• Korean Journal of Materials Research
• /
• v.29 no.1
• /
• pp.52-58
• /
• 2019

The microstructure, hardness, and wear behaviors of a High Velocity Oxygen Fuel(HVOF) sprayed WC-CoFe coating are comparatively investigated before and after laser heat treatments of the coating surface. During the spraying, the binder metal is melted and a small portion of WC is decomposed to $W_2C$. A porous coating is formed by evolution of carbon oxide gases formed by the reaction of the free carbon and the sprayed oxygen gas. The laser heat treatment eliminates the porosity and provides a more densified microstructure. After laser heat treatment, the porosity in the coating layer decreases from 1.7 % to 1.2 and the coating thickness decreases from $150{\mu}m$ to $100{\mu}m$. The surface hardness increases from 1440 Hv to 1117 Hv. In the wear test, the friction coefficient of coating decreases from 0.45 to 0.32 and the wear resistance is improved by the laser heat treatment. The improvement is likely due to the formation of oxide tribofilms.

• Journal of the Korean institute of surface engineering
• /
• v.55 no.6
• /
• pp.376-382
• /
• 2022

Yb₂Si₂O₇ has a coefficient of thermal expansion similar to that of the base material of SiC and has excellent corrosion resistance in a high-temperature oxidizing atmosphere including water vapor, so it is being studied as one of the materials for environmental barrier coatings (EBCs). In this study, Yb₂Si₂O₇ powder granule is deposited using atmospheric plasma spraying (APS) with different Ar/He ratios. Phase formation and microstructural characteristics are investigated with the coated specimens. In the coating layer, the crystallinity decreased, and the amorphous content increased from an increase in the ratio of Ar. In addition, the various types of particles involved by local volatilization of Si according to the Ar/He ratios were identified.

• Korean Journal of Metals and Materials
• /
• v.48 no.5
• /
• pp.401-409
• /
• 2010

This study was performed to develop an antibacterial film that can be dried at room temperature. A nanosized TiO$_2$ particle-dispersed solution was prepared by the hydrothermal treatment of peroxo-titanic acid at 160${^{\circ}C}$ for 4h. The binder was synthesized through the hydrolysis and condensation reactions of TEOS (10cc) and GPTS (3.5cc) in the mixture of H$_2$O (30cc) and EtOH (30cc). The synthesized binder was mixed with 0.1 M of TiO$_2$ solution in a volume ratio of binder/TiO$_2$ solution=0.25~0.5. The glass substrate was coated after using the dip coating method, which was then followed by drying for over 2h at room temperature. Although the TiO$_2$ particles did not chemically-bond to the binder, the coating layer strongly adhered to the substrate and displayed good antibacterial properties.

• Korean Journal of Metals and Materials
• /
• v.49 no.3
• /
• pp.270-274
• /
• 2011

Plasma electrolytic oxidation (PEO) treatment was performed on squeeze cast AZ31 alloy and $Al_{18}B_4O_{33}w/AZ31$ composite. Scanning electron microscope (SEM) was employed to characterize the surface morphology and cross-section microstructure of the coating. The phase structures of the PEO coating were analyzed by X-ray diffraction (XRD). The corrosion resistance of the PEO coating was evaluated by electrochemical method. The results showed that the $Al_{18}B_4O_{33}$ whisker on the surface of the composite was decomposed and $MgAl_2O_4$ was formed in the PEO coating layer of $Al_{18}B_4O_{33}w/AZ31$ composite during PEO treatment. As a result, the electrochemical corrosion potential of the PEO coated $Al_{18}B_4O_{33}w/AZ31$ composite was increased compared with that of AZ31 alloy.

• Progress in Superconductivity and Cryogenics
• /
• v.22 no.4
• /
• pp.14-19
• /
• 2020

Here we present the comparative experimental study of the stability of the superconducting state in 4 mm YBCO tapes with copper lamination against local heat disturbances at 77 K. The samples are either directly cooled by immersing a bare YBCO tape into a liquid nitrogen pool or operate in nearly-adiabatic conditions when the tape is covered by a 0.6 mm layer of Kapton insulation. Main quench characteristics, i.e. minimum quench energies (MQEs) and normal zone propagation (NZP) velocities for both samples are measured and compared. Minimum NZP currents are determined by a low ohmic resistor technique eligible for obtaining V - I curves with a negative differential resistance. The region of transport currents satisfying the stationary stability criterion is found for the different cooling conditions. Finally, we use the critical temperature margin as a universal scaling parameter to compare the MQEs obtained in this work for YBCO tapes at 77 K with those taken from literature for low-temperature superconductors in vacuum at 4.2 K, as well as for MgB2 wires cooled with a cryocooler down to 20 K.

