Structure and interfacial properties of nanocrystalline aluminum/mullite composites

Using the mechanical attrition method, nanocrystalline aluminum powder with grain size of 27 nm, and submicrometer-sized mullite particles with grain size of 67 nm were obtained. The ultrafine mullite particle reinforced nanocrystalline aluminum composite samples were fabricated by consolidation using hot isostatic pressing at pressures up to 1.5 GPa, and temperatures ranging from 300 to 450 °C. The density of the nanocomposite sample with 20% mullite by weight was 96.5% of the theoretical value. The microstructure of the nanocrystalline aluminum/mullite composite samples was investigated using X-ray diffraction and transmission electron microscopy analyses. The atomic components in the interface between mullite particle and aluminum matrix were determined using energy dispersive X-ray spectrometry. The microscopy investigations showed that the mullite particles tended to agglomerate, resulting in significant voids mainly existing around the large mullite particles and a lower-than theoretical density. The components of Al, O and Si changed nearly linearly over the interface range, indicating that the interface was formed by atomic diffusion. Atomic diffusion played an important role in the aluminum wetting the mullite particles.