• 한국분말재료학회지
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• 제17권6호
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• pp.477-481
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• 2010

Cu-Sn based alloys were manufactured by gas atomization spray casting route in order to achieve a fine scale microstructure and a high tensile strength. The spray cast Cu-10Sn-2Ni-0.2Si alloy had an equiaxed grain microstructure, with no formation of brittle ${\delta}-Cu_{41}Sn_{11}$ phase. Aging treatment promoted the precipitation of finely distributed particles corresponding to ${\delta}-Ni_2Si$ intermetallic phase throughout the $\alpha$-(CuSn) matrix. The cold-rolled Cu-Sn-Ni-Si alloy had a very high tensile strength of 1200 MPa and an elongation of 5%. Subsequent aging treatment at $450^{\circ}C$ for 1h slightly reduced the tensile strength to 700 MPa and remarkably increased the elongation up to 30%. This result has been explained by coarsening the precipitates due to over aging and reducing the dislocation density due to annealing effects.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.299-302
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• 2005

Semisolid A356 slurries were prepared by electromagnetic stirring casting and by inoculation of Al-5Ti-B master alloy. As stirring time and addition of Al-5Ti-B are different, the grain size of the primary phase is different. Through the experiment of rheocast in a Buhler horizontal die casting machine, it was found that the finer the equiaxed primary dendrites, the smoother the die filling and better cast quality. Small equiaxed primary dendrite also results in less liquid segregation on the surface.

• 한국재료학회지
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• 제9권7호
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• pp.657-662
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• 1999

기판온도 $320^{\circ}C$에서 알루미나 기판 위에 형성한 NTC 써미스터용 Mn-Ni계 산화물 박막의 산소가스 농도 변화와 막 형성 후 열처리에 따른 미세구조, 결정상 비저항, B정수 변화에 관하여 연구하였다. 미세구조는 주상 구조(columnar structure)를 지녔으며 열처리 온도가 증가함에 따라 $700^{\circ}C$ 부근에서 등축 결정립 (equiaxed grain) 형태의 미세구조로 바뀌기 시작하였다. 박막의 결정상은 대부분 입방 스피넬 (cubic spinel) 상과 입방 $Mn_2$$O_3$, 상이 공존하였으며 산소농도 0.16%~0.7%의 경우 $800^{\circ}C$에서 열처리하였을 때 입방 스피넬 상만이 존재하였다. 분위기 산소의 농도가 증가함에 따라 비저항과 B정수도 급격하게 감소하다가 다소 증가하였으며, $600^{\circ}C$-$700^{\circ}C$ 로 열처리할 경우 이 값들이 대체로 낮고 안정된 특성을 보였다.

• 열처리공학회지
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• 제34권1호
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• pp.17-24
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• 2021

In this study, Ti-X (X=Mn, Fe, Mo) powder alloys were designed and manufactured by both powder metallurgy (PM) and metal powder injection molding (MIM) process to improve strength and formability compared to CP-Ti powder materials. It was found that the lamellar microstructure consisted of α and β phases was formed in PM-processed alloys. However, MIM-processed alloys showed not the lamellar microstucture but the equiaxed α + β microstructure. It was also revealed that the contents of X component and feedstock were not affected to microstructure evolution. The reason why different microstructure was appeared between PM-processed and MIM-processed alloys is not clear yet, but supposed to be the effect of intersticial elements such as C, H and N derived from feedstock during debinding process of MIM.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2009년도 춘계학술대회 논문집
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• pp.177-181
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• 2009

Compositional gradient CrNx coatings were fabricated using arc ion plating in Ar/$N_2$ gaseous mixture by gradually increasing $N_2$ flux rate from 0 to 120 SCCM. The effect of negative substrate bias on the film microstructure and mechanical properties were systematically investigated with XRD, GDOES, and SEM. The results show that substrate bias has an important influence on film growth and microstructure of gradient CrNx coatings. The coatings mainly crystallized in the mixture of hexagonal $Cr_{2}N$ and fcc CrN phases. By increasing substrate bias, film microstructure evolved from an apparent columnar structure to an equiaxed one. With increasing substrate bias, deposition rate first increased, and then decreased. The maximum of deposition rate was 15 nm/min obtained at a bias of -50V.

