Structural characterization of the β-si₃n₄ whisker-al interfaces in a β-si₃n₄ whisker-al alloy 6061 composite material

Abstract

The structural characterization of the whisker-matrix interface in a β-Si₃N₄ whisker-Al alloy 6061 composite was investigated by high-resolution transmission electron microscopy (HRTEM). It was shown that there existed a nearly amorphous layer (2–3 nm thickness) between the whiskers and the Al matrix. Mg segregation at the whisker-Al interface was revealed by energy-dispersive X-ray analysis. HRTEM observations indicated that MgO and MgAl₂O₄ nanocrystalline particles were easily formed at the whisker-Al interface in the composite owing to Mg segregation at the interface during the manufacturing of the composite. The Mg₂Si particles (strengthening phase in the matrix) precipitated preferentially at the whisker-Al interface when the composite had been given a T6 heat treatment. Specific orientation relationships between the MgAl₂O₄ or Mg₂Si particles and the β-Si₂N₄ whiskers were found. The problems associated with characterizing the microstructure of a whisker-matrix interface in an Al alloy composite reinforced by whiskers are also discussed.