• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.5
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• pp.20-28
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• 2014

The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.3
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• pp.285-293
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• 2016

The high velocity oxygen fuel(HVOF) thermal spray is a kind of surface modification techniques to produce the sprayed coating layer. This process is to form the coating layer after spraying the powder to molten or semi-molten state by the ultra-high speed at the high-temperature heat source and conflicting with a substrate. The efficiency of thermal spraying is dropped, however, because the semi-molten powder in a spray process become a factor that degrades the mechanical property by the formed pore within the coating layer. Therefore, it is necessary to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesive force. In this study, to improve the wear resistance, corrosion resistance and heat resistance, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps used in ironworks are manufactured with STS $420J_2$ and are coated by the powders of WC-Co-Cr and WC-Cr-Ni including the WC of high hardness using a HVOF thermal sprayer developed in this laboratory. These are called by the surface-modified plungers. The surface roughness, hardness, and surface and cross-sectional microstructure of these two surface-modified and conventional ceramic plungers are measured and compared before operation with after operation for 100 days. It is found that the values of centerline average surface roughness and maximum height for conventional ceramic plunger are 9.5 to 10.8 and 5.2 to 5.7 times higher than those of surface-modified ones coated by WC-Co-Cr and WC-Cr-Ni because the fine tops and bottoms on surface roughness curve of conventional ceramic plunger are approximately 100 times higher than those of surface-modified ones. In addition, the pores and scratches in the surface microstructure are considerably formed in the order of conventional ceramic, WC-Cr-Ni and WC-Co-Cr surface-modified plungers. The greater the WC content of high hardness powder is less the change in the plunger surface.

• The Journal of Korean Academy of Prosthodontics
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• v.44 no.6
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• pp.740-750
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• 2006

Statement of problems. In an attempt to reduce screw loosening, dry lubricant coatings such as pure gold or tefron have been applied to the abutment screw. However, under repeated tightening and loosening procedures, low wear resistance and adhesion strength of coating material produced free particles on the surface of abutment screw and increased frictional resistance resulting in screw tightening problems. Purpose. The aim of this study was to compare friction coefficient, adhesion strength, vickers hardness and evaluate coating surface of titanium alloy specimens coated with TiN(titanium nitride), ZrN(zirconium nitride) and WC(tungsten carbide). Material and method. Titanium alloy(Ti-6Al-4V) discs of 12mm in diameter and 1mm in thickness divided into 4 groups. TiN, ZrN and WC was coated for the specimens of 3 groups respectively, and those of 1 group were not coated. Each group was made up of 4 specimens. In this study, sputtering method was used among the PVD(Physical Vapor Deposition) techniques available for TiN, ZrN and WC coatings. Friction coefficient, adhesion strength, vickers hardness and coating surface of 4 groups were measured. Results. 1. For all three coating conditions, friction coefficient was significantly decreased. Especially, ZrN coated surface showed the lowest value. $TiN(0.39{\pm}0.02)$, $ZrN(0.24{\pm}0.01)$, $WC(0.31{\pm}0.03)$. 2. TiN coating showed the highest adhesion strength, however ZrN coating had the lowest value. $TiN(25.3N{\pm}1.6)$, $ZrN(14.8N{\pm}0.6)$, $ WC(18.4N{\pm}0.7)$. 3. Vickers hardness of all three coatings was remarkably increased as compared with that of none coated specimen. TiN coating had the highest Vickers hardness, however WC coating showed the lowest value. $TiN(1865.2{\pm}33.8)$, $ZrN(1814.4{\pm}18.6)$, $WC(1008.5{\pm}35.9)$. 4. The ZrN or WC coated specimen showed a homogeneous and smooth surface, however the rough surface with defects was observed for TiN coating. Conclusions. When TiN, ZrN and WC coating applied to the abutment screw, frictional resistance would be reduced, as a result, the greater preload and prevention of the screw loosening could be expected.

