Papers by Author: Truan Sheng Lui

Abstract: mplants made of titanium and its alloys are widely used in dental and orthopedic fields due to their excellent chemical stability and mechanical properties. However, due to the bio-inert properties of titanium and its alloys, it is difficult to achieve a chemical bond with bone tissue and to form a new bond on the surface. To improve biocompatibility, surface treatments are often used to modify the chemical and morphological properties. Besides, the mussel-inspired molecule of 3,4-dihydroxy-L-phenylalanine (dopamine) shows excellent biological responses. The aim of this study is to investigate the physicochemical and biomedical properties of CaP porous coating with dopamine. The CaP porous coating was prepared on titanium by micro-arc oxidation, and then bio-inspired molecular of dopamine modified surface to improve the cell behavior. Characteristics of the morphology, chemical composition, and interfacial properties of dopamine-functionalized CaP porous architecture was performed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The osteoblastic cell behaviour, such as differentiation and morphology is evaluated. The nitrogen signal in XPS spectrum was indicated that the dopamine existed in the porous coating. The anatase and rutile phases of porous coating with dopamine were identified. Morphologies of porous coating with dopamine showed the uniform and three-dimensional structure. Cell culture experiments demonstrate that the porous coating with dopamine would improve cell behavior. All findings in this study indicated that CaP porous coating with dopamine have good bioactivity for clinical applications.

Abstract: This study coats complex colloid mixed with Sn-xAl powders and polyethylene on glass to examine the shield effect on electromagnetic interference (EMI). In addition, the sputtering specimens and powder coating specimens were compared. The results show that adding Al to the Sn-xAl powders can increase the electromagnetic interference (EMI) shield at lower frequencies. Notably, the number of cavities in the coating layer increased with the coating thickness, with the result that the EMI shield could not improve with an increase in the coating thickness at higher frequencies. However, the EMI shield of sputtering films had a tendency to increase as the thