Influence of processing and microstructure on the local and bulk thermal conductivity of selective laser melted 316L stainless steel
Influence of processing and microstructure on the local and bulk thermal conductivity of selective laser melted 316L stainless steel
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DOI：
10.1016/j.addma.2019.100996
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发表时间：
2020-03-01
影响因子：
11
通讯作者：
Schiffres, Scott N.
中科院分区：
文献类型：
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作者：
Simmons, Jacob C.;Chen, Xiaobo;Schiffres, Scott N.
由于用于生产部件的独特工艺，通过选择性激光熔化制成的部件的材料特性与散装基础材料的公认特性不同。与此同时，增材制造越来越多地用于需要高热导率的热交换器和排热装置。热性能对于许多无损检测技术也很重要。研究了选择性激光熔凝316 L不锈钢的热导率随工艺条件和成形方向的变化。相对于加工条件测量孔隙率和热导率。观察到44.4J/mm（3）的临界能量密度，低于该临界能量密度，孔隙率增加并且热导率降低。对于孔隙率最低的样品，采用频域热反射的局部热导率图显示不锈钢热导率在10.4和19.8 W/m-K之间变化，而热导率图的平均热导率为14.3 W/m-K，在测量不确定度范围内，与体热导率测量值一致。孔隙率不能完全解释热导率的趋势，因为有效介质模型无法预测该趋势。用透射电镜观察了激光选区熔化不锈钢晶粒中的非晶条纹。这些无定形区域也导致随着孔隙率的增加而降低的X射线衍射强度。假设非晶区域在更快的激光扫描速度下由于在升高的温度下的时间更少而降低热导率。我们还发现，当能量密度大于这个临界值时，印刷平面和贯穿印刷平面的热导率具有相同的值。当能量密度降低到该临界量以下时，面内电导率超过贯穿面。
Material properties of parts made via selective laser melting are not the same as the well-established properties for bulk base materials, due to the unique processes used to produce the parts. Meanwhile, additive manufacturing is increasingly being used for heat exchangers and heat removal devices, which demand high thermal conductivities. The thermal properties are also important for many non-destructive testing technologies. The thermal conductivity of selective laser melted 316 L stainless steel was studied as a function of processing conditions and build orientation. The porosity and thermal conductivity were measured versus processing conditions. A critical energy density of 44.4 J/mm(3) was observed below which the porosity increased and the thermal conductivity decreased. For the lowest-porosity sample, the local thermal conductivity map taken with frequency domain thermoreflectance showed a variation in the stainless steel thermal conductivity between 10.4 and 19.8 W/m-K, while the average thermal conductivity of 14.3 W/m-K from the thermal conductivity map agreed, within measurement uncertainty, with the bulk thermal conductivity measurements. The thermal conductivity trend was not fully explained by the porosity, as effective medium models fail to predict the trend. Amorphous stripes in the selective laser melted stainless steel grains were identified by transmission electron microscopy. These amorphous regions also resulted in decreased x-ray diffraction intensities with increasing porosity. The amorphous regions are hypothesized to lower the thermal conductivity at faster laser scanning speeds due to less time at elevated temperatures. We also found that in-print plane and through-print plane thermal conductivities have the same value when the energy density is greater than this critical amount. When the energy density reduces below this critical amount, the in-plane conductivity exceeds the through-plane.