Effect of Cr content on microstructure, mechanical properties and corrosion resistance of additively manufactured AlCrxCoFeNi2.1 high-entropy alloy

In this study, novel AlCr x CoFeNi 2.1 ( x = 1.25, 1.50, 1.75, 2.00 and 2.25) high-entropy alloys (HEAs) were additively prepared by laser direct energy deposition (LDED). The effect of the Cr content on the microstructure, mechanical properties, and corrosion resistance of the AlCr x CoFeNi 2.1 HEAs was investigated and discussed. The results showed that with the increasing Cr content, the microstructure transformed from lamellar structures featured by face-centered cubic (FCC)/body-centered cubic (BCC) dual phases into Widmanstatten-like structures characterized by fragmental FCC phase and BCC/B2 coherent precipitation. The additional Cr notably enhanced the microhardness and improved the ultimate tensile strength with a reasonable deterioration of toughness by facilitating the formation of BCC/B2 coherent precipitation in which dispersedly embedded BCC nanoparticles nucleate severe dislocation pile-up. Excellent mechanical performance (424.6 HV, 1401.9 MPa, 13.9%) was achieved in the AlCr 2.25 CoFeNi 2.1 HEA. The corrosion resistance was significantly promoted, owing to the weakening of galvanic corrosion between the FCC phase and BCC/B2 coherent precipitation and the stability improvement of the passive films by the dramatically increased Cr 2 O 3 . These results contribute to the exploration and regulation of novel HEAs with excellent comprehensive performance using coherent precipitation.