Mechanical Activation-Assisted Solid-State Aluminothermic Reduction of CuO Powders for In-Situ Copper Matrix Composite Fabrication

Abstract

In this study, combustion synthesis involving mechanical milling and subsequent sintering process was utilised to fabricate Cu/AlxCuy/Al2O3 in-situ composite through the aluminothermic reduction of CuO powders. First, CuO and Al powders were mixed, and ball milled for 30–150 min to facilitate self-propagating high-temperature synthesis (SHS). Then, mechanically activated Al-CuO powders were mixed with elemental Cu powders and experienced subsequent cold compaction and sintering processes. The reactions during synthesis were studied utilising differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Densification and hardness of green and sintered bodies were also obtained. The results indicated that despite the negative free energy of the aluminothermic reaction, an initial activation energy supply is required, and mixed Al-CuO powders did not show significant progress in the combustion synthesis method. The aluminothermic reaction became probable whenever the activation energy was entirely provided by high-energy ball milling or by the sintering of ball-milled Al-CuO mixed powders. DTA results showed that the aluminothermic reaction temperature of Al-CuO decreased with milling times, whereas after 150 min of ball milling, the reaction was completed. XRD patterns revealed that the formation of Al2Cu and Al2O3 reinforcing phases resulted from CuO reduction with Al. Al4Cu9, Cu solid solution, and Al oxide phases were observed in sintered samples. The relative density of the samples was reduced compared to the green compacted parts due to the nature of the Cu-Al alloy and the occurrence of the swelling phenomenon. The hardness results indicated that in-situ formation of reinforcing phases in samples that experienced thermally assisted thermite reaction yielded superior hardness.