Investigation of non-equiatomic AlCuCrFeNi-based HEAs consolidated by FAST/SPS

In this study, a mechanically alloyed equiatomic AlCuCrFeNi high-entropy alloy (HEA) was used as the starting point for a thermodynamically guided alloy design aimed to promote the formation of an FCC solid-solution microstructure. Two modified alloy compositions were developed by adjusting the elemental ratios to enhance phase stability based on thermodynamic parameters such as mixing enthalpy, configurational entropy, atomic-size mismatch, and valence electron concentration. The alloys were synthesized using mechanical alloying (MA), followed by the Field Assisted Sintering Technique/Spark Plasma Sintering (FAST/SPS) to obtain a fine-grained microstructure. The experimental results revealed that a multiphase microstructure was obtained, which consists of an FCC matrix, a secondary FCC phase, carbides, and intermetallic compounds, indicating that a single-phase FCC solid solution was only partially stabilized under the applied processing conditions. Mechanical testing showed high compressive strengths of 1893 MPa and 1882 MPa, respectively, combined with limited plasticity at room temperature. When tested at 300°C, the compressive strength decreased by approximately 20%, while ductility was significantly enhanced. Fractographic analysis revealed a shear-type fracture, showing brittle, carbide-induced crack initiation at room temperature and a transition to more ductile fracture behavior at elevated temperatures. Both alloys exhibited high Vickers macrohardness values ranging from 522 to 552 HV10 at room temperature, surpassing that of conventional Ti–6Al–4 V. Furthermore, the contributions of grain refinement and solid-solution hardening to the measured macrohardness were theoretically estimated, revealing that solid-solution hardening is the dominant strengthening mechanism. • Equiatomic AlCuCrFeNi HEA was thermodynamically optimized to stabilize a predominantly FCC phase. • Mechanical alloying combined with FAST/SPS produced a fine-grained microstructure and achieved nearly full densification at 1100 °C. • XRD, SEM and EBSD analyses confirmed FCC matrix with Cr-rich M₇C₃ carbides at particle boundaries, leading to formation of a secondary FCC phase. • Modified alloys showed macrohardness > 520 HV10 and compressive strength > 1800 MPa with limited ductility at room temperature.