Achieving High Strength and Good Ductility in a Nb-Containing CoCrNi-Based High-Entropy Alloy by Grain Boundary and Precipitates Strengthening

Abstract

Face-centered cubic (FCC) high-entropy alloys (HEAs) have attracted considerable attention due to their excellent mechanical properties; however, an insufficient yield strength (YS) limits their widespread engineering applications. To improve the strength of FCC HEAs, the present work aims to develop fine-grained Nb-containing CoCrNi-based HEAs with precipitates. In the present work, a single-phase FCC CoCrNi1.5Nb0.2 HEA was processed by cold rolling followed by annealing at a higher temperature and aging at a lower temperature, yielding fine- and ultra-fine-grained FCC matrices and two types of precipitates: ultra-fine granular C15 Laves phase CoCrNb-based precipitates and ultra-fine lath-shaped D019-structured ε-Ni3Nb-based precipitates. The resultant alloy exhibits a combination of high strength (approximately 1409 MPa of yield strength) and good ductility (10.1% of uniform elongation). The contributions of grain boundary and precipitation strengthening to YS were analyzed and calculated. The mechanisms underlying good ductility were discussed.

Keywords

• high-entropy alloys
• grain boundary strengthening
• precipitation strengthening
• strength
• ductility