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Directed Energy Deposition에서 흄의 생성 원인 및 대책
김강형,정찬현,정대용,현승균 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.6
Pores and cracks are known as the main defects in metal additive manufacturing (MAM), including directed energy deposition(DED). A gaseous fume is often produced by laser flash (instantaneous high temperature) during laser processing, which may cause various defects such as porosity, lack of fusion, inhomogeneity, low flowability and composition change, either. However the cause and harmful effects of fume generation in DED are known little. In laser processing, especially laser welding, many studies have been conducted on the prevention of fume because it generates defects that hinder uniform reactions between the laser beam and the materials. Generally, the fume occurs with easily vaporizing low melting point components or sensitive oxidizing elements. Unsuitable conditions are also known to have an effect, including laser power, travel speed, powder feed rate and shielding gas supply. Practically, there are many more fume generating factors in the DED process, and the lack of understanding requires a lot of trial and error. In this article the laser-related and weld metallurgy literatures were reviewed, focusing on the prevention of fume in powder DED. The causes of the fume, were explained to result from the stages of cavitation bubbles generated by the laser induced plasma and the nanoparticles released. Additionally, the effects of alloying components and environmental conditions for fume generation in the DED process were investigated, and suggestions are proposed to prevent fume.
권동일,김강형,김진관,이성훈,윤재홍 國立 昌原大學校 産業技術硏究所 1994 産技硏論文集 Vol.8 No.-
0.1V강의 표면경도를 향상시키기 위해서 Boronizing처리를 실시하여 Hv=1500∼2000의 높은 경도값을 나타내는 붕화물층을 얻었다. 붕화물층의 두께와 처리시간과의 사이에는 방물선관계를 나타내었으며 붕화물층 생성 겉보기 활성화에너지는 94kJ/mol이다. 또한 900˚C, 3시간 침붕처리했을 때가 가장 높은 경도분포값을 나타내었으며 그 이상 장시간 처리하면 오히려 경도가 감소하는 경향을 나타낸다. 그리고 침붕층은 20% HCl, 20% H₂SO₄용액에서는 뛰어난 내식성을 가지나, 20% HNO₃용액에 대해서는 상대적으로 내식성이 떨어졌다. 그리고 내고온산화성은 대기중 800˚C까지는 침붕처리한 시편이 우수했으나 900˚C부터는 오히려 감소했다. To improve the surface hardness of the 0.1V steel, by Boronizing Treatment, We got boride layer showing high hardness, Hv=1500∼2000. A parabola relationship was appeared between boride layer thickness and treatment time, and apparent activation energy to form the boride layer 94kJ/mol. Moreover, We obtained the most high hardness distribution value when had the boronizing treatment for 3 hours at 900˚C. On the contrary, If we did boronizing treatment above 3 hours, the hardness appeared decreasing tendency. The boride layer had a good corrosion resistance at a solution of 20% HCl and 20% H₂SO₄, but correlatively the corrosion resistance of the boride layer was declined at a solution of 20% HNO₃. And the boronized specimen had a good high temperature oxidation resistance until 800˚C in the atmosphere but the high temperature oxidation resistance go down above 900˚C.
마찰력과 열처리에 따른 아크용사 및 아크용접된 Fe-Cr-B 합금 피복층의 변화
이찬규,유인석,김강형,구본흔,박맹로 國立 昌原大學校 産業技術硏究所 1995 産技硏論文集 Vol.9 No.-
Variations of arc thermal sprayed and arc welded Fe-Cr-B alloy coating with frictional loading and heat treatment were investigated by means of X-ray diffraction, optical microscopy, scanning electron microscopy, electron probe microanalysis and hardness test. The as-coated layers were shown to be crystalline state but peaks with the frictional loading largely disappeared in X-ray diffraction profiles. The splat is relatively wavy with the boundary in arc thermal spray coating. After heat treatment, the amount of porosity was found to be decreased and the intersplat distance was increased. As annealing temperature increased, interface layer for arc welding coating increased by the diffusion of Cr atoms. The wear type observed in arc thermal spray coatings is splat delamination. The hardness of the arc thermal spray coation layer was superior to that of the arc welding layer. Hardness of coated layer is reduced and microstructures become to be uniformed by the heat treatment.