Powder bed metal additive manufacturing (AM) utilizes a high-energy heat source scanning at the surface of a powder layer in a predefined area to be melted and solidified to fabricate parts layer by layer. It is known that powder bed metal AM is primarily a thermal process, and further, heat conduction is the dominant heat transfer mode in the process. Hence, understanding the powder bed thermal conductivity is crucial to process temperature predictions, because powder thermal conductivity could be substantially different from its solid counterpart. On the other hand, measuring the powder thermal conductivity is a challenging task. The objective of this study is to investigate the powder thermal conductivity using a method that combines a thermal diffusivity measurement technique and a numerical heat transfer model. In the experimental aspect, disk-shaped samples, with powder inside, made by a laser powder bed fusion (LPBF) system, are measured using a laser flash system to obtain the thermal diffusivity and the normalized temperature history during testing. In parallel, a finite element (FE) model is developed to simulate the transient heat transfer of the laser flash process. The numerical model was first validated using reference material testing. Then, the model is extended to incorporate powder enclosed in an LPBF sample with thermal properties to be determined using an inverse method to approximate the simulation results to the thermal data from the experiments. In order to include the powder particles’ contribution in the measurement, an improved model geometry, which improves the contact condition between powder particles and the sample solid shell, has been tested. A multipoint optimization inverse heat transfer method is used to calculate the powder thermal conductivity. From this study, the thermal conductivity of a nickel alloy 625 powder in powder bed conditions is estimated to be 1.01 W/m K at 500°C. [DOI: 10.1115/1.4040877]
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机译：粉末床金属增材制造（AM）利用高能热源在预定区域内的粉末层表面进行扫描，以进行熔化和固化，从而逐层制造零件。已知粉末床金属AM主要是热处理，并且，热传导是该过程中的主要传热方式。因此，了解粉末床的导热系数对工艺温度的预测至关重要，因为粉末导热系数可能与固体导热系数显着不同。另一方面，测量粉末的导热率是一项艰巨的任务。这项研究的目的是使用结合了热扩散率测量技术和数值传热模型的方法来研究粉末的导热系数。在实验方面，使用激光闪光系统测量由激光粉末床熔合（LPBF）系统制成的内部粉末的盘状样品，以在测试过程中获得热扩散率和标准化温度历史记录。同时，开发了一个有限元（FE）模型来模拟激光闪光过程的瞬态热传递。首先使用参考材料测试对数值模型进行了验证。然后，将模型扩展为合并包含在具有热性质的LPBF样品中的粉末，并使用逆方法将模拟结果近似为来自实验的热数据，从而确定模型。为了将粉末颗粒的贡献包括在测量中，已经测试了改进的模型几何形状，该模型改善了粉末颗粒与样品固体外壳之间的接触条件。采用多点优化逆传热方法计算粉末的导热系数。根据这项研究，在粉末床条件下，镍合金625粉末在500°C下的热导率估计为1.01 W / mK。 [DOI：10.1115 / 1.4040877]
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