Effect of heat treatment on microstructure and mechanical properties of in-situ synthesized Ni2CrCoNb0.16 multi-principal element alloy manufactured by directed energy deposition

Abstract

The variety of multi-principal element alloys (MPEAs) provide the possibility to develop new materials with excellent mechanical properties. In this study, an in-situ synthesized age-hardening Ni2CrCoNb0.16 MPEA suitable for directed energy deposition (DED) was designed, and its microstructural evolution and mechanical properties after different heat treatment processes were systematically investigated. The DED-fabricated samples showed typical hierarchical microstructure characteristics including epitaxially grown columnar grains, micron-sized cellular substructures, and a high density of dislocations. Numerous annealing twins are produced during the annealing process (at 1403 K for 1 h), and the original cellular substructures and the <001> fiber texture along the building direction are maintained in the direct aging treatment (DA) (at 923 K for 30 h, 50 h, 85 h, 110 h). The samples after DA for 85 h exhibited a promising mechanical performance readily characterized by a yield strength (YS) of 753.04 MPa, ultimate tensile strength (UTS) of 1004.75 MPa and an elongation of 26.85%. Its YS and UTS are increased by 167.39% and 81.54% compared with the Ni2CrCo sample, and the advantageous combination between strength and ductility can be attributed to the prevailing substructures boundaries, solid solution strengthening, precipitation strengthening, dislocation strengthening. The findings provide new insights for achieving high-performance DED MPEAs.