• 열처리공학회지
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• 제9권4호
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• pp.289-299
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• 1996

This study has been performed to investigate into some effects of power density and traverse speed of laser beam on the microstructure, hardness and residual stress of AISI 4140 treated by laser surface hardening technique. Optical micrograph has shown that large martensite and a small amount of retained austenite in outermost surface layer and fine lath martensite in inner surface hardened layer are formed under the condition of a given power density and traverse speed. Hardness measurements have revealed that as the power density increases at a given 2.0m/min of the traverse speed, the maximum hardness values of outermost surface hardened layer is increased from Hv=635 to Hv=670. X-ray analysis for residual stress has exhibited that low compressive residual stress values are obtained in center point of the cress section of surface hardened layer with in mid point between the edge and the center point, about 1.5mm from the center point, due simply to a difference in self-quenching rate. It has been shown that the higher the power density at a given traverse speed and the olwer the traverse speed at a given power density, the more the compressive residual stress values are increased due to an increase in the input heat of laser beam.

• 열처리공학회지
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• 제16권6호
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• pp.329-334
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• 2003

Microstructure and mechanical properties of $(Ti_{1-x}Alx)N$ films, Produced by the the Ion Beam Sputtering(IBS) method, were studied by changing the Ti, Al contents. The compositions of films determined by RBS were $(Ti_{0.75}Al_{0.25})N$, $(Ti_{0.61}Al_{0.39})N$ and $(Ti_{0.5}Al_{0.5})N$, and XPS binding energies of Ti2P, A12p and N1s shifted to higher energies than those of pure Ti, Al and N, which indicated that nitrides were formed. XRD results indicated that the NaCl structure for $$x{\leq_-}0.39$$ changed into amorphous structure at x=0.5. For films with $$x{\leq_-}0.39$$, the lattice parameter decreased in proportion to the Al content. Nanoindentation hardness value were above HV=3300 at Al content up to x=0.39. However, the hardness of films with x=0.5 abruptly decreased to HV=1800, and this lower hardness values were attributed to different crystal structure. Critical load(Lc) in scratch test showed 23N at x=0.25, 22N at x=0.39 and 22N at x=0.5, which indicated that films with different Al contents showed similar adhesion behavior.

• 한국분말재료학회지
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• 제22권3호
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• pp.181-186
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• 2015

In this study, the effect of the friction stir welding (FSW) was compared with that of the gas tungsten arc welding (GTAW) on the microstructure and microhardness of Cu-Ni alloy weldment. The weldment of 10 mm thickness was fabricated by FSW and GTAW, respectively. Both weldments were compared with each other by optical microstructure, microhardness test and grain size measurement. Results of this study suggest that the microhardness decreased from the base metal (BM) to the heat affected zone (HAZ) and increased at fusion zone (FZ) of GTAW and stir zone (SZ) of FSW. the minimum Hv value of both weldment was obtained at HAZ, respectively, which represents the softening zone, whereas Hv value of FSW weldment was little higher than that of GTAW weldment. These phenomena can be explained by the grain size difference between HAZs of each weldment. Grain size was increased at the HAZ during FSW and GTAW. Because FSW is a solid-state joining process obtaining the lower heat-input generated by rotating shoulder than heat generated in the arc of GTAW.

• 한국재료학회지
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• 제26권10호
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• pp.513-520
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• 2016

The effect of NaOH concentration on the properties of electrolytic plasma processing (EPP) coating formed on AZ61A Mg alloy is studied. Various types of EPP were employed on magnesium alloy AZ61A in a silicate bath with different concentrations of NaOH additive. Analysis of the composition and structure of the coating layers was carried out using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that the oxide coating layer mainly consisted of MgO and $Mg_2SiO_4$; its porosity and thickness were highly dependent on the NaOH concentration. The Vickers hardness was over 900 HV for all the coatings. The oxide layer with 3 g/l of NaOH concentration exhibited the highest hardness value (1220 HV) and the lowest wear rate. Potentiodynamic testing of the 3 g/l NaOH concentration showed that this concentration had the highest corrosion resistance value of $2.04{\times}10^5{\Omega}cm^2$; however, the corrosion current density value of $5.80{\times}10^{-7}A/cm^2$ was the lowest such value.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.726-731
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• 2002

