Microstructural and Mechanical Characteristics of AlCoCrFeNi-YSZ High Entropy Alloy Matrix Composite

In this study, high-entropy alloy matrix composites (HEAMCs) consisting of an AlCoCrFeNi matrix reinforced with zirconia-based particles were fabricated using mechanical alloying (MA) followed by spark plasma sintering (SPS). Microstructural analysis revealed the presence of both FCC and BCC phases after 30 hours of mechanical alloying and subsequent sintering at 1000 °C. Rietveld refinement analysis indicated that the weight fraction of the FCC phase remained nearly constant in both the HEA and HEA–YSZ composites. However, the addition of YSZ particles decreased the BCC phase content and restricted grain growth during sintering. Compressive test results showed that the specimen containing 5 wt.% YSZ exhibited the highest yield strength (1760 MPa), attributed to its higher BCC phase fraction (40%). In contrast, the specimen with 10 wt.% YSZ demonstrated reduced yield strength due to a lower BCC phase content (36%). These findings indicate that AlCoCrFeNi composites reinforced with YSZ possess higher yield strength than those reinforced with ZrO₂ when comparable reinforcement levels are used. This improvement is attributed to the higher BCC phase content and the superior intrinsic properties of YSZ. Fracture surface analysis confirmed the coexistence of both ductile and brittle fracture modes in the tested specimens.