Papers by Author: Kwang Ho Kim

Abstract: Due to its ability of photocatalysis and photoinduced superhydrophilicity, TiO₂ was paid significant attentions in recent years. In this study, TiO₂ films were deposited at room temperature and 300 °C by pulsed dc reactive magnetron sputtering. The gas pressure was varied in the range of 0.3-1.1 Pa by filling Ar/N₂ gas mixture with the ratio of 1:1. The surface morphologies, phase structure and optical property of the TiO₂ films were investigated. TiO₂ films with good crystalline quality containing mainly of anatase phase were obtained by deposition using gas pressure of 0.7 Pa at room temperature and gas pressure of 1.5 Pa at 300 °C.

Abstract: Ti-Al-Si-N and Ti-Al-N coatings were deposited on WC-Co substrates by a DC magnetron sputtering method. The oxidation behavior of two kinds of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N coatings were comparatively investigated by XRD patterns and GDOES depth profiles. Si addition of 8 at.% into Ti-Al-N film modified its microstructure to a fine composite comprising, Ti-Al-N crystallites and amorphous Si3N4, and to a smoother surface morphology. While the solid solution Ti0.75Al0.25N film had superior oxidation resistance up to around 700°C, the composite Ti-Al-Si-N film showed further enhanced oxidation resistance. Both Al2O3 and SiO2 layers played roles as a barrier against oxygen diffusion for the quaternary Ti-Al-Si-N film, whereas only the Al2O3 oxide layer formed at surface did a role for the Ti-Al-N film. The cutting performances of two coated carbide ball-end mills were evaluated by cutting of AISI D2 cold-worked die steel (60 HRC) under high-speed cutting condition. The tool wear and cutting temperature are discussed along with coating characteristics.

Abstract: In this work, the Ti-Al-Si-C-N coatings were synthesized on Stainless steel and Si wafer by a hybrid coating system, where arc ion plating (AIP) technique was combined with a magnetron sputtering technique. Also, the effect of Si content on the microstructure and mechanical properties of Ti-Al-C-N coatings were systematically investigated. The Ti-Al-Si-C-N coatings characterized by a nanocomposite comprising nano-sized Ti-Al-C-N crystallites embedded in amorphous Si3N4 phase. The micro-hardness values of Ti-Al-Si-C-N coatings were largely depended on Si content and the micro-hardness value of Ti-Al-Si-C-N coatings significantly increased from 38Gpa of Ti-Al-C-N coatings to approximately 56 GPa with the addition Si content of 9.8 at.%. The enhanced hardness values of Ti-Al-Si-C-N coatings were explained with the refinement of Ti-Al-C-N crystallites and composite microstructure characteristics by the percolation of amorphous Si3N4/SiC phase. The average friction coefficient of Ti-Al-Si-C-N decreased from 0.6 of Ti-Al-C-N to 0.23 with increasing the Si content up to 15.3 at. %. The decreased friction coefficients of Ti-Al-Si-C-N coatings was elucidated by the formation of SiO2 or Si(OH)2 layer known as self-lubricant materials.

Abstract: CrN-based multi-component coatings were deposited by a hybrid coating system combining the arc ion plating (AIP) and sputtering technique. In this work, comparative studies on microstructure and mechanical properties of microhardness and wear behavior among CrN, Cr-Mo- N, Cr-Si-N coatings were systematically conducted. Adding Mo and Si atoms into CrN coatings had important effects on microstructural change and mechanical properties of CrN coatings. The maximum hardness values of Cr-Mo-N and Cr-Si-N coatings were the same value of 34GPa, These values were much enhanced compared with 18GPa of CrN coating. The average friction coefficient of CrN-based coatings decreased to 0.37 and 0.2 with the incorporation of Mo and Si content

Abstract: Ti–B–C–N and Ti–Si–B–C–N nanocomposite coatings were deposited on AISI 304 stainless steel substrates by DC unbalanced magnetron sputtering from two (80mol% TiB2–20mol% TiC and 40mol% TiB2–60mol% TiC) composite targets in various Si target powers. The relationship among microstructures, mechanical properties, and tribologiacal properties was investigated. The synthesized Ti–B–C–N and Ti–Si–B–C–N coatings were characterized using x–ray diffraction (XRD) and x–ray photoelectron spectroscopy (XPS). These analyses revealed that the Ti–Si–B–C–N coatings are nanocomposites consisting of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous TiSi2, SiC, and SiB4 matrix including some carbon, BN, CNx, TiO2, and B2O3 components. The addition of Si to the Ti–B–C–N coating led to percolation of amorphous TiSi2, SiC, and SiB4 phases. The Ti–Si–B–C–N coatings exhibited high hardness and H/E values, indicating high fracture toughness, of approximately 35 GPa and 0.098, respectively. Furthermore, the Ti–Si–B–C–N coatings exhibited very low wear rates ranging from ~3×10-7 to ~16×10-7 mm3/(N·m). The minimum friction coefficient of the Ti–Si–B–C–N coatings was approximately 0.15 at low Si target power between 25W and 50W. A systematic investigation on the microstructures, mechanical properties, and tribological properties of Ti–Si–B–C–N coatings prepared from two TiB2–TiC composite targets and one Si target is reported in this paper.

Abstract: Ternary Ti-Cx-N1-x coatings were deposited on stainless steel substrates by arc ion plating (AIP) technique using Ti target at the temperature of 300
with a negative substrate bias voltage of -25 V. The carbon content in Ti-Cx-N1-x coatings linearly increased with increasing CH4/(CH4+N2) gas flow ratio at a constant arc current of 60 A. The microstructure and mechanical properties such as micro-hardness and average friction coefficient of Ti-Cx-N1-x coatings were investigated as a function of carbon content. As the carbon content in Ti-Cx-N1-x coatings increased, the microhardness values of Ti-Cx-N1-x coatings increased from 20 GPa for TiN coatings and reached the maximum value of approximately 32 GPa at x=0.52 in Ti-Cx-N1-x coatings. The variation of microhardness of Ti-Cx-N1-x coatings had a relationship with the change of residual stress. The average friction coefficient of Ti-Cx-N1-x coatings largely decreased with increasing carbon content.