• 한국표면공학회지
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• 제37권1호
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• pp.40-48
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• 2004

Hardness and internal stress are very important in nickel electroforming. Nickel sulfamate bath has been widely used in electroforming because of its low internal stress and moderate hardness. Nickel sulfamate bath without chloride was chosen to investigated the effect of plating variable such as temperature, PH, current density and sodium naphthalene trisulfonate as addition agent on the hardness and internal stress. It was found that hardness increased with increasing temperature and decreasing current density and ranged from 150∼310 DPH. The hardness was highest at $55^{\circ}C$ and 10∼40 mA/$\textrm{cm}^2$. The internal stress increased with increasing current density and decreasing temperature. It was minimum at PH 3.0∼3.8. Low internal stress within $\pm$1,500 psi was obtained at both $50^{\circ}C$ and $55^{\circ}C$ in 10-20 mA/$\textrm{cm}^2$. The addition of sodium naphthalene trisulfonate was found to be effective in refine columnar grains thus resulted in decreasing internal stress, increasing hardness and improving brightness.

• 한국재료학회지
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• 제28권3호
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• pp.174-181
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• 2018

Three kinds of STS304-Zr alloys were fabricated by varying the Zr content, and their microstructure and fracture properties were analyzed. Moreover, we performed heat treatment to improve their properties and studied their microstructure and fracture properties. The microstructure of the STS304-Zr alloys before and after the heat treatment process consisted of ${\alpha}-Fe$ and intermetallics: Zr(Cr, Ni, Fe)2 and Zr6Fe23. The volume fraction of the intermetallics increased with an increasing Zr content. The 11Zr specimen exhibited the lowest hardness and fine dimples and cleavage facets in a fractured surface. The 15Zr specimen had high hardness and fine cleavage facets. The 19Zr specimen had the highest hardness and large cleavage facets. After the heat treatment process, the intermetallics were spheroidized and their volume fraction increased. In addition, the specimens after the heat treatment process, the Laves phase (Zr(Cr, Ni, Fe) 2) decreased, the Zr6Fe23 phase increased and the Ni concentration in the intermetallics decreased. The hardness of all the specimens after the heat treatment process decreased because of the dislocations and residual stresses in ${\alpha}-Fe$, and the fine lamellar shaped eutectic microstructures changed into large ${\alpha}-Fe$ and spheroidized intermetallics. The cleavage facet size increased because of the decomposition of the fine lamellar-shaped eutectic microstructures and the increase in spheroidized intermetallics.

• 한국주조공학회지
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• 제41권5호
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• pp.411-418
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• 2021

Ni 혹은 Cu 첨가에 따른 고규소 고용강화 페라이트계 구상흑연주철의 기계적 성질과 미세조직 변화를 실험적으로 확인하기 위해, Ni 및 Cu 투입량을 3.0wt% 이내 그리고 0.9wt% 이내에서 조절하여 시편단위 사형주조를 진행하였다. 실험 결과 고용강화 페라이트계 구상흑연주철 내 Ni 혹은 Cu 함량이 증가하면 합금 내 강도 특성과 경도가 증가하였고 연성은 감소하였다. 한편, 합금 내 Ni 및 Cu 함량이 비슷한 경우, Ni이 포함된 고용강화 페라이트계 구상흑연주철보다 Cu가 포함된 합금이 더 높은 펄라이트 분율을 나타내었다. Ni이 포함된 고용강화 페라이트계 구상흑연주철의 미세조직에 미치는 기계적 성질의 경우에는 펄라이트 분율이 10% 이내 일 때 강도, 경도, 연신율이 우수하였으나, 펄라이트 분율이 10% 이상 증가할 경우 급격한 연신율 감소를 나타내었다. 한편, Cu가 첨가된 고용강화 페라이트계 구상흑연주철의 경우에는 펄라이트 분율 증가에 따라 강도와 경도는 점점 증가하였으며 연신율은 점점 감소하는것을 확인하였다. 고용강화 페라이트계 구상흑연주철 내 첨가원소에 따른 이러한 미세조직과 기계적 성질 차이는 Cu 대비 Ni의 낮은 펄라이트 안정화 효과와 첨가원소 함량에 따른 기지상 강화효과 차이가 복합적으로 작용하였기 때문으로 판단된다.

