteristic multiple crack spacing normalized by intermetallic thickness during tensile loading and relative strength of each phase, it was concluded that the reverse tensile behavior of micro-laminated composites were brought from different fracture strength of brittle intermetallic phase. The fracture toughness results by the SENB (Single Edge Notched Beam Bending) test showed R-curve behavior with upward curvature based on LSB (Large Scale Bridging) condition. Bridging stress based on LSB condition was estimated to 250∼300MPa that was about three times of yield strength of unconstrained pure Ni foils. Transformation of fracture modes from multiple cracking to single cracking when the intermetallic volume fraction increased was explained by combined model of shear lag and LEFM(Linear Elastic Fracture Mechanics). The stress field changes according to intermetallic volume fraction were analyzed by FEM and these results were in good agreements with experimental results.