Nanoparticle-strengthened Ni2CoCrNb0.2 medium-entropy alloy with an ultrastrong cryogenic yield strength fabricated by additive manufacturing

To improve the yield strength of metallic materials at low temperatures, a strategy of combining the cal-culation of phase diagrams (CALPHAD) technique with the overall valence electron concentration (OVEC) principle is applied, and a Ni2CoCrNb0.2 medium-entropy alloy (MEA) with D0 22 superlattice (noted as the & gamma;? ? phase) is designed. Bulk MEA samples without defects were successfully fabricated using laser additive manufacturing (AM), followed by solution treatment at 1200 & DEG;C for 1 h and then aging at 650 & DEG;C for 120 h. The nanoscale & gamma;? ? phase precipitated. The tensile results indicated that the MEA had supe-rior yield strengths of-1180 MPa and-1320 MPa and tensile strengths of-1335 MPa and-1552 MPa at 293 K and 77 K, respectively. The yield strength obtained was superior to that of currently re -ported medium/high-entropy alloys and typical advanced cryogenic steel. The mechanical properties of the Ni2CoCrNb0.2 MEA demonstrated a strong temperature dependence, and the increased yield strength was mainly attributed to the increase in lattice friction stress at low temperatures. This research provides a new strategy for producing materials with ultrastrong cryogenic yield strengths by AM.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.