• Journal of Welding and Joining
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• v.15 no.1
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• pp.125-134
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• 1997

This study was conducted by L9 orthogonal array to obtain optimum spray parameters for This study was conducted by L9 orthogonal array to obtain optimum spray parameters for $Cr_3C_2 - 7wt%$(80wt%Ni-20wt%Cr) coating powder. The factors were hydrogen flow rate, oxygen flow rate, gun-to-work distance, powder feed rate. And evaluation methods for the coating were surface roughness, oxygen concentration, micro-hardness, pore size and distribution, low angle ($30^{\circ}$) erosion rate, and microstructure of coating. The optimum HVOF spray conditions were proved as follows : hydroen flow rate ; 681 SLPM, oxygen flow rate ; 215 SLPM $H^2/O^2 ratio= 3.16), gun-to-work distance ; 22cm, powder feed rate; 25g/min. The hardness (Hv300) was 1147 and the erosion rate ($30^{\circ}$degree) was $3.16\times10^{-4}$g/g. It is believed that the optimized spray conditions can be improved the wear-resistance and anti-erosion characteristics of the coating.

• Journal of Welding and Joining
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• v.15 no.1
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• pp.116-124
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• 1997

A scope of this study is to establish the optimum plasma spray conditions for fine ($5\mu\textrm{m}$) $Al_2O_3$ powder. However, the flowability of the $Al_2O_3$ powder is not so good because of irregular particle shape and fine particle size. Therefore, powder feeding system was modified by 1) change of powder feeding line material from polymer to copper 2) shorten the powder feeding tube length 3) heating the powder feeding system to $80^{\circ}C$4) vibrating the powder feeding line continuously, in order to feed the fine powder homogeneously. The homogeneous powder feeding conditions were obtained with the modified powder feeding system by controlling the powder carrier gas flow and the powder flow rate indicator. The best plasma spraying conditions for the fine $Al_2O_3$ powder were found out as 40kw gun power, 80 g/min. powder feed rate and 50 mm working distance after characterizing the microstructure, hardness and wear loss of the $Al_2O_3$ coating layer.

• Journal of Welding and Joining
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• v.20 no.2
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• pp.109-115
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• 2002

In the case of using high temperature by coating ceramic/metal, large stress was produced due to difference of thermal expansion coefficient between those. And then lead to delamination. In order to relaxation of the stress A1$_2$O$_3$/SS316 composite powders with $10wt.%Al_2O_3$ compositional gradient and $10wt.%Al_2O_3$ agglomerated powder were made by spray drying method. These powders were sintered to improve the strength and to be plasma sprayed in order to fabricate the FGC(functionally graded coating). The influence of gun power, working distance and Ar pressure on the microstructure of the coating layer was studied in order to optimize the plasma spray conditions. It was proven that the optimum conditions were 40kw gun power, 5cm working distance and $100ft^3/h$ Ar flow for both powders. FGC with 10 compositional steps was fabricated and the total thickness was 1.3mm. FGC was heat treated at $1100^{\circ}C$for 10hours to evaluate the heat resisting characteristics.

• Journal of the Korean Ceramic Society
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• v.53 no.6
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• pp.628-634
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• 2016

The 8 wt% yttria($Y_2O_3$) stabilized zirconia ($ZrO_2$), 8YSZ, a typical thermal barrier coating (TBC) for turbine systems, was fabricated under different starting powder conditions and coating parameters by atmospheric plasma spray (APS) coating process. Four different starting powders were prepared by conventional spray dry method with different additive and process parameter conditions. As a result, large- and small-size spherical-type particles and Donut-type particles were obtained. Dense structure of 8YSZ coating was produced when small size spherical-type or Donut-type particles were used. On the other hand, 8YSZ coating with a porous structure was formed from large-size spherical-type particles. Furthermore, a segmented coating structure with vertical cracks was observed after post heat treatment on the surface of dense structured coating by argon plasma flame at an appropriate gun distance and power condition.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.238-239
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• 2006

Nozzle geometry influences gas dynamics making sprayed particle behavior one of the most important parameters in cold spray process. Gas flows at the entrance convergent section of the nozzle takes place at relatively high temperature and are subsonic. Thus, this region is a very suitable environment for heating spray particle. In this study, numerical simulation and experiments were conducted to investigate the effect of nozzle contour, entrance geometry of nozzle and powder injection position at nozzle on the cold spray process. The process changes were observed through numerical simulation studies and the results were used to find a correlation with coating properties.

