Microstructure, thermal, and mechanical properties of Al-4CNT/GNP hybrid composites

A mixture of aluminum, carbon nanotubes (CNTs), and graphene nanoplates (GNPs) was mechanically alloyed (MA) for 15, 30, and 60 min in a planetary ball mill to produce Al-4mass%. CNT/GNPs hybrid composites, namely P15, P30, and P60. The X-ray diffraction (XRD) analysis indicates no chemical reaction between the Al matrix and the reinforcing phases. A homogeneous distribution of reinforcement is observed at 60 min of milling, along with a smaller crystallite size of approximately 224 nm. The lattice parameter of the Al matrix remains almost constant at about 0.4050 ± 10 –4 nm. Differential scanning calorimetry (DSC) curves of the milled powders on heating show endothermic peaks in the 100–700 °C range for all three samples. However, upon cooling, the DSC curves of the P-15 and P-30 samples show two exothermic peaks, whereas the P-60 sample exhibits only one peak. The Rietveld refinement reveals the formation of the Al 4 C 3 carbide in the P-60/DSC powders. For the heated powders at 20 °C min −1 up to 700 °C, the evolution of γ-Al 2 O 3 hinders the formation of Al 4 C 3 . The powder composites were consolidated by conventional sintering (CS) at 600 °C for 30 min and by spark plasma sintering (SPS). The CS increases microhardness, reaching a maximum of 189.8 HV in the P-60 sample. In contrast, the SPS composite suppresses interfacial reactions and oxidation, resulting in a moderate hardness of 125.45 HV.