• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2214-2218
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• 2007

The effects of bath temperature on electrochemical behavior, alloy composition, crystallographic structure, morphology and the magnetic properties of electrodeposited Co-Pt-W(P) films were investigated. Electrochemical studies show that alloy electrodeposition has been shifted to more positive potentials and the critical time for nucleation decreased as electrolyte temperature increased. As the temperature increased from 40 oC to 80 oC, tungsten content in the deposit increased, while phosphorus content decreased. The films deposited at T = 40 oC exhibited soft magnetic properties. However, electrodeposited at T = 70 oC, the films exhibited hard magnetic properties. It is also demonstrated that higher temperature more than 70 oC could weaken hard magnetic properties. XRD results indicated that the deposits obtained at 50 oC-70 oC showed enhancement of [00.1] P.O. (preferred orientation) with the bath temperature, which resulted in the stronger perpendicular magnetic anisotropy.

• 동력기계공학회지
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• 제12권3호
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• pp.66-71
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• 2008

Diamond-like-carbon (DLC) coatings could be good candidates as solid lubricants for cutting tools in dry machining of aluminum alloy. In this work, DLC thin films were produced as a friction reduction coating for WC-Co insert tip using the plasma immersion ion beam deposition (PIIED) technique. DLC coatings were also coated on $Al_2O_3$ specimens and high temperature wear tested up to $400^{\circ}C$ in dry air to observe the survivability of the DLC coating in simulated severe cutting conditions using a pin-on-disc tribotester with Hertzian contact stress of 1.3GPa. It showed reduced friction coefficients of minimum 0.02 up to $400^{\circ}C$. And cutting performance of DLC coated WC-Co insert tips to Al 6061 alloy were conducted in a high speed machining center. The main problems of built-up edge formation in aluminum machining are drastically reduced with improved surface roughness. The improvements were mainly related to the low friction coefficient of DLC to Al alloy and the anti-adhesion of Al alloy to WE due to the inertness of DLC.

• 한국표면공학회지
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• 제50권3호
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• pp.147-154
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• 2017

This research was conducted to investigate the electrochemical properties of the thin air-formed oxide film-covered AZ31 Mg alloy. Native air-formed oxide films on AZ31 Mg alloy samples were prepared by knife-abrading method and the changes in the electrochemical properties of the air-formed oxide film were investigated in seven different electrolytes containing the following anions $Cl^-$, $F^-$, $SO{_4}^{2-}$, $NO_3{^-}$, $CH_3COO^-$, $CO{_3}^{2-}$, and $PO{_4}^{3-}$. It was observed from open circuit potential (OCP) transients that the potential initially decreased before gradually increasing again in the solutions containing only $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions, indicating the dissolution or transformation of the native air-formed oxide film into new more protective surface films. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) showed that there was growth of new surface films with immersion time on the air-formed oxide film-covered specimens in all the electrolyte. The least resistive surface films were formed in fluoride and sulphate baths whereas the most protective film was formed in phosphate bath. The potentiodynamic polarization curves illustrated that passive behaviour of AZ31 Mg alloy under anodic polarization appears only in $CO{_3}^{2-}$, or $PO{_4}^{3-}$ ions containing solutions and at more than $-0.4V_{Ag/AgCl}$ in $F^-$ ion containing solution.

• 한국재료학회지
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• 제4권5호
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• pp.535-540
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• 1994

Thin film magnet was fabricated by radio frequency magnetron sputtering using $Nd_13/(Fe.Co)_{70}B_{17}$ alloy target and magnetic properties were investigated according to sputtering conditions from the metallurgical point of view. we could obtain the best preferred orientation of $Nd_2Fe_{14}B$ phase at substrate temperatures between $450^{\circ}C$ and $460^{\circ}C$ with the input power 150W, and thin films had the anisotropic magnetic properties. But, as the thickness of thin film increased, the c-axis orientation gradually tended to be disordered and magnetic properties also become isotropic. Just like Nd-Fe-B meltspun ribbon, the microstructure of thin film magnet was consisted of very find cell shaped $Nd_2Fe_{14}B$ phase and the second phase along grain boundary. While, domain structure showed maze patterns whose magnetic easy axis was was perpendicular to film plane of thin film. It was concluded from these results that the perpendicualr anisotropy in magnetization was attributed to the perpendicular alignment of very find $Nd_2Fe_{14}B$ grains in thin film.

• 한국표면공학회지
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• 제29권6호
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• pp.628-633
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• 1996

Large saturation magnetization $4pM_s$ is essentially required for soft magnetic thin layers used in magnetic recording devices. Amorphous Co-based alloys and Fe-Co alloys may be regarded as one of the candidates for soft magnetic materials which possess large $4\piM_s$. Some preparation process to improve soft magnetism of these films were performed in this study. Addition of Ta seemed to be effective to change the magnetostriction constant $\lambda$ from positive value to negative one. The magnetoelastic energy $K_e$ is strongly dependent on $\lambda$. $(Co_{95.7}Zr_{4.3})_{100-x}Ta_x$ films with $K_e$ of negative value have sufficiently soft magnetic characteristics. $Fe_{90}Co_{10}$ alloy exhibits extremely large $4\piM_s$, of about 24 kG. Addition of N and Ta to $Fe_{90}Co_{10}$ films improved the soft magnetism of them. The $Fe_{82.0}Co_{7.6}Ta_{10.4}$:N/Ti multilayered films exhibit better soft magnetic properties and better thermal stability than Fe-Co-Ta:N singlelayer films.

