Papers by Author: Jow Lay Huang

Abstract: Electrochromism have been widely investigated due to their potential applications such as automobile and building window. In this study, tantalum oxide thin films used as ion conducting layer were deposited on WO₃/ITO at room temperature by magnetron sputtering. The thickness of tantalum oxide films were varied to investigate their effects on composition, microstructure, optical properties, and electrochromic properties determined by X-ray diffraction, UV-visible spectrometer, Atomic force microscope (AFM), and field-emission scanning electron microscope (FE-SEM). Experimental results indicated Ta₂O₅ at thickness of 300 nm with low packing density were favorable for ions transmission deposited on WO₃/ITO had better electrochromic property.

Abstract: Micro-hardness measurements of thin coatings have to face the problem of the influence of the substrate. Based on relative method and the relationship between the composite hardness (the hardness of the coated sample) and the substrate hardness, a new model is proposed to evaluate the absolute hardness of ceramic coatings. Indentation tests with various load levels were carried out with specimens of (Ti,Al)xN1-x/SiyN1-y composite coating on SKH51 steel substrate. The results were analyzed by the new model and compared with those calculated by J-H (Jönsson and Hogmark) and L-C (Lesage and Chicot) models. The mean coating hardness obtained from this model shows similar results with the J-H model but a little higher than that from L-C model.

Abstract: In this study, multilayers of TiN/NbN were deposited by d.c. magnetron sputtering on die steel substrates. The structure, morphology and nano-hardness were assessed using X-ray diffraction, atomic force microscopy (AFM), stylus profiler (XP-2 stylus profiler) and nanoindentation, respectively. Wear tests were performed on pin-on-disk configuration and dry sliding conditions, at 5N load by using hardened steel ball. The result shows TiN with highly (111) preferred orientation. On mechanical properties, Young’s modulus and hardness values increase for layers number increase. At 64 layers films had the highest nano-hardness, Young’s modulus values. The TiN/NbN multilayer films presented changes in its morphology becoming more granulated and density after heating up to 500°C. A significant decrease in friction coefficient has been achieved for TiN/NbN multilayers against steel ball.

Abstract: Ti3SiC2 has been a spectacular material, as it combines many of the best properties of metals and ceramics. This new material has potential applications for fabrication of jet engines and in bonding phases. Microstructure can further enhance the mechanical properties, such as strength, wear resistance and chemical stability. In the current research the different starting powder systems were used to synthesize Ti3SiC2 by hot pressing. The contents of Si were controlled appropriately to obtain Ti3SiC2/TiC ceramic composites. Preliminary results indicated that the fracture toughness and strength were improved. The influences of TiC contents on the microstructure and mechanical properties were investigated and the fracture mechanisms of Ti3SiC2/TiC ceramic composites are discussed qualitatively.

Abstract: Nanoscaled Cr2O3 powders coated on alumina particles have been produced by means of metal organic chemical vapor deposition (MOCVD) in a fluidized bed, using the pyrolysis of Cr(CO)6 precursor. In order to prepare the nanoscaled Cr3C2 powder from the Cr2O3, carbonizing behavior of the Cr2O3 particles was investigated. The carbon is from the decomposition of Cr(CO)6. It was found that Cr2O3 transformed into Cr3C2 at 1150 oC in graphite furnace in a vacuum level of 10-4 torr, while it could not carbonize at 1150oC in a vacuum level of 100 torr. In the present study, two reactions for Cr2O3 are carried out. One is that Cr2O3 reacts with Al2O3 to form a solid solution; the other is that Cr2O3 reacts with carbon to transform into chromium carbide. Consequently, a nanocomposite comprising the matrix of solid solution of Al2O3 - Cr2O3 and second phase Cr3C2 was prepared after hot-pressed.

Abstract: The effects of TiN addition to Si3N4 on its mechanical and wear properties were investigated. The size and content of TiN particles were found having effects on the strength and toughness of Si3N4-based composites. The friction and wear behavior of Si3N4 based composites against AISI-52100 steel were investigated in the ball -on- disc mode in a non-lubrication reciprocation motion. It has been found that under the conditions used all the ceramic components exhibited rather low friction and wear coefficients. For monolithic silicon nitride materials, high friction coefficients between 0.6 and 0.7 and wear coefficients between 1.63 × 10-8 and 1.389 × 10-6 mm3/N.m were measured. The contact load was varied from 100 to 300 N. By adding titanium nitride, the friction coefficients was reduced to a value between 0.4 and 0.5 and wear coefficients between 1.09×10-8 and 0.32×10-6 mm3/N.m at room temperature.

Abstract: A radio frequency power (r.f.) of 200W was supplied to ZnO target, and a direct current (d.c.) power of 30W was supplied to Ti target for the preparation of Ti-doped ZnO (ZnO:Ti) films. The Ti content was controlled by d.c. power, and maintained at 1.1 at.% as measured by XPS. The as-deposited ZnO:Ti films had polycrystalline structure and low resistivity (9.69×10-3
-cm). After annealing in N2 or O2, ZnO:Ti films exhibited poor crystallinity, and the resistivity increased substantially. The lower optical energy gap (3.31 eV) could be obtained as ZnO:Ti film annealing in O2. However, the weak absorption in the visible region of the spectrum terminated at shorter wavelengths with the onset of the ultraviolet absorption edge for all samples. Annealing in N2 or O2 did not improve the properties of ZnO:Ti films.

Abstract: A radio frequency power (rf) was supplied to ZnO target, and a direct current (dc) power was supplied to Al target for the preparation of heavily Al-doped ZnO (ZnO:Al) films. The advantage of this kind of deposited method is that the Al content could be changed in a wide range. The ZnO:Al films prepared at different dc powers showed different surface morphologies, and corresponded to the different surface roughness. The ZnO:Al films prepared at high dc powers showed the amorphous structures, and resulted in very high resistivity. The resistivity of ZnO:Al film prepared at dc power of 40W was lower (8.52×10-3
-cm). It was mainly due to the relatively higher mobility, which probably resulted from the relatively low surface roughness, and corresponded to the surface morphology in the shape of cobblestone. In addition, the ZnO:Al films prepared at different dc powers showed different optical properties.

Abstract: Mechanical properties of coatings are usually affected by the substrate behavior and the thickness of the coating. The film on a substrate can’t be tested like a monolithic sample. Therefore, the absolute value of the mechanical properties of the film is often difficult to obtain, but the properties of a coated sample and a monolithic sample could be measured, and there must be a unique relation between them. Based on this consideration, a relativity method was proposed to evaluate the mechanical properties of coatings, including the hardness, elastic modulus. Satisfactory results have been obtained from the experiments using this clue. Moreover, residual stresses caused by mismatch of the coefficients of thermal expansion between the coating and substrate was calculated based on the uneven strain mode, it indicates that the interfacial shear stress concentrated at edges and maximum stress in coating is at the center.

Abstract: The present paper deals with the nano-indentation of SiC-micro and Si3N4/SiCmicro/ nano ceramic materials. The investigated SiC-micro and Si3N4/SiC-micro/nano ceramics were prepared by liquid phase sintering. Liquid phase was formed from different sintering additives (Y2O3, Yb2O3, Sm2O3). In the case of Si3N4/SiC-micro/nano ceramics the SiC nano-grains were created from SiNC amorphous powder. SiNC precursor decomposed to SiC and Si3N4 particles during sintering. The comparison of nano- and macro-hardness of investigated ceramic materials showed that nano-hardness is significantly higher. The indentation modulus correlated with the measured nano-hardness. Remarkable influence of grain boundaries and SiC nano-inclusions on hardness was observed.