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Al 3003 alloy was manufactured by strip casting process, and the effect of post heat-treatment on tensile and fatigue properties was investigated. The strip cast Al 300 alloy exhibited a unique globular shaped rapid-cooled solidification structure, and the microstructural characteristic remained after heat-treatment. Asstrip cast (F) and heat-treated (O) alloys were commonly composed of Al matrix and strengthening phases such as Al6(Mn,Fe), α-Al(Mn,Fe)Si. In the phase analysis and Factsage simulation result, Al6(Mn,Fe) fraction increased while α-Al(Mn,Fe)Si fraction decreased after heat-treatment. Strengthening phases were more uniformly and finely distributed in the case of O alloy, than F alloy. In the Vickers hardness results, F alloy (measured 59.7 Hv) showed higher hardness than O alloy (measured 53.4 Hv). The yield strengths (YS) and ultimate tensile strengths (UTS) measured 124.8 MPa and 166.4 MPa (F alloy), and 111.2 MPa and 167.2 MPa (O alloy), respectively. F alloy exhibited superior YS compared to O alloy, while UTSs were similar in both alloys. For elongation, the F alloy (19.6%) had a lower value than the O alloy (23.0%). High cycle fatigue tests were performed at room temperature under a stress ratio (R) of 0.1 and frequency (F) of 10 Hz. The F alloy exhibited higher fatigue than the O alloy under all cyclic stress conditions. However, the deviation in the fatigue property of the F alloy was relatively broader than the O alloy. Tensile and fatigue fracture surfaces were examined, and the tensile and fatigue deformation mechanisms of the strip cast Al 3003 alloy were also discussed. (Received September 18, 2019; Accepted December 16, 2019)

keyword : strip casting, Al 3003, Al-Mn alloy, tensile property, high cycle fatigue, heat treatment

A superelastic titanium alloy was subjected to uniaxial tensile deformation at room temperature. The microstructural evolution and deformation mechanisms of the superelastic titanium alloy were investigated by electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Multiple deformation mechanisms including stress-induced martensitic transformation (SIMT), dislocation slip, {332}<113> and {112}<111> mechanical twinning were identified with the increase in uniaxial strain. In the early stage of deformation, a SIMT from the bcc beta phase to orthorhombic martensite phase dominantly occurred. As the deformation proceeded, the phase fraction of the remained martensite which did not return to beta phase obviously increased due to dislocation slip and mechanical twinning. The kernel average misorientation (KAM) value obtained from EBSD data gradually increased with increasing the deformation, indicating that the dislocation evolution was produced by slip. This was well matched with the trend in the full width at half maximum (FWHM) value of the peak profile obtained from XRD data. In addition, the fraction of the {332}<113> twin was lower than that of the {112}<111> twin in the initial specimen. However, the {332}<113> twin rapidly increased compared to the {112}<111> twin as deformation increased. Therefore, it is confirmed that {332}<113> twinning and dislocation slip were the dominant mechanisms during plastic deformation. (Received November 25, 2019; Accepted January 13, 2020)

keyword : superelastic titanium alloy, stress-induced martensitic transformation, twinning, dislocation slip

The effects of alloy composition on the coating structure and corrosion resistance of hot-dip Znbased alloy coated steel products were investigated. Zn-based alloy coating layers with different Al and Mg compositions were fabricated using a batch-type galvanizing simulator. Various intermetallic compounds including Zn, Zn/MgZn₂ binary eutectic, Zn/Al binary eutectoid and Zn/Al/MgZn₂ ternary eutectic phases were formed in the coating layer. The surface and cut-edge corrosion resistance of the Zn-based alloy coating were superior to those of the Zn coating. Zn-based alloy coating containing 15% Al and 3% Mg showed the best corrosion resistance, with red rust formed on the flat surface after 120 hours in the salt spray test. The corrosion products of the Zn-based alloy coating consisted of Simonkolleite (Zn₅(OH)₈Cl₂·H₂O), Hydrozincite (Zn₅(CO₃)₂(OH) and zinc oxide (ZnO). Al-containing corrosion products, Zn₂Al(OH)₆Cl₂·H₂O and Al₂O₃, were formed when more than 5 wt% Al was added. Al-containing corrosion products improved the corrosion resistance of the flat surface of Zn-based alloy coating, but did not affect corrosion resistance in the cut-edge area. (Received July 22, 2019; Accepted January 9, 2020)

