• 한국분말재료학회지
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• 제7권2호
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• pp.63-70
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• 2000

Thermal spray coating process has proven to be effective at producing hard, dense, wear resistance coatings on the relatively mild substrates. Among several spraying techniques, HVOF (High Velocity Oxygen Fuel) and plasma coating processes, which are preferentially used for the wear resistance application such as capstans, have been applied in this study. The effects of pre-treatment, it-process and post-treatment parameters on the wear and mechanical properties of WC+12%Co, Cr3C2 and Al2O3 powder coatings have been investigated and correlated with the microstructures. The results indicated that the carbide coating was more preferable to the oxide coatings and the post-treatments consisting of vacuum annealing and sealing on carbide coatings led to significant improvements in wear resistance, adhesive strength and coating phase stabilization over the other processing techniques in this application.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.509-510
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• 2006

Correlations between in-flight particle, splat and coating microstructure of thermally sprayed Ni20Cr were investigated. Flame spray and arc spray systems were employed for spraying Ni20Cr powder and Ni20Cr wire, respectively. The results showed that the arc spray process produced a broader size distribution for both in-flight particles and splats compared to flame process. Flower-like splat morphology was obtained from the arc spray whereas a pancake-like splat was obtained by flame spray. Ni20Cr coating sprayed by arc process had a denser microstructure, lower porosity and better adhesion at the interface.

• Journal of Welding and Joining
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• 제24권5호
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• pp.57-61
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• 2006

For the production of functional $TiO_2$-biodegradable plastic (polybutylene succinate:PBS) composite material with photocayalytic activity, we attempted to prepare $TiO_2$ coatings on PBS substrate by HVOF and plasma spraying techniques under various conditions. The microstructures of coatings were characterized with SEM and XRD analysis, and the photocatalytic efficiency of coatings was evaluated by the photo degradation of gaseous acetaldehyde. The effects of primary particle size and spraying parameters on the formation behavior, photocatalytic performance of the coatings have been investigated. The results indicated that for both the HVOF sprayed $P_{200}$ and $P_{30}$ coatings, the high anatase ratio of 100% can be achieved regardless of fuel gas pressure. On the other hand, the HVOF sprayed $P_7$ coating exhibited a largely decreased anatase ratio (from 100% to 49.1%) with increasing the fuel gas pressure, which may be attributed to much higher susceptibility of heat for 7 nm agglomerated powder. HVOF sprayed $P_{200}$ and $P_{30}$ coatings show better performance as compared to that of plasma sprayed $P_{200}$ coatings owing to the higher anatase ratio. However, the HVOF sprayed $P_7$ coatings did not show the photocatalytic activity, which may result from the extremely small reaction surface area to the photocatalytic activity and low anatase ratio.

• Design & Manufacturing
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• 제14권1호
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• pp.36-41
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• 2020

Recently, due to the development of MEMS technology, researches for the production of effective micro structures and shapes have been actively conducted. However, the process technology based on chemical etching has a number of problems such as environmental pollution and time problems due to multi-process. Various processes to cope with this process are being studied, and one of the mechanical etching processes is the powder blasting process. This process is a method of spraying fine particles, which has the advantage of being an effective process in manufacturing hard brittle materials. However, it is also a process that adversely affects the material surface roughness and material properties due to the impact of the injection of fine particles. In this study, after fabricating micro-channels in fused silica glass with excellent optical properties among the hard brittle materials, we used the nano indentation system to analyze the micro parts using nano-particles as well as machinability and surface roughness analysis of the processed surface. The analysis was performed for the effective processing of powder blasting.

• 한국재료학회지
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• 제24권7호
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• pp.357-362
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• 2014

Thermal barrier coatings(TBCs) are being applied in many industrial fields such as thermal power generation, aviation and seasonal fields. $ZrO_2-Y_2O_3$(8%) thermal spray coating powders are commercially used as thermal-barrier coating materials to protect against oxidation and corrosion of heat-resistant alloys at elevated temperatures. Currently, $ZrO_2-Y_2O_3$(8%) thermal-spray powder is made using the industrial co-precipitation process, which is very complex and requires a lot of time. In this study, orthorhombic $ZrO_2$ and $Y_2O_3$ powders were fabricated by mechanical mixing, which is more economical than the co-precipitation process. A tetragonal, yttria-stabilized zirconia(YSZ) coating-layer was produced by plasma spraying, using orthorhombic $ZrO_2-Y_2O_3$(8%) powder. Our experimental results indicate that $ZrO_2-Y_2O_3$(8%) mixed powder can be used economically in industry because it is no longer necessary to make this powder by liquid and gas-phase methods.