• Structural Engineering and Mechanics
• /
• v.76 no.5
• /
• pp.561-578
• /
• 2020

The present work addresses the surface integrity and chip morphology in finish hard turning of AISI D3 steel under nanofluid assisted minimum quantity lubrication (NFMQL) condition. The surface integrity aspects include microhardness, residual stress, white layer formation, machined surface morphology, and surface roughness. This experimental investigation aims to explore the feasibility of low-cost multilayer (TiCN/Al2O3/TiN) coated carbide tool in hard machining applications and to assess the propitious role of minimum quantity lubrication using graphene nanoparticles enriched eco-friendly radiator coolant based nano-cutting fluid for machinability improvement of hardened steel. Combined approach of central composite design (CCD) - analysis of variance (ANOVA), desirability function analysis, and response surface methodology (RSM) have been subsequently employed for experimental investigation, predictive modelling and optimization of surface roughness. With a motivational philosophy of "Go Green-Think Green-Act Green", the work also deals with economic analysis, and sustainability assessment under environmental-friendly NFMQL condition. Results showed that machining with nanofluid-MQL provided an effective cooling-lubrication strategy, safer and cleaner production, environmental friendliness and assisted to improve sustainability.

• Korean Journal of Materials Research
• /
• v.31 no.11
• /
• pp.601-607
• /
• 2021

Laser cladding a surface treatment process that grants superior characteristics such as toughness, hardness, and corrosion resistance to the surface, and rebuilds cracked molds; as such, it can be a strong tool to prolong service life of mold steel. Furthermore, compared with the other similar coating processes - thermal spray, etc., laser cladding provides superior bonding strength and precision coating on a local area. In this study, surface characteristics are studied after laser cladding of low carbon steel using 18%Cr-2.5%Ni-Fe powder (Rockit404), known for its high hardness and excellent corrosion resistance. A diode laser with wavelength of 900-1070 nm is adopted as laser source under argon atmosphere; electrical power for the laser cladding process is 5, 6, and 10 kW. Fundamental surface characteristics such as crossectional microstructure and hardness profile are observed and measured, and special evaluation, such as a soldering test with molten ALDC12 alloy, is conducted to investigate the corrosion resistance characteristics. As a result of the die-soldering test by immersion of low carbon alloy steel in ALDC12 molten metal, the clad layer's soldering thickness decreases.

• Journal of the Semiconductor & Display Technology
• /
• v.21 no.2
• /
• pp.38-44
• /
• 2022

Plasma density in semiconductor fabrication equipment becomes higher to achieve the improved the throughput of the process, but the increase of surface corrosion of the ceramic coated chamber wall has been observed by the increased plasma density. Plasma chamber wall coating with aerosol deposition prefer to be firm and uniform to prevent the potential creation of particle inside the chamber from the deformation of the coating materials, and the aerosol discharge nozzle is a good control factor for the deposited coating condition. In this paper, we investigated the design of the nozzle of the aerosol deposition to form a high-quality coating film. Computational fluid dynamics (CFD) study was employed to minimize boundary layer effect and shock wave. The degree of expansion, and design of simulation approach was applied to found out the relationship between the divergence angle and nozzle length as the key parameter for the nozzle design. We found that the trade-off tendency between divergence angle and nozzle length through simulation and quantitative analysis, and present the direction of nozzle design that can improve the uniformity of chamber wall coating.

• Structural Engineering and Mechanics
• /
• v.82 no.2
• /
• pp.163-172
• /
• 2022

Zinc-rich epoxy (ZRE) is used to overcome corrosion problems in reinforced concrete (RC) beams and coat steel rebars to protect them from humidity and chlorides. An extra coating layer of Sikadur-31 epoxy (SDE) is utilised to increase bond strength because the use of ZRE reduces the bond strength between concrete and steel rebars. However, the low melting point of SDE indicates that concrete specimens are vulnerable to fire. An experimental investigation on flexural performance of RC beams incorporating ZRE-SDE coating of steel rebars that were destroyed by fire is performed in this study. Twenty beams of five concrete mixes with different cementitious contents were tested to compare fire exposure for coated and uncoated rebars of the same beams at room temperature and determine the optimal cementitious content. Scanning electron microscopy (SEM) was also applied to investigate characteristics of fired mixture samples. Results showed that the use of SDE-ZRE at room temperature improves flexural strengths of the five mixes compared with uncoated rebars with percentages ranging from 8.5% to 12.3%. All beams with SDE-ZRE lost approximately 50% of their flexural strength due to firing. Moreover, the mix incorporating SF (silica fume) of 15% and cement content of 400 kg/m³ introduces optimum behaviour compared with other mixes. All results were supported and verified by the SEM analysis and compressive strength of cubic specimens of the same mixes.

• Transactions of Materials Processing
• /
• v.31 no.4
• /
• pp.186-193
• /
• 2022

The application of UHSS sheet is being expanded up to 50% to reduce the weight of automobiles and improve safety. However, due to the high strength and low elongation of the ultra-high tensile strength steel sheet, product defects such as spring back and mold defects such as cracks and chippings also occur. In this study, Pin/Ring on Disc and Spiral wear tests were conducted to evaluate the durability of Ti/Cr-coated molds for forming 1.2GPa grade UHSS sheets. Component analysis and thickness were measured for each coating layer, and hardness and adhesion were investigated to determine mechanical properties. Combining the results of various wear tests, it was found that the TiAlN coating had the best wear and sticking resistance.