The microstructure and mechanical properties of novel Fe-rich Fe–Cr–Ni–Ta eutectic multi-principal element alloys

Co-Cr-Fe-Ni-Ta eutectic multi-principal element alloys (MPEAs) demonstrate great potential to replace structural alloys in engineering applications. However, the cost of these alloys is high due to the usage of a number of precious metals. To decrease the cost, the present work developed a set of novel Fe55Cr15Ni30−xTax (x = 0, 5, 8, 10 and 15 at.%) eutectic MPEAs and the effect of Ta on microstructure and compressive mechanical properties were investigated for the first time. As the Ta content increases, the microstructure change from a single-phase FCC solid solution (x = 0) to hypoeutectic microstructure (x = 6), then to eutectic microstructure (x = 8), and eventually to hypereutectic microstructure (x = 10 and 15). The yield strength and the hardness increase at the expense of ductility reduction with increasing Ta content. The strengthening mechanism of this alloy system is mainly second-phase strengthening caused by Laves phase and grain boundary strengthening produced by eutectic interface, supplemented by solid solution strengthening. The Fe55Cr15Ni22Ta8 and Fe55Cr15Ni20Ta10 alloy present the excellent comprehensive mechanical properties. The yield strength, fracture strength and fracture strain of the former are 838 MPa, 1994 MPa and 45.1%, respectively. The yield strength, fracture strength and fracture strain of the latter are 1029 MPa, 1956 MPa and 43.0%, respectively. The phase formation of Fe55Cr15Ni30−xTax alloys can be predicted by Md criterion. When Md ≥ 0.89, the alloys consist of FCC phase and Laves phase. Otherwise, the alloys consist of FCC single phase.