Abstract Laser direct metal deposition (DMD) is an efficient and flexible additive manufacturing technique which has broad application prospects, but it is also limited due to defects and mechanical anisotropy. Laser remelting (LR) is a process that after each layer is deposited, re-scan the deposition layer with the same slice data but without powder deliver, and it is often used during selective laser melting. Herein, LR process has been applied during the DMD process of a 17-4 PH steel to enhance the densification level and relieve the mechanical anisotropy. It is found that the thermal history, porosity and microstructural evolution are dependent on the LR energy density. Moreover, the roughness of top surface of the deposited layer and intralayer porosity decrease with increase of the laser remelting energy density. While for interlayer defects, there is an optimal LR energy density corresponding to the lowest interlayer porosity. Furthermore, LR process can enhance the holding time at high temperature, even sometimes heat the sample above Ac1, resulting in change in contents of austenite and carbide. In addition, LR process greatly dilutes the pre-solidified texture. It was also proved that the flat defects in-plane to the interlayer and the anisotropy of the crystallographic orientations are extremely harmful for the mechanical isotropy of the DMDed samples. Finally, sample manufactured with laser remelting at 15.0 J/mm2 has the lowest porosity and most random crystallographic orientations resulting in near isotropous tensile strength, but the contribution of laser remelting to eliminate anisotropy in elongation is limited because of the interlayer defects.

中文翻译：

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激光重熔处理对17-4 PH不锈钢激光直接金属沉积组织和力学性能的影响

摘要 激光直接金属沉积（DMD）是一种高效灵活的增材制造技术，具有广阔的应用前景，但也因缺陷和机械各向异性而受到限制。激光重熔（LR）是在每一层沉积后，用相同的切片数据重新扫描沉积层但不送粉的过程，通常用于选择性激光熔化。在此，LR 工艺已应用于 17-4 PH 钢的 DMD 工艺，以提高致密化水平并减轻机械各向异性。发现热历史、孔隙率和微观结构演变取决于LR能量密度。此外，随着激光重熔能量密度的增加，沉积层顶面的粗糙度和层内孔隙率降低。而对于层间缺陷，存在对应于最低层间孔隙率的最佳LR能量密度。此外，LR工艺可以增加高温保持时间，甚至有时将样品加热到Ac1以上，导致奥氏体和碳化物含量发生变化。此外，LR工艺极大地稀释了预凝固的纹理。还证明，层内平面缺陷和晶体取向的各向异性对 DMD 样品的机械各向同性极为有害。最后，用 15.0 J/mm2 激光重熔制造的样品具有最低的孔隙率和最随机的晶体取向，导致接近各向同性的拉伸强度，但由于层间缺陷，激光重熔对消除伸长率各向异性的贡献有限。