• 한국주조공학회지
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• 제37권3호
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• pp.63-70
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• 2017

In the present study, effects of an addition of Sn on the microstructure and corrosion behavior were investigated in Mg-4%Zn-(0-3)%Sn casting alloys. With an increase in the Sn content, the ${\alpha}-(Mg)$ dendritic cell size was reduced, whereas the total amount of precipitates increased due to the formation of the $Mg_2Sn$ phase. It was found in immersion and electrochemical corrosion tests that the addition of Sn has a detrimental effect on the corrosion resistance of the Mg-4%Zn alloy. Microstructural examinations of the corrosion product and the corroded surface indicated that an accelerated micro-galvanic effect by the $Mg_2Sn-phase$ particles and a less protective corrosion product on the surface were responsible for the increased corrosion rate at a higher Sn content.

• 한국생산제조학회지
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• 제23권2호
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• pp.152-156
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• 2014

Lightweight materials such as aluminum and magnesium have recently received much attention in the automotive industries because of environmental and fuel-efficiency concerns. Using the powder metallurgy (PM) process for these materials creates significant opportunities for the cost-effective manufacture of lightweight automotive parts. In the present study, an Al-Cu-Mg alloy was fabricated using conventional PM processes. Primarily, the effects of the alloying elements on the sintering characteristics and mechanical behavior after heat treatment were investigated. A microstructural analysis was performed using an optical microscope and a scanning electron microscope to investigate the behavior of liquid phase sintering, including the formation of precipitates. The dependence of the mechanical behavior on the alloying elements was evaluated based on the transverse rupture strength.

• 한국세라믹학회지
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• 제29권4호
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• pp.273-282
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• 1992

The effects of intrinsic and extrinsic gettering on the formation of microdefects in the wafer and on the electrical performance at near-surfaces of three different oxygen-bearing Czochralski silicon single crystal wafers were investigated by varying the combinations of the pre-heat treatments and the phosphorus diffusion through the back-surface of the wafers. The wafers which had less than 10.9 ppma of oxygen formed no gettering zones irrespective of any pre-heat treatments, while the wafers which had more than 14.1 ppma of oxygen and were treated by Low+High pre-heat treatments generated the gettering zone comprising oxygen precipitates, staking faults, and dislocation loops. The effects of extrinsic gettering by phosphorus diffusion were evident in all samples such that the minority carrier lifetimes were increased and junction leakage currents were decreased. However, the total gettering effects among the different pre-heat treatments did not necessarily correspond to the gettering structure revealed by synchrotron radiation section topograph.

• 한국주조공학회지
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• 제32권4호
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• pp.181-189
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• 2012

The microstructures of self-designed 7000 series Aluminium alloys added with Sc are observed. Moreover, the mechanical properties of the Sc-added Aluminium alloys are evaluated as a function of tensile temperature to establish the conditions of a following extrusion process. New casting conditions in the aluminium alloys added with Sc could be established by changing the casting speed and stirring time in the existing casting conditions of Aluminium alloys. The Sc addition results in $Al_3(Sc,Zr)$ precipitates in the cast alloys, and leads to the formation of equal-axed grains and fine grains. After homogenization heat treatment at $450^{\circ}C$, the Sc-added Aluminium alloys showed the highest elongation values in the temperature ranging from $300{\sim}400^{\circ}C$.

• 한국해양공학회지
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• 제11권3호
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• pp.48-55
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• 1997

The steel for automotive exhaust system needs a good corrosion resistance at the atmosphere of high temperature NaCl. Effect of the alloying elements Me, Ti, Nb on the NaCl induced hot corrosion behavior was investigated at the temperatures between 55$0^{\circ}C$ and 75$0^{\circ}C$ for 18Cr ferritic stainless steels. The weight loss by corrosion has increased linearly with corrosion cycle time, and the corrosion rate has accelerated at higher temperature. The alloying of Mo significantly improved corrosion resistance of the steel and the effect was more pronounced at higher temperature. The addition of alloying elements Ti, Nb have also shown improved corrosion resistance by formation of Ti(C,N) or Nb(C, N) precipitates.

• 열처리공학회지
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• 제9권4호
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• pp.229-233
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• 1996

This work has been carried out to reduce the softening of heat affected zone on laser surface alloying. Iron based rapid solidification material with $Cr_{5-10}$, $V_{1-3}$, $Mo_{3-7}$, $W_{2-5}$, $B_{7-8}$, $C_{2-3}$, $Si_{0.5-1}at%$ was alloyed on the surface of SM45C steel. The excellent softening resistance in alloyed and heat affected zone showed, which could be attributed to the formation of stable high temperature precipitates.