Reaction synthesis is a process to form ceramics, intermetallics and their composites from elemental powder mixture. Application of this process to a surface modification techniques has a possibilities to enable the process at a lower temperature or for a shorter time, although synthesized materials are likely to include voids and unreacted elements. This paper intend to examine the effect of Si addition to the mixture of Al and Ni on the densification of synthesized Ni-Al intermetallic compounds and to evaluate the surface properties of obtained coatings. By the Si addition, exothermic reaction temperature to form Ni-Al intermetallic was lowered to be below the melting point of Al. Si soluted $Al_3$Ni$_2$, $Al_3$Ni and $Al_{6}$Ni$_3$Si were mainly formed in the coating layer when powder mixture was heated to 973K for 300s. Besides, densification was enhanced by increasing hot press pressure, Si additions and heating rate. When the composition of eutectic Al-Si reaches 78%, void ratio of sintered compact reduced to 0.4%. It is caused by higher flowability of Al-Si liquid phase generated and its infiltration into the void. Since the hardness of NiAl(Si) compound (about 600HV) formed in the coating layer is higher than that of Ni-Al compound (about 400HV), coating layer with high density and superior wear property is obtained by hot press using reaction synthesis from Al-Ni-Si powder mixture.

• 한국결정성장학회지
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• 제27권5호
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• pp.229-234
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• 2017

본 연구에서는 자동차 터보차저(turbo charger)용 터빈휠을 제조하기 위하여 고속원심주조법을 이용하여 TiAl 합금을 주조하였다. 여러 가지 조성의 주형을 사용하여 주조결함이 최소화 되는 최적의 몰드 조건을 찾고자 하였으며, 주조된 TiAl 합금의 결정구조와 미세조직을 고찰하였다. TiAl 샘플의 XRD 분석 결과 ${\gamma}$-TiAl 상과 ${\alpha}_2-Ti_3Al$ 상으로 구성되어 있음을 확인하였으며, 광학현미경과 FE-SEM 분석을 통하여 TiAl 샘플은 6-fold 및 4-fold 대칭성으로 이루어진 두 개의 수지상(dendrite) 형태로 이루어져 있음을 확인할 수 있었다. 또한 샘플의 단면에서 표면과 가까운 지점과 내부에서 측정한 원소함량의 차이를 확인할 수 있었으며, 마이크로비커스 경도계를 이용하여 표면에서 $50{\mu}m$ 미만의 영역에서 경도상승 영역 alpha-case 층이 형성되었음을 확인하였다.

• 비파괴검사학회지
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• 제33권2호
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• pp.212-218
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• 2013

A transfer method of neutron radiography was developed to measure the size of the end plug and a gap of an intact K102L-2, the irradiated fuel of a ballooned K174L-3, a ballooned and ruptured K98L-3. A typical irradiation time of 25 min. was determined to obtain a film density of between 2 and 3 of SR X-ray film with neutrons of $1.5{\times}10^{11}n{\cdot}cm^{-2}$. To validate and calibrate the results, a RISO fuel standard sample, Cd plate and ASTM-BPI/SI were used. An activated latent image formed in the $100{\mu}m$ Dy foil was subsequently transferred in a dark room for more than 8 hours to the SR film which is a maximum of three half-lives. Due to the L/D ratio an unsharpness of $9.82-14{\mu}m$ and a magnification of 1.0003 were given. After digitizing an image of SR film, the ballooning gap of the plug was discernible by an H/V filter of image processing. The gap size of the ballooned element, K174L-3, is equal to or greater than 1.2 mm. The development of a transfer method played a pivotal role in developing high burn-up of Wolsung and PWR nuclear fuel type.

