• 한국재료학회지
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• 제30권7호
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• pp.350-358
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• 2020

A variety of composite powders having different aluminum and carbon contents are prepared using various organic solvents having different amounts of carbon atoms in unit volume as ball milling agents for titanium and aluminum ball milling. The effects of substrate temperature and post-heat treatment on the texture and hardness of the coating are investigated by spraying with this reduced pressure plasma spray. The aluminum part of the composite powder evaporates during spraying, so that the film aluminum content is 30.9 mass%~37.4 mass% and the carbon content is 0.64 mass%~1.69 mass%. The main constituent phase of the coating formed on the water-cooled substrate is a non-planar α₂ phase, obtained by supersaturated carbon regardless of the alloy composition. When these films are heat-treated at 1123 K, the main constituent phase becomes γ phase, and fine Ti₂AlC precipitates to increase the film hardness. However, when heat treatment is performed at a higher temperature, the hardness is lowered. The main constitutional phase of the coating formed on the preheated substrate is an equilibrium gamma phase, and fine Ti₂AlC precipitates. The hardness of this coating is much higher than the hardness of the coating in the sprayed state formed on the water-cooled substrate. When hot pressing is applied to the coating, the porosity decreases but hardness also decreases because Ti₂AlC grows. The amount of Ti₂AlC in the hot-pressed film is 4.9 vol% to 15.3 vol%, depending on the carbon content of the film.

• 한국세라믹학회지
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• 제24권3호
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• pp.235-242
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• 1987

This study was about to make zirconia ceramics with yttria, using spraying precipitation method for the purpose of powder control. The powder properties and the characterization of sintered body, were studied. As the results, 1. The synthesized powder had homogeneity of spherical shape, and average particle size was 2-3 um. 2. Crystallization temperature increased with Y2O3 content. 3. Apparent density of sintered body (fired above 1500$^{\circ}C$) was higher than 98% of theoretical value in 3 mol% Y2O3 content. 4. High KIC values(19kg/㎣/2) in 3 mol % Y2O3 content resulted from sintering density increasement.

• 한국재료학회지
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• 제11권9호
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• pp.763-768
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• 2001

Molybdenum-based thermal spray powder is widely used for coating the moving parts of the internal combustion engines due to its excellent wear resistance. A composite powder of the $Mo_{40}(Al_{1-x}Si_x)_{60}$ system was synthesized using the SHS method. The synthesized bulk was pulverized and specially treated to produce thermal spray powder. It was found that the synthesis reaction consisted of two-steps: the formation of $Al_8/Mo_3$ and the formation of Mo(Al,Si)$_2$. Both the temperature and the rate of the SHS reaction linearly increased with the increase of the value of x in $Mo_{40}(Al_{1-x}Si_x)_{60}$, The temperature and the rate of the reaction were also affected by the compacting density of the specimens, exhibiting the maximum valves at 62% and 60%, respectively. Since spherical shape is advantageous to the thermal spraying process, shape-control of the powder was attempted with PVA as a binding additive, resulting in the successful production of almost perfectly spherical powder of 80 $\mu\textrm{m}$ Ø$(d_{50})$ mean particle size.

• Journal of Welding and Joining
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• 제11권4호
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• 한국정밀공학회지
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• 제17권6호
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• pp.162-168
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• 2000

The automatic die polishing machine by liquid honing has been developed and experimented on the surface of machined die. The goal of development in the automatic die polishing machine by liquid honing is to increase the accuracy and the productivity in die polishing. To reach this goal, the polishing machine consists of the automatic measuring device for contour of die, the nozzle and pumping system to spray the powder mixed with liquid, and the 3-axis guides. Before polishing, the measuring device with a semiconductor laser scans the surface of mould to get the data of contour. The data store a PC and use to control the nozzle head to move above a couple of centimeters on the machined surface of die. The experimental parameters are the spraying time, the pressure, the size of abrasive grain and the mixing ratio between abrasive grain and liquid. The surface roughness is measured on the polished die which are SKDl 1 and Al7075 machined by NC. The surface roughness indicates the values of Rmax 0.5${\mu}{\textrm}{m}$ for Al7075 and Rmax 1.4${\mu}{\textrm}{m}$ for SKDl 1. It reduces the polishing time significantly and reduces the monotonous work for labors. As the results, the liquid honing system is useful method to apply for the die polishing and the automatic die polishing machine using liquid honing shows that it's very effective processing ability.

