• Korean Journal of Materials Research
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• v.8 no.8
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• pp.757-765
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• 1998

This study was performed to investigate the influence of fuel/oxygen ratio (F/O= 3.2, 3.0, 2.8) on the oxidation behavior of two kinds of (20wt%NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$, and 7wt%NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$) composite powder with different manufacturing method. The results show that the oxidation behavior between the 20wt% NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ and 7wt% NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ coating was widely different. The surface morphology of the coating composed of 7wt% NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ was changed to porous with F/O ratio by the aggressive evolution of gas phases($\textrm{CO}_2$, CO and $\textrm{CrO}_3$) and the oxide cluster composed of Ni and Cr were grown after oxidation at $1000^{\circ}C$ for 50 hours. But the surface morphology of the coating composed of 20wt% NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ was not changed to porous after oxidation at $1000^{\circ}C$ for 50 hours. Therefore, the reason for high oxidation rate is due to activation of $\textrm{Cr}_{3}\textrm{C}_{2}$ to oxidation by entrapped oxygen gases within coating layer, and to closely relate with the decomposition of $\textrm{Cr}_{3}\textrm{C}_{2}$ to $\textrm{Cr}_{7}\textrm{C}_{3}$ phase. Accordingly, On the evidence of these results, the study about the oxidation behavoir of the HVOF sprayed $\textrm{Cr}_{3}\textrm{C}_{2}$ coating depending on hydrogen flow rate must be done.

• Journal of Powder Materials
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• v.25 no.5
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• pp.408-414
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• 2018

This study investigates the microstructure and wear properties of cermet (ceramic + metal) coating materials manufactured using high velocity oxygen fuel (HVOF) process. Three types of HVOF coating layers are formed by depositing WC-12Co, WC-20Cr-7Ni, and Cr3C2-20NiCr (wt.%) powders on S45C steel substrate. The porosities of the coating layers are $1{\pm}0.5%$ for all three specimens. Microstructural analysis confirms the formation of second carbide phases of $W_2C$, $Co_6W_6C$, and $Cr_7C_3$ owing to decarburizing of WC phases on WC-based coating layers. In the case of WC-12Co coating, which has a high ratio of $W_2C$ phase with high brittleness, the interface property between the carbide and the metal binder slightly decreases. In the $Cr_3C_2-20CrNi$ coating layer, decarburizing almost does not occur, but fine cavities exist between the splats. The wear loss occurs in the descending order of $Cr_3C_2-20NiCr$, WC-12Co, and WC-20Cr-7Ni, where WC-20Cr-7Ni achieves the highest wear resistance property. It can be inferred that the ratio of the carbide and the binding properties between carbide-binder and binder-binder in a cermet coating material manufactured with HVOF as the primary factors determine the wear properties of the cermet coating material.

• Journal of Welding and Joining
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• v.19 no.1
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• pp.95-103
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• 2001

The properties of the detonation sprayed cermet coating are investigated through the mechanical, corrosion and erosion test. The test results are also compared with the properties of the substrate materials, STS 329J1, dual phase stainless steel and the plasma sprayed cermet coatings. The two kinds of carbide cermet power, WC+NiCr, Cr$_3$C$_2$+NiCr were used in this experiment. The experimental results showed that the anti-corrosive and anti-erosive properties of the detonation sprayed cermet coatings are superior to the plasma sprayed cermet coatings. The WC+NiCr cermet coating appears to be more effective than Cr$_3$C$_2$+NiCr cermet coating in abrasive erosion environment, whereas the Cr$_3$C$_2$+NiCr cermet coatings are more effective in cavitation erosion environment.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.849-855
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• 1998

The purpose of this study was performed to compare to the characteristics (microstructure, phase change and hardness, erosion rate) of HVOF sprayed coatings with 20wt% NiCr claded and 7wt%NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ powder. In the case of the 20wt% NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ powder, microstructural feature showed that the primary $\textrm{Cr}_{3}\textrm{C}_{2}$ was remained in the coating but was barely remained in the mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ coating. As a results of XRD analysis, both 20wt%NiCr claded and 7wt% NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ powder was decomposed during spraying but the degree of decomposition of the 20wt%NiCr claded was lower than 7wt%NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ powder. After spraying the mixed powder for microhardness was higher than claded $\textrm{Cr}_{3}\textrm{C}_{2}$ powder and which was increased up to $\textrm{Hv}_{300}$= 1665 after heat treatment to $1000^{\circ}C$. however. 20wt%NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ became to decrease at $600^{\circ}C$ which was the maximum.

