A new approach to ceramic particulate reinforced composites: High entropy (HfTiZrVTa)B₂ reinforcement in Al10Si matrix

This study includes the production of hard and brittle high entropy (HfTiZrVTa)B₂ boride (HEB) reinforcement in different ratios (1, 2, 5, 10, and 15 wt.%) to Al-10 wt.% Si (Al10Si) matrix by traditional powder metallurgy methods. To the best of our knowledge, there are a few studies on Al matrix composites produced with HEB reinforcement. Furthermore, the fact that this study was conducted using traditional methods makes it unique. Firstly, HEB reinforcement was produced by mechanical alloying (MA) during 72 h and spark plasma sintering (SPS, 2000 °C, 30 MPa). As a result, a single-phase HEB structure with low-intensity oxides was produced in bulk form. In the meantime, the Al10Si matrix was prealloyed during 4 h. Then, crushed HEB reinforcement was added to the prealloyed matrix with 2 wt.% stearic acid, and then they were mechanically alloyed for 6 h. The compositions formed by cold pressing were first debinded at 420 °C for 2 h and then pressureless sintered at 630 °C for 2 h. Phase analysis of the compositions with using X-ray diffractometry (XRD), microstructural characterization using scanning electron microscopy/energy dispersive spectrometry (SEM/EDS), physical characterization with Archimedes' and pycnometer methods, and mechanical characterization in terms of hardness and dry sliding wear tests were conducted. As the reinforcement increased in the sintered compositions, intermetallics formed and Fe contamination originating from the milling media released. The relative density value decreased with increasing amounts of hard particle reinforcement (from ∼99 % to ∼84 %). The highest and lowest hardness values were obtained in Al10Si-15HEB (∼3.87 GPa) and Al10Si-1HEB (∼2.19 GPa), respectively. In contrast, the highest wear rate is investigated in Al10Si-2HEB (∼7.2 × 10−4 mm3/N·m) while the lowest is in Al10Si-10HEB (∼2.3 × 10−4 mm3/N·m).