• Journal of the Korean Society for Heat Treatment
• /
• v.13 no.4
• /
• pp.217-223
• /
• 2000

The boronizing effects of STD 61 steel have been studied on the micro structure and hardness. The STD 61 Steel was soaked in molten salt, consisted of KCl, $BaCl_2$, NaF, $B_2O_3$, FeB, and Ce, at various temperatures and times. The boronizing conditions for the peak hardness were the temperature range of $900^{\circ}C$ to $950^{\circ}C$ for 5 hr and that of $1000^{\circ}C$ for 3 hr, respectively. Four boride layers such as FeB, $Fe_2B$, ${\alpha}$ and matrix layer surface were observed from the microscopic surface examination. The thickness of boride layer was increased by increasing the boronizing time and the temperature. The structure of boride layer was tooth shape.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.2
• /
• pp.71-77
• /
• 2003

We investigate the phase formation in the compound layer of cast irons during the gaseous nitrocarburising of four different cast irons, that contain different types of graphites in the shape and size. We examine the change in the surface roughness with the nitrocarburising time. The observation of cross-sectional microstructure and X-ray diffraction analysis indicate that the compound layer consists of single ${\varepsilon}-Fe_{2-3}(N,C)$ phase and that its thickness increases in a parabolic manner with the treatment time. The surface roughness parameters, Rz and Ra increase with increasing treatment time. In other words, the roughness parameters increase as the thickness of compound layer increases. The parameters also depend on the shape and size of graphite in the individual cast irons.

• Journal of Surface Science and Engineering
• /
• v.33 no.1
• /
• pp.17-24
• /
• 2000

The microstructures and corrosion properties of Al-Si diffusion coated PWA1426 and PWA658 alloys have been investigated. The coated layer and corrosion properties were analysed by SEM, EDS and hot corrosion test. According to the results of SEM, it is supposed that the coated layers were composed of mixed, denuded and inter-diffusion layer. The coated PWA1426 alloy improved corrosion properties, compared to the PWA658 alloy. Corrosion debris generated during hot corrosion test of PWA658 alloy are identified as NiO, $TiO_2$and $NiAl_2$$O_4$from coated layer which increase oxidation rate and decrease adhesion. The PWA1426 alloy heat treated at $1080^{\circ}C$ showed that NiAl and $Al_2$$O_3$formed on coated layer.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
• /
• 2003.02a
• /
• pp.58-61
• /
• 2003

A typical HTS power transmission cable has multi-layer conductor structure to increase the current capacity. The current distribution among the conductor tapes is controlled mainly by pitches and winding directions of the layers, because the inductance of the layer is determined by the pitch and the winding direction. However, usually the current is not evenly distributed among the layers. This paper describes a method to make the current distribution more uniform and hence reduce the AC loss. If we choose a good combination we can find the optimal pitches and make an even current distribution. We studied the effect of the winding direction on a 2-layer cable by a statistical way. Calculation results and discussions will be presented.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.302-302
• /
• 2013

본 연구는 이온질화시 self-sputtering에 의한 AISI D2 소재의 표면경화에 대한 연구를 진행하였다. 이를 위해 이온질화시 질소가스와 아르곤 가스를 이용해 이온질화를 수행하였다. 이에 대한 결과는 optical micrograph (OM), scanning electron microscopy (SEM), X-ray diffraction(XRD), transmission electron microscopy (TEM)를 이용해 분석하였다. 실험결과, 소재의 경도는 570 HV에서 약 1470 HV까지 상승하였다. 극표면에 CrN-enriched layer의 형성 및 극표면 아래층에서 질소의 과포된 화합물층을 관찰할 수 있었다. 표면경화는, 극표면에 CrN-enriched layer의 형성과, 아래 N의 과포화에 의한 ${\gamma}$?autenite) phase, 그리고 diffusion layer의 형성에 의한 multi-layer의 형성으로 표면에 강화에 기여한것으로 사료된다.

