• Title/Summary/Keyword: High velocity oxygen-fuel thermal spray coating

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The Effect of High Velocity Oxygen Fuel Thermal Spray Coating on Fatigue Crack Growth Behavior for Welded SM490B (SM490B 용접부의 피로균열 성장 거동에 미치는 초고속 용사코팅 효과)

  • Yoon, Myung-Jin;Choi, Sung-Jong;Cho, Won-Ik
    • Transactions of the Korean Society of Automotive Engineers
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    • v.14 no.4
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    • pp.99-106
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    • 2006
  • High velocity oxygen-fuel thermal spray coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks, and also these coating are well-known method to improve the fatigue strength of material. In this study, HVOF coated SM490B are prepared to evaluation of the effect of coating on tension and fatigue crack growth behavior. The pre-crack of the fatigue crack growth test specimens machined at deposited material area, heat affected zone and boundary, respectively. Through these test, the following results are obtained: 1) Tensile strength was about 498 MPa, and fracture occurred on base metal area. 2) The fatigue crack of coated specimens propagated more rapidly than non-coated specimen in all specimens. 3) In the same coating thickness specimens, the specimens with pre-crack at boundary more rapidly propagated than the specimens with pre-crack at HAZ and deposited material area. These results can be used as basic data in a structural integrity evaluation of rolled SM490B weldments considering HVOF coating.

Spray Coating Technology (스프레이 코팅 기술)

  • Lee, Chang-Hee
    • Journal of ILASS-Korea
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    • v.13 no.4
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    • pp.193-199
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    • 2008
  • Spray coating is a versatile surface modification technology in which coating is built-up based on the successive deposition of micron-scaled particles. Depending on the coating materials, the coatings can meet the required mechanical properties, corrosion resistance, and other properties of base materials. Spraying processes are mainly classified into thermal and kinetic spraying according to their bonding mechanism and deposition characteristics. Specifically, thermal spraying process can be further classified into many categories based on the design and mechanism of the process, such as frame spraying, arc spraying, atmospheric plasma spraying (APS), and high velocity oxygen-fuel (HVOF) spraying, etc. Kinetic spraying or cold gas dynamic spraying is a newly emerging coating technique which is low-temperature and high-pressure coating process. In this paper, overall view of thermal and kinetic spray coating technologies is discussed in terms of fundamentals and industrial applications. The technological characteristics and bonding mechanism of each process are introduced. Deposition behavior and properties of technologically remarkable materials are reviewed. Furthermore, industrial applications of spray coating technology and its potentials are prospected.

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Effect of Post Heat Treatment on the Microstructure and Mechanical Properties of BCuP-5 Filler Metal Coating Layers Fabricated by High Velocity Oxygen Fuel Thermal Spray Process on Ag Substrate (고속 화염 용사 공정으로 제조된 BCuP-5 필러 금속 코팅층/Ag 기판 클래드 소재의 후열처리에 따른 미세조직 및 기계적 특성 변화)

  • Park, So-Yeon;Youn, Seong-June;Park, Jae-Sung;Lee, Kee-Ahn
    • Journal of Powder Materials
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    • v.29 no.4
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    • pp.283-290
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    • 2022
  • A Cu-15Ag-5P filler metal (BCuP-5) is fabricated on a Ag substrate using a high-velocity oxygen fuel (HVOF) thermal spray process, followed by post-heat treatment (300℃ for 1 h and 400℃ for 1 h) of the HVOF coating layers to control its microstructure and mechanical properties. Additionally, the microstructure and mechanical properties are evaluated according to the post-heat treatment conditions. The porosity of the heat-treated coating layers are significantly reduced to less than half those of the as-sprayed coating layer, and the pore shape changes to a spherical shape. The constituent phases of the coating layers are Cu, Ag, and Cu-Ag-Cu3P eutectic, which is identical to the initial powder feedstock. A more uniform microstructure is obtained as the heat-treatment temperature increases. The hardness of the coating layer is 154.6 Hv (as-sprayed), 161.2 Hv (300℃ for 1 h), and 167.0 Hv (400℃ for 1 h), which increases with increasing heat-treatment temperature, and is 2.35 times higher than that of the conventional cast alloy. As a result of the pull-out test, loss or separation of the coating layer rarely occurs in the heat-treated coating layer.

A Study on Durability Characteristics for Plungers of Conventional Ceramic and Surface Modification by Powder Coating Using High Velocity Oxygen Fuel Thermal Spray (기존 세라믹 및 초고속 용사 분말피막 표면개질 플런저의 내구성 특성에 관한 연구)

  • Bae, Myung-whan;Park, Byoung-ho;Jung, Hwa
    • Transactions of the Korean Society of Automotive Engineers
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    • v.24 no.3
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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.