• Journal of the korean academy of Pediatric Dentistry
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• v.28 no.4
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• pp.673-682
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• 2001

The use of resin composites has continued to increase over the last several years. In spite of their growing popularity, composites continue to exhibit a number of undesirable characteristics. One of the major deficiencies of composite restorative resins is their inadequate resistance to wear. Of the multitude of factors that have been associated with wear, subsurface degradation within the restoration is considered to be one. The aim of this study was to evaluate the resistance to degradation of four commercial composite resins in an alkaline solution. This solution with a high concentration of hydroxyl ions is a convenient medium for accelerated degradation of silane coupling and filler particles. The brands studies were Definite($Degussa-H\ddot{u}ls$ AG, Germany), Prodigy(Kerr, USA), Pyramid(Bisco, USA) and Synergy(Coltene, Swiss). Preweighed discs of each brand were exposed to 0.1N NaOH solution at $60^{\circ}C$. After 14 days they were removed, neutralized with HCl, washed with water and dried. Resistance to degradation was evaluated on the basis of following parameters : (a) mass loss(%)-determined from pre-and post-exposed specimen weights : (b) Si loss(ppm)-obtained from ICP-AE analysis of solution exposed to specimens; and (c) degradation $depth({\mu}m)$-measured microscopically (SEM) from polished circular sections of exposed specimens. The results were follows: 1. Mass loss of Synergy was $1.24{\pm}0.002%$, it was the highest, there was no significant difference among the materials. 2. The degree of degradation layer depth of Synergy was $107.83{\pm}2.52{\mu}m$, it was the highest, there was no significant difference among any other materials than Synergy. 3. There was no difference among the four materials in Si loss. 4. The correlation coefficient between mass loss and degradation depth was relatively high(r=0.06, p<0.05). 5. There was no coefficient correlation between Si loss and mass loss, the degree of degradation layer depth and Si loss. 6. When observed with SEM, destruction of bonding is observed between resin matrix and filler.

• Journal of Sericultural and Entomological Science
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• v.23 no.1
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• pp.47-55
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• 1981

Silk textile finishing has been studied for many years by many workers in order to meet more utilities for various endusers. Such studies, however, could not be successful because any natural fibers are hardly change their natures by artificial treating methods. Textile finishing is of course to improve the mechandise qualities and the poor natures of silk so that it may be available as the best textile fiber in the world. Sometimes, famous trade marked textile plays more power than its quality in the silk market, nevertheless, this should be over line of research activities. Meantime, the silk demand has been also transferred from ladies stocking to other clothes since nylon or other synthetic fibers were developed. That is why, the extension of silk demand should be developed by various research works. Specially, silk is known as difficult textile to handle it during washing or ironing process which happened to depress down the silk usage for house wives. In order to solve such problems, the reporter has been worked for many years and now, he believes that he has developed a proper finishing method to coversuch problems. The developed finishing method may be said to eligible with economical aspect and shorten the dry duration after water washing in half against normal silk textile without harming the specific silk nature. As all of us know, silk fiber starts to denature since it was spinned by silkworm and the fiber is formed as overlapped "S" type curves during its concooning process. After it is made as raw silk or sericin silk, it shows as straight line form, but it changes in to waved form in case refining or degumming process in order return to its original spinned form. Such nature is continued during its textile form and ends with hard ironing nature than other textile fibers. Mean while, the silk fiber keeps to continue its denaturing and this is iniciated by repeat of washing and drying which takes many years to reach its final stage, The reporter has found the iniciating denature of silk by his finishing process, with out heat, decreasing the swollen nature which ended with shortening the drying duration after wash. Each washing was carried out by soaking the previously weighed sample in cold water for one hour, then pressed the sample for ten minutes to eliminate its free water component before weighing with same condition. According to this, the treated silk showed much denaturing after the finishing, but the standard silk progressed the denaturing by and by with the repeat of washing and drying, finally reached the same swollen degree of treated silk, Such treating result explains that the treated silk happened to be stebilized nature by the treating immediately. On the other that the treated silk happened to be stebilized nature by the treating immediately. On the other hand, standard silk may reach to such condition by the time of worn out clothes after repeat of washing and drying for many years while the clothes will be no more useful. The decreased swelling nature has brought about the drying period in half against standard silk after all. Not only the tests of tenacity and elongation but also crease resistance recovery, stiffness and shrinkage tests were carried out after each washing and drying which he has found better result on the treated silk textile against the standard silk. The most important thing was to keep the textile feeling of silk by such finishing work before improve any poor nature of silk. The general silk has a nature to absorb smoke or dirt from its surrounding air and reaches to dirty color shade upon such exposure, but the treated one has improved such nature because of its artificial denaturing, another word, it keeps clean longer than the normal silk. Many previous finishing works could improve some specific nature of silk, but it happened to deprave other important natures. The reporters work is, however, specialized to improve the silk to be useful as Wash and Wear Silk without harming its standard natures. So far, this work happened to be a overall innovative finishing method of silk textile.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.111-112
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• 2009

