Influence of ZnO nanoparticles on the microstructure of a CoCrFeMoNi matrix via powder metallurgy

In the last decade, extensive research has been carried out on the microstructural behavior of high-entropy alloys (HEA), for which the in-situ formation of nanoparticles has been reported. However, studies of the incorporation of nanoparticles in HEA have been rarely reported. In this work, the addition of zinc oxide nanoparticles (ZnO NP) as reinforcement in a CoCrFeMoNi high-entropy alloy matrix, as well as the morphological, structural, and microstructural evolution of composites synthesized via powder metallurgy, were studied. Scanning electron microscopy and X-ray diffraction analysis were performed in order to study the microstructural and phase characterization of the composites. After sintering, it was found that the ZnO NP addition (0.5wt%, 1wt% and 2wt%) had a significant influence on the microstructure and hardness of the CoCrFeMoNi high-entropy alloy. Stronger bonding among metal particles was promoted with the additions of ZnO NP. A reduction in porosity as a function of ZnO NP content was also observed. The microhardness results showed that the composite reached its highest reinforcement in bulk samples with 1wt% ZnO NP (HV 870), which represented a 20% improvement over the unreinforced HEA matrix.