The effect of cooling rate on the microstructure evolution and the mechanical properties of ingots and rods of 2–5 mm diameter of (Ni0.92Zr0.08)100−xAlx (0 ≤ x ≤ 4 at.%) ultrafine eutectic composites have been investigated. The microstructure of the composites is comprised of micrometer size γ-Ni dendrites embedded in a nano/-ultrafine lamellar fcc γ-Ni and Ni5Zr matrix. The evolution of the microstructure at a wide range of cooling rates (10–104 K/s) has been analyzed in respect of volume fraction of the phases, lamellar spacing, and secondary dendritic arm spacing. All these composites exhibit high hardness up to 4.6 GPa and yield strength up to 1.6 GPa with large compressive plasticity up to 22% at room temperature. The effect of cooling rates on the strength and hardness, and the plasticity of the nanolamellar composites with wide range of alloy composition have been correlated.

We developed an Al2O3 and Al3Ni intermetallic reinforced Al-based metal matrix composite by sintering an Al-20 wt% NiO powder compact at 1000 °C. Differential thermal analysis showed that a two-step reaction took place between Al and NiO in the temperature range 600–650 °C. The initial stage was a solid-state reaction, but it was soon paused by the newly formed Al2O3 and Al3Ni phases that separated the Al and NiO grains. A liquid–solid reaction was later resumed as the temperature was increased above the eutectic temperature of Al–Al3Ni at 640 °C when molten Al–Ni appeared. When the molten sample was quenched to room temperature, a two-phase Al–Al3Ni eutectic was found in the sample. In comparison with the air-quenched and the oil-quenched samples, the sizes of proeutectic Al3Ni grains and Al–Al3Ni eutectic phases in the salt-solution-quenched sample were much finer. The eutectic contained Al3Ni nanofibers with a diameter of approximately 50 nm. A reaction model of Al and NiO was proposed. A thermodynamic model was also proposed to describe the formation of the composite.