Diamond-like carbon (DLC) is a convenient term to indicate the compositions of the various forms of amorphous carbon (a-C), tetrahedral amorphous carbon (ta-C), hydrogenated amorphous carbon and tetrahedral amorphous carbon (a-C:H and ta-C:H). The a-C film with disordered graphitic ordering, such as soot, chars, glassy carbon, and evaporated a-C, is shown in the lower left hand corner. If the fraction of sp3 bonding reaches a high degree, such an a-C is denoted as tetrahedral amorphous carbon (ta-C), in order to distinguish it from sp2 a-C [2]. Two hydrocarbon polymers, that is, polyethylene (CH2)n and polyacetylene (CH)n, define the limits of the triangle in the right hand corner beyond which interconnecting C-C networks do not form, and only strait-chain molecules are formed. The DLC films, i.e. a-C, ta-C, a-C:H and ta-C:H, have some extreme properties similar to diamond, such as hardness, elastic modulus and chemical inertness. These films are great advantages for many applications. One of the most important applications of the carbon-based films is the coating for magnetic hard disk recording. The second successful application is wear protective and antireflective films for IR windows. The third application is wear protection of bearings and sliding friction parts. The fourth is precision gages for the automotive industry. Recently, exciting ongoing study [1] tries to deposit a carbon-based protective film on engine parts (e.g. engine cylinders and pistons) taking into account not only low friction and wear, but also self lubricating properties. Reduction of the oil consumption is expected. Currently, for an additional application field, the carbon-based films are extensively studied as excellent candidates for biocompatible films on biomedical implants. The carbon-based films consist of carbon, hydrogen and nitrogen, which are biologically harmless as well as the main elements of human body. Some in vitro and limited in vivo studies on the biological effects of carbon-based films have been studied [$2{\sim}5$].The carbon-based films have great potentials in many fields. However, a few technological issues for carbon-based film are still needed to be studied to improve the applicability. Aisenberg and Chabot [3] firstly prepared an amorphous carbon film on substrates remained at room temperature using a beam of carbon ions produced using argon plasma. Spencer et al. [4] had subsequently developed this field. Many deposition techniques for DLC films have been developed to increase the fraction of sp3 bonding in the films. The a-C films have been prepared by a variety of deposition methods such as ion plating, DC or RF sputtering, RF or DC plasma enhanced chemical vapor deposition (PECVD), electron cyclotron resonance chemical vapor deposition (ECR-CVD), ion implantation, ablation, pulsed laser deposition and cathodic arc deposition, from a variety of carbon target or gaseous sources materials [5]. Sputtering is the most common deposition method for a-C film. Deposited films by these plasma methods, such as plasma enhanced chemical vapor deposition (PECVD) [6], are ranged into the interior of the triangle. Application fields of DLC films investigated from papers. Many papers purposed to apply for tribology due to the carbon-based films of low friction and wear resistance. Figure 1 shows the percentage of DLC research interest for application field. The biggest portion is tribology field. It is occupied 57%. Second, biomedical field hold 14%. Nowadays, biomedical field is took notice in many countries and significantly increased the research papers. DLC films actually applied to many industries in 2005 as shown figure 2. The most applied fields are mold and machinery industries. It took over 50%. The automobile industry is more and more increase application parts. In the near future, automobile industry is expected a big market for DLC coating. Figure 1 Research interests of carbon-based filmsFigure 2 Demand ratio of DLC coating for industry in 2005. In this presentation, I will introduce a trend of carbon-based coating research and applications.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.5
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• pp.407-415
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• 2008

The tubes in heat exchanger are typically made from copper alloy, stainless steel, carbon steel, titanium alloy material. type-439 ferritic stainless steel is ferromagnetic material, and furnish higher heat transfer rates than austenitic stainless steels and higher resistance to corrosion-induced flaws. Ferritic stainless steel can typically be found in low-pressure(LP) feedwater heaters and moisture separator reheaters(MSRs). LP feedwater heaters generally utilize thin wall type-439 stainless steel tubing, whereas MSRs typically employ a heavier wall tubing with integral fins. Service-induced damage can occur on the OD(outside diameter) surface of type-439 ferritic stainless steel tubing which is employed for MSRs tubing, and the most typical damage mechanism is vibration-induced tube-to-TSP(tube support plate) wear and fatigue cracking. The wear has been reported that occurs mainly on the OD surface. Accordingly, in this study, we have evaluated the flaw sizing capability of magnetic saturation eddy current technique using magnetic saturation probe and flawed specimen.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.3
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• pp.41-50
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• 2009

