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Evaluation of scratch resistant properties of electroless Ni-P-Al2O3 composite coatings
Gobinda Gyawali,Dhani Ram Dhakal,Bhupendra Joshi,Jin-Hyuk Choi,Soo Wohn Lee 한양대학교 세라믹연구소 2019 Journal of Ceramic Processing Research Vol.20 No.1
Ni-P-Al2O3 composite coatings were prepared from electroless plating method on copper substrate with different contents ofAl2O3 powder. Thus obtained composite coatings were heat treated at 400 oC for 1 h in an inert environment and subjectedto scratch tests. Compared to Ni-P coating, codeposition of Al2O3 exhibited the nodular structure and slightly increased surfaceroughness of the composite coatings. Low P nickel coating with approximately 4 wt% of codeposited Al2O3 into the depositwas obtained with 10 g/L Al2O3 concentration into the plating bath. Enhanced Vickers microhardness of the composite coatingwas due to the synergistic effects of the precipitation hardening by Ni3P phase and co-deposited hard Al2O3 particles. Furthermore, Ni-P-Al2O3 composite coatings have shown considerable improvement in load-bearing capacity of the coatingmatrix, thereby, enhancing the scratch resistant properties of the composite coating.
Electrodeposition and Characterization of Ni-TiB2 Composite Coatings
GYAWALI GOBINDA,조성훈,이수완 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.1
Nickel-titanium diboride (Ni-TiB2) composite coatings were successfully fabricated by pulse electrodeposition techniques from nickel sulfamate bath containing dispersed submicron TiB2 particles. The effect of TiB2 codeposition on the morphological, microstructural, microhardness and anti-corrosive properties of the composite coatings have been investigated by using scanning electron microscopy coupled with energy dispersive spectroscopy system, X-ray diffraction (XRD), vickers microhardness, and electrochemical impedance spectroscopy (EIS) techniques. Incorporation of TiB2 particles into the nickel matrix has modified the regular crystal growth of nickel. The XRD patterns revealed that the preferred (100) crystallite orientation of pure nickel has been modified into mixed orientations by the enhancement of (111) and attenuation of (200) diffraction intensities by the incorporation of TiB2 particles into the nickel matrix. Vickers microhardness of the Ni-TiB2 composite coating is found to be increased which is nearly 3 times higher than pure nickel coating. The results obtained by polarization curves and EIS analysis in 3.5 wt% NaCl solution have shown the improved corrosion resistance properties of Ni-TiB2 composite coating over pure nickel electrodeposit.
Gobinda Gyawali,Dongjin Woo,Soo Wohn Lee 한국표면공학회 2010 한국표면공학회지 Vol.43 No.6
Ni-TiO₂ nano composite coatings were fabricated using pulse current electrodeposition technique at 100 ㎐ pulse frequency with a constant 50% pulse duty cycles and reference was taken with respect to the direct current (dc) electrodeposition. The properties of the composite coatings were investigated by using SEM, XRD, Wear test and Vicker’s microhardness test. Pulse electrodeposited composite has exhibited enhancement of (111), (220), and (311) diffraction lines with an attenuation of (200) line. The results demonstrated that the microhardness of composite coatings under pulse condition was significantly improved than that of pure nickel coating as well as dc electrodeposited Ni-TiO₂ composite coatings. Wear tracks have shown the less plastic deformation in pulse plated composite. Coefficient of friction was also found to be lower in pulse plated composite coatings as compared to dc plated composite coatings.
Gobinda Gyawali,이수완 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.2
Nanocrystalline Ni-SiC-h/BN composite coatings were fabricated by pulse current electrodeposition process from nickel sulfamate bath. Different contents of SiC nanoparticles and h/BN nanosheets (5-20 g/L each) were dispersed in the electrolyte to investigate the effects of dispersed particles on final properties of the composite coatings. Surface morphologies, microstructures, mechanical and tribological properties of the electrodeposited composite coatings were evaluated by using scanning electron microscopy (SEM), optical microscope, X-ray diffraction (XRD), Vickers microhardness, wear and coefficient of friction. Studies revealed that as compared to pure nickel coatings, electrodeposited Ni-SiC-h/BN composite coatings exhibited smooth and compact surface, increase in Vickers microhardness, grain refinements and enhanced tribological properties. In addition, as compared to either of Ni-SiC or Ni-h/BN composite coatings, presence of both types of particles together into nickel matrix revealed overall improved performance.
Pulse Electrodeposition and Characterization of Ni-Si<sub>3</sub>N<sub>4</sub> Composite Coatings
Gyawali, Gobinda,Woo, Dong-Jin,Lee, Soo-Wohn The Korean Institute of Surface Engineering 2010 한국표면공학회지 Vol.43 No.5
$Ni-Si_3N_4$ nano-composite coatings were prepared by pulse current (PC) electrodeposition and direct current (DC) electrodeposition techniques. The micro-structure of the coatings was characterized by scanning electron microscopy (SEM), vickers microhardness, X-Ray Diffraction (XRD) and wear-friction tests. The results showed that the micro-structure and wear performance of the coatings were affected by the electrodeposition techniques. Pulse current electrodeposited $Ni-Si_3N_4$ composite coatings exhibited higher microhardness, smooth surface, and better wear resistance properties as compared to coatings prepared under DC condition. The $Ni-Si_3N_4$ composite coatings prepared at 50 Hz pulse frequency with 10% duty cycles has shown higher codeposition of nano-particles. Consequently, increased microhardness and less plastic deformations occurred in coatings during sliding wear test. The XRD patterns revealed that the increased pulse frequencies changed the preferred (100) nickel crystallite orientations into mixed (111) and (100) orientations.
Sonochemical synthesis, characterization, and photocatalytic activities of PbMoO4 photocatalyst
Gobinda Gyawali,Bhupendra Joshi,이수원 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.3
PbMoO4 photocatalysts were synthesized by the facile sonochemical method at 20 kHz frequency with the variable ultrasonicpowers, and the results were compared with the sample prepared by conventional co-precipitate method. The synthesizedpowders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), ScanningElectron Microscopy (SEM), and Diffuse Reflectance Spectroscopy (UV-Vis DRS) to investigate the crystal structure, elementalcomposition, morphology, and optical properties of the photocatalyst. Photocatalytic activities of the PbMoO4 samples wereevaluated by the degradation of Methylene Blue (MB), and Indigo Carmine (IC) dyes under UV irradiation. It has beenobserved that the photocatalyst sample prepared by the sonochemical method at an ultrasonic power of 600 W showed theenhanced photocatalytic performance towards the dyes degradation.
Effect of Plating Parameters on the Electrodeposition of Ni-alumina Nanocomposite
Gobinda Gyawali,Dongjin Woo,Soo Wohn Lee 한국표면공학회 2010 한국표면공학회지 Vol.43 No.4
Ni-Al₂O₃ nanocomposite coatings were fabricated by conventional electrodeposition technique using nickel sulfamate bath. Effect of plating parameters on electrodeposition of Ni-Al₂O₃ nanocomposite were studied. The properties of the nano composite were investigated by using SEM, XRD, and Vicker’s microhardness test. The results demonstrated that Al₂O₃ incorporation in the composite coatings was found to be increased by increasing stir rate and Al₂O₃ content in plating bath. Microhardness of the composite coatings was also increased with increasing content of the nano particles in the plating bath. The surface morphologies of the nanocomposite coatings were found to be varied with varying pH, current densities as well as alumina content in the plating bath.