Enhancing mechanical and anti-corrosion properties in a L12 nanoprecipitates reinforced Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 multi-principal element alloy via tailoring grain size

A Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 multi-principal element alloy (MPEA) reinforced by L1(2) nanoprecipitates was fabricated with four different grain sizes (similar to 19, similar to 50, similar to 127 and similar to 361 mu m) to optimize mechanical and corrosion properties. All samples exhibit a similar microstructure, showing spherical L1(2) nanoprecipitates embedded in the FCC matrix at grain interiors, accompanied by a small fraction of plate-like L1(2) and B2-ordered phases at grain boundaries. As grain size decreases, both yield strength and ultimate tensile strength progressively increase, while ductility decreases. The sample with a grain size of similar to 50 mu m demonstrates the most excellent combination of strength and ductility, displaying a yield strength of similar to 700 MPa, an ultimate tensile strength of similar to 1130 MPa, and a total elongation of similar to 29.4 %. Concurrently, corrosion resistance in 3.5 wt% NaCl solution improves as grain size decreases from similar to 361 mu m to similar to 50 mu m, but notably deteriorates at similar to 19 mu m. These results suggest that the L1(2) nanoprecipitates reinforced Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 MPEA with grain size of similar to 50 mu m has achieved outstanding combination of mechanical and anti-corrosion properties. Precipitation strengthening and grain boundary strengthening are responsible for the enhanced mechanical properties in the studied samples. Electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) revealed that the passive film on the similar to 50 mu m grain size sample is the thickest (3.09 nm), composed primarily of Cr2O3 and Fe2O3, which acts as an effective barrier against Cl- penetration. In a word, tailoring grain size proves to be an effective means to achieve enhanced mechanical and anti-corrosion properties.