The Al₂O₃–ZrB₂ Nanocomposite Synthesis using Mechanically Assisted SHS: The Effects of Mechanical Activation and Al₂O₃ Diluent

ZrB₂ stands out among ultra-high-temperature ceramics due to its exceptional thermal resistance, chemical stability, high hardness, high electrical and thermal conductivity, and low density. In this work, the Al₂O₃–ZrB₂ nanocomposite was fabricated using mechanically activated self-propagating high-temperature synthesis. The effect of mechanical activation, using three different milling times (i.e., 0, 3, and 5 h), and addition of Al₂O₃ as a reaction diluent on Al₂O₃–ZrB₂ nanocomposite properties were investigated. The combustion behavior of different powder mixtures was evaluated using DSC. The phase analysis and microstructure of synthesized samples were investigated by X-ray diffraction (XRD) and scanning electron microscopy. Results indicated that 5 h ball milling of initial powder mixture synthesis caused the combustion reaction to start at about 650 °C which was lower than that of the unmilled sample (1140 °C). The microstructure of pre-milled samples contained a uniform distribution of ZrB₂ particles in the Al₂O₃ matrix. The addition of Al₂O₃ to the initial mixture (up to a 6 wt.%) increased the amount of heat energy released upon heating the sample. The DSC and XRD results showed that the sample milled for 3 h, in which 6 wt.% Al₂O₃ was added to the mixtures had the most tendency to combustion and the most purity of the final microstructure. Further addition of Al₂O₃ up to 10 wt.% reduced the system’s ability to perform self-propagating high-temperature synthesis.