| 초록 |
Recently, direct energy deposition (DED), also referred to as 3D printing, is new emerging manufacturing process which enables fabrication of three-dimensional complex shaped metal products and structures. Distinct from powder bed fusion (PBF), DED allows for multiple powder suppliers, providing unique opportunities for functionally graded parts with respect to material type and/or amount in real time. Additive manufacturing is similar to the combination of welding and directional solidification. Welding has a cracking problem in the case of material that has poor weldability and directional solidification also has a cracking problem if the material has poor castability. When it comes to additive manufacturing, it is basically welding of layer by layer and because of the substrate as a heat sink, directional solidification happens. It contains the features of welding and directional solidification both, so liquation and solidification cracking can happen if the material has poor printability. Therefore, about the additive manufacturing, i.e. matal 3D printing, it is safe to say that improving printability from hot cracking is the most important thing. Even though IN738 alloy shows notable strength and oxidation resistance behavior in high-temperature among the Ni-based superalloy, hot-cracking behavior resulting from poor weldability is the detrimental factor on the application of metal 3D printing. This study aims the clarification of effects of oxygen with the oxide formation or oxygen enrichment on the microstructure and hot cracking behavior during DED. For the experiment, gas-atomized IN738 alloy powder was used. The microstructure of manufactured samples was observed by using a scanning electron microscope with EDS and EBSD. as a results, since the surrounding microstructure at crack showed its characteristic, it is expected that could be the additional key to clarify the mechanism of hot-cracking behavior. |