• Journal of Surface Science and Engineering
• /
• v.13 no.2
• /
• pp.81-86
• /
• 1980

The mechanical properties of aluminized steel were investigated after the JIS SB 41 plates were dipped in molten aluminum bath. (1) The growth rate of iron-aluminum alloy layer was fast in early stage of alumizing, and then gradually decreased with increasing time. However, over the time period above 10 minutes the growth of alloy layer did not occur. (2) The constituent of alloy layer formed on the steel surface was identified to be intermetallic compound of $Fe_2\;Al_5$. (3) The ultimate tensile strength and elongation of aluminized steel showed a nearly constant value over all thickness below about 0.15 mm. However, both properties decreased rapidly in showed a nearly constant value over all thickness above about 0.20 mm. (4) In case of aluminized steel with greater thickness, crack was formed below yield point of base metal, which is considered to be attributed to the alloy layer failure.

• Plant Journal
• /
• v.6 no.4
• /
• pp.63-71
• /
• 2010

The best way to prevent the corrosion of piston rod is a selection of quality of the material and method of construction which minimize the porosity. The high velocity oxy fuel(HVOF) method, which generates lower porosity than existing plasma spray, was applied to ceramic laminated bond layer. Porosity percentage fell to bellow 2%, lower than that of plasma spray at 7%. Coating material of ceramic-coated main layer was selected as the $Cr_2O_3$ affiliation material, which is more dense than $Al_2O_3$ affiliation. To fill up the pores formed after the coating process, we sealed the bond layer and main layer. Sealing process was performed twice, once after the coating and once after the grinding. Upon the anti-corrosion test on the sealed sample and on the non-sealed sample, it is confirmed that the sealed sample was not corroded for 1,000 hours while the non-sealed sample was corroded within 48 hours.

• Solar Energy
• /
• v.6 no.2
• /
• pp.15-21
• /
• 1986

In this study, an experimental double diffusive thermohaline system heated from below was constructed and the phenomena of each layer developed in the system were observed. The experiment was performed with the initial salt concentration gradient of $-436.2kg/m^4$ and the net heat flux of approximately $176w/m^2$. An electroconductivity-temperature probe was made and used for the measurements of salt concentration. As the result of this study, it was found that the salt concentration decreased in the bottom mixed layer and increased in the top mixed layer during the experiment while the salt concentration gradient in the diffusive layer unchanged. It was also found that the interfacial boundary layers were due largely to variations in salt concentration rather than temperature.

• Electrical & Electronic Materials
• /
• v.10 no.2
• /
• pp.119-125
• /
• 1997

In this study, piezoelectric transducers were designed and manufactured using PZT-5A which had relatively high electromechanical coefficient, nondestructive testing system was developed which was able to inspect automatically using stepping motors, PC-Lab, and PC-Scope. The optimum design conditions for NDT were presented and verified comparing PZT-5A probes with comercial probes. It was proved by simulation and experiments that Epoxy is a good material as matching and backing layers. The envelope was reduced 60% with matching layer and 76% with matching and backing layer. NDT was successfully carried out for aluminum test pieces. Distance error of PZT-5A probe was 2.8%.

• Journal of electromagnetic engineering and science
• /
• v.16 no.2
• /
• pp.106-111
• /
• 2016

A resistive and capacitive (RC) microwave absorber with a layer thickness less than a quarter of a wavelength is investigated based on closed-form design equations, which are derived from the equivalent circuit of the RC absorber. The RC absorber is shown to have a theoretical 90% absorption bandwidth of 93% when the electrical layer thickness is $57^{\circ}$ (about ${\lambda}_0/6$). The trade-offs between the layer thickness and the absorption bandwidth are also elucidated. The presented formulation is validated by a design example at 3 GHz. The RC absorber is realized using a silver nanowire resistive rectangular structure with surrounding gaps. The measured 90% absorption bandwidth with a layer thickness of ${\lambda}_0/8$ is 76% from 2.3 GHz to 5.1 GHz in accordance with the theory and EM simulations. The presented design methodology is scalable to other frequencies.