Formation of Al₃Ni Nanofibers in an Al-Based Metal Matrix Composite Fabricated by Reaction Sintering

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.