Construction of bio-inspired gradient heterogeneous structures in high-entropy alloys by laser-directed energy deposition: Microstructure, strength-ductility balance, and tribological properties

Overcoming the inherent trade-offs among strength, ductility, and wear resistance in metal materials is a key challenge to enhance their engineering application value. Inspired by the rigid-flexible coupled (RFC) structure of bamboo, 316L/FeCoCrNiMn bionic gradient heterostructured material was prepared by laser-directed energy deposition (LDED) technology. The microstructure, crystallographic properties, mechanical properties and wear properties of the three samples were systematically investigated. The results show that all samples exhibit a single face-centered cubic (FCC) phase characteristic, and the microstructure contains epitaxial columnar grains, equiaxed grains, and cellular grains. In RFC materials designed with a biomimetic strategy, the presence of dislocation networks and recrystallization phenomena contributes to enhanced strength, ductility, and wear resistance. The RFC material exhibits excellent strong plastic synergistic effects when loaded along the deposition direction, reaching an elongation of 41 % (a 36.7 % enhancement over the FeCoCrNiMn high-entropy alloy). The ultimate flexural strength of RFC materials can reach 1740 MPa. The wear resistance of the RFC material is improved compared to both 316L and FeCoCrNiMn samples, and its wear mechanism changes with load variation. The specific performance is from oxidized wear and slight abrasive wear, gradually changed to adhesive wear, severe abrasive wear and fatigue wear synergistic mode.