• Journal of Welding and Joining
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• v.17 no.2
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• pp.104-111
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• 1999

The interfacial microstructure and bond strength were examined for WC-Co/Cu/SM45C steel join using a nickel-plated copper in vacuum at 1323K for 0.6ks∼3.6ks. After bonding, microstructure in bonding interface was observed by OM(Optical Microscopy), SEM(Scanning Electron Microscopy) and EPMA(Eelectron Probe Micro Analyzer). The oil cooling was carried out at 353K, the cooling rate in air and furnace was 22K/s and 4.4K/s. respectively. It was found that dendritic widths increased with the content of cobalt and bonding times at 1323K. As a whole, bond strength values at the same bonding condition decreased in this order: WC-13wt.%Co/SM45Csteel. WC-8wt.%Co/SM45Csteel and WC-4wt.%Co/SM45Csteel. The bond strength of WC-13wt.%Co/S45C steel joint in oil cooling was 273MPa. This value was greatly higher than those of 125MPa in furnace cooling and 93MPa in air cooling at 1323K for 0.6ks. The bond strength values were found to be closely associated with the content of cobalt in WC-Co and cooling rate.

• Journal of Powder Materials
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• v.25 no.5
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• pp.408-414
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• 2018

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

• Journal of Korean Academy of Fundamentals of Nursing
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• v.16 no.1
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• pp.14-20
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• 2009

Purpose: The purpose of this study was to identify how accurately body mass index (BMI) and waist circumference (WC) detect obesity in young adult women. Method: Measurements of height, weight, WC, and percent body fat (% BF) were obtained and bioelectrical impedance analysis was used to estimate body fat in 329 female college students. The sensitivity and specificity to screen obesity by BMI and WC were determined using SPSS. Received operating characteristic (ROC) curve analysis was used to assess the appropriate BMI and WC predicting % BF. Results: % BF-defined obesity $(\geq30%)$ had higher prevalence than BMI-defined obesity $(\geq25kg/m^2)$ and WC-defined obesity $(\geq80cm)$. BMI $\geq25kg/m^2$ and WC $\geq80cm$ had high specificity (both, 100%), but low sensitivity (respectively, 13.5% and 22.9%) in detecting % BF-defined obesity. The BMI and WC cutoff values corresponding to % BF-defined obesity were 21.2kg/$m^2$ and 73cm, which were lower than recommended reference values for Korean women. These values decreased specificity but increased sensitivity to detect obesity. The areas under the ROC curve were good (0.84, 0.86) for BMI and WC. Conclusion: BMI and WC have good specificity but miss more than $77\sim86%$ of people with excess fat. Therefore, BMI and WC cutoff values need to be revised and body fat should be considered when screening for obesity in young adult women.

• Journal of Korean Medicine for Obesity Research
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• v.9 no.2
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• pp.47-56
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• 2009

Objectives The purpose of this study was to investigate the progress of weight and waist circumference(WC) through oriental obesity treatment and clarify the correlation between weight loss and WC change. Methods The subjects were treated from January 2007 to September 2009 in J Oriental Medical Center. Herbal medicine, electroacupuncture, oriental obesity physiotherapy were performed for a month. We checked the change of weight and WC at every treatment. We classified the WC into upper, middle, lower parts specifically and measured them individually. Measurements were analyzed by using one-way repeated measures ANOVA and we also investigated correlation between weight loss and WC change. Results (1) During the first and second treatment sessions, the weight loss was the highest, $0.96{\pm}0.86\;kg$($1.46{\pm}1.32\;%$) and during the 5th and 6th treatment sessions, the lowest $0.37{\pm}0.616\;kg$. The final weight loss was $3.71{\pm}1.476\;kg$($5.51{\pm}2.12\;%$). (2) After 8 treatment sessions, the reductions of upper, middle and lower WC were $3.59{\pm}2.26\;%$, $5.93{\pm}2.75\;%$, $5.51{\pm}3.22\;%$, respectively. As the patients received more treatment, there was a progressive decline in the variation of weight and middle WC. However, the decline rate of upper and middle WC fluctuated during the treatments, forming a W-shaped curve. (3) Analysis of the correlation between the weight loss and WC change shows that the reduction of middle WC was most closely associated with the weight loss. Conclusions This study indicated that the rate of weight loss and WC reduction showed stagnation during the 5th and 6th treatment sessions, and the reduction of middle WC was most closely associated with the weight loss. Since the progress of weight and WC change is an important field of research on obesity, further systemic studies would be needed for the foundation of a clinical guideline.

