Microstructure and mechanical properties of in-situ SiO2-reinforced mechanically alloyed CoCrFeNiMnX (X= 5, 20, 35 at.%) high-entropy alloys

Abstract

The CoCrFeNiMnX (X = 5, 20, and 35 at.%) alloys, reinforced with 5 at.% SiC powder, were prepared by mechanical alloying and spark plasma sintering. This preparation method resulted in microstructural refinement of the FCC solid solution grains, while the SiC addition reacted with residual oxygen to form homogeneously distributed ultrafine SiO2 particles. Additionally, the alloys contained Cr7C3 carbides, which were significantly larger than the SiO2 particles and enriched with the alloy's elements, including Mn. Among the tested materials, the reinforced CoCrFeNiMn20 alloy exhibited the highest hardness and compressive yield strength (CYS), achieving 392 ± 9 HV30 or 476 ± 3 HVIT1 and 1024 ± 18 MPa, respectively. This alloy also maintained superior CYS (956 ± 35 MPa) even after 100 h of annealing at 800 °C. The reduction in CYS after annealing was smallest for the CoCrFeNiMn5 alloy (35 MPa) and increased with higher Mn content, highlighting Mn's significant role in diffusion-related processes. At elevated temperatures (600 and 800 °C), the CoCrFeNiMn5 alloy had the highest CYS of 190 ± 33 MPa, while the CoCrFeNiMn35 alloy had the lowest at 80 ± 6 MPa. This trend was also observed in wear rate tests, where the CoCrFeNiMn5 alloy had the lowest specific wear rate coefficient of 3.54 ± 0.09 × 10-4 mm³ N⁻1 m⁻1. This was due to matrix softening and oxide lubrication without significant spalling. Thus, the CoCrFeNiMn5 alloy demonstrated superior mechanical properties and wear resistance under various conditions, making it a promising candidate for applications requiring high strength and durability.

Keywords

• High-entropy alloys
• Mechanical alloying
• Spark plasma sintering
• Microstructure
• Mechanical properties
• Tribology