Effect of interfacial reaction on bending strength of Al₁₈B₄O₃₃ whisker-reinforced aluminum composites

The present study deals with the mechanism of the interfacial reaction and the microstructure of the interface in aluminum borate whisker-reinforced pure aluminum matrix composites prepared by a squeeze casting process. By means of X-ray diffraction analysis (XRDA), differential thermal analysis (DTA), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HRTEM), it has been found that no interfacial reaction occurred under the as-cast condition, whereas aluminum reacted with the whiskers when the composite was reheated at a temperature higher than 726 °C. The reaction produced γ-Al₂O₃. Based on HRTEM observation, it is considered that the whiskers bond to the aluminum matrix directly after squeeze casting. The observation also shows that there is a specific orientation relationship between the reaction product and whisker, {002} Al₁₈B₄O₃₃ ∥ {220} γ-Al₂O₃, 〈200〉 Al₁₈B₄O₃₃ ∥ 〈111〉 γ-Al₂O₃, which leads to a coherent interface with a mismatch of less than 1 pet. The interfacial bonding state changed after heating under different conditions. Propagation of cracks in each interfacial state was observed by SEM, and the effects of the interfacial reaction on the bending strength were studied with the microstructure of the interface.