• Journal of the Korea Convergence Society
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• v.9 no.1
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• pp.233-240
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• 2018

The aim of this study was to investigate the cardiometabolic risk factors (CRF) of community dwelling women based on a combination of body mass index (BMI) and waist circumference (WC). This cross-sectional study was based on 1,447 subjects between 30 and 60 years of age. Subjects were categorized into 4 groups by BMI and WC [group 1, BMI<$25kg/m^2$ and WC<85 cm; group 2, BMI<$25kg/m^2$ and WC>85 cm; group 3, BMI>$25kg/m^2$ and WC<85 cm; and group 4 (BMI>$25kg/m^2$ and WC>85 cm. Logistic regression analyses showed that subjects in group 2 had 1.75 times increased risk of clustering of 2 or more CRFs compared with subjects in group 1 (p<0.001). In conclusion, early detection of people with normal weight but high waist circumference may prevent them from getting worse by implementation of lifestyle intervention, consisting of regular exercise and healthy eating. In addition, further studies on appropriate exercise contents for them should be examined.

• Tribology and Lubricants
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• v.27 no.6
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• pp.308-313
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• 2011

In this study, friction tests were performed in order to investigate the effect of sliding velocity and normal load on the friction characteristics of DLC (a-C:H) and WC/C (a-C:H:W) using a ball-on-disk type friction tester. DLC and WC/C were deposited on AISI 52100 steel balls. Friction tests against carburized SCM 415 Cr-Mo steel disks were carried out under various sliding velocity (0.1, 0.78, 1.56, 3.13, 6.25, 12.5, 25, 50 and 100 mm/s) and normal load (2.4, 4.8 and 9.6 N) conditions while the relative humidity was 20~40 % R.H. and air temperature was $16{\sim}24^{\circ}C$. As results, kinetic friction coefficients of DLC and WC/C were obtained under each test condition. The results show that the kinetic friction coefficients of DLC and WC/C generally increase with the increase in sliding velocity. And, under the same sliding velocity condition, the kinetic friction coefficients are almost constant regardless of normal load. In addition, the kinetic friction coefficients of DLC are lower than those of WC/C under the same test conditions.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.152-156
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• 2007

Tungsten carbide powder was synthesized by SHS (self-propagating high-temperature synthesis). Except $WO_{3}$, each concentration of raw material ($WO_{3},\;Mg,\;NaCl,\;Na_{2}CO_{3},\;C$) was investigated. Final product was characterized by XRD and SEM. X-ray data demonstrated that the $NaCl+Na_{2}CO_{3}$ combined mixture has superiority in the WC formation process. Single phase and submicrometer WC powder was synthesized at the temperature below $1600^{\circ}C$. The role of sodium salts in combustion process was discussed, and chemical mechanism of WC formation was proposed. WC powder prepared by salt-assisted combustion synthesis has a size $0.2{\sim}3\;{\mu}m$ and low agglomeration degree.

• Journal of Welding and Joining
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• v.14 no.6
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• pp.101-108
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• 1996

In this study, WC-l7wt% Co composite powder for thermal spray was fabricated by spray drying method. The agglomerated composite powder had spheroidal morphology and the particle size distribution was 20~60${\mu}{\textrm}{m}$. WC and Co were distributed homogeneously. However, the strength of the spray-dried agglomerate was low due to the pores within the agglomerate. Therefore, the spray-dried agglomerate was broken down during HVOF thermal spray and the microstructure was inhomogeneous with many pores within the coating layer. And the decomposition of WC to W and $W_{6}$ $C_{2.54}$ was accelerated. The strength and flowability of the agglomerate were greatly improved by sintering heat treatment(110$0^{\circ}C$, 1 hour, hi atmosphere), and then the coating layer showed dense and homogeneous microstructure with well-developed splats. The hardness of the coating layer was H $v_{300}$ = 1072.2.2.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.2
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• pp.102-111
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• 1997

This paper deals with the machinability based on turning of WC-Co allows with the coated and the sintered diamond tools. The main conclusions obtained are as follows. (1) When machining WC-10%Co alloy, the flank wear of sintered diamond tool increases more largely with the increase of cutting speed in comparison with coated diamond tool. The tool wear decreases with the increase of the grain size and nose radius of sintered diamond tool. (2) When machining WC-20%Co alloy, the tool wear and cutting force decrease with the decrease of rake angle. Their exists a certain cutting speed range to exhibit the smallest tool wear in machining the WC-20%Co alloy, and this critical cutting speed becomes higher by 2 times in the case of coated diamond tool compared with sintered diamond tool. (3) The machinability becomes better with the increase of Co content. The effects of cutting speed and feed rate on the roughness of machined surface become smaller with the increase of Co content.

• Korean Journal of Materials Research
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• v.18 no.7
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• pp.357-361
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• 2008

Microstructure and mechanical properties of WC-3 wt% Co cemented carbides, fabricated by a spark plasma sintering (SPS) process, were investigated in this study. The WC-3 wt%Co powders were sintered at $900{\sim}1100^{\circ}C$ for 5min under 40MPa in high vacuum. The density and hardness were increased as the sintering temperature increased. WC-3 wt%Co compacts with a relative density of 97.1% were successfully fabricated at $1100^{\circ}C$. The fracture toughness and hardness of a compact sintered at $1100^{\circ}C$ were $21.6 MPa{\cdot}m^{1/2}$ and 4279 Hv, respectively.