Effect of YSZ Particle Size and Content on Microstructure, Mechanical and Tribological Properties of (CoCrFeNiAl)1-x(YSZ)x High Entropy Alloy Composites

High entropy alloy composites (HEACs) have recently been explored for use in industrial applications. This study investigates the impact of particle size (micro or nano) and content (5 and 10 wt%) of YSZ on the microstructure and tribological properties of AlCoCrFeNi. The samples were prepared using a combination of mechanical alloying and spark plasma sintering. XRD results and Rietveld analysis reveal that HEACs with micro-sized YSZ have a higher BCC/FCC ratio. FESEM and EDS results confirmed the evolution of Al-rich regions in the vicinity of the reinforcements. Especially, in HEA-10NanoYSZ-sample, due to higher interfacial regions, a huge amount of Al-rich phase has been formed which yields the reduction of BCC phase content in this sample. Microhardness and pin-on-disc wear tests show that the samples reinforced with microparticles demonstrate better performance compared to nanocomposite samples. For example, HEA-10MicroYSZ-sample exhibits the highest hardness (5.1 GPa) and the lowest wear characteristics (with a coefficient of friction of 0.8 and a wear rate of 4 x 10(-4) mm(3)/N.m). This can be correlated to the higher hardness and BCC phase content, and grain boundary strengthening in the microcomposites.