• 동력기계공학회지
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• 제4권4호
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• pp.48-53
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• 2000

This study was aimed at observing the influence of laser irradiation on a $ZrO_2-8%Y_2O_3$ ceramic coating layer fabricated by plasma spraying. The $ZrO_2-8%Y_2O_3$ ceramic powder was plasma sprayed onto SS400 carbon steel substrate and laser irradiated on the coating layer under various conditions of laser power and beam diameters. As to the as-sprayed specimen and laser-treated specimen, a hardness test and a microstructure analysis were performed. Hardness was measured by a microhardness tester; microstructure was observed by an optical microscope and a scanning electron microscope. The result was that the microstructure of the laser-irradiated coating layer was dense; porosities almost disappeared and hardness increased. It was also observed that microcracks occured in the laser-irradiated coating layer.

• Journal of Welding and Joining
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• 제14권4호
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• pp.43-52
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• 1996

The plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical properties of the plasma sprayed Cr$_{2}$C$_{2}$-NiCr coatings were examined in this study. The distribution of the residual stress with the coating thickness was also examined by X-ray diffraction method. The pore in the coatings could be classified into two types ; one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occurred at the interface of top coat and substrate or top coat and bond coat depending on the existence of bond coat. It was found that the compressive residual stress near the interface decreased with the increase of the top coat thickness. The tensile adhesion strength of the coating without bond coat was higher than that with bond coat, because the coating with bond coat has higher horizontal crack density near the interface between bond coat and top coat.

• 한국세라믹학회지
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• 제38권7호
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• pp.602-607
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• 2001

Zirconia powder containing 3 mol% yttria (3Y-PSZ) was casted on the cast iron substrate by plasma spraying method. Coated specimens were then heat treated at 500$\^{C}$ in nitrogen plasma. Wear tests were performed on nitrogen heat treated and non heat treated samples at temperatures from 25$\^{C}$ to 600$\^{C}$. Wear results showed that the friction coefficient and the wear loss of both the treated and the non-treated samples showed maximum value at 400$\^{C}$. These results were explained by low temperature thermal degradation due to the monoclinic transformation. Nitrogen plasma treatment significantly improved the tribological performance. The effect of nitrogen heat treatment on tribological behavior was explained by the increased micro-hardness and decreased monoclinic faction.

• Journal of Welding and Joining
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• 제8권4호
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• pp.58-68
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• 1990

The formation of thermal stresses by plasma spraying is generally considered as adverse. Therefore, the knowledge of stress distribution in the deposited layer during and after plasma spraying will be of special interest. In this study finite difference heat transfer analysis and finite element stress analysis were carried out to predict the change of stress distribution in the plasma coated layer with the variations of preheat temperature, number of scan, particle size, and bond coat. The results of the numerical analysis were as follows: 1) Transient stresses developed in the coated layer were up to the level of yiedl strength at the temperature. 2) The tensile stresses were developed in the deposited layer and the surface of the substrate, but the compressive stresses were developed in the rest of the substrate. 3) Transient and residual stresses were significantly affected by the preheat temperature. 4) The variations of temperature of powder particle and number of torch scan changed tensile stress distribution, but made no difference on the magnitude of the stresses. 5) Bond coated layer reduced the stree level of deposited layer.

• 한국분말재료학회지
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• 제6권3호
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• pp.224-230
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• 1999

Oxide powders of $Cr_2O_3 \;and\;Cr_2O_3+3{\%}TiO_2$ were prepared by spray drying, plasma densification and fused+crushed processes. The oxide coating layers were made by plasma spray and characterized by microstructure, hardness, adhesion strength and relative density. The optimum spray distance for the high quality coatings by spraying dried powders was found to be 9cm. A small amount addition of $TiO_2\;in\;Cr_2O_3$ powder significantly improved coating characteristics by lowering the melting point of powders. The hardness and relative density of coating layers of the plasma densified powders were comparable to fused and crushed powders, however, the adhesion strength was much higher in the former case.