Friction Behavior of High Velocity Oxygen Fuel (HVOF) Thermal Spray Coating Layer of Nano WC-Co Powder

  • Cho, T.Y.;Yoon, J.H.;Kim, K.S.;Fang, W.;Joo, Y.K.;Song, K.O.;Youn, S.J.;Hwang, S.Y.;Chun, H.G.
    • Journal of the Korean institute of surface engineering
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    • v.40 no.4
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    • pp.170-174
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    • 2007
  • High Velocity Oxygen Fuel (HVOF) thermal spray coating of nano size WC-Co powder (nWC-Co) has been studied as one of the most promising candidate for the possible replacement of the traditional hard plating in some area which causes environmental and health problems. nWC-Co powder was coated on Inconel 718 substrates by HVOF technique. The optimal coating process obtained from the best surface properties such as hardness and porosity is the process of oxygen flow rate (FR) 38 FMR, hydrogen FR 57 FMR and feed rate 35 g/min at spray distance 6 inch for both surface temperature $25^{\circ}C\;and\;500^{\circ}C$. In coating process a small portion of hard WC decomposes to less hard $W_2C$, W and C at the temperature higher than its decomposition temperature $1,250^{\circ}C$ resulting in hardness decrease and porosity increase. Friction coefficient increases with increasing coating surface temperature from 0.55-0.64 at $25^{\circ}C$ to 0.65-0.76 at $500^{\circ}C$ due to the increase of adhesion between coating and counter sliding surface. Hardness of nWC-Co is higher or comparable to those of other hard coatings, such as $Al_2O_3,\;Cr,\;Cr_2O_3$ and HVOF Tribaloy 400 (T400). This shows that nWC-Co is recommendable for durability improvement coating on machine components such as high speed spindle.

Porosity Prediction of the Coating Layer Based on Process Conditions of HVOF Thermal Spray Coating (HVOF 용사 코팅 공정 조건에 따른 코팅층의 기공도 예측)

  • Jeon, Junhyub;Seo, Namhyuk;Lee, Jong Jae;Son, Seung Bae;Lee, Seok-Jae
    • Journal of Powder Materials
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    • v.28 no.6
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    • pp.478-482
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    • 2021
  • The effect of the process conditions of high-velocity oxygen fuel (HVOF) thermal spray coating on the porosity of the coating layer is investigated. HVOF coating layers are formed by depositing amorphous FeMoCrBC powder. Oxygen pressure varies from 126 to 146 psi and kerosene pressure from 110 to 130 psi. The Microstructural analysis confirms its porosity. Data analysis is performed using experimental data. The oxygen pressure-kerosene pressure ratio is found to be a key contributor to the porosity. An empirical model is proposed using linear regression analysis. The proposed model is then validated using additional test data. We confirm that the oxygen pressure-kerosene pressure ratio exponentially increases porosity. We present a porosity prediction model relationship for the oxygen pressure-kerosene pressure ratio.

Property Evaluation of HVOF Sprayed Multi-walled Carbon Nanotube Aluminum Composite Coatings (고속 화염 용사를 통하여 형성된 다중벽 탄소 나노튜브 알루미늄 복합소재 코팅의 특성 평가)

  • Kang, Ki-Cheol;Park, Hyung-Kwon;Lee, Chang-Hee
    • Journal of the Korean institute of surface engineering
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    • v.45 no.1
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    • pp.1-7
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    • 2012
  • Multi-walled carbon nanotube (MWCNT) aluminum composite powders were deposited to form coatings using a high velocity oxygen fuel (HVOF) spraying process. High thermal energy and contact with atmospheric oxygen were supplied as the MWCNT aluminum composite particles were exposed to a gas flow field at high temperature (${\sim}3.0{\times}10^3$ K) during HVOF spraying. As a result, the particles underwent full or partial melting and rapid solidification due to the high thermal energy, and the exposure to oxygen induced the interfacial reaction of MWCNTs within the particle. The electrical and mechanical properties of MWCNT aluminum composite coatings were evaluated based on microstructure analysis. Electrical resistivity, elastic modulus, and micro-hardness, of the MWCNT aluminum composite coatings were higher than those of pure aluminum coating. The contribution of MWCNTs to the aluminum matrix can be attributed to their high electrical conductivity, dispersion hardening and anchoring effects. The relationship among the properties and the interaction of the MWCNTs with the aluminum matrix is discussed.