• Korean Journal of Materials Research
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• v.9 no.1
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• pp.73-80
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• 1999

The effect of alloy compositions of the bond coating on the plasma sprayed-thermal barrier coatings was investigated. The performance of the coating composed of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ and Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$was evaluated by isothermal and thermal cyclic test in an ambient atmosphere at 115$0^{\circ}C$. The failure of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ coatings was occurred at the bond coating/ceramic coating interface while Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$ coating was failed at the substrate/bond coating interface after thermal cyclic test. The lifetime of Rene80/NiCrAl/ZrO$_2$-CeO$_2$-Y$_2$O$_3$coatings was longer than Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$coating. The oxidation rate of the NiCrAl bond coating examined by TGA was lower than CoNiCrAlY bond coatings. In summary, these results suggest that Rene80/CoNiCrAlY/ZrO$_2$-CeO$_2$-Y$_2$O$_3$system as thermal barrier coating be not suitable considering the durability of the coating layer for high temperature oxidation and thermal stress.

• 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.4
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• pp.126-135
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• 1997

$H_2/O_2$ 비에 따른 Hybrid HVOF 용사된 $Cr_3C_2$-7wt%(NiCr) 용사층의 특성 및 산화거동 This study was performed to investigate the influence of fuel/oxygen ratio (F/O=3.2, 3.0, 2.8) on the characteristics and the oxidation behavior of the hybrid-HVOF sprayed $Cr_3C_2$-7wt%NiCr coatings. Decomposition and the oxidation of the $Cr_3C_2$was occured during spraying. The degree of transformation from $Cr_3C_2$to $Cr_7C_3$ was increased with decreasing the F/O ratio. The microstructural differences of the as sprayed coating with F/O ratio can not be distinguished, However, large pores were diminished and then the coatings became dense by heat treatment. Microhardness of the as-sprayed specimen which sprayed with F/O=3.0 condition was hightest ($Hv_{300}$=1140) and the hardness was increased to 1500 after heat treatment at $600^{\circ}C$ for 50hrs in air. It was supposed that hardness was increased due to the formation of $Cr_2O_3$ within $Cr_3C_2$/$Cr_7C_3$matrix and the densification of coating layer during heat treatment. Apparent activation energy for oxidation was varied from 21.2 kcal$mol^{-1}K^{-1}$ to 23.8 kcal$mol^{-1}K^{-1}$ with respect to the F/O ratio. The surface morphology was changed to porous and oxide chusters were grown after oxidation $1000^{\circ}C$ for 50 hours by the aggressive evolution of gas phase ($CrO_3$ and$CO_2$). The oxide cluster was composed of Ni and Cr.

• Journal of Welding and Joining
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• v.11 no.4
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.7 s.166
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• pp.1245-1252
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• 1999

The sliding wear behavior of $Al_2O_3/NiCr$ coating deposited on steel(SM45C) was investigated under lubrication. The parameters of sliding wear are normal loads, coating thickness. As a result, the wear resistance of $Al_2O_3/NiCr$ coating was remarkably greater than that of $Al_2O_3$ coating. The optimized coating thickness was found to be $300{\mu}m$ to ensure good anti-wear. The bond coating played important role in decreasing residual stress. The residual stress had much influence on wear mechanism. These results were correlated with the stress state of coating and the microstructure of coating.

• Journal of Powder Materials
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• v.30 no.5
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• pp.415-423
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• 2023

With the increasing attention to environmental pollution caused by particulate matter globally, the automotive industry has also become increasingly interested in particulate matter, especially particulate matter generated by automobile brake systems. Here, we designed a coating composition and analyzed its mechanical properties to reduce particulate matter generated by brake systems during braking of vehicles. We designed a composition to check the mechanical properties change by adding Cr₃C₂ and YSZ to the WC-Ni-Cr composite composition. Based on the designed composition, coating samples were manufactured, and the coating properties were analyzed by Vickers hardness and ball-on-disk tests. As a result of the experiments, we found that the hardness and friction coefficient of the coating increased as the amount of Cr₃C₂ added decreased. Furthermore, we found that the hardness of the coating layer decreased when YSZ was added at 20vol%, but the friction coefficient was higher than the composition with Cr₃C₂ addition.