• Journal of Welding and Joining
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• 제12권4호
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• pp.102-109
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• 1994

The thick and hard alloyed layer was formed on the surface of Aluminum Cast Alloy(AC2B) by PTA overlaying process with Cr, Cu and Ni metal powders under the condition of overlaying current 150A, overlaying speed 150mm/min and different powder feeding rate 5-20g/min. The characteristics of hardening and were resistance of alloyed layer have been investigated in relation to microstructure of alloyed layer. As a result, it was made clear that Cu powder was the most superier one in three metal powders used due to an uniform hardness distribution of Hv 250-350, good wear resistance and freedom from cracking in alloyed layer of which microstructure consisted of hypereutectic. On the contrary, irregular hardness distribution was usually obtained in Cr or Ni alloyed layers of which hardness was increased as Cr or Ni contents and reached to maximum hardness of about Hv 400-850 at about 60wt% Cr or 40wt% Ni in alloyed layer. However the cracking occurred in these alloyed layers with higher hardness than Hv 250-300 at more than 20-25wt% of Cr or Ni contents in alloyed layer. Wear rate of alloyed layer was decreased to 1/10 in Cu alloyed layer and 1/5 or 1/3 in Cr or Ni alloyed layer with same hardness of about Hv 300 in comparison with that of base metal at higher sliding speed.

• 한국재료학회지
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• 제26권3호
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• pp.130-135
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• 2016

To alloy high melting point elements such as boron, ruthenium, and iridium with copper, heat treatment was performed using metal oxides of $B_2O_3$, $RuO_2$, and $IrO_2$ at the temperature of $1200^{\circ}C$ in vacuum for 30 minutes. The microstructure analysis of the alloyed sample was confirmed using an optical microscope and FE-SEM. Hardness and trace element analyses were performed using Vickers hardness and WD-XRF, respectively. Diffusion profile analysis was performed using D-SIMS. From the microstructure analysis results, crystal grains were found to have formed with sizes of 2.97 mm. For the copper alloys formed using metal oxides of $B_2O_3$, $RuO_2$, and $IrO_2$ the sizes of the crystal grains were 1.24, 1.77, and 2.23 mm, respectively, while these sizes were smaller than pure copper. From the Vickers hardness results, the hardness of the Ir-copper alloy was found to have increased by a maximum of 2.2 times compared to pure copper. From the trace element analysis, the copper alloy was fabricated with the expected composition. From the diffusion profile analysis results, it can be seen that 0.059 wt%, 0.030 wt%, and 0.114 wt% of B, Ru, and Ir, respectively, were alloyed in the copper, and it led to change the hardness. Therefore, we verified that alloying of high melting point elements is possible at the low temperature of $1200^{\circ}C$.

• 한국분말재료학회지
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• 제3권3호
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• pp.188-195
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• 1996

In recent times the potential application of the high speed steel produced by HIP process for wear resistant and cutting materials are increasing. In this work the microstructure of Anval 30 produced by HIP process was investigated and the effect of WC, TiC addition on microstructure formation and wear properties were studied. After HIP process at 1150 $^{\circ}C$, the original feature of spherical raw powders was not removed and consequently, nonuniform microstructure was formed. However the WC added by simple powder mixture incereased the sinterbility of high speed steel and uniform microstructure formed. The wear characteristics of Anval 30 with carbide addition were tested at RT and $600^{\circ}C$. The uniform microstructure played an more important role in wear resistance as compared with the hardness.

