내부 격자구조를 가지는 모재에 직접에너지적층 공정으로 적층된 이종소재에 관한 연구

Abstract

Recently, additive manufacturing approaches for manufacturing complex structures have been used to manufacture components with lattice structures. This study investigated the deposited materials and interface characteristics exhibited when directed energy deposition(DED) was performed on a substrate with a lattice structure. The heat transfer on the substrate during DED was studied for two types of substrates(solid and lattice samples). Temperature-monitoring experiments demonstrated that the lattice substrate underwent rapid heating(during DED) and cooling(after DED). The rapid heating of the lattice substrate increased the temperature of the melting pool, thereby affecting the layer creation. Therefore, in the transition zone formed in the lattice sample, excellent fusion occurred at the interface between the substrate and deposited layer. In addition, the rapid cooling of the lattice substrate induced the formation of a dense microstructure and inhibited the formation of the Laves phase. Bending tests were performed to assess the adhesion of the deposited interface in relation to the substrate conditions. Cracks in the deposited layer of the lattice sample penetrated the substrate after crossing the interface, however, they did not propagate along the interface. In contrast, in the solid sample, a crack generated at the surface propagated to the interface, and separation between the deposited layer and substrate was observed. A wear test was performed to evaluate the mechanical properties of the deposited material according to the substrate. As a result, the latte sample showed excellent wear characteristics. Even in the latte sample, the double-layered latte sample has the best wear characteristics. The fast cooling speed shown in the heat transfer experiment increased the average hardness of the deposited material. This moderated the coefficient of friction measured during the wear test. Therefore, the amount of wear loss was the most reduced, and the width and width of the wear track were the narrowest of the three specimens. The surface of the wear track of the double-layered lattice sample was the cleanest and softest. In the end, it shows that even if the same heterogeneous material is deposited, it has better wear resistance in the case of a lattice sample. As a result of the tensile test of the sample including the substrate-deposited material interface, all samples had soft fracture. The fracture position of most samples was the base material. This is because the substrate material(STS316L) has weaker mechanical strength than the deposited material(Inconel 718), and is a flexible material. However, all lattice samples were broken at the substrate, but some solid samples were broken because the interface was separated. This is because no transition zone occurred in the solid sample. Therefore, the relatively weak interface bonding caused the crack to occur at the interface. And some of the deposits came off. As a result of the tensile test of a sample processed with only the deposited material, the top-layer lattice sample with the highest surface hardness has the best yield strength. This is because the rapid cooling rate of the substrate controlled the generation of laves phase. In addition, high-temperature melt pool suppressed the production of defects in the deposited material. Therefore, plastic deformation occurred at the highest yield strength. These results indicated that the lattice sample had excellent interface bonding properties. This suggests that the application of an inner lattice structure for a substrate can produce excellent metallurgical and mechanical properties in the deposited material.