• 한국의류산업학회지
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• 제4권6호
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• pp.564-566
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• 2002

Protective clothing for firefighters typically consists of a flame resistant outer shell and inner layers. The inner layers are generally composed of a moisture barrier and a thermal barrier. On performing the task in fire place the heat and perspiration generated from the body become trapped inside the protective clothing. Those heat and moisture result into heat-stress and physical fatigue of fire fighter, which hinder the work. Therefore, the system of clothing designs and material layers must be chosen carefully to balance protection and comfort. 3 kinds of protective clothing of 3 layer structure were used in the experiment of physiological comfort. From the comparison of wear trials with the 3 kinds of layers in firefighters clothing, it indicates that the moisture dissipation of A+B2+C was highest, following A+BI+C andA+B3+C. And the heat dissipation of A+BI+C and A+B2+C were better than A+B3+C. In the protective clothing with A+B3+C, heat and perspiration generated through exercise remained in clothing system long and caused discomfort.

• 한국주조공학회지
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• 제16권2호
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• pp.141-148
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• 1996

In high chromium cast iron, the control of matrix microstructure as well as carbide structure is important to the performance as a wear resistant material. In this study, 3.0% C-24.0% Cr white cast irons with various molybdenum contents(residual, 1.0%, 3.0% and 5.0%) were solidified conventionally and unidirectionally for studying their effects on the microstructure and hardness. In the conventional casting, two sets of castings were poured from each melt. One set of the castings consisted of cylindrical bars of 10 and 20mm by 155mm long. The second set of the castings was a cylindrical bar of 30mm by 200mm long. On the other hand, a pep-set mold set on the Cu plate was employed to make the solidification unidirectionally. X-ray diffraction method was used to observe retained austenite and carbides in the high chromium cast iron. The morphology of eutectic $M_7C_3$ carbides changed from needle-like type to nodular type with the increase of Mo content. And, the presence of $M_2C$ carbides was identified in the sample where Mo was added over 3.0 %. Primary and eutectic carbides appeared as rod type and corngrain type, respectively in the unidirectionally solidified samples which were cut to parallel to the solidification direction. In the EDX analysis, Cr concentration was higher in the primary and eutectic $M_7C_3$ carbides, Mo in the $M_2C$ carbides, and Fe in the matrix.

• 한국산학기술학회논문지
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• 제6권2호
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• pp.110-115
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• 2005

표면 경화가 요구되는 소재에 코발트계 합금 분말을 용사 소모재로 하고 플라즈마 트랜스퍼드 아크(PTA) 용사 공정을 이용하여 표면 개질부를 제조하였다. 표면 개질부는 다른 용사 변수는 일정하게 유지한 상태에서 용사 전류만을 변화하여 제조하였다. 용사 전류를 80에서 140 amp까지 20 amp씩 증가하면서 개질층을 제조하였다. 두께가 일정한 모재에 전류를 변화하여 표면 개질층을 제조하는 경우 용사후 모재에서 발생하는 냉각 효과가 다르게 되고 이는 개질층의 폭과 두께 등의 기하학적 형상과 미세 조직, 그리고 미세경도 등의 특성에 영향을 미치는 것으로 나타났다. 용사 전류를 120amp로 사용한 경우 미세조직이 조밀하고 미세경도 값이 가장 높은 값을 나타내는 개질층을 얻을 수 있었다. 전류를 증가함에 따라 개질층의 폭은 증가하지만 높이는 큰 변화가 없는 것으로 나타났다.

• 한국재료학회지
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• 제12권4호
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• pp.308-316
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• 2002

The cavitation erosion behavior of wear-resistant hardfacing alloys such as Co-base Stellite 6, Fe-base Norem 02 and new Fe-base alloy were investigated up to 50 hours by using a 20kHz vibratory cavitation erosion test equipment. The crack, initiated easily at the interfaces between matrix and hard second phase, was repressed effectively in Stellite 6 because the matrix was hardened by phase transformation. For this reason, Stellite 6 showed an excellent cavitation erosion resistance compared to Norem 02. The phase transformation also occurred in Norem 02, but the increase of volume fraction of the interfaces caused the crack to be initiated frequently, thus resulting in a 1arge material loss. The matrix of NewAlloy was hardened effectively by vlongrightarrow$\alpha$' phase transformation and the volume fraction of the interfaces was very small compared to Norem 02. This caused the propagation of crack to the matrix to be repressed effectively. Therefore, NewAlloy showed a very excellent cavitation erosion resistance. It wasn't considered that the cavitation erosion resistance of NewAlloy was influenced the temperature of the bath filled with a distilled water up to $80^{\circ}C$.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
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• pp.7-11
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• 2012

Plasma electrolytic oxidation of magnesium alloys is a well known technique to produce corrosion and wear resistant coatings. The addition of particles to the electrolyte provides a possibility to produce coatings with an increasing range of composition by in-situ incorporation of those particles into the coating. An extensive literature review has revealed that the mode of incorporation depends mainly on the melting point of the used particles and the energy provided by the discharges of the PEO process. The spectrum ranges from inert to partly reactive incorporation, but a complete reactive incorporation and a formation of a new single phase coating was not observed so far. Thus a new approach in PEO processing is introduced using specific particles as a kind of sintering additive, changing not only the composition but lowering the melting temperature and increase the liquid phase fraction during the discharges, resulting in a new amorphous coating.