• Korean Journal of Materials Research
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• v.22 no.4
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• pp.211-214
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• 2012

Optimal conditions for HA plasma spray-coating on Ti6Al4V alloy were investigated in order to obtain enhanced bone-bonding ability with Ti6Al4V alloy. The properties of plasma spray coated film were analyzed by SEM, XRD, surface roughness measurement, and adhesion strength test because the film's transformed phase and crystallinity were known to be influential to bone-bonding ability withTi6Al4V alloy. The films were formed by a plasma spray coating technique with various combinations of plasma power, spray distance, and auxiliary He gas pressure. The film properties were analyzed in order to determine the optimal spray coating parameters with which we will able to achieve enhanced bone-bonding ability with Ti6Al4V alloy. The most influential coating parameter was found to be the plasma spray distance to the specimen from the spray gun nozzle. Additionally, it was observed that a relatively higher film crystallinity can be obtained with lower auxiliary gas pressure. Moderate adhesion strength can be achievable at minimal plasma power. That is, adhesion strength is minimally dependent on the plasma power. The combination of shorter spray distance, lower auxiliary gas pressure, and moderate spray power can be recommended as the optimal spray conditions. In this study, optimal plasma spray coated films were formed with spray distance of 70 mm, plasma current of 800 A, and auxiliary gas pressure of 60 psi.

• Transactions of Materials Processing
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• v.24 no.4
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• pp.287-292
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• 2015

The possibility of chemical precipitation for recycled ammonium paratungstate (APT) was studied. WO₃ particles were synthesized by chemical precipitation method using a 1:2 weight ratio of APT:DI-water. At the 500℃ sintering temperature, the X-ray diffraction results showed that APT completely decomposed to WO₃. For the granulated powder WC-Co, vacuum heat treatment at proper temperatures increases tap density and flow-ability. Hardness of the WC-Co thermal spray coating layer was measured in the range HV 831~1266. Spray conditions for the best characteristic values were an oxygen flow rate=1500 scfh, a fuel flow rate = 5.25gph and a gun distance = 320mm.

• Korean Journal of Materials Research
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• v.25 no.5
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• pp.226-232
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• 2015

High temperature plasma coating technology has been applied to recover damaged aluminum dies from wear by spraying pure aluminum and alumina powder. However, the coated mixed powder layer composed of aluminum and alumina often undergoes a detachment from the substrate, making the coated substrate die unable to maintain its expected life span. In this study, in order to increase the bonding strength between the substrate and the coating layer, a pure aluminum layer was applied as an intermediate bond layer. In order to prepare the specimen with variable bond coating conditions, the bond coat layers with a various gun speed from 10 cm/sec to 30 cm/sec were prepared with coating cycle variations ranging from three to nine cycles. The specimen with a bond coat layer coated with a gun speed of 20 cm/sec and three coating cycles exhibited ~13MPa of adhesion strength, while the specimen without a bond coat layer showed ~6 MPa of adhesion strength. The adhesion strength with a variation of bond coat layer thickness is discussed in terms of coating parameters.

• Journal of the Korean institute of surface engineering
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• v.30 no.6
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• pp.400-405
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• 1997

The experimental study has been performed to deposit to deposit chromia powder on magnssium alloy for tribological and mechanical properties. The optimal condition was obtained by changing the spray condition such as working distance and gun power. As ceramics was coated onto the a light metal such as Mg according to the weight reduection of the car engine block, it could acquire that the engine efficiency deu to the weight reduction and properties such as resistance to heat, as well as wear. Coating qualities are discussed with respect to hardness, tribologicalproperty, and microstructure. The tribological and mechanical properties are investigated by using the reciprocal configuration tribometer and microharduess tester. Wear mode is determined by observing the SEM morhpology of wear track and cross section view of wear track.

• Journal of the Korean Wood Science and Technology
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• v.36 no.6
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• pp.113-120
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• 2008

This study was performed to develop environmentally-friendly finishing materials for construction. In order to abate formaldehyde and ammonia in indoor air, liquid coating agents for indoor finishing were formulated with bamboo charcoal powder, cypress extracted water, and water-borne acrylic binder. Deodorization rate, far-infrared ray emission rate, anions emission amount, and anti-bacterial effect were investigated. Deodorization rate was increased as cypress extracted water content increased. Deodorization rates of the coating agents were 60.0~98.6% on formaldehyde and 76.7~86.2% on ammonia. No differences on far-infrared ray emission rate, anions emission amount, and anti-bacterial effect were found depending on different formulations. A 91.7% of far-infrared ray emission rate, 77 ea/cc of anions emission amount, and 99.4% of anti-bacterial effect were detected for all formulations. More effective application method of the coating agents revealed was a spray-gun. A $0.66kg/m^2$ of coating agent with a spray-gun and $0.94kg/m^2$ of coating agent with a brush was consumed each.