• 한국지하수토양환경학회지:지하수토양환경
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• 제18권4호
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• pp.50-57
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• 2013

For the last couple of decades, the Fenton (-like) systems have been extensively studied for oxidation of organic contaminants in water. Recently, zero-valent iron (ZVI) has received attention as a Fenton catalyst as well as a reducing agent capable of producing reactive oxidants from oxygen. In this study, the ZVI-based Fenton reaction was assessed for the oxidative degradation of phenol using $ZVI/O_2$, $ZVI/H_2O_2$, ZVI/Oxalate/$O_2$ and hv/ZVI/Oxalate/$O_2$ systems. Reaction parameters such as pH and reagent dose (e.g., ZVI, $H_2O_2$, and oxalate) were examined. In the presence of oxalate (ZVI/Oxalate/$O_2$ and hv/ZVI/Oxalate/$O_2$ systems), the degradation of phenol was greatly enhanced at neutral pH values. It was found that ZVI accelerates the Fenton reaction by reducing Fe(III) into Fe(II). The conversion of Fe(III) into Fe(II) by ZVI was more stimulated at acidic pH than at near-neutral pH values.

• Journal of Advanced Marine Engineering and Technology
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• 제22권5호
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• pp.660-669
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• 1998

In this paper the Hardness and Electro-chemical corrosion of the Nimonic 80A superalloy were studied. It aging heat treatments was carried out at $650^{\circ}C$, $700^{\circ}C$, $750^{\circ}C$,$800^{\circ}C$ and $850^{\circ}C$ with different time of 20min , 30min 1hour, 2hours, 4hours, and 16hours additionally 64hours and 128hours at $650^{\circ}C$. The obtained results were as follows; 1. As aging temperature increased the time for the maximum hardness was reduced from 128hours at $650^{\circ}C$ to 30min at $850^{\circ}C$ whereas the highest hardness was reduced from Hv 381 at $650^{\circ}C$ to Hv 321 at $850^{\circ}C$. 2. In the Electro-chemical corrosion test as a function of aging heat treatment time and tem-perature the corrosion potential was reversely proportional to Hardness which indicated the effects of ${\gamma}/{\gamma}'$ coherency of base material and precipitate. 3. Initiation point of the pitting was observed at grain boundary twin boundary and near${\gamma}'$ pre-cipitates. The results of composition analysis by EDS at this point indicated that sulphur originat-ed from 1N $H_2SO_4$ solution was found in depletion at the grain boundaries and the pit which arouse in the near precipitates were lack of Al Ti and Ni which are the main element of ${\gamma}'$ The depletion of such element was cause breakdown of passive film.

• 한국진공학회지
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• 제6권1호
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• pp.1-8
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• 1997

SUS 316 합금의 노출 조건에 따른 오염 과정과 구조를 x-ray photoelectron spectroscopy실험을 통해 보았다. SUS표면에 부착된 오염 물질은 주로 metal-oxide, metal-H-oxide, CO, COH, 그리고 CxHy임을 보았다. 오염 물질의 층별 형성 구조는 $C_xH_y$/CO(COH)/metal-H-oxide/metal-oxide가 SUS합금 위에 있는 형태이다. 오염 과정은 주로 금속 구성물의 산화와 $C_xH_y$의 흡착과정 두 가지에 의해서 이루어지는 것을 볼 수 있 었다. 초고진공 환경에서는, 오염은 주로 산화층 형성에 의한 것으로 노출 시간이 증가함에 따라 산화층의 두께가 계속 증가하였다. 고진공 또는 높은 압력 환경에서는 노출 초기에 대 부분의 산화층이 형성되고, 노출 시간의 증가에 대해서는 주로 $C_xH_y$에 의한 오염이 계속 증 가하였다. 스테인레스 표면 안에 깊이 분포하고 있는 metal-oxide의 농도는 지수형으로 감 소하는 형태의 분포를 가지며 그 두께는 대기 노출된 시료의 경우 광전자의 평균자유행로 규모로 형성되는 것을 보았고, 특히 Fe-oside가 Cr-oxide를 덮고 있는 표면 편석 현상이 보 였다.