keyword : thin film, surface treatment, wet coating, microstructure

In recent automobile trends, the functions of opening and closing the vehicle door are accomplished by touch sensor and smart-phone NFC (Near Field Communication) systems. These convenience features are incorporated into the outdoor handle. However, this function can’t be used when chrome plating is applied to this part for design purposes. To solve the problem of chrome plating, we studied a metal sputtering deposition process technology, which can preserve the metal feeling without interfering with NFC and touch sensor operation. To achieve this interface communication and sensing performance, we developed a surface treatment that can generate micro-cracks in the thin film layer. We also investigated how the door handle manufacturing process affected the shape of the micro-cracks in the thin film. Results showed that the thickness of the thin film and the target power played a crucial role in controlling the residual tensile stress in the thin film, which was one of major factors responsible for generating micro-cracks in the thin film layer. The shape of the micro-cracks in the thin film was affected by the adjacent layers of the thin film, the primer paint and UV top coat. The surface energy of the primer paint and the shear stress produced by the hardening of the UV top coat were found to affect the shape of the micro-cracks. In addition, we found that there was no change in the shape of the micro-cracks with additional heat treatment, if the residual tensile stress was sufficiently relieved by the micro-cracks formed in the thin film. The slits between the micro-cracks in the outdoor handle cover allowed the Capacitance Sensor and NFC to perform. (Received September 16, 2019; Accepted January 3, 2020)

keyword : sputtering, residual stress, micro-cracks, NFC, capacitance sensor, out-door handle

Quarternay carbides of Ti₃Al_xSi_1-xC₂ (x=0.3, 0.5, and 0.7) were oxidized at 400, 600, and 800 °C for 0.5-6 months in order to study their long-time oxidation behavior in air. When they were oxidized at 400- 600 ℃ for 0.5-3 months, oxidation proceeded relatively slowly with moderate weight gains. However, further oxidation at 400-600 ℃ for 6 months resulted in the oxidation-induced microcracking of oxide scales due to large volume expansion and large stress induced owing to the formation of Al₂O₃, SiO₂. TiO₃, and TiO₂ in oxide scales. However, at 800 ℃, microcracking of oxide scales, which could lead to pulverization of Ti₃Al_xSi_1-xC₂, did not occur due to stress relaxation in oxide scales. Instead, at 800 ℃, Ti₃Al_xSi_1-xC₂ oxidized rapidly to form thick, somewhat porous oxide scales, which consisted primarily of an outer TiO₂ layer with some Al₂O₃, an intermediate Al₂O₃ layer with some TiO₂, and an inner TiO₂ layer with some (SiO₂+Al₂O₃). The overall longtime oxidation resistance of Ti₃Al_xSi_1-xC₂ at 400-800 °C was considered to be poor. Factors that determined the oxidation rates of Ti₃Al_xSi_1-xC₂ were; (1) How fast titanium oxidized to semi-protective titanium oxides, (2) How fast Al and Si oxidized to Al₂O₃ and SiO₂ barrier oxides, and (3) Whether oxidation-induced microcracking occurred in oxide scales or not. The ratio of Al/Si in Ti₃Al_xSi_1-xC₂ and the matrix grain size were apparently not dominant factors, because the basic oxidation mode of Ti₃Al_0.3Si_0.7C₂, Ti₃Al_0.5Si_0.5C₂, and Ti₃Al_0.7Si_0.3C₂ was similar under the identical oxidation condition. (Received December 31, 2019; Accepted January 13, 2020)

keyword : Ti₃AlC₂, Ti₃SiC₂, oxidation

Transparent conductive ZnO 50 nm/Ag 10 nm/SnO2 50 nm (ZAS) tri-layer films were deposited on glass substrates by magnetron sputtering, and then the surface was subjected to intense electron beam irradiation to investigate the effects of electron irradiation on the structural, optical, and electrical properties of the films. After deposition, the ZAS thin films were electron-irradiated for 10 minutes, with varying electron incident energies of 300, 600, and 900 eV. The films that were electron irradiated at 900 eV showed higher optical transmittance of 83.6% in the visible wavelength region, and lower resistivity, of 4.75 × 10^-5 Ωcm, than the other films. From the observed electrical properties and optical band gap, it was concluded that the optical band gap increased with the incident electron energy up to 600 eV. The optical band gap increased from 4.12 to 4.23 eV, with carrier density increasing from 7.09 to 8.55 × 10²¹ cm^-3. However, the film electron irradiated at 900 eV showed a decrease in optical band gap energy of 4.16 eV due to the decreased carrier density of 8.25 × 10²¹ cm^-3. The figure of merit revealed that the ZAS thin films electron-irradiated at 900 eV had higher optical and electrical performance than the other films prepared in this study. (Received September 30, 2019; Accepted December 23, 2019)

keyword : ZnO, Ag, SnO₂, magnetron sputtering, figure of merit.