• Corrosion Science and Technology
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• 제10권4호
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• pp.143-150
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• 2011

Copper electroplating has been applied to various fields such as decorative plating and through-hole plating. Technical realization of high strength copper preplating for wear-resistant tools and molds in addition to these applications is the aim of this work. Brighters and levelers, such as MPSA, Gelatin, Thiourea, PEG and JGB, were added in copper sulfate electrolyte, and the effects of these organic additives on the hardness were evaluated. All additives in this work were effective in increasing the hardness of copper electrodeposits. Thiourea increased the hardness up to 350 VHN, and was the most effective accelarator in sulfate electrolyte. It was shown from the X-ray diffraction analysis that preferred orientation changed from (200) to (111) with increasing concentration of organic additives. Crystallite size decreased with increasing concentration of additive. Hardness was increased with decreasing crystallite size, and this result is consistent with Hall-Petch relationship, and it was apparent that the hardening of copper electrodeposits results from the grain refining effect.

• 한국주조공학회지
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• 제17권4호
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• pp.393-401
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• 1997

Commercial flake graphite cast iron substrate was coated with titanium powder by low pressure plasma spraying and was irradiated with a $CO_2$ laser to produce the wear resistant composite layer. From the experimental results of this study, it was possible to composite TiC particles on the surface layer by direct reaction between carbon existed in the cast iron matrix and titanium with thermal sprayed coating by remelting and alloying them using laser irradiation. The cooling rate of laser remelted cast iron substrate without titanium coating was about $1{\times}10^4$ K/s to $1{\times}10^5$ K/s in the order under the condition used in this study. The microstructure of alloyed layer consisted of three zones, that is, TiC particule crystallized zone (MHV $400{\sim}500$), the mixed zone of TiC particule+ledebulite (MHV $650{\sim}900$) and the ledebulite zone (MHV $500{\sim}700$). TiC particules were crystallized as a typical dendritic morphology. The secondary TiC dendrite arms were grown to the polygonized shape and were necking. And then the separated arms became cubic crystal of TiC at the slowly solidified zone. But in the rapidly solidified zone of fusion boundry, the fine granular TiC particules were grouped like grape.

• 한국표면공학회지
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• 제26권6호
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• pp.316-326
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• 1993

Adhesion and hardeness are the most important properties of a hard coated layer which is applied to wear-resistant devices. Zr/ZrN layer was deposited on tool steel(SKH9) and stainless steel(SUS304) by a re-active D.C. magnetron sputtering technique and their microhardness and adhesion strength were measured for the films processed by changing the partial pressures of $N_2$ gas (4~10$\times$$10^{-4}$mbar) and the substrate bias voltage(0~250V). The adhesion strength was evaluated by acoustic signals through the scratch-test with the incremental applied load. As the partial pressure of $N_2$ gas and the substrate bias voltage were increased, the adhesion strength of tool steel was observed to be stronger than that of the stainless steel. The adhesion strength was generally, observed to decrease with the same tendency regardless of the kinds of substrates. The adhesion strength of tool steel was increased more and more strongly than that of stainless steel as heat-treated temperature was increased. The strength of tool steel was appeared to be high adhesion strength at $400^{\circ}C$. From the failure mode of the film during the scratch adhesion test, the cohesive failure was observed to be obvious and the adhesive failure in a minor portion in the Zr/ZrN doublelayer regardless of the kinds of substrates.

• 대한금속재료학회지
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• 제50권11호
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• pp.809-815
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• 2012

Recently, as the interest in improving energy efficiency has grown, the demand for vehicle and machine parts that are resistant in high temperature corrosive conditions and abrasive environments has increased. Pack chromizing treatment of sintered steels is a profitable method that satisfies both corrosion resistance and low friction properties. Since austenitic stainless steels have good corrosion resistance but low mechanical hardness, if they are replaced by sintered steel parts with pack chromizing treatment, all the desirable properties such as low price, easy molding, high hardness, low frictional coefficient, and high corrosion resistance, can be obtained. The higher corrosion resistance of the chromized parts over that of the austenitic stainless steels was acquired by coating chromium carbides and a thin chromium oxides layer on the surface. Moreover, the surface morphology of chromized parts, which were composed of chromium rich phases and hardened chromium carbides by diffusing and alloying, had a peak-and-valley shape so that the dimple effect by the wrinkled morphology and high hardness induced a low friction coefficient.

• 한국재료학회지
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• 제10권10호
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• pp.703-708
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• 2000

최근에 상용차용 디젤 엔진의 성능 향상을 목적으로 엔진 설계가 급격히 변화되면서 캠 팔로우어(cam follower)와 캠(cam) 사이에 작용하는 접동면 하중의 증가로 접동면에서의 마모가 중요한 문제가 되고 있다. 본 연구에서는 기존의 주절체 및 소결합금 캠 팔로우어에 비해 내마모성이 우수한 세라믹 캠 팔로우어를 개발하였다. 잔류 응력을 완화시켜주는 중간층을 사용하지 않고 질화규소($Si_3N_4$) 팁과 중탄소강을 활성납재를 사용하여 직접 접합후 냉각시키는 과정에서 두 모재의 열팽창계수차에 의한 크라우닝(crowning, R) 이 형성되도록 하였다. 접합에 사용한 중탄소강은 열팽창시 이력(hysteresis) 거동을 나타내었으며, $A_{c1}$ 변태점인 $723^{\circ}C$ 이하에서 접합할 경우 원하는 크라우닝이 형성되었다. 접합온도가 $723^{\circ}C$ 이상이 되면 크라우닝 (R) 값이 온도에 따라 지수함수적으로 증가하였으며 이는 중탄소강의 상변태에 의한 열팽창.수축의 이력 특성으로 설명되어질 수 있었다. 규격에 맞는 크라우닝이 형성되는 최적 접합 온도는 $700~720^{\circ}C$의 범위였다. 질화규소와 중탄소강의 직접 접합방법으로 접합과 동시에 크라우닝을 형성시키고 제어함으로써 난가공재인 세라믹을 곡면 가공하지 않고도 적당한 곡률을 갖는 저가의 세라믹 캠 팔로우어를 제조할 수 있었다.