By optimizing the laser powder-bed fusion process parameters, the work aims to fabricate crack-free and highly dense MNiHEA high-temperature high-entropy alloys with no lack-of-fusion porosity, so as to reduce defect rates and enhance mechanical properties, thus providing valuable references for advancing laser powder-bed fusion additive manufacturing processes for high-temperature resistant alloys. With pre-alloyed MNiHEA powder as the raw material, an orthogonal experiment was conducted to design laser power and scanning speed, and both single-track and cubic block samples were subsequently fabricated. Additionally, linear energy density was introduced as a key indicator to systematically investigate the effect of laser power and scanning speed on the cross-sectional geometry and surface topography of single-track molten pools, as well as on the formation of lack-of-fusion pores, microcracks, and the densification behavior in cubic block samples. Subsequently, a comprehensive microstructural analysis was performed on the high-density samples fabricated under the optimized process parameters. When the scanning speed was set at 1 600 mm/s, balling phenomenon was observed across the entire laser power range of 100- 400 W. As the laser power increased to 200-250 W and 300-400 W, with corresponding scanning speed reducing to 1 400 mm/s and 1 200 mm/s respectively, the balling effect remained pronounced. Samples free from lack-of-fusion pores and microcracks, with a relative density exceeding 99.9%, were achieved under the combined condition of a linear energy density of 0.25- 0.33 J/mm, laser power of 150-250 W, and scanning speed of 600-800 mm/s. The internal pores within the samples primarily consisted of spherical keyhole pores and solidification gas pores. Furthermore, four sets of high-density samples were obtained, whose microstructures exhibited typical "fish-scale" morphology. With the increasing linear energy density, the molten pool depth progressively increased. Both the interior and boundary regions of the molten pools were composed of metastable, micron-scale dislocation cells. High scanning speed is more likely to induce balling phenomenon, and the critical scanning speed for balling decreases with the increasing laser power. Within the process window of linear energy density at 0.25-0.33 J/mm, laser power at 150-250 W, and scanning speed at 600-800 mm/s, high-density samples free from lack-of-fusion pores and microcracks can be obtained. Reducing the scanning speed to increase energy density readily leads to the formation of microcracks, while further increasing the laser power exacerbates the occurrence of both lack-of-fusion pores and microcracks. The high cooling rates inherent to the laser powder-bed fusion process promote non-equilibrium rapid solidification, resulting in the formation of sub-micron cellular structures and fine dendritic features.
Key words
additive manufacturing /
laser powder-bed fusion /
crack-resistant high-temperature high-entropy alloy /
process parameter optimization /
microstructure
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Funding
Chongqing Talent Recruitment Programme (CSTB2025YCJH-KYXM0001); Chongqing Municipal Science and Technology Bureau Project “Key Technologies and Equipment for Multi-Material Laser Precision Additive Manufacturing”; National Natural Science Foundation of China (52401215, 52401214, 52201051); Shanghai Magnolia Talent Plan Pujiang Project (24PJD035); Innovation Program of Shanghai Municipal Education Commission (2021-01-07-00-09-E00114); Technology Plan Program of Shanghai Municipal Commission of Science and Technology (25CL2902300); Shanghai Municipal Explorer Program (25TS1401900)
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