Conventional fabrication methods struggle to achieve the rapid forming of complex components of FeCoNiCrMn high-entropy alloy. Laser melting deposition (LMD) technology offers a novel approach for the integrated fabrication and forming of high-entropy alloys. Nevertheless, the rapid melting–solidification kinetics inherent to LMD tend to induce microstructural gradients within deposited components, thereby influencing their mechanical performance. This study aims to systematically investigate the gradient evolution of the microstructure with deposition position in FeCoNiCrMn high-entropy alloy during LMD and to elucidate the mechanism governing mechanical property uniformity under structural heterogeneity. The findings provide valuable insights for controlling microstructural and mechanical uniformity of additively manufactured high-entropy alloys.

FeCoNiCrMn high-entropy alloy single-wall samples were fabricated using laser melting deposition (LMD). Phase analysis was conducted via X-ray diffraction (XRD), and the microstructure, including grain morphology, size, and orientation, at the deposition center, edges, and various heights from bottom to top, was systematically characterized using a scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD). Microhardness testing and uniaxial tensile tests at room temperature were performed to evaluate mechanical properties at different deposition positions (bottom, middle, and top), establishing correlations between microstructure and macroscopic performance.

The research found that, under fixed LMD processing parameters, the samples exhibited a regular microstructural gradient: from the bottom to the top of the single-wall samples, grains continuously grew due to the thermal accumulation effect of layer-by-layer deposition, resulting in gradually increasing grain sizes. Horizontally, the central region of deposition was dominated by columnar grains, whereas the wall edges, subjected to higher cooling rates, formed equiaxed grains, presenting a “center-to-edge” grain morphology transition (Fig.4 and Fig.5). Despite this, all regions maintained a single face-centered cubic (FCC) solid solution structure (Fig.3). Notably, this pronounced structural gradient did not lead to fluctuations in mechanical properties. Hardness test results showed that the average hardness value across different positions remained stable at 154 HV (Fig.8). Tensile tests further confirmed that bottom, middle, and top samples all exhibited similar and excellent mechanical performances, with average tensile strength and elongation reaching 542.5 MPa and 50%, respectively, and all showing ductile fracture (Fig.9, Fig.10). Analysis suggested that the single stable FCC phase composition formed the basis for property uniformity, while the 001 texture observed in edge regions (Fig.7) may have positively contributed to maintaining good plasticity. With the subsequent thermal history during laser melting deposition, segregated particles formed by local decomposition induced by thermal cycling provided a certain strengthening effect, compensating for the adverse influence of large columnar grains at the bottom.

This study successfully prepared FeCoNiCrMn high-entropy alloy via laser melting deposition technology and revealed the unique coexistence of “structural gradient and uniform performance”. The main conclusions are as follows. First, the LMD forming process inevitably creates a grain size gradient from bottom to top, as well as a morphological gradient from columnar grains at the center to equiaxed grains at the edges within the single-wall samples. Second, despite the presence of these microstructural gradients, the overall component maintains a single FCC phase structure, thereby ensuring highly uniform distribution of hardness and tensile properties (including strength and plasticity) across different deposition positions. This finding indicates that, within a reasonable processing window, LMD technology can produce high-entropy alloy components that combine complex microstructural features with stable and excellent mechanical properties, demonstrating its significant potential for the customized manufacturing of high-performance components.