Inconel 718 (IN718) is a nickel-based superalloy that exhibits excellent tensile and impact resistant properties along with good corrosion resistance at high temperatures. Due to the work hardening property of IN718, the machinability of this superalloy is low , which paves a path to adopt the selective laser melting (SLM) process to fabricate IN718. SLM process is governed by process parameters like hatch spacing, scan speed, layer thickness, scan pattern and laser power. This variation in these parameters shall influence the microstructural properties. The various scan patterns adopted for this study are chess, stripes, flow-optimized, and customized scan strategy. These various scan patterns shall cause a variation in the area of the heat-affected zones to change the temperature gradient, which thereby determines the grain size ranging from equiaxed to elongated. There is a difference between the magnitude of thermal gradients generated between the lower layers and top-most layers during the build process. As the microstructure of the part is dependent on the thermal intensity between the layers, it is necessary to study the effect of scan strategy on the microstructure. The study focuses on the effect of the variation in scan patterns on the microstructure of the part.
Inconel 718 (IN718), a nickel-based superalloy, is commonly used in rocket nozzles and turbines. Conventional manufacturing of complex IN718 geometries is difficult due to its high stiffness values. Consequently, Additive Manufacturing (AM) methods like selective laser melting (SLM), offers a viable solution for the fabrication of parts using IN718 with high accuracy. One of the limitations of this technique is its need for supports in order to fabricate overhanging structures. These supports need to be designed carefully and tend to consume a significant amount of resources. In this research, we studied the angled structures fabricated without supports. The overhangs were fabricated using uniform process parameters for varying thicknesses. Microstructural and hardness analyses were carried out to determine variations in melt pools and Vickers hardness. The outcome of this study will help us in predicting the need for supports in overhangs and inclined structures used within a part having complex geometry.
The introduction and development of additive manufacturing (AM) has led to rapid rise in the innovative design and fabrication of lightweight metallic porous structures. This fabrication technique removes the difficulties presented by conventionally manufactured porous structures. Characteristics of conventionally manufactured porous include simple shapes and high cost because of its complicated manufacturing processes such as roll forming, brazing, and resistance welding. Porous structures with different levels of porosity offer customized mechanical properties, reduction in weight, and material quantity while improving functionality and hence can fulfill the demand for lightweight structures compared to a solid structure. Typically, the structures have high equivalent stiffness, strength, energy absorption, and heat dissipation. This concept is applied in various fields like medical and aerospace for its lightweight property. In this project, CAD models are developed with different porous structures, including BCC, BCC-Z, FCC, FCC-Z, Gyroid, Schwartz, and Diamond. The parts are then fabricated on an EOS M290 metal printer using Inconel 718 powder material. Detailed microstructure and mechanical characterization were carried out in order to obtain an in-depth understanding of the cellular parts with same level of porosity, but different porous structure. This study provides an insight on how to effectively choose the porosity type in a way to maximize the functionality of cellular structures for a specific application.
Additive manufacturing is a modern manufacturing technique that provides extreme design freedom and ability to manufacture multiple parts with high complexities at the same time. Various fabrication techniques have been developed and this study focuses on selective laser melting (SLM) due to its ability to provide near-perfect complex parts at low cost, while being able to work with a wide range of materials. In SLM, the part is manufactured layer-by-layer, by melting and solidification of powder material under controlled inert conditions. The fabrication of complex geometries is not possible without proper allocation of support structures for the part, which keeps the component intact and retains structural stability while manufacturing. Supports are attached to the part and are to be removed after fabrication in such a way that the required surface finish is not compromised. The challenge is to provide appropriate support structures after analyzing the part and the part orientation while ameliorating the functionality of removability, reducing material consumption, and enhancing structural support. Inconel 718 is a type of high-strength corrosion resistant super alloy, which consists of nickel and chromium. It can withstand extremely high pressure and heat which makes it suitable for high-end applications such as aerospace and petroleum. This study focuses on the surface topography for Inconel 718 parts after the removal of various support structures. A comprehensive report on optimal support structure design is provided after studying the fundamental parameters from design, fabrication, and testing phases. Varying the support structure design resulted in a range of surface qualities.
Selective laser melting (SLM) is an additive manufacturing technique designed to use a high power-density laser to melt and fuse metallic powder to fabricate complex parts with high accuracy. The accuracy and the functional properties of the fabricated part are greatly dependent on the process parameters. Thus, depending on the desired properties and the material, the parameters need to be optimized before fabrication. The processing parameters that control the SLM process comprise of the laser power, scan speed, hatch spacing, layer thickness and scan strategy. These process parameters are dependent on each other and therefore make the task of optimizing the process parameters an important one. This research is concerned with the optimization of several process parameters as well as the development of a model to predict the best properties for Inconel 718 superalloy. This study uses the Design of Experiment (DOE) system coupled with the full factorial Composite Central Design (CCD) of the Response Surface Methodology (RSM) to perform the regression analysis on laser power, scanning speed, and hatch spacing in order to predict the CAD model deviation, hardness values, and, variation in the phase composition using X-ray Diffraction (XRD). The simulated models obtained using the RSM technique were then analyzed. These results provided valuable information and helped us in controlling the functional properties of the fabricated part.
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