Fabrication and mechanical properties of ultra-fine grained γ-Ni–20Fe/Al2O3 composites

High-dense (relative density D ≥ 98%) ultra-fine grained γ-Ni–20Fe/Al2O3 composites were fabricated by using a mechano-chemical process plus hot-pressing. Microstructure investigations revealed that fine γ-Ni–20Fe particles with the dimensions of several hundreds of nanometers dispersed homogeneously at the matrix grain boundaries. Mechanical tests indicate that fracture toughness increases monotonously from 4.7 MPa m1/2 for monolithic alumina to 8.4 MPa m1/2 for ∼19 vol.% Ni–20Fe/Al2O3 composites. Fracture strength σf increased with addition of Ni–20Fe phase as Ni–20Fe content was low (≤5 vol.%). However, σf decreased with further increase of Ni–20Fe content, exhibiting a maximum strength of ∼600 MPa at ∼5 vol.% Ni–20Fe. The improvement of the mechanical properties could be ascribed to the microstructure refinement of the composites and increase of cracking resistance introduced by the dispersed Ni–Fe phase, which was supported by fracture characteristic observations.