Fabrication of a novel magnetic high entropy alloy with desirable mechanical properties by mechanical alloying and spark plasma sintering

Abstract

In this study, a novel magnetic CoCuFeMnNi high entropy alloy (HEA) was synthesized using mechanical alloying (MA) and spark plasma sintering (SPS). Thermodynamic analysis showed that the solid solution state of the CoCuFeMnNi alloy system has the highest negative Gibbs free energy (−59.34 kJ/mol), meaning that the solid solution state is very stable. Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis confirmed the formation of an FCC solid solution after 50 h mechanical alloying. The vibrant sample magnetometer (VSM) test illustrated a soft magnetic behavior with 48 emu/g magnetic saturation (MS) and 15 Oe coercivity field (HC) in 1 T (T) applied magnetic field. The maximum of densification and microhardness were attained at 850 °C, and the ultimate values of shear strength and tensile strength were 320 MPa and 576 MPa, respectively. The CoCuFeMnNi HEA was subjected to a pin-on-disc dry sliding wear test at various temperatures from room temperature to 600 °C. A detailed microscopic characterization of the worn surfaces revealed a transition in the predominant wear mechanism from delamination wear at room temperature to oxidative and delamination wear at elevated temperatures. The formation of an oxidized tribo-layer at 600 °C on the worn surfaces led to a low wear rate and low coefficient of friction, enabling the CoCuFeMnNi HEA for high-temperature applications.