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질소가스를 이용한 Ti-6Al-4V의 레이저 표면 질화처리
황태우(T. W. Hwang),김재현(J. H. Kim),우영윤(Y. Y. Woo),길태동(T. D. Kil),문영훈(Y. H. Moon) 한국소성가공학회 2015 한국소성가공학회 학술대회 논문집 Vol.2015 No.5
Surface nitriding of Ti-6Al-4V can be achieved by laser melting in a flow of nitrogen gas, and high surface hardness values could be obtained. In this study, the effect of process parameters on surface nitriding of a Ti-6Al-4V alloy has been investigated to achieve higher surface hardness without process-induced cracks. The effects of process parameters were experimentally studied and process window is provided on the basis of microstructure, microhardness, and cracking of the nitride layers. It is shown that hardened layers having various depth and hardness can be obtained by controlling the processing parameters. High scanning speed coupled with lower nitrogen flow rate results in crack-free layer at the expense of both a lower hardness and a shallower melt depth.
변형공정지도를 이용해 Gd가 듀플렉스 스테인리스 강에 미치는 영향
박성환(S. H. Park),길태동(T. D. Kil),오일영(I. Y. Oh),우영윤(Y. Y. Woo),문영훈(Y. H. Moon) 한국소성가공학회 2016 한국소성가공학회 학술대회 논문집 Vol.2016 No.4
In this study, cracking susceptibility of PREN 50 grade duplex stainless steel is predicted by using deformation processing map. To develop deformation processing map, dynamic materials model has been used on the basis of Gleeble compression test. Deformation processing map indicating η(the efficiency of power dissipation) which means how efficiently applied power dissipated through microstructural evolution. During compression test, unit deformation volumes in specimen have different microstructure ratio because they are deformed at different working conditions. To predict cracking susceptibility, quantitative index has been suggested. As a quantitative index, summation of η multiplied by unit deformation volume fraction has been produced. For the validation of quantitative index, the predicted condition has been experimentally compared.
Direct Laser Melting 공정시 분말 형태가 적층 품질에 미치는 영향
이성훈(S. H. Lee),길태동(T. D. Kil),박준영(J. Y. Park),한상욱(S. W. Han),문영훈(Y. H. Moon) 한국소성가공학회 2016 한국소성가공학회 학술대회 논문집 Vol.2016 No.4
Direct laser melting(DLM) process is an additive manufacturing process that can produce parts by solidification of molten metallic powder layer by layer. The properties of fabricated parts strongly depend on characteristics of metallic powder. Atomized powders having spherical morphology have commonly been used for DLM process. Mechanical ball-milling is a powder processing technique involving repeated cold welding, and re-welding of powder particles in a high-energy ball mill. Mechanical ball-milling can provide non-spherical powders in solid state without melting. The aim of this study is to investigate the performance of powder morphologies on the deposition quality in DLM process. To characterize the morphological effect, the performances of respective powders, both mechanical ball-milled and atomized powders have been compared through single- and multi-track DLM experiments. Single-track melting tests were performed at various laser process parameters such as laser power and scan rate, and the deposition quality were compared. For the multi-track melting tests, quadrangle structures were fabricated by DLM using metallic powders made by both mechanical ball-milling and atomizing. The surface roughness, cross-section bead shape and process defects such as balling or non-filled area were compared and discussed in this study.