Microstructural Characterization of 3D Deposited Metal Structures

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Solomon, Jordan
Materials Science , Electrodeposition , Additive Manufacturing , Selective Laser Melting , 316L Stainless Steel , Transmission Electron Microscopy , Scanning Electron Microscopy , Transmission Kikuchi Diffraction , Electron Backscatter Diffraction , Nickel , Crystallography , Crystallographic Texture , Materials Characterization , Microstructure
The microstructure of deposited materials is characterized using a variety of techniques. The two specific types of deposited materials studied are electrodeposited nickel and additive manufactured stainless steel. A focus is on utilizing optimal cross-sectional characterization techniques to observe the microstructure, where optimal refers to the length scale being probed and the cost of preparation and characterization methods. Techniques ranging from optical transmission electron microscopy are used. Three different length scales of electrodeposited nickel are observed, and a set of 16 SLM processed 316L stainless steel weld tracks are observed. The largest length scale nickel material is a commercially available foam, likely produced by electroplating nickel onto a sacrificial polymer template. The foam was prepared for EBSD using modification to standard metallography techniques. The average grain size was 5.73 µm with a random texture, suggesting a heat treatment used to remove the polymer template. Secondly, we studied mesoporous nickel samples. A measure of particle size as well as deposition layer thickness was performed using ImageJ in conjunction with SEM imaging. The smallest microstructural length scale of nickel materials was a set of nanostructured electrode catalysts. The grain size seen in the deposition layers was in the hundreds of nanometers, and an overall growth texture in the {112} direction was observed. The 316L stainless steel weld tracks were polished using standard metallographic techniques and etched in oxalic acid. This revealed a cellular structure. The cell sizes of two weld tracks were measured in ImageJ and compared with their applied energy densities. It was found that the track with the lower energy density had a slightly smaller cell size, the sizes being 4.7 ± 1.5 µm and 6.2 ± 1.2 µm respectively. An EBSD map of one weld track was also taken, illustrating the directional growth of SLM processed grains.
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