• Journal of Powder Materials
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• v.25 no.2
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• pp.137-143
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• 2018

In this study, two types of SKD61 tool-steel samples are built by a selective laser melting (SLM) process using the different laser scan speeds. The characteristics of two kinds of SKD61 tool-steel powders used in the SLM process are evaluated. Commercial SKD61 tool-steel power has a flowability of 16.68 sec/50 g and its Hausner ratio is calculated to be 1.25 by apparent and tapped density. Also, the fabricated SKD61 tool steel powder fabricated by a gas atomization process has a flowability of 21.3 sec/50 g and its Hausner ratio is calculated to be 1.18. Therefore, we confirmed that the two powders used in this study have excellent flowability. Samples are fabricated to measure mechanical properties. The highest densities of the SKD61 tool-steel samples, fabricated under the same conditions, are $7.734g/cm^3$ (using commercial SKD61 powder) and $7.652g/cm^3$ (using fabricated SKD61 powder), measured with Archimedes method. Hardness is measured by Rockwell hardness testing equipment 5 times and the highest hardnesses of the samples are 54.56 HRC (commercial powder) and 52.62 HRC (fabricated powder). Also, the measured tensile strengths are approximately 1,721 MPa (commercial SKD61 powder) and 1,552 MPa (fabricated SKD61 powder), respectively.

• Journal of Powder Materials
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• v.24 no.4
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• pp.302-307
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• 2017

In this study, Fe-Cu-C alloy is sintered by spark plasma sintering (SPS). The sintering conditions are 60 MPa pressure with heating rates of 30, 60 and $9^{\circ}C/min$ to determine the influence of heating rate on the mechanical and microstructure properties of the sintered alloys. The microstructure and mechanical properties of the sintered Fe-Cu-C alloy is investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The temperature of shrinkage displacement is changed at $450^{\circ}C$ with heating rates 30, 60, and $90^{\circ}C/min$. The temperature of the shrinkage displacement is finished at $650^{\circ}C$ when heating rate $30^{\circ}C/min$, at $700^{\circ}C$ when heating rate $60^{\circ}C/min$ and at $800^{\circ}C$ when heating rate $90^{\circ}C/min$. For the sintered alloy at heating rates of 30, 60, and $90^{\circ}C/min$, the apparent porosity is calculated to be 3.7%, 5.2%, and 7.7%, respectively. The hardness of the sintered alloys is investigated using Rockwell hardness measurements. The objective of this study is to investigate the densification behavior, porosity, and mechanical properties of the sintered Fe-Cu-C alloys depending on the heating rate.

• Journal of the Korean Magnetics Society
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• v.21 no.4
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• pp.136-140
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• 2011

Mechanical properties of degraded materials must be measured for evaluating the integrity of the facilities operating at high temperature. In fact it is complicated to obtain the different degraded specimens from an operating facility. Specimens of 1Cr-0.5Mo steel prepared by the isothermal heat treatment at $700^{\circ}C$ were tested, which has been widely used as tubes for heat exchangers and as plates for pressure vessels. The magnetic properties and Rockwell hardness (HRB) were measured at room temperature. The peak interval of Barkhausen noise envelope (PIBNE), coercivity, and hardness decreased with the increase of degradation. The magnetic and mechanical softening of matrix is likely to govern the properties of the specimen more than the hardening of grain boundary by carbide precipitations. The degradation of test material may be determined by the linear correlation of PIBNE and HRB. Degradation of 1Cr-0.5Mo steel could well be nondestructively evaluated by PIBNE measured with surface type probe.

• Journal of the Korean institute of surface engineering
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• v.46 no.2
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• pp.68-74
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• 2013

