Compositional limit between the formation of a high entropy alloy and intermetallic compounds in MnCoFeGe(Si) alloys obtained by mechanical alloying

A single BCC solid solution was formed after thermal treatment of an amorphous precursor MnCo 0.8 Fe 0.2 Ge 0.5 obtained by mechanical alloying, demonstrating the formation of high entropy alloys (HEAs) beyond conventional thermodynamic stability criteria. Although X-ray diffraction analysis shows no changes in phase identification, Mössbauer spectroscopy and magnetization measurements of thermally treated samples reveal a strong dependence of the local environment of Fe atoms on the thermal treatment conditions. These results suggest the coexistence of disordered BCC and ordered B2 structures. The addition of Si to these systems leads to the formation of intermetallic compounds, including the coexistence of austenite and martensite. The MnCo 0.8 Fe 0.2 Ge 0.5 Si x series (x = 0, 0.25 and 0.50) was studied, establishing the compositional limit between the formation of a high entropy alloy and intermetallic phases in the range 0.25 < x < 0.50. • HEA formed by mechanical alloying beyond the stability thermodynamic criteria. • Stability of supersaturated solid solution up to high temperature (1123 K). • Evolution of magnetic properties due to local ordering from BCC to B2 phase. • BCC HEA is formed in MnCo0.8Fe0.2Ge0.5Six (x = 0 and 0.25) by mechanical alloying. • Mixed martensite/austenite found in mechanically alloyed MnCo0.8Fe0.2Ge0.5Si0.5.