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Das, H.,Lee, K. J.,Hong, S. T. SPRINGER INTRNATIONAL 2017 JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE Vol.26 No.7
<P>Friction stir lap welding of dual phase 590 steel has been successfully performed within the A1 to A3 temperature range upon adjusting the process parameters. The microstructures and the texture have been characterized using scanning electron microscopy and electron back scattered diffraction analysis. The martensite volume fraction increases with an increasing travel speed from 100 to 300 mm/min for a constant tool rotational speed of 300 rpm. Under severe deformation and high strain rate during friction stir welding, the grain orientation < 101 > shifts toward the < 111 > and < 001 > directions compared to the base metal. The base metal shows gamma fiber components, whereas the friction stir welded specimen shows strong brass with weak cube fibers.</P>
Degradation of TiN Coatings on Inconel 617 and Silicon Wafer Substrates Under Pulsed Laser Ablation
Jeon, S.,Lee, H.,Jo, I.,Shin, D.,Lee, K. S. SPRINGER INTRNATIONAL 2014 JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE Vol.23 No.5
The degradation behavior of TiN coatings on Inconel 617 and silicon (Si) wafer substrates was compared following Nd:YAG pulsed laser ablation to apply thermomechanical stress. Surface cracks and pores were observed on the TiN coating on the Inconel 617 after five pulses, and melting of the coating was occurred over ten pulses. The TiN coating on the Si wafer also showed surface cracks and pores, but there was no surface melting. As the pulses were increased, the surface roughness of the TiN coating on Inconel 617 increased more than the TiN coating on the Si wafer, and interfacial cracking was the dominant degradation behavior on the Si wafer. The hardness of the TiN coating decreased below 50% of its initial value (2200 HK) after five pulses on the Inconel 617, whereas over 70% of the initial value (2400 HK) was maintained on the Si wafer. The TiN coating on Inconel 617 showed diffusion of substrate atoms to the surface, while Si was not found in the TiN coating on the Si wafer even after 25 pulses. It was determined that the decrease in hardness was influenced by the cracking behavior and the diffusion of atoms from the substrate.
Koo, H.,Shin, D.,Bae, S. H.,Ko, K. E.,Chang, S. H.,Park, C. SPRINGER INTRNATIONAL 2014 Journal of materials engineering and performance Vol.23 No.2
CeO2-VO2 bilayer structure was fabricated to investigate the effect of depositing CeO2 film on the optical properties of VO2 film for smart window application. CeO2 was employed as an antireflection (AR) layer material of VO2 film because of its advantages which include high transparency in the visible-near infrared range and high refractive index. All the films were deposited on soda-lime glass substrate by pulsed laser deposition method. Optical calculations were carried out using transfer-matrix method for the purpose of designing CeO2-VO2 bilayer structure with enhanced integrated luminous transmittance (T (lum)) and switching efficiency (Delta T (sol)). The optical constants of VO2 and CeO2 films needed for the optical calculation were measured by spectroscopic ellipsometer. The curve of T (lum) the shape of which depends on the thickness of CeO2 layer, was calculated in each VO2 sample, which showed two maxima. The samples were divided into two groups; one for the highest enhancement of T (lum) and the other for balanced enhancement between T (lum) and Delta T (sol). The sample with the structure of similar to 60 nm CeO2 AR layer on 39-nm thick VO2 film showed large increase of T (lum) (similar to 27%) with Delta T (sol) of similar to 5%, which is the largest increase in T (lum) reported so far. Two samples in the other group showed the balanced enhancement in T (lum) (similar to 57, similar to 50%) and Delta T (sol) (similar to 9, similar to 10.5%). The effect of CeO2 AR layer on the optical properties of VO2 film was confirmed with the optical calculation and the experimental results. CeO2-VO2 bilayer structure showed notable improvement of optical properties compared to the single VO2 film, indicating that CeO2 layer can be effectively used as the antireflection layer while working as a protective layer that can prevent the oxidation of VO2 layer as well.