GH3536 superalloy is a typical difficult-to-machine material with high micro-strengthening phase hardness, severe work hardening, high shear stress resistance, and low thermal conductivity. When processing GH3536 superalloys using traditional methods, problems such as low-quality machined surfaces and serious tool breakages are often encountered. The preparation of GH3536 superalloy parts using selective laser melting (SLM) has become an important research topic. However, forming defects of the structural parts of SLM restrict the rapid manufacturing and application of nickel-based superalloys. Hence, research on the corresponding basic scientific issues is urgently required. This study focuses on the forming process of GH3536 superalloys; the printing process of an SLM GH3536 alloy is systematically studied by simulating the temperature and flow fields in the transient process and typical experiments. Heat transfer, liquid metal flow, the formation of inter-track pore defects, and temperature-time variations are explored, providing a basis for the optimization of the manufacturing process parameters and the improvement of the manufacturing quality.

Numerical simulation can comprehensively reveal the complex changes in the temperature and stress fields during the printing process and visualize multi-physics and molten pool's behavior and distribution characteristics under dynamic control conditions, and then support the prediction and real-time control of manufacturing defects. Our simulation can be summarized in the following steps. First, a heat and mass transfer model was established to simulate the SLM GH3536 superalloy printing process. Second, the temperature and flow fields of the molten pool during SLM were studied by changing the laser power, scanning speed, scanning distance, and number of printing layers. Finally, the GH3536 SLM experiment was carried out, and the deposition morphologies were characterized using an optical microscope. The simulation and experimental data deepened our understanding of the temperature and flow fields of laser additive manufacturing and the mechanism of their correlation with defects.

Computational fluid dynamics is widely used to simulate the heating and melting effects of a laser on metal particles, enabling the complex flow behavior of liquid metal between particles to be studied. In this paper, a heat-flow coupled model at the powder scale is established to simulate the printing process of an SLM GH3536 superalloy (Fig. 1). As the scanning speed increases from 0.94 m/s to 1.25 m/s, the width of the molten pool formed by a single-layer and single-pass SLM decreases from 126 μm to 113 μm, and the depth of the molten pool decreases from 86 μm to 60 μm (Fig. 2). When the laser power increases from 190 W to 250 W, the width of the single-layer and single-track increases from 126 μm to 140 μm, and the depth of the molten pool increases from 86 μm to 93 μm (Fig. 5). When the scanning distance is 110 μm for multi-layer and multi-track printing, some unmelted powder and surface-pore defects occur in the intertrack (Fig. 9). Using key parameters such as laser power, scanning speed, scanning distance, and the number of printing layers, changes in the flow of molten pool and temperature field during SLM are studied to comparatively analyze pore distribution under different conditions.

To achieve the forming quality and process parameter optimization requirements of an SLM GH3536 superalloy, we study the characteristics and defect formation mechanisms of the printing process of a GH3536 superalloy under different process parameters. Our results find that the interaction time between the laser heat source and powder layer decreases as the scanning speed increases, which results in a decrease in the size of the molten pool; the photothermal action area increases with the increase of laser power, which results in an increase in the area of molten pool. For multi-layer multi-track printing, we used a laser power of 190 W, scanning speed of 1.08 m/s, and a scanning distance of 90 μm, which can remelt the deposited metal and eliminate some of the pores from the previous printed layer.