Effects of Powder Mixing on the Mechanical Properties of Thermally Sprayed WC-Co-Cr Coating Layers (WC-Co-Cr 용사코팅시 분말의 혼합이 코팅층의 기계적 특성에 미치는 영향)

  • Lee, Chang Woo;Han, Jun Hyun;Shin, Myung Chul;Kwun, S.I.
    • Korean Journal of Metals and Materials
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    • v.47 no.5
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    • pp.290-296
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    • 2009
  • We report on the effects of mixing of powders with various particle sizes on fracture toughness and wear resistance of thermally sprayed WC-10Co-4Cr coating layers fabricated by HVOF (high-velocity oxygen fuel) process. The size and the mixing ratio of powders were changed in order to get high fracture toughness and wear resistance. The mixing of small amount of coarse powders with fine powders resulted in the highest fracture toughness and wear resistance due to the lowest porosity in coating layers.

A Study on Characteristics of Durability for Plunger of High Speed and Ultra-High Pressure Reciprocating Pump Using High Velocity Oxygen Fuel Spraying (초고속 용사 적용 고속 초고압 왕복동 펌프 플런저의 내구성 특성에 관한 연구)

  • Bae, Myung-Whan;Park, Byoung-Ho;Jung, Hwa;Park, Hui-Seong
    • Transactions of the Korean Society of Automotive Engineers
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    • v.22 no.5
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    • pp.20-28
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    • 2014
  • The high velocity oxygen fuel spraying (HVOF) is a kind of surface modification process technology to form the sprayed 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. It is desirable to melt completely the thermal spray powder in order to produce the coating layer with an optimal adhesion, however, because a semi-molten powder in a spray process has the low efficiency and become a factor that degrades the mechanical property by the inducement of pore-forming within the coating layer. To improve the wear resistance, corrosion resistance and heat resistance, in this study, the plungers of high-speed and ultra-high pressure reciprocating hydraulic pumps for oil and water used in ironwork are produced with $420J_2$ and the coating layers of plungers are formed by the powders of WC-Co-Cr and WC-Cr-Ni including the high hardness WC. The surface of these plungers is modified by the super-mirror face grinding machine using variable air pressure developed in this laboratory, and then the characteristics of cross-sectional microstructure, and surface roughness and hardness values between no operation and 100 days-operation are examined and made a comparison. The fine tops and bottoms on surface roughness curve of oil-hydraulic pump plunger sprayed by WC-Cr-Ni are molded more and higher than those of water-hydraulic pump sprayed by WC-Co-Cr because the plunger diameter of oil-hydraulic pump is 0.4 times smaller than that of water-hydraulic pump and the pressure of oil-hydraulic pump exerted on the plunger is operated with the 70 bars higher than that of water-hydraulic pump. As a result, it is found that the values of centerline average surface roughness and maximum height for oil-hydraulic pump plunger are bigger than those of water-hydraulic pump plunger.

Behaviors of Cavitation Damage in Seawater for HVOF Spray Coated Layer with WC-10Co4Cr on Cu Alloy (WC-10Co4Cr으로 초고속 화염용사 코팅된 Cu 합금의 해수내 캐비테이션 손상 거동)

  • Han, Min-Su;Kim, Min-Sung;Jang, Seok-Ki;Kim, Seong-Jong
    • Journal of the Korean institute of surface engineering
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    • v.45 no.6
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    • pp.264-271
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    • 2012
  • Due to the good corrosion resistance and machinability, copper alloy is commonly employed for shipbuilding, hydroelectric power and tidal power industries. The Cu alloy, however, has poor durability, and the seawater application at fast flow condition becomes vulnerable to cavitation damage leading to economic loss and risking safety. The HVOF(High Velocity Oxygen Fuel) thermal spray coating with WC-10Co4Cr were therefore introduced as a replacement for chromium or ceramic to minimize the cavitation damage and secure durablility under high-velocity and high-pressure fluid flow. Cavitation test was conducted in seawater at $15^{\circ}C$ and $25^{\circ}C$ with an amplitude of $30{\mu}m$ on HVOF WC-10Co4Cr coatings produced by thermal spray. The cavitation at $15^{\circ}C$ and $25^{\circ}C$ exposed the substrate in 12.5 hours and in 10 hours, respectively. Starting from 5 hours of cavitation, the coating layer continued to show damage by higher than 160% over time when the temperature of seawater was elevated from $15^{\circ}C$ to $25^{\circ}C$. Under cavitation environment, although WC-10Co4Cr has good wear resistance and durability, increase in temperature may accelerate the damage rate of the coating layer mainly due to cavitation damage.