• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.921-924
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• 2004

This paper is to investigate a crack for plasma sprayed MCrAlY coated material by acoustic emission method in 4-point bending test. The CoNiCrAlY is coated on Inconel-718 by vacuum plasma spray process. Micro-hardness measurement was conducted by means of Micro Vickers-hardness indentor. The porosity of coating layer was measured using a SEM and Image Analyzer. AE monitoring system is composed of PICO type sensor, a wide band preamplifier(40dB), a PC and AE DSP(16/32 PAC) board. The AE count, Hit and energy of coating specimens is measured according to coating thickness.

• Journal of Powder Materials
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• v.6 no.3
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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.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1205-1210
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• 1999

Ceria based electrolytes were fabricated by a plasma spraying method. The porosity which was crated during the plasma spraying process was infiltrated with Ce0.8Gd0.2O2 sol by ultrasonic treatment and heat treatment at 90$0^{\circ}C$ in order to improve physical and electrical properties. The porosity decreased from 9.8% to 6.5% and gas permeability at 80$0^{\circ}C$ decreased from 16.7$\times$10-3 to 5.7$\times$10-3 cm3(STP)/cm2.s.cmHg as the number of treatment increased 10 cycles. The ionic conductivity was also increased about 30% after 10 times of sealing.

• Journal of Periodontal and Implant Science
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• v.23 no.3
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• pp.493-506
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• 1993

For maintenance of an ailing or failed implant it is essential to treat the implant fixture surface so as to remove bacterial endotoxin and make a surface tolerated by surrounding soft and hard tissue. Thus in this study the method that makes the smoothest surface treated with a high speed diamond bur, a low speed diamond bur, a stone, a rubber point or Jetpolisher was studied. With the profilomenter a mean value of $R_{max}$ was measured. The hight speed diamond, the rubber point and the Jetpolisher showed a mean $R_{max}\;7.77{\mu}m$. The low speed diamond bur, the rubber, point and the Jetolisher made a mean value of $R_{max}\;8.44{\mu}m$. The stone, the rubber point and the Jetolisher showed the smoothest surfaces with a mean value of $R_{max}\;6.24{\mu}m$. TPS (titanium plasma sprayed) areas showed a mean vlaue of $R_{max}\;24.42{\mu}m$, and the smooth surfaced titanium disc manufactured by the company (IMZ, Germany) shows a mean value of $R_{max}\;3.00{\mu}m$. Under the SEM examination the disc treated with a high speed diamond bur, a rubber point and a Jetpolisher showed partially remaining TPS particles, but the height of these particles were reduced remarkably compared with those of the original TPS. The disc treated with a low speed diamond bur, a rubber point and a Jetpolisher showed a rough topography with remaining TPS on the entire surface. A stone, a rubber point and a Jetpolisher removed almost TPS and the bulk titanium metal was exposed and some scratches were made by the stone. All treated discs were revealed as rougher than the smooth surface disc manufactured by the company. An untreated TPS disc shows a very irregular surface and a $40{\mu}m$ height of the plasma sprayed areas.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.851-856
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• 2002

Tribological behavior of plasma-sprayed $Cr_2O_3$-based coatings containing $MoO_3$ at 450$^{\circ}C$ was investigated to understand the influence of $MoO_3$. A reciprocal disc-on-plate type tribo-tester was employed to examine fricition and wear behavior of the specimens. The microstructure and phase composition of the coating was characterized with Transmission Electron Microscopy(TEM). The TEM analysis indicated that $MoO_3$ was dispersed into the grain boundary, resulting in the increase of the hardness and density of the coating. Worn surfaces were investigated by scanning electron microscopy and chemistry of the worn surfaces was analyzed using a X-ray Photoelectron Spectrometer(XPS). The results showed that the friction coefficient of the $MoO_3$-added coatings was lower than that without $MoO_3$ addition. The larger protecting layers were observed at the worn surface of plasma spray coated specimens with $MoO_3$ composition in the protecting layer appears to be more favorable in reducing the friction.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.51-52
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• 2006

