• 한국표면공학회지
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• 제48권6호
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• pp.269-274
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• 2015

In this experiment, post-nitriding treatment was performed at $400^{\circ}C$ on AISI 316 stainless steel which was plasma carburized previously at $430^{\circ}C$ for 15 hours. Plasma nitriding was implemented on AISI 316 stainless steel at various gas compositions (25% $N_2$, 50% $N_2$ and 75% $N_2$) for 4 hours. Additionally, during post nitriding Ar gas was used with $H_2$ and $N_2$ to observe the improvement of surface properties. After treatment, the behavior of the hybrid layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. Meanwhile, it was found that the surface hardness increased with increasing the nitrogen gas content. Also small percentage of Ar gas was introduced in the post nitriding process which improved the hardness of the hardened layer but reduced the corrosion resistance compared with the carburized sample. The experiment revealed that AISI 316L stainless steel showed better hardness and excellent corrosion resistance compared with the carburized sample, when 75% $N_2$ gas was used during the post nitriding treatment. Also addition of Ar gas during post nitriding treatment degraded the corrosion resistance of the sample compared with the carburized sample.

• Journal of Oral Medicine and Pain
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• 제21권2호
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• pp.207-224
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• 1996

This study was designed to determine the most effective concentration of fluoride and energy density of laser irradiation for the anticarious effect. For this study surface hardness in enamel was measured before and after irradiation with pulsed Nd;YAG laser and the topical application of fluoride. Of the permanent mandibular anterior hovine teeth, healthy, carious free ones were used. Three hundred specimens were made. Specimens within 25~45 Vickers hardness numbers were assigned to 20 control and experimental stoops ; each containing 15 specimens. After forming artificial carious lesions, 10 J/$\textrm{cm}^2$, 20 J/$\textrm{cm}^2$, and 30 J/$\textrm{cm}^2$ energies were irradiated on the enamel surface of each experimental group. Also NaF, NH4F, Elmex gel(amine fluoride) and APF gel fluoride compounds were applied topically. Next, all the specimens were placed into the pH circulatory procedures for eight days. Vickers hardness numbers were measured using a microhardness tester. Surface changes of the enamel were observed using an scanning electron microscope. The comparative ana1ysis yielded the following results : 1. The reduction of surface hardness of the enamel surface was less in all groups with fluoride application than in the group without fluoride application. 2. The APF gel croup with 10 J/$\textrm{cm}^2$ irradiation showed the lowest reduction of surface hardness. 3. The reduction of surface hardness of the enamel surface in the group of laser irradiation without fluoride application not showed any significant difference according to the energy density of the laser. 4. Under the scanning electron microscope, in enamel irradiated with 10J/$\textrm{cm}^2$ showed appearance similar to acid etching surface. In enamel irradiated with 20 J/$\textrm{cm}^2$, line enamel crack was detected. In enamel irradiated with 30j/$\textrm{cm}^2$, severe enamel crack and fusion of enamel were detected. These results suggest that one could obtain the best anticariogenic effects without damage to teeth in the group of application of APF gel after laser irradiation with 10 J/$\textrm{cm}^2$.

• 대한기계학회논문집
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• 제12권5호
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• pp.1071-1082
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• 1988

본 연구에서는 시편의 재료를 회주철(Grey Cast Iron:GC 30)을 선정하였으며 보올의 지름이 각각 다른 5종류의 강철 보올(steel ball)을 사용하였다.

• Restorative Dentistry and Endodontics
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• 제11권1호
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• pp.43-52
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• 1985

The purpose of this study was to measure the Micro-Knoop Hardness of three commercial visible light-cured composite resins (Plurafil-super, He1iosit and Durafi) according to the difference of depth and shade. Specimens of the resin were prepapared in plastic tubes 5mm in diameter with height of 5mm, and the tubes were put into the columned holes in stone molds. The molds were exposed to the visible light through the hole 5mm in diameter in metal plate. Specimens were sectioned (longitudinally) with disk. Knoop Hardness measurements were made at the depth of surface, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0mm from the surface to the deep portion. Knoop Hardness numbers were taken on each depth under 20gm load for 10 seconds with Shimadzu Tester. The following results were: 1. The highest hardness value was measured at 0.5mm depth. Then the deeper the depth, the lesser the hardness was observed. 2. The value of hardness was directly propotional to the time of exposure to the light. 3. The hardness of light shade resin was higher than the that of the dark shade. 4. The pattern of hardness change at varying depth is similar to all the experimental materials with no relation to the shade nor exposure time.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.85-90
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• 2003

Although wear resistance of material improves with increasing its hardness, it is known that the wear resistance of steel is varied with hardness of counter material. In this context, wear properties of steel must be depended on the difference of hardness between the testpiece and the counter material. In this study, using the pin-on-disc type wear machine, annealed carbon steels were tested against ahoy tool steels with various levels of hardness. Then the changes of wear properties of carbon steel according to the hardness of counter material were investigated and the morphology of worn surface after test were evaluated. The results indicate that if there are no remarkable difference of hardness between them, wear resistance of carbon steel in running-in wear decreases with increasing the hardness of counter material. However, its wear properties at the range of high sliding speed have no relation with hardness of counter material. It is clear that wear properties is influenced by the formation of oxide of steel on their worn surface during wear.

