High-entropy alloys (HEAS) based on CrMnFeCoNi have generated considerable interest because of their outstanding mechanical properties and structural stability. In this study, we synthesized the baseline CrMnFeCoNi alloy and a niobium-modified version, (CrMnFeCoNi)۹۸Nb۲, through mechanical alloying followed by spark plasma sintering (SPS). The mechanical alloying process produced homogeneous alloyed powders, which we then densified in a graphite die at ۱۰۵۰ °C under ۳۵ MPa axial load for ۱۰ minutes. This approach yielded nearly fully dense compacts with minimal porosity and refined microstructures. Our mechanical characterization revealed impressive strengthening when we added just ۲ at.% Nb. Vickers microhardness tests showed the base CrMnFeCoNi alloy had hardness values between HV ۳۵۵-۳۶۵, while the Nb-containing alloy reached HV ۴۰۰-۴۱۰ roughly a ۱۰-۱۵% improvement. We attribute this increase to solid-solution strengthening from Nb atoms and possibly to Nb-rich nanoscale precipitates that formed during consolidation. Tensile testing confirmed this substantial boost in mechanical strength (Fig ۱). The base CrMnFeCoNi alloy fractured at around ۶۹۸ MPa, whereas the (CrMnFeCoNi)۹۸Nb۲ alloy achieved approximately ۹۳۸ MPa nearly a ۳۰% increase. The steeper initial slope and higher peak stress we observed in the SPS-processed Nb-containing alloy suggest more efficient load transfer, enhanced lattice distortion strengthening, and likely some precipitation hardening [۴]. We also compared the tensile behavior of both SPS-processed alloys against their as-cast counterparts. As Fig ۱ shows, the cast samples performed significantly worse in both strength and ductility. The cast CrMnFeCoNi alloy exhibited an extended but less steep strain-hardening region, and while the cast Nb-containing alloy showed moderate strengthening, it still fell well short of the SPS-processed samples. This comparison underscores how Nb addition and rapid SPS consolidation work together to enhance mechanical performance [۱,۲,۳,۵]. In summary, our results demonstrate that adding small amounts of Nb when combined with SPS processing significantly improves the hardness, fracture strength, and overall mechanical response of CrMnFeCoNi-based HEAS. These findings point to Nb microalloying as an effective approach for strengthening FCC-based high-entropy alloys.
