Effect of micron and nano-sized ZrB₂ addition on the microstructure and properties of spark plasma sintered graphite–aluminum hybrid composite

The need to improve the thermal properties of materials used in electronics and automobile industries has led to the search for light materials such as graphite aluminum (Gr–Al) composites. This work was aimed at studying the effect of micron and nano-sized zirconium diboride (ZrB₂) on the microstructure and properties of Gr–Al composite. In this study, ZrB₂ powder with average particle size of 5.91 μm was milled for 24 h using planetary mill. The particle sizes and shapes of the micron and nano-sized particles were studied using scanning electron microscopy. Sintering of Gr–Al composite reinforced with 2, 4, 6 and 8 % of micron and nano-sized ZrB₂ particles was done at a temperature of 550 °C and pressure of 50 MPa. The heating rates were 50 and 100 °C/min with a soaking time of 10 min. The average nano particle size obtained after the milling process was 60 nm with regular and irregular shapes. The results show that the electrical conductivity only improved slightly in the temperature range 219–282 °C for 6 % micron size addition and 230–251 °C for 4 % nano size addition. In addition, nano ZrB₂ improved the densification, hardness and the peak intensity ratio of Gr–Al composite with the highest values being 99.3 %, 38 HV_0.1 and 92.23 % respectively. A significant reduction in the coefficient of thermal expansion from 0.238 × 10⁻⁶/°C for the matrix to 0.0.980 × 10⁻⁷/°C for the hybrid composite was also noticed. These improvements were more obvious at 4 and 6 % composition and a heating rate of 50 °C/min.