• 한국표면공학회지
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• 제32권3호
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• pp.428-432
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• 1999

As metallic surface has its unique lustrous appearance and optical reflectance in visible range of light, the metallization of plastic surface has been an essential drive toward weight reduction for fuel economy and decorations in transportation industry and has been put into practiced from wet chemical-electrochemial to dry vacuum process in view of an environmental effect. Electron-beam metallization was used in this work with an aim at improving the scratchproof surface hardness of plastic substrate with metallic finish character. Thin film of Al ($1000\AA$) and $SiO_2$($7000\AA$) were metallized on substrate of PC and PMMA and the films were evaluated by pencil test for surface hardness and by cross-cut tape test for adhesion. The ion beam treatment improved around twice as hard as non-treat surface. The ion beam is effect on its hardness and adhesion to surface hardened PC substrate.

• 반도체디스플레이기술학회지
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• 제20권2호
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• pp.43-50
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• 2021

The properties of materials which are widely used in industry fields like automobile, shipbuilding, casting, and electronics are strongly needed to have higher surface hardness, lower surface roughness, and higher compressive residual stress. As mentioned above, for the purpose of satisfying three factors, a variety of researches with respect to surface improvement have been actively studied and applied to every industry. SKD61 which is mostly used for die casting process of cold chamber method must meet a countless number of problems which are thermal, mechanical and chemical from highly specific working environment at high temperature over 600℃. Above all, in case of plunger sleeves used for die casting process, thermal fatigue has a bad effect on the surface of an inlet where molten metal is repeatedly injected. On account of it, plunger sleeves cause manufacturers to deteriorate quality of products. Therefore, in this paper, to improve the surface of an inlet of plunger sleeve, multilayer PVD coating using Ti, Cr and Mo is suggested. Furthermore, The surface characteristics such as surface roughness(Rsa, Rsq), surface hardness(HRB, HRC) and residual stress using XRD(X-ray diffractometer) of coated samples and specimens are studied and discussed.

• Restorative Dentistry and Endodontics
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• 제36권6호
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• pp.483-489
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• 2011

연구목적: 본 연구의 목적은 글리세린의 도포가 복합레진의 중합 후 표면경도에 미치는 효과를 알아보고자 하였다. 연구 재료 및 방법: 디스크 형태의 황동 몰드에 복합레진(Z-250, 3M ESPE)을 충전 후 다음과 같이 광중합 하였다. 1군(대조군)은 복합레진 표면을 공기 중에 노출한 후 40초 동안 광조사, 2군은 표면을 Mylar strip으로 덮은 후 40초 광조사, 3군은 표면을 glycerin으로 도포 후 40초 광조사, 4군은 공기 중에 노출시켜 20초 광조사한 다음 시편 표면에 glycerin으로 도포한 후 추가로 20초 동안 광조사 하였다. 각 그룹당 20개의 시편을 준비하였고, 연마 후 또는 연마를 하지 않고 시편의 표면경도를 측정하였다. 5일 후 각 시편의 표면경도를 재 측정하였다. 데이터는 three-way ANOVA와 Tukey's post hoc test를 이용하여 분석하였다. 결과: 중합 직 후, 연마하지 않은 시편의 표면경도는 2군 > 3군 > 4군 > 1군의 순이었다. 연마한 경우 각 군 사이의 유의한 차이는 없었다. 같은 군 내에서는 5일 후 표면경도가 중합 직 후 보다 증가하였고 연마한 경우가 연마하지 않은 경우보다 더 높은 표면경도를 나타냈다. 결론: 중합 후 복합레진의 표면경도를 증가시키기 위한 가장 좋은 방법은 연마였고, 중합 전 Mylar strip의 사용이나 glycerin의 도포 역시 중합된 복합레진의 표면경도를 증가시켰다.

• 한국표면공학회지
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• 제37권1호
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• pp.28-39
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• 2004

The effect of trace metallic additives on microstructure, surface appearance and hardness of zinc electrodeposits was investigated by using sulfate bath and flow cell system. The preferred orientation of Zn deposit with Fe additive was (103)(104)+(002) mixed texture and that of Zn deposits with both Fe-Ni and Fe-Co additives was (10 1), while Zn deposits with Fe-Cr additives had (002) preferred orientation. The surface morphology of the zinc deposits was closely related to the preferred orientation of the deposits. The glossiness of Zn deposit with Fe-Ni additives was higher than that of pure Zn deposit, while the glossiness of Zn deposits with both Fe-Co and Fe-Cr additives was lower than that of pure Zn deposit. The hardness of Zn deposits with both Fe-Ni and Fe-Co additives was noticeably higher than that of Zn-Fe deposit, while that of Zn deposit with Fe-Cr additives was similar to that of Zn-Fe deposit.

• 한국가구학회지
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• 제19권4호
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• pp.229-234
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• 2008

In a previous study, it was revealed that three major softwoods, Japanese pine, Korean pine and Japanese larch, heat-treated at $220^{\circ}C$, could produce high quality dark-colored boards. It is known that heat treatment decreases the hygroscopicity of wood. The hygroscopicity of major domestic softwoods and hardwoods heat-treated at $220^{\circ}C$ was investigated by a saturated salt solution method and compared with that of black and white charcoals. Equilibrium moisture contents of wood decreased with the increase of heat treatment time. Isotherm shapes of wood species were different from those of charcoals. Heat treatment decreases the equilibrium moisture contents of black locust more than those of Korean pine and Japanese larch. It was found that surface hardness of wood is improved by heat treatment to a certain extent, but a longer heat treatment causes thermal degradation, resulting in the decrease of the surface hardness.