ABSTRACT

A crack-free Inconel 718 – Stainless steel 316 L bimetallic structure has been fabricated using the laser powder bed fusion (LPBF) process. Firstly, an optimum process parameter set resulting in defect-free bonding of both materials has been predicted by carrying out a parametric study. Thereafter, microstructural and mechanical characterization such as optical microscopy, X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, hardness and tensile testing have been carried out to investigate the characteristics of the bimetallic interface. The porosity quantification shows a density greater than 99.5% with no observable cracks or porosity at the transition zone. The secondary electron micrographs reveal a small inter-diffusion region at the interface. The interface and the nearby region consist of both cellular and columnar grains. The tensile strength of the bimetallic-structure approaches the strength of stainless steel 316 L. Even with the material discontinuity, the fracture happens at the weaker side (stainless steel 316 L) indicating the strong strength of the dissimilar interface. The fractography of the fractured surface displays a typical ductile cup and cone type of fracture. The results strongly suggest the suitability of the LPBF process for fabricating defect-free high-strength IN718-SS316L bimetallic structures.

摘要

无裂纹 Inconel 718 – 不锈钢 316 L 双金属结构已使用激光粉末床融合 (LPBF) 工艺制造。首先，通过参数研究预测了导致两种材料无缺陷粘合的最佳工艺参数集。此后，进行了微观结构和机械表征，如光学显微镜、X 射线衍射、扫描电子显微镜与能量色散 X 射线光谱、硬度和拉伸测试，以研究双金属界面的特性。孔隙率量化显示密度大于 99.5%，在过渡区没有可观察到的裂缝或孔隙率。二次电子显微照片显示界面处有一个小的相互扩散区​​域。界面和附近区域由蜂窝状和柱状颗粒组成。双金属结构的抗拉强度接近不锈钢 316 L 的强度。即使材料不连续，断裂也会发生在较弱的一侧（不锈钢 316 L），表明异种界面的强度很高。断裂面的断口形貌显示出典型的韧性杯锥型断裂。结果强烈表明 LPBF 工艺适用于制造无缺陷的高强度 IN718-SS316L 双金属结构。断裂发生在较弱的一侧（不锈钢 316 L），表明异种界面的强度很高。断裂面的断口形貌显示出典型的韧性杯锥型断裂。结果强烈表明 LPBF 工艺适用于制造无缺陷的高强度 IN718-SS316L 双金属结构。断裂发生在较弱的一侧（不锈钢 316 L），表明异种界面的强度很高。断裂面的断口形貌显示出典型的韧性杯锥型断裂。结果强烈表明 LPBF 工艺适用于制造无缺陷的高强度 IN718-SS316L 双金属结构。