• 소성∙가공
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• 제18권6호
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• pp.476-481
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• 2009

The present work demonstrates the mechanical and electrical responses of submicrocrystalline Cu-3%Ag alloy as a function of strain imposed by equal channel angular pressing(ECAP). From transmission electron microscope observation, the resulting microstructures of Cu-3%Ag alloy deformed by ECAP for 8-pass or more consist of reasonably fine, equiaxed grains without having a strong preferred orientation, suggesting that microstructure evolution is slower than that of pure-Al and its alloys owing to low stacking fault energy. The results of room temperature tension tests reveal that, as the amount of applied strain increases, the tensile strength of submicrocrystalline Cu-3%Ag alloy increases whereas losing both the ductility and the electrical conductivity. Such phenomenon can be explained based on microstructure featured by the non-equilibrium grain boundaries.

• 열처리공학회지
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• 제35권3호
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• pp.150-158
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• 2022

The effects of scandium addition on the Al-6Si-2Cu Alloy were investigated. The Al-6Si-2Cu-Sc alloy was prepared by gravity die casting process. In this study, scandium was added at 0.2 wt%, 0.4 wt%, 0.8 wt%, and 1.0 wt%. The microstructure of Al-6Si-2Cu-Sc alloy was investigated using Optical Microscope, Field Emission Scanning Electron Microscope, Electron Back Scatter Diffraction, and Transmission Electron microscope. The microstructure of Al-6Si-2Cu alloy with scandium added changed from dendrite structure to equiaxed crystal structure in specimens of 0.4 wt% Sc or more, and coarse needle-shape eutectic Si and β-Al₅FeSi phases were segmented and refined. The nanosized Al₃Sc intermetallic compound was observed to be uniformly distributed in the modified Al matrix.

• Journal of Welding and Joining
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• 제30권2호
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• pp.70-75
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• 2012

In this study, effect of nitrogen volume in the shielding gas of Ar-$N_2$ mixing gas on the bead shape, hardness and microstructure of GTA welds of 3mm thick Commercial Pure Ti was investigated. As the nitrogen volume increased, the welding current for full penetration was reduced and hardness in the fusion zone significantly increased compared with that of the base metal, but there is no difference in the hardness of HAZ. Microstructure in the fusion zone with pure Ar gas changed from equiaxed alpha of the base metal to serrated alpha. On the other hand, microstructure using Ar-$N_2$ mixing gas changed to acicular alpha. With the increasing of nitrogen content, the amount of acicular alpha increased and the size of that was fine.

• 한국해양공학회지
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• 제26권6호
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• pp.27-32
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• 2012

The effects of reheating during welding on the microstructure and impact toughness of weld metal in 25% Cr super duplex stainless steels were investigated. Using different heat inputs, weld metals with different reheated regions were obtained. This showed that, depending on the reheating temperature, the microstructure in the reheated region was quite different from that of the as-deposited microstructure. When reheated into the ${\gamma}+{\alpha}$ temperature range, fine intragranular austenite was formed in the as-deposited columnar structure. However, when reheated above the ${\alpha}$ solvus temperature range, most of the columnar structure disappeared and fine equiaxed austenite and ferrite were formed. Because of the larger amount of fine austenite in the reheated region, a higher impact toughness was obtained in the weld metal with a higher amount of reheated region.

• 열처리공학회지
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• 제31권2호
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• pp.56-62
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• 2018

Many researchers have studied on the precipitation control after solution treatment to improve the damping capacity without decreasing the strength. However, studies on the damping capacity and microstructure changes after deformation in the solid solution strengthening alloys were inadequate, such as the Al-Zn series magnesium alloys. Therefore, in order to investigate the effect of annealing condition on microstructure change and damping a capacity of AZ61 magnesium alloy. In this study, it was confirmed that the microstructure changes affect the damping capacity and hardness when annealed AZ61 alloy. AZ61 magnesium alloy was rolled at $400^{\circ}C$ with rolling reduction of 30%. These specimens were annealed at $350^{\circ}C$ to $450^{\circ}C$ for 30-180 minutes. After annealing, microstructure was observed by using optical microscopy, and damping capacity was measured by using internal friction measurement machine. Hardness was measured by Vickers hardness tester under a condition of 0.3 N. In this study, static recrystallization was observed regardless of the annealing conditions. In addition, uniform equiaxed grain structure was developed by annealing treatment. Hardness is decreased with increasing grain size. This is associated with Hall-Petch equation and static recrystallization. In case of damping capacity, bigger grain size show the larger damping capacity.