Sol-gel prepared Ni-alumina composite materials - Part I Microstructure and mechanical properties

The sol-gel method has been utilized for the preparation of dense, homogeneous ceramic-metal composites with up to 50% Ni in Al₂O₂. Examination by SEM and TEM shows that the materials consist of micrometre-size Al₂O₃ with metallic Ni in isolated regions from ∼50 μm down to nanometre size. The density ranges from ∼97% (10% Ni) to ∼74% (50% Ni) of the theoretical number. The hardness decreases from ∼18 GPa for pure alumina to ∼10 GPa for alumina containing 50% Ni. The fracture toughness increases significantly from K_1c=3-4 MPa m^1/2 to K_1c=∼8.5 MPa m^1/2. The elastic and shear moduli decrease from E=∼400 GPa and G=∼160 GPa for pure alumina to E=∼320 GPa and G=∼135 GPa when containing 50% Ni. The electrical resistivity is ∼10⁶ωm with 10 to 40% Ni but decreases drastically at 50% Ni content.