• 한국자기학회지
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• 제11권5호
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• pp.184-188
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• 2001

DC-스퍼터를 이용하여 기판온도를 실온과 20$0^{\circ}C$로 변화시켜 , 균일한 내부구조를 갖는 구조와 결정립내부에 미세한 자가정렬나노구조(SONS)를 갖는 Co-22%Cr 합금 박막을 각각 제조하고 이들의 미세구조와 도메인구조를 투과전자현미경(TEM)과 자기력현미경(MFM)을 이용하여 확인하였다. Co가 먼저 부식되도록 조치하고 관찰한 투과전자현미경 결과, 실온에서 제작된 박막의 경우에는 결정립 내부가 균일한 조성을 보인 반면, 기판온도가 20$0^{\circ}C$인 Co-22%Cr합금 박막은 결정립 내부에 SONS를 형성하여 판상의 미세 Co-과잉상을 가지는 특이한 미세구조를 가지는 것을 확인하였다. 자기력현미경에 의해 확인된 결과, SONS가 없는 시편(기판온도를 실온으로 유지한 경우)은 주기 5000 정도의 미로형 도메인(domains)이 생겼다. 미로형 도메인은 결정간의 교환에너지가 큰 경우 발생하는 구조로서 고밀도 자기기록이 불리할 것이 예상되었다. 이와 비교해서 SONS가 생성된 (기판온도를 20$0^{\circ}C$로 유지한 경우)시편은 주기 500 정도의 매우 미세한 구형 도메인을 보였다. 미세구형 도메인은 각 도메인간의 교환에너지가 작아 열적 변화에도 데이터가 안정하므로 고밀도 기록에 유리하다고 예상되었다.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 추계총회 및 학술대회 논문집
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• pp.179-180
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• 2012

Aluminum alloys are widely known as non-ferrous metal with light weight and high strength. Consequently, these materials take center stage in the aircraft and automobile industry. The Al7075 aluminum alloy is based on the Al-Zn-Mg-Cu and one of the strongest wrought aluminum alloys. Aluminum nitride has ten times higher thermal conductivity($319W/m{\cdot}K$) than Al2O3 and also has outstanding electric insulation($1{\times}1014{\Omega}{\cdot}cm$). Furthermore, it has high mechanical property (430 MPa) even though its co-efficient of thermal expansion is less than alumina For these reasons, it has great possibilities to be used for not only the field which needs high strength lightweight but also electronic material field because of its suitability to be applied to the insulator film of PCB or wafer of ceramic with high heat conduction. This paper investigates the mechanical properties and corrosion behavior of aluminum alloy Al7075 deposited with aluminum nitride thin films To improve the surface properties of Al7075 with respect to hardness, and resistance to corrosion, aluminum nitride thin films have been deposited by pulsed DC reactive magnetron sputtering. The pulsed DC power provides arc-free deposition of insulating films.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.96.2-96.2
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• 2017

This research was conducted to investigate the electrochemical properties of the thin air-formed oxide film-covered AZ31 Mg alloy. In this work, native air-formed oxide films on AZ31 Mg alloy samples were prepared by knife-abrading method and the changes in the electrochemical properties of the air-formed oxide film were investigated in seven different electrolytes containing the following anions $Cl^-$, $F^-$, $SO{_4}^{2-}$, $NO_3{^-}$, $CH_3COO^-$, $CO{_3}^{2-}$ and $PO{_4}^{3-}$. It was observed from open circuit potential (OCP) transients that the potential initially decreased before gradually increasing again in the solutions containing only $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions, indicating the dissolution or transformation of the native air-formed oxide film into new more protective surface films. The Nyquist plots obtained from electrochemical impedance spectroscopy (EIS) showed that there was growth of new surface films with immersion time on the air-formed oxide film-covered specimens in all the electrolytes; the least resistive surface films were formed in fluoride and sulphate baths whereas the most protective film was formed in phosphate bath. The potentiodynamic polarization curves illustrated that passive behaviour of AZ31 Mg alloy under anodic polarization appears only in $CO{_3}^{2-}$ or $PO{_4}^{3-}$ ions containing solutions and at more than $-0.4V_{Ag/AgCl}$ in $F^-$ ion containing solution.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.117-117
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• 2003

• 한국표면공학회지
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• 제31권5호
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• pp.261-265
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• 1998

We investigated compositional separation of Co-23%Cr magnetic alloy thin films with varying film thicknesses. Saturation magnetization and magnetic microstructures were investigated using vibrating sample magnetometer (VSM) and scanning probe microscope (SPM), respectively. Saturation magnetization was as 700 emu/cc for films below 50 nm-thick, and changed to 430 emu/cc for the ones above 2000 nm-thick. This may be due to increment of molar volume of Cr-enriched phase as film thickness increases. The surface grain size in AFM (atomic force microscope) measurement becomes larger as film thickness increases. The MFM (magnetic force microscope) reveals that magnetic microstructure is changed from the fine spherical domains to the maze type domains as film thickness increases. We conclude that employing thickness of Co-22%Cr films below 50 nm is favorable for high density recording in order to enhance perpendicular saturation magnetization and SNR (signal to noise ratio).