DED 공정을 이용한 인코넬 718 대체적 적층 시 경로 의존 잔류응력 특성분석

Abstract

Directed Energy Deposition (DED) processes selectively dissolve and solidify the material using a high density energy source to produce a desired product. In the DED processes a sudden variation of the thermal history, including rapid heating and cooling in taken place in the vicinity of the deposited region. the sudden variation of the thermal stress causes an excessive residual stress in the vicinity of the deposition region. The residual stress provokes undesired deformation and premature cracking of the fabricated part. The residual stress increased when the deposition volume augmented. In order to overcome these problems, it is necessary to analyze residual stress characteristics during the deposition of material using DED process. The goal of this thesis is to investigate on the effects of the deposition strategy on residual stress characteristics in a large volume deposition of Inconel 718 using a DED process. Various candidate deposition strategies were selected through the investigation of previous research works. In order to select appropriate deposition strategies, repeated thermo-mechanical analyses were performed for thin-layer depositions. Using the results of thermo-mechanical analyses for thin-layer depositions, two appropriate deposition strategies and two comparative deposition strategies for a large volume deposition were obtained. In addition, an optimum deposition strategies for a large volume deposition was estimated from the comparison of residual stress distributions for different deposition strategies. Large volume deposition experiments were carried out to obtain thermal histories during the deposition using the DED process. In order to obtain a proper thermo-mechanical analysis model, thermal histories of thermo-mechanical analyses were compared to those of experiments. Finally, the influence of preheating temperature on residual stress distributions was examined to obtain a proper preheating temperature of the substrate.