Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels
Tensile properties, strain rate sensitivity, and activation volume of additively manufactured 316L stainless steels
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DOI：
10.1016/j.ijplas.2019.05.009
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发表时间：
2019-09-01
影响因子：
9.8
通讯作者：
Wang, Y. Morris
中科院分区：
文献类型：
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作者：
Li, Zan;Voisin, Thomas;Wang, Y. Morris
添加制造(AM)金属和合金的拉伸性能是影响这些材料潜在应用的最重要变量之一。在这里，我们通过12组优化的激光加工工艺参数，研究和报道了用激光粉床熔化技术(L-PBF)制备的AM 316L不锈钢的拉伸性能，获得了密度为98.8+/-0.10%的材料。在所有L-PbF样品中都观察到了不均匀的显微组织，包括位错、胞壁、元素偏析、局部取向偏差、杂质、析出物和大量的小角度晶界(2-10度，类似于40-60%)。由高角度晶界(>；10度)定义的平均晶粒度类似于30-50微米。拉伸测试表明，直接打印的样品的屈服强度为552-635兆帕，拉伸伸长率为0.09-0.42，而用预制的矩形薄板加工的样品的屈服强度为592-690兆帕，拉伸断裂伸长率(TEF)为0.29-0.50。在所有样品中，我们观察到拉伸屈服强度在类似于15%的TEF范围内的变化，但不是TEF，这表明尽管激光加工参数范围很大，但微观结构发生了轻微变化。TEF在直接打印样品中的大散射源于薄规几何形状(类似于2分钟(2)的横截面面积)对内置缺陷的敏感性。我们测量了L-PBF 316L的应变速率敏感性(m类似于0.02-0.03)，与粗晶(类似于0.006)的应变速率敏感性相比，以及与20-30b(3)相似的小的激活体积(其中b是316L的Burgers矢量)。这些变形动力学参数表明，L-PBF316L的拉伸塑性是由比测量的晶粒度小得多的微观组织长度尺度控制的，这与这些材料中看到的高强度和并置的纳米与宏观组织是一致的。讨论了AM材料拉伸性能优化的策略。
The tensile properties of additively manufactured (AM) metals and alloys are among the most important variables that impact the potential applications of these materials. Here we examine and report on the tensile properties of AM 316L stainless steels fabricated by the laser powder-bed-fusion (L-PBF) technique, via twelve sets of optimized laser processing parameters that produce materials with density > 98.8 +/- 0.10%. A heterogeneous microstructure is observed in all L-PBF samples, including microscopic features such as dislocations, cellular walls, elemental segregations, local misorientations, impurities, precipitates, and a large fraction of low-angle grain boundaries (2-10 degrees, similar to 40-60%). The derived average grain size defined by high-angle grain boundaries ( > 10 degrees) is similar to 30-50 mu m. Tensile testing reveals a yield strength ranging from 552 to 635 MPa and a tensile-elongation-to-failure (TEF) of 0.09-0.42 for directly-printed samples, whereas these values are 592-690 MPa and 0.29-0.50 for samples machined from the as-built rectangular thin plates. In all samples, we observe a variation of tensile yield strength within similar to 15% but not the TEF, suggesting marginal microstructural changes despite a wide range of laser processing parameters. The large scatter of TEF in directly-printed samples originates from the sensitivity of thin gauge geometry (similar to 2 min(2) cross-section area) to the built-in flaws. We measured a substantially higher strain rate sensitivity (m similar to 0.02-0.03) of L-PBF 316L compared to the coarse-grained counterparts (similar to 0.006), together with a small activation volume of similar to 20-30b(3) (where b is the Burgers vector of 316L). These deformation kinetics parameters suggest that the tensile plasticity of L-PBF 316L is controlled by a much finer microstructural length scale than the measured grain size, consistent with the high strength and juxtaposed nano- to macro-structures seen in these materials. Strategies to optimize the tensile properties of AM materials are discussed.