For the coating of diamond films on WC-Co tools, a buffer interlayer is needed because Co catalyzes diamond into graphite. W and Ti were chosen as candidate interlayer materials to prevent the diffusion of Co during diamond deposition. W or Ti interlayer of $1{\mu}m$ thickness was deposited on WC-Co substrate under Ar in a DC magnetron sputter. After seeding treatment of the interlayer-deposited specimens in an ultrasonic bath containing nanometer diamond powders, $2{\mu}m$ thick nanocrystalline diamond (NCD) films were deposited at $600^{\circ}C$ over the metal layers in a 2.45 GHz microwave plasma CVD system. The cross-sectional morphology of films was observed by FESEM. X-ray diffraction and visual Raman spectroscopy were used to confirm the NCD crystal structure. Micro hardness was measured by nano-indenter. The coefficient of friction (COF) was measured by tribology test using ball on disk method. After tribology test, wear tracks were examined by optical microscope and alpha step profiler. Rockwell C indentation test was performed to characterize the adhesion between films and substrate. Ti and W were found good interlayer materials to act as Co diffusion barriers and diamond nucleation layers. The COFs on NCD films with W or Ti interlayer were measured as less than 0.1 whereas that on bare WC-Co was 0.6~1.0. However, W interlayer exhibited better results than Ti in terms of the adhesion to WC-Co substrate and to NCD film. This result is believed to be due to smaller difference in the coefficients of thermal expansion of the related films in the case of W interlayer than Ti one. By varying the thickness of W interlayer as 1, 2, and $4{\mu}m$ with a fixed $2{\mu}m$ thick NCD film, no difference in COF and wear behavior but a significant change in adhesion was observed. It was shown that the thicker the interlayer, the stronger the adhesion. It is suggested that thicker W interlayer is more effective in relieving the residual stress of NCD film during cooling after deposition and results in stronger adhesion.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.1-19
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• 1998

After polymerizing composite resin with argon laser and visible light, four test, to be concretely, measurement of compressive strength using Instron testing machine, surface microhardness using Rockwell hardness tester, quantitative analysis of residual monomer using HPLC and analysis of degree of conversion using FTIR, were accomplished. Test groups were a sort of specimen with 3mm diameter, 4mm thickness for measuring compressive strength, two sort of specimen with 7mm diameter, 2mm and 3mm thickness for measuring surface microhardness, quantitative analysing of residual monomer after curing and measuring the degree of conversion, each were divided by six groups according to the condition of light exposure. In case of argon laser, in 1.0W and 0.5W output, the exposure time for specimen were 5 sec, 10 sec respectiyely. In case of visible light, the exposure time for specimen were 20 sec, 40 sec respectively. The test were accomplished and following results were obtained. 1. Compressive strength of composite resin was the highest in the group of 1 W output, exposing for 10 sec with argon laser, followed by the group of 0.5W, exposing for 10 sec with argon laser, the group of exposing for 40 sec with visible light. But there were statistically no significant difference between these three groups(p>0.05). 2. Surface microhardness of composite resin wasn't significantly affected by light curing conditions. 3. BIS-GMA within residual monomer was least detected in the group of exposing for 40 sec. TEGDMA was least detected in the group of 1 W output, exposing for 10 sec with argon laseboth 2mm and 3mm thickness specimen. 4. The degree of conversion of all groups in the 2mm thickness specimen were more than 50%, similar to each other but in the group of 1W, exposing 10 sec with argon laser the degree of conversion was highest in the 3mm thickness specimen. 5. Argon laser could make composite resin to has similar properties with 25% lesser exposure time than visible light.

• Journal of Conservation Science
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• v.26 no.3
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• pp.311-324
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• 2010

The purpose of this study aims to reveal characteristics of reproduced potteries which made with clays of various chemical compositions in different firing temperatures and thereafter to provide comparative samples for identifying the manufacturing techniques of earthenwares from archaeological excavation by reproducing and characterizing sample under controlled conditions. For this study, various samples of earthenware are reproduced using different types of raw clays at several different firing temperature, followed by physical and structural characterization. Chemical specification were varied from different types of clay, which were calculated by Seger formula, and four different types of clay were selected based on different mole ratio of acidic oxide. The temperatures of firing of 7 samples were varied between $600^{\circ}C$ to $1200^{\circ}C$ at the interval of $100^{\circ}C$ for each sample. The result of analysis revealed that each reproduced earthenware has different chemical compositions divided into two groups: 1. Sample Y(6.10) and Sample G(5.85) clay; 2. Sample H(3.41) and Sample S(2.85) clay. The former which has higher mole ratio of acidic oxide than the latter, shows higher level of rockwell hardness at the same firing temperature. In addition, all four samples presented that as the firing temperature was increased, absorption rates of Y and G were abruptly dropped at $1200^{\circ}C$. Furthermore the more mole ratio of acidic oxide increase, the more microtexture of samples were vitrificated. Such result reveals that mole ratio of acidic oxide influence physical and microtextural characteristics of earthenwares, and it can be used as the comparison data in the understanding of manufacture techniques for the earthenwares of similar chemical composition.