In this study, the effect of post annealing time on the physical properties of NiTe₂ thin films with 2D structure deposited by co-sputtering was investigated. After heat treatment for 10 min, nickel ditelluride thin films with a composition of Ni : Te = 1 : 2 exhibited transmittance of 46% and a resistivity of 40 μΩ · cm. When using both Ni and Te targets, the formation of NiTe₂ with 2D structure was found to depend on the co-sputtering and heat treatment conditions. Thin films with the composition of NiTe₂ were deposited on glass substrates by co-sputtering (Radio Frequency : Te, Direct Current : Ni). The Ni : Te = 1: 2 composition was confirmed by X-ray Photo Electron Spectroscopy (XPS) after in situ heat treatment in the sputter chamber (10 min, 20 min, 40 min, 80 min). In this study, we confirmed that the NiTe₂ thin film with the ratio of Ni : Te = 1 : 2 can be obtained by co-sputtering, followed by in situ heat treatment. We believe that the NiTe₂ thin film is a potential candidate for transparent electrodes because of its high electrical conductivity and 2D structure. It should be possible to reduce the thickness of the NiTe₂ films with 2D structure by exfoliation, thus increasing their optical transparency. (Received January 6, 2020; Accepted January 21, 2020)

keyword : NiTe₂, sputtering, two-dimensional materials, thin film, post-annealing, binding energy

Anti-reflective (AR) coatings are popular because they offer high durability with effective reflectance and glare reduction, and they can endure both physical and environmental damage. Magnesium fluoride (MgF₂) has been used as a nanoparticle coating on AR coating materials by many researchers because they exhibit high transmittance and antireflection characteristics in the visible region, due to its low refractive index. When using MgF₂ nanoparticles on a coated AR film, however, a binder is needed to improve abrasion resistance because the binding strength between particles is weak. In this study, AR coating films were prepared by adding MgTFA as a precursor to improve the adhesion resistance of the AR coating films. The AR coating films were characterized by UV-Vis, XRD, TEM, as well as viscosity and abrasion tests. The binder added to MgF₂ to improve the bonding strength between the particles showed excellent durability. The MgF₂ with added binder had a stronger film strength than a binderless MgF₂ film, even at low drying temperatures. It also exhibited lower reflectance. These characteristics are expected to be valuable for camera lenses, for thin films that require high light extraction efficiency, and in anti-reflection films on solar cell surfaces. (Received December 9, 2019; Accepted January 7, 2020)

keyword : anti-reflective, coatings, MgF₂, binder, thin film

Materials with very small dimensions exhibit different physical and mechanical properties compared to their bulk counterparts. This becomes significantly important for the thin films that are widely used as components in micro-electronics and functional materials. In this study, a chromium (Cr) thin film was deposited on a silicon (Si) wafer by DC-magnetron sputtering. The intrinsic hardness of the Cr thin film on Si-wafer was evaluated by the nanoindentation method. We especially investigated ways of measuring the intrinsic hardness of the Cr thin film, and influential factors including the substrate effect and surface roughness effect. To further characterize the intrinsic hardness of the Cr thin film on Si-wafer, we used Xray diffraction (XRD), scanning electron microscopy (SEM), and atomic force microscopy (AFM). Two additional methods, the Meyer-plot and a profile for hardness versus indentation depth, were also employed. As a result of these two methods, we found that the profile for hardness versus indentation depth was valuable for evaluating the intrinsic hardness of Cr thin film on a Si-wafer substrate. The measured intrinsic hardness of the Cr thin film and Si wafer were about 900 Hv and 1143 Hv, respectively. The profile for hardness versus indentation depth can be widely used to evaluate the intrinsic hardness of metallic thin films on substrates. (Received December 2, 2019; Accepted December 26, 2019)

keyword : nanoindentation, thin film on substrate, intrinsic hardness, Meyer-plot, surface roughness