다층적층 된 금속재료의 결함 방지를 위한 손상저감층 설계에 관한 연구

Abstract

One of hot issues of the manufacturer for the hot forging die is the improvement of the operation life through the diminution of the failure of the die. The hot forging die is damaged by mixed failure modes including the wear, the thermal crack, the impact crack, the corrosion crack, etc.. Hence, in order to extend the operation life of the hot forging die, the development of the diminution technology of the mixed failure modes is needed. Recently, the multi-layer deposition technology using the metal three-dimensional printing process is introduced as an alternative technology for the diminution of the mixed failure modes. The objective of this research work is to investigate the design of the damage diminution layer (DDL) for the prevent of defects of multi-layer deposition metallic materials. Through the literature survey, Hestelloy X, SUS304 and P21 are chosen as the candidated material of the DDL. Two types of the DDL designs are chosen as a reference design of the DDL according to assignment of the DDL in the multi-layer deposited region. In order to obtain proper material and thickness of the DDL, heat transfer and thermal stress analyses are performed using ABAQUS V6.12. In order to carry out the heat transfer and thermal stress analyses, temperature dependent material properties are used. From the results of the heat transfer and thermal stress analyses, influence of the material and the thickness of the DDL on thermal stress-strain distributions in the vicinity of the multi-layers deposited region and the deviation of major stress and strain in boundary regions of different materials are investigated. Through the results of the investigation, appropriate material and thickness of the DDL are estimated. In order to obtain a proper assignment design of the DDL in the multi-layers deposited region, thermal fatigue experiments are carried out. Two types of specimens, including Type A and B, are designed according to the assignment of the DDL. Those specimens are fabricated from a laser-aided direct metal rapid tooling process and a post-processing. The morphology of the specimens is observed using a optical microscope, a micro-focus X-ray computed tomography system and a scanning electron microscope. From the results of the observation, the Type A design with the DDL between the hardfaced layer and the thermal stress control layer is determined as an appropriate assignment design of the DDL.