In this paper, the microstructure, defects, hardness, and tensile strength of the 17-4PH specimens manufactured additively using the selective laser melting (SLM) technique were studied. The analyzed parts (10 mm size cubic specimens and tensile specimens) were manufactured with different defocus parameter values (−1, 0, +1 mm) in order to evaluate this effect with a low power laser (38 W). The study was carried out on three different sections of each cubic specimen, one perpendicular to the laser beam or SLM manufacturing direction (transversal section), and another two parallel to the laser beam direction (longitudinal sections). The specimens microstructures were analyzed with an X-ray diffraction technique, as well as optical, scanning electron, and transmission electron microscopes. Image J software was used to characterize the defects and phase ratio. In addition, hardness and tensile tests were performed according to the corresponding standards. The results show that the amount of austenitic phase and the average grain size varied with defocusing. The percentage of defective area was less than 0.25%. The analyzed defocus distance did not affect the number and average size of the defects. Adjusting the defocusing SLM parameter is important for manufacturing parts with good mechanical properties.

中文翻译：

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低能量输入下激光散焦对SLM附加制造的17-4PH零件的组织和缺陷的影响

本文研究了使用选择性激光熔化（SLM）技术相加制造的17-4PH试样的微观结构，缺陷，硬度和拉伸强度。用不同的散焦参数值（-1、0，+ 1毫米）制造被分析的零件（10毫米大小的立方试样和拉伸试样），以便用低功率激光（38 W）评估这种效果。研究是在每个立方试样的三个不同部分上进行的，一个垂直于激光束或SLM制造方向（横向截面），另外两个平行于激光束方向（纵向截面）。使用X射线衍射技术以及光学，扫描电子和透射电子显微镜对样品的微观结构进行了分析。使用Image J软件表征缺陷和相比。另外，根据相应的标准进行了硬度和拉伸试验。结果表明，奥氏体相的数量和平均晶粒尺寸随散焦而变化。缺陷区域的百分比小于0.25％。分析的散焦距离不影响缺陷的数量和平均尺寸。调整散焦SLM参数对于制造具有良好机械性能的零件很重要。分析的散焦距离不影响缺陷的数量和平均尺寸。调整散焦SLM参数对于制造具有良好机械性能的零件很重要。分析的散焦距离不影响缺陷的数量和平均尺寸。调整散焦SLM参数对于制造具有良好机械性能的零件很重要。