Mechanical and magnetic properties of γ-Ni–xFe/Al2O3 composites

Abstract Ultra-fine grained γ-Ni– x Fe ( x = 20, 50, and 64 (nominal)) dispersed Al 2 O 3 -matrix composites were fabricated by a mechano-chemical process plus hot-pressing, and their mechanical and magnetic properties were explored. The results indicated that all composites incorporated with different γ-Ni– x Fe alloys possessed high densities (relative density D ⩾ 98%) and sub-micrometer-sized matrix dispersed with γ-Ni– x Fe particles of sizes below ∼500 nm. As compared to other two composite systems, γ-Ni–20Fe/Al 2 O 3 had finer microstructures and displayed superior fracture toughness and strength. In high iron-contained γ-Ni–64Fe/Al 2 O 3 composite undesired FeAl 2 O 4 phase formed on the matrix grain boundaries, which is mainly responsible for its inferior mechanical properties. Although Young’s modulus and hardness of Ni–20Fe/Al 2 O 3 composite system decreased, its fracture toughness increased monotonously with increasing the alloy content in the composition range investigated. Moreover, incorporation of ferromagnetic γ-Ni– x Fe particles led all the composite systems to display ferromagnetism with their saturation magnetization increasing almost linearly with increasing alloy content. In addition, experiments showed that their ferromagnetism had high thermal stability ( T c = ∼580 °C), no obvious magnetism degradation and magnetic interactions of the alloys with the matrix being observed. The combination of good mechanical properties with excellent magnetic performance would make this material be very valuable in industry.