The flash memory has many advantages such as low power consumption, strong shock resistance, fast I/O and non-volatility. And it is increasingly used in the mobile storage device. Many researchers are studying the YAFFS, NAND flash file system, which is widely used in the embedded device. However, the existing YAFFS has two problems. First, it takes long time to mount the YAFFS file system because it scans whole spare areas in all pages. Second, the cleaning policy of the YAFFS does not consider the wear-leveling so that it cannot guarantee the duration of data completely. In order to solve these problems, this paper proposes a new content-based YAFFS that consists of a mounting time reduction technique and a content-cleaning policy by using content-based block management. The proposed method only scans partial spare areas of some special pages and provides the block swapping which enables the wear-leveling of data blocks. We performed experiments to compare the performance of the proposed method with those of the JFFS2 system and YAFFS system. Experimental results show that the proposed method reduces the average mounting time by 82.2% comparing with JFFS2 and 42.9% comparing with YAFFS. Besides, it increases the life time of the flash memory by 35% comparing with the existing YAFFS whereas no overheat is added.

• Restorative Dentistry and Endodontics
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• v.20 no.1
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• pp.193-213
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• 1995

The purpose of this study is to investigate a possible contribution of nonspecific esterases, which occur in the oral cavity, to the degradation of ester bonds in polymethacrylates. One of the problems connected with the use of composite resins for restorations is their inadequate resistance to wear. It has been shown that methacrylate hydrolysis can be catalyzed by enzymes and that a carboxylic hydrolase (porcine liver esterase) catalyzed the hydrolysis of several mono - and dimethacrylates. The softening effect on a BISGMA/TEGDMA polymer induced by hydrolase will accelerate the in vivo wear of the polymer. Porcine liver esterase (EC 3.1.1.1) 3.2 mol/L $(NH_4)_2$ $SO_4$ was obtained from Sigma Chemical Company. The esterase activity of one unit is defined as the amount of enzyme capable of hydrolyzing $l{\mu}mol$ ethyl butyrate per min at pH 8.0 AT $25^{\circ}C$. Phosphate buffer, 10mmol/L, pH 7.0, was made by adjustment of a solution of $Na_2HPO_4$ with $H_3PO_4$. Composite resins used in this study are Silux Plus, Z-100, Durafil VS, and Prisma APH. Cylindrical specimens, 14mm in diameter and 3mm thick, of Silux Plus, Z-100, Durafil VS, Prisma APH were polymerized under the celluloid strip. 60 specimens were divided into 2 groups. One group was emersed only in buffer solution, the other group was emersed in buffer and enzyme solution. Silux Plus and Z-100 were divided into 2 subgroups, one subgroup was cured only Visilux 2. And the other subgroup was cured Visilux 2 and Triaid II. Thereafter, specimens were polished to its best achievable surface according to manufacture's directions. The Vickers hardness of the specimens was measured after 1, 2, 4, 7, 9, 15, 50 days. The solutions were changed after each measurement. Composite resin surfaces were evaluated for the surface roughness with profilometer (${\alpha}$-step 200, Tencor instruments, USA) after 1 and 50 days. And then surfaces of specimens were pictured with stereosopy after 1 and 50 days. The results were as follows. 1. The surface hardness of Silux plus, durafil VS, and Prisma APH were decreased with time. But, the surface hardness of Z-100 was not decreased. 2. The surface hardness of all composite resins was decreased by esterase. 3. Composite resins, which were light-cured by Visilux 2 and concomitantly baked by oven, showed more hardened surface than light-cured by Visilux 2 only. 4. Significant surface changes were occured in Silux plus after esterase treatment.

• Korean Journal of Materials Research
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• v.1 no.4
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• pp.221-228
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• 1991

In this study we have investigated the sealing characteristics of glasses suitable for producing the magnetic gap of the ferrite head cores which have been widely used for VTR and computer magnetic heads. $PbO-B_2O_3$ g1asses were evaluated by measuring microhardness, thermal expansion coefficient and sliding wear resistance. Concentration distribution of elements at the interface was observed by WDS. wettability was measured by high temperature microscopy. The results were as follows ; 1. In sealing glasses of $PbO-B_2O_3$ system, thermal expansion coefficient and wear volume were increased with increasing PbO content, and were decreased with increasing $B_2O_3$ content. 2. The contact angle of $PbO-B_2O_3$ Systems was mainly influenced by PbO content. 3. The sealing temperature showed a tendency to decrease proportionally with the increase of the coefficient of thermal expansion. 4. The diffusion at the interface between Mn-Zn single crystal ferrite and sealing glasses of $PbO-B_2O_3$ system was dominated by small amount of diffusion of ferrite content into glass part, which was very little affected by sealing heat treatment time.