[ $Ti_{45}Zr_{38}Ni_{17}$ ] powders were thermally sprayed onto mild steel substrates in air and under a reduced pressure of argon. Several oxides were formed after thermally-spraying the mechanically-alloyed powders in air. After spraying in a reduced pressure of argon, the coating layers obtained from the gently mixed powders consisted of the elemental metals, but an amorphous phase primarily appeared in the thermally-sprayed mechanically-alloyed powders, which transformed into the icosahedral quasicrystal phase and a minor $Ti_2Ni-type$ crystal phase after annealing at 828 K. The Vickers hardness and the contact angle with pure water for the quasicrystal layers were about 7 GPa and $92^{\circ}$ respectively.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.1
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• pp.142-149
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• 1997

Ceramic-coated anilox roll for printing is resistant to corrosion and wear, and hence has enhanced life and quality. Laser engraving is used typically for machining holes to store ink in this roll. Since engraved hole size and shape are directly related to laser processing parameters, it is necessary to know the rela- tionships among these parameters. In this study, the parameters for engraving of ;oasma sprayed ceramic coatings with Nd:YAG laser were studied. Relationships between hole shape and processing parameters were analyzed. Cr$_{2}$O$_{3}$ceramic was found to be most suitable for Nd:YAG laser engraving. It was found that hole depth can be increased by using higher energy pulses. Effect of using different assistant gases was small to the final results. For better results, it was suggested to use a very stable laser with shorter pulses and higher pulse energy.

• Journal of the Korean institute of surface engineering
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• v.34 no.5
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• pp.499-502
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• 2001

Functionally gradient NiCrAlY/$ZrO_2$-$Y_2$$O_3$ and NiCrAlY/$ZrO_2$- $CeO_2$-$Y_2$$O_3$ coatings were prepared by APS. The as-sprayed microstructure consisted of metal-rich and ceramic-rich regions, between which $Al_2$$O_3$-rich layers existed owing to the oxidation during APS. During oxidation between 900 and $1100^{\circ}C$ in air, the pre-existing $Al_2$$O_3$-rich scales grew, due mainly to the preferential reaction of Al with inwardly transporting oxygen along the heterogeneous phase boundaries. As the amount of ceramics in the coating increased, the oxidation resistance increased.

• Journal of Ocean Engineering and Technology
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• v.15 no.4
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• pp.60-65
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• 2001

Thermal spray coating is formed by a process in which melted particles flying with high speed towards substrate, then crash and spread on the substrate surface cooled and solidified in a very short time, Stacking of the particles makes coating. In this study, the exfoliation of $Al_2$O$_3$ and Ni-4.5wt.%Al thermally sprayed coating which were deposited by an atmospheric plasma spray apparatus are investigated using an AE method. A tensile test is conducted on notch specimens in a stress range below the elastic limit of substrate. The wave forms of AE generated from the three coating specimens can be classified by FFT analysis into two types which low frequency(type I waveform is considered to corresponds exfoliation of coating layers and type II waveform corresponds the plastic deformation of notch tip or the resultant fracture of coating. The fracture of the coating layers can estimate by AE event and amplitude, because AE features increase when the deformation generates.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.444-450
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• 1999

Hydroxyapatite(HA) was spray-coated to alloy substrate(Ti-6Al-4V) using plasma-spray process for bioceramic application The coating morphology composition and crystallinity were influenced by following process parameters ; stand-off distance spray power level and auxiliary gas pressure. These parameters have been systematically varied in the present study to evaluate their relative influence on the coating qual-ity and to seek an optimum spraying condition. Amorphicity and decomposition of HA increased with stand-off distance and the imperfect coating layer was obtained at the short stant-off distance (55mm). The cry-stallinity of HA coating decreased with spray power level and auxiliary gas pressure but the bond strength between the HA coated layer and Ti alloy substrate increased with the spray power level.