• 한국분말재료학회지
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• 제21권4호
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• pp.271-276
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• 2014

15Cr-1Mo base oxide dispersion strengthened (ODS) steel which is considered to be as a promising candidate for high- temperature components in nuclear fusion and fission systems because of its excellent high temperature strength, corrosion and radiation resistance was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Torsion tests were performed at room temperature, leading to two different shear strain routes in the forward and reverse directions. In this study, microstructure evolution of the ODS steel during simple shearing was investigated. Fine grained microstructure and a cell structure of dislocation with low angle boundaries were characterized with shear strain in the shear deformed region by electron backscattered diffraction (EBSD). Grain refinement with shear strain resulted in an increase in hardness. After the forward-reverse torsion, the hardness value was measured to be higher than that of the forward torsion only with an identical shear strain amount, suggesting that new dislocation cell structures inside the grain were generated, thus resulting in a larger strengthening of the steel.

• 한국분말재료학회지
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• 제22권1호
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• pp.32-38
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• 2015

The effect of heat treatment environment on the microstructure and properties of tantalum coating layer manufactured by kinetic spraying was examined. Heat treatments are conducted for one hour at $800^{\circ}C$, $900^{\circ}C$, and $1000^{\circ}C$ in two different environments of vacuum and Ar gas. Evaluation of microstructure and physical properties are conducted. High density ${\alpha}$-tantalum single phase coating layer with a porosity of 0.04% and hardness of 550 Hv can be obtained. As heat treatment temperature increases, porosity identically decreases regardless of heat treatment environment (vacuum and Ar gas). Hardness of heat treated coating layer especially in Ar gas environment deceases from 550 Hv to 490 Hv with increasing heat treatment temperature. That in vacuum environment deceases from 550 Hv to 530 Hv. The boundary between particles became vague as heat treatment temperature increases. Oxygen distribution of tantalum coating layer is minute after heat treatment in vacuum environment than Ar gas environment.

• 한국표면공학회지
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• 제35권3호
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• pp.133-140
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• 2002

The Ti-Si-N coating layers were synthesized on SKD 11 steel substrate by a DC reactive magnetron co-sputtering technique with separate Ti and Si targets. The high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analyses for the coating layers revealed that microstructure of Ti-Si-N layer was nanocomposite, consisting of nano-sized TiN crystallites surrounded by amorphous $Si_3$$N_4$ phase. The highest hardness value of about 39 GPa was obtained at the Si content of ~11at.%, where the microstructure had fine TiN crystallites (about 5nm in size) dispersed uniformly in amorphous matrix. As the Si content in Ti-Si-N films increased, the TiN crystallites became from aligned to randomly oriented microstructure, finer, and fully penetrated by amorphous phase. Free Si appeared in the layers due to the deficit of nitrogen source at higher Si content. Friction coefficient and wear rate of the Ti-Si-N coating layer significantly decreased with increase of relative humidity. The self-lubricating tribe-layers such as $SiO_2$ or (OH)$Si_2$ seemed to play an important role in the wear behavior of Ti-Si-N film against steel.

• 소성∙가공
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• 제14권1호
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• pp.71-77
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• 2005

Thermal stability and dry sliding wear behavior of ultra-fine grained 6061 Al alloy fabricated by an accumulative roll-bonding (ARB) process have been investigated. After 4 ARB cycles, an ultra-fine grained microstructure of the 6061 Al alloy composed of grains with average size of 500nm, and separated mostly by high-angle boundaries was obtained. Though hardness and tensile strength of the ARB processed Al alloy increased with ARB cycles up to 4 cycles, the processed alloy exhibited decreased ductility and little strain hardening. Thermal stability of the ARB-processed microstructure was studied by annealing of the severely deformed alloy at $423K{\sim}573K$. The refined microstructure of the alloy remained stable up to 473K, and the peak aging treatment of the alloy at 450K for 8 hrs increased the thermal stability of the alloy. Sliding-wear rates of the alloy increased with the number of ARB cycles in spite of the increased hardness with the cycles. Wear mechanisms of the ultra-fine grained alloy were investigated by examining worn surfaces, wear debris, and cross-sections by a scanning electron microscopy (SEM).