Microstructure and mechanical properties of additively manufactured FeCoCrMnNi high-entropy alloy composite after aging

Abstract

High-entropy alloy composites (HEACs) have attracted significant attention due to their exceptional mechanical properties and chemical stability. By adjusting the content of reinforcing particles in the high-entropy alloy and by employing advanced additive manufacturing techniques, high-performance HEACs can be fabricated. However, there is still considerable room for improvement in their performance. In this study, CoCrFeMnNi HEA powders were used as the matrix, and NiCoFeAlTi high-entropy intermetallic powders were used as the high-entropy reinforcement (HER). CoCrFeMnNi/NiCoFeAlTi HEACs were fabricated using selective laser melting technology. The study results indicate that after aging, the microstructure of HEACs with HER exhibits Al- and Ti-rich nano-oxide precipitates with an orthorhombic CMCM type structure system. After aging at 873 K for 2 h, HEACs with HER achieved excellent overall mechanical properties, with an ultimate tensile strength of 731 MPa. This is attributed to the combined and synergistic effects of precipitation strengthening, dislocation strengthening, and the high lattice distortion caused by high intragranular defects, which provide a multi-scale strengthening and hardening mechanism for the plastic deformation of HEACs with HER. This study demonstrates that aging plays a crucial role in controlling the precipitate phases in complex multi-element alloys.

1. Introduction

Due to their unique composition and structure, high-entropy alloy (HEA) matrix composites exhibit excellent mechanical properties, high-temperature stability, and corrosion resistance, making them a promising candidate for a wide range of applications in aerospace, automotive manufacturing, energy, etc [1−4]. Currently, HEA composites (HEACs) mainly include metallic particles [5−8], ceramic particles, and carbides [9−13] as reinforcements. In addition, some multi-component alloys, such as amorphous materials, have been proven to be excellent reinforcement phases for HEAs, exhibiting high strength and better compatibility with HEA [14, 15]. In 2016, LIU et al [16] fabricated CoCrFeNiMo0.3 HEACs with yield strength, tensile strength, and elongation at room temperature of ~816 MPa, ~1.2 GPa, and ~19%, respectively. ROGAL et al [17] fabricated SiC/CoCrFeMnNi HEACs using hot isostatic pressing. The results showed that adding 5% SiC significantly improved the compressive performance of the HEACs, reaching 1480 MPa at room temperature. LIANG et al [18] fabricated a composite material of amorphous alloy and HEA using ultrasonic vibration, which exhibited an impressive tensile strength of 887 MPa. However, research on HEACs reinforced with HEA particles is relatively limited. TAHERINIYA et al [19] successfully prepared HEA-HEA composites by joining CoCrFeMnNi and HfNbTaTiZr discs using a high-pressure torsion method.

Generally, HEACs are fabricated using the conventional techniques like casting [20−22], plastic deformation [17−19, 23], and/or powder metallurgy [24−26]. However, these methods restrict the fabrication of parts with complex geometries. Hence, additive manufacturing (AM) processes that can fabricate complex shapes without restrictions can be used for fabricating HEACs [27−33]. Among various AM techniques, selective laser melting (SLM) technology which offers high cooling rates (10⁵−10⁶ K/s) can be a suitable process to fabricate these HEACs [34−36]. LI et al [37] utilized SLM to fabricate Fe-based amorphous alloy-reinforced HEACs, confirming the excellent compatibility between amorphous alloys and HEAs, both being multi-component systems.