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This study delves into the impact of positive and negative defocusing distances on the surface quality， densification， and mechanical properties of 316L stainless steel specimens fabricated through laser powder bed fusion （LPBF）. The results show that specimens form with positive defocus outperformed those formed with negative defocus， a phenomenon attributes to the enhanced stability of the molten pool under positive defocus conditions. When the defocusing distance reaches ±3 mm （surpassing the Rayleigh length）， it leads to a sharp decline in laser power density and a substantial deterioration in spot penetration capability. Under these circumstances， incomplete melting of the metallic powder occurs， which undermines the interlayer metallurgical bonding and triggers a proliferation of defects within the specimens， ultimately resulting in a degradation of their mechanical properties. As the defocusing distance increases from -3 mm to 3 mm， the laser power density initially roses and then declines. The laser power density attains at a defocusing distance of +0.5 mm， reaching 61.33 kW/mm². At this optimal condition， the part exhibits superior performance： the upper surface hardness is 200.1HV5， the lateral surface hardness is 206.2HV5， the tensile strength is （647 ± 27） MPa， the yield strength is （525 ± 30） MPa， and the elongation reaches （49.4 ± 3.1）%. An optimal power density input facilitates effective regulation of the molten pool morphology， achieving a dual-process optimization： ensuring adequate melting of the powder while simultaneously suppressing defect generation.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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