This work aims to investigate the effect of the process parameters on the densification and microstructure of Inconel 939 (IN939) alloy processed by laser powder bed fusion (LPBF). IN939 is a Ni-based superalloy with high creep and corrosion resistance that can be used up to around 850 °C under load, resulting in higher operative temperatures than the ones commonly allowed for Inconel 718 and Inconel 625 alloys (around 650 °C). However, this alloy can suffer from poor weldability involving possible crack formation. In order to minimize the residual porosity and the cracking density, specific process parameters were investigated. The parameters to generate IN939 samples almost pores-free (porosity ≤0.22%) with a cracking density ≤1.36 mm/mm² as well as samples almost crack-free (≤0.10 mm/mm²) with limited residual porosity (≤0.89%) were determined. The microstructure revealed fine dendritic/cellular structures with the formation of sub-micrometric phases. A high concentration of these phases was also found along the intergranular cracks, suggesting that their presence, coupled to the high thermal stresses, can be the primary reason for crack formation during the LPBF process.

中文翻译：

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工艺参数对激光熔床Inconel 939致密化和微观组织发展的影响

这项工作旨在研究工艺参数对激光粉末床熔合（LPBF）处理的Inconel 939（IN939）合金的致密化和微观结构的影响。IN939是一种具有高抗蠕变性和耐蚀性的镍基高温合金，在负载下可在高达850°C的温度下使用，从而导致其工作温度高于Inconel 718和Inconel 625合金通常允许的工作温度（约650°C）。但是，这种合金的可焊性较差，可能形成裂纹。为了使残留孔隙率和裂化密度最小化，研究了特定的工艺参数。生成IN939样品的参数，这些样品几乎没有孔（孔隙度≤0.22％），裂纹密度≤1.36mm / mm ²，并且样品几乎没有裂缝（≤0.10mm / mm ²确定了残留孔隙率（≤0.89％）有限的）。微观结构显示出细小的树突/细胞结构，并形成了亚微米相。沿晶间裂纹也发现了这些相的高浓度，这表明它们的存在与高热应力一起可能是LPBF过程中裂纹形成的主要原因。