Metal additive manufacturing (AM), as a disruptive technology in the field of fabricating metallic parts, has shown its ability to design component with macrostructural complexity. However, some of these functionally complex structures typically contain a wide range of feature sizes, namely, the characteristic length of elements in AM-produced components can vary from millimeter to meter-scale. The requisite for controlling performance covers nearly six orders of magnitude, from the microstructure to macro scale structure. Understanding the mechanical variation with the feature size is of critical importance for topology optimization engineers to make required design decisions. In this work, laser metal deposition (LMD) is adopted to manufacture 316L stainless steel (SS) samples. To evaluate the effect of defects and specimen size on mechanical properties of LMD-produced samples, five rectangular sample sizes which ranged from non-standard miniature size to ASTM standard sub-sized samples were machined from the block. Tensile test reveals that the mechanical properties including yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (ε_f) are almost the identical for samples with ASTM standard size. Whilst, relatively lower YS and UTS values, except for ε_f, are observed for samples with a miniature size compared with that of ASTM standard samples. The ε_f values of LMD-produced 316L SS samples show a more complex trend with sample size, and are affected by three key influencing factors, namely, slimness ratio, cluster of pores, and occupancy location of lack of fusion defects. In general, the ε_f values exhibit a decreasing trend with the increase of slimness ratio. Microstructure characterization reveals that the LMD-produced 316L samples exhibited a high stress status at low angle grain boundaries, whilst its location changed to high angle grain boundaries after plastic deformation. The grain size refinement and austenite-to-martensite phase transformation occurred during plastic deformation might be responsible for the very high YS and UTS attained in this study. The experimental works carried out in this study is expected to provide a guideline for evaluating the mechanical properties of LMD-produced parts with complex structure, where critical parameter such as a certain slimness ratio has to be considered.

金属增材制造 (AM) 作为金属零件制造领域的一项颠覆性技术，已显示出其设计具有宏观结构复杂性的组件的能力。然而，这些功能复杂的结构中的一些通常包含范围广泛的特征尺寸，即 AM 生产的组件中元素的特征长度可以从毫米到米级不等。控制性能的必要条件涵盖了近六个数量级，从微观结构到宏观结构。了解特征尺寸的机械变化对于拓扑优化工程师做出所需的设计决策至关重要。在这项工作中，采用激光金属沉积 (LMD) 制造 316L 不锈钢 (SS) 样品。为了评估缺陷和试样尺寸对 LMD 生产样品机械性能的影响，从块中加工出从非标准微型尺寸到 ASTM 标准小尺寸样品的五个矩形样品尺寸。拉伸试验表明，机械性能包括屈服强度 (YS)、极限拉伸强度 (UTS) 和断裂伸长率 (ε _f ) 对于具有 ASTM 标准尺寸的样品几乎相同。同时，与 ASTM 标准样品相比，对于具有微型尺寸的样品，观察到相对较低的 YS 和 UTS 值（ ε _f除外） 。LMD 生产的 316L SS 样品的εf_值随样品大小呈现更复杂的趋势，并受三个关键影响因素的影响，即细化率、孔隙簇和未融合缺陷的占据位置。一般来说，ε _f值随着纤细率的增加呈下降趋势。微观结构表征表明，LMD 生产的 316L 样品在低角度晶界处表现出高应力状态，而其位置在塑性变形后变为高角度晶界。在塑性变形过程中发生的晶粒细化和奥氏体到马氏体的相变可能是本研究中获得非常高的 YS 和 UTS 的原因。本研究中进行的实验工作有望为评估 LMD 生产的具有复杂结构的零件的机械性能提供指导，其中必须考虑一定的细长比等关键参数。