• 한국자동차공학회논문집
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• 제24권3호
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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.

• 한국분무공학회지
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• 제11권2호
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• pp.59-68
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• 2006

Experimental results of the metal powder production with internal mixing, internal impinging and the atomizer coupled with substrate design are presented in this paper. In a test with internal mixing atomizer, mean powder size was decreased from $37{\mu}m\;to\;23{\mu}m$ for Pb65Sn35 alloy as the gas-to-melt mass ratio was increased from 0.04 to 0.17. The particle size further reduces to $16.01{\mu}m$ as the orifice area is increased to $24mm^2$. The micrograph of the metal powder indicates that very fine and spherical metal powder has been produced by this process. In a test program using the internal impinging atomizers, the mean particle size of the metal powder was decreased from $22{\mu}m\;to\;12{\mu}m$ as the gas-to-melt-mass ratio increased from 0.05 to 0.22. The test results of an atomizer coupled with a substrate indicates that the deposition rate of the molten spray on the substrate is controlled by the diameter of the substrate, the height of the substrate ring and the distance of the substrate from the outlet of the atomizer. This in rum determines the powder production rate of the spraying processes. Experimental results indicate that the deposition rate of the spray forming material decreases as the distance between the substrate and the atomizer increases. For example, the deposition rate decreases from 48% to 19% as the substrate is placed at a distance from 20cm to 40cm. On the other hand, the metal powder production rate and its particle size increases as the subsrate is placed far away from the atomizer. The production of metal powder with mean particle size as low as $3.13{\mu}m$ has been achieved, a level which is not achievable by the conventional gas atomization processes.

• 열처리공학회지
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• 제20권5호
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• pp.231-236
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• 2007

High velocity oxy-fuel (HVOF) spraying was used to coat Ti(Al,O)/$Al_2O_3$ powder onto the SS41 steel plate. Macrostructure of the coated specimen has been investigated by scanning electron micrograph (SEM). High temperature oxidation behavior of the coated specimen and SS41 steel have been studied. From the results of SEM observation, Ti(Al,O)/$Al_2O_3$ powder was coated well onto the substrate SS41 steel. Porosity onto the coated layer was only 0.38%. The oxidation results showed that Ti(Al,O)/$Al_2O_3$ powder coated SS41 steel have improved little oxidation resistance at $900^{\circ}C$ in air, but improved remarkably oxidation resistance at $800^{\circ}C $ in air compare to the substrate SS41 steel.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1069-1074
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• 2019

A novel fabrication method of oxide dispersion strengthened (ODS) steel cladding tubes for advanced fast reactors has been investigated using the cold spray powder-based materials deposition process. Cold spraying has the potential advantage for rapidly fabricating ODS cladding tubes in comparison with the conventional multi-step extrusion process. A gas atomized spherical 14YWT (Fe-14%Cr, 3%W, 0.4%Ti, 0.2% Y, 0.01%O) powder was sprayed on a rotating cylindrical 6061-T6 aluminum mandrel using nitrogen as the propellant gas. The powder lacked the oxygen content needed to precipitate the nanoclusters in ODS steel, therefore this work was intended to serve as a proof-of-concept study to demonstrate that free-standing steel cladding tubes with prototypical ODS composition could be manufactured using the cold spray process. The spray process produced an approximately 1-mm thick, dense 14YWT deposit on the aluminum-alloy tube. After surface polishing of the 14YWT deposit to obtain desired cladding thickness and surface roughness, the aluminum-alloy mandrel was dissolved in an alkaline medium to leave behind a free-standing ODS tube. The as-fabricated cladding tube was annealed at $1000^{\circ}C$ for 1 h in an argon atmosphere to improve the overall mechanical properties of the cladding.

• 한국분말재료학회지
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• 제16권6호
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• pp.403-409
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• 2009

Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.