• 대한의용생체공학회:의공학회지
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• 제15권4호
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• pp.389-394
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• 1994

The age-hardening behavior and the structural changes in a commercial dental Au-Ag-Cu-Pd alloy were investigated by means of hardness test, optical and scanning electron microscopic observation, energy dispersive spectroscopy and X-ray diffraction study. The drastic reduction in hardness by prolonged aging occurred after a rapid increase in hardness at the initial stage by the isothermal aging at $350^{\circ}C$. This softening was due to the broad precipitates formation of the lamellar structure which was composed of the f.c.t. AuCu I ordered f.c.t. phase containing Pd and the f.c.c. Ag-rich $\alpha$1 solid solution f.c.c.phase containing Au.

• Journal of Advanced Marine Engineering and Technology
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• 제14권1호
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• pp.83-89
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• 1990

Electrochemical methods have been proposed as non-destructive, rapid and quantitative means for determining the degree of sensitization associated with Chromium depleted zones surrounding precipitates of Cr carbide and formation of secondary phase in stainless steel. In this study, the specimen of AISI 304 stainless steel and its welded sections, which welded by TIG, MIG, $CO_2$ and ARC, were tested corrosion resistance by electrochemical methods in 0.5N HCl and 1N $H_2SO_4$ with or without 0.01N KSCN. The results were confirmed that electrochemical methods could be used as a test method of corrosion resistance evaluation for the welded AISI 304 stainless steel.

• 한국재료학회지
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• 제7권2호
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• pp.129-135
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• 1997

용탕단조법에 의해 제조된 Mg-6AI-xZn(x=0,1,2)합금의 기계적 성질에 미치는 시효열처리의 영향을 조사하였다. 주조상태에서의 미세조직은 초정 Mg고용체, 과포화된 상태의 Mg상, 응고과정에서 형성된 $\beta(Mg_{17}AI_{12}$)화합물 등 3개의 상으로 구성되어 있었다. 용체화처리 수 $200^{\circ}C$및 $240^{\circ}C$에서 시효열처리한 결과 Mg-6AI-xZn(x=0,1,2)합금은 $\beta$ 석출물에 의한 피크 경도값이 나타났으며, 석출물의 형태는 $200^{\circ}C$에서는 lamella 형태의 불연속 석출물이, $240^{\circ}C$에서는 미세분산분포된 연속석출물의 형태를 보였다. 용탕단조방법에 의해 제조된Mg-6AI-xZn합금의 기계적 성질은 사형주조법에 비해 인장강도 및 연신율에서 우수한 특성을 보였으며 Zn의 첨가량이 증가함에 따라 Zn의 고용강화 효과에 따라 강도값이 증가되었다.

• 자원환경지질
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• 제52권6호
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• pp.519-528
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• 2019

본 논문에서는 2017년 경주시 내남면 용장리 트렌치 단면에서 퇴적층을 관찰할 때 고려해야하는 토양화 과정과 지하수의 유동에 기인하여 나타나는 특성을 기술하였다. 지표로부터 굴착된 트렌치 단면은 토양화 과정과 지하수 유동에 의한 흔적을 포함하고 있어 퇴적학자들의 관찰에 영향을 줄 수 있다. 이 사이트 토양은 비교적 초기단계의 토양화 과정에 있어서 퇴적층의 특징을 관찰하는데 크게 어려움을 주지 않으나, 퇴적층리 관찰을 가장 어렵게 하는 요인은 지하수의 이동에 따른 망간산화물과 철산화물의 침전이었다. 지하수면을 따라 형성된 이 침전물은 퇴적층의 경계면에 형성되어 있기도 하고, 지하수면의 위치 또한 접하고 있는 퇴적층의 입자 크기에 따라 달라지므로 여러 위치에서 침전물이 관찰되었다. 또 이들 지하수면 상하부에서는 각기 철의 산화환원 상태에 따라 색변화가 관찰되므로 퇴적층 기술에 주의가 요구된다. 미세기공을 통해 모세관 현상으로 상부로 이동하는 지하수에 의해 일부 세립질 퇴적층이 지하수면 수 미터 상부까지 환원상태를 유지하면서 환원철 상태를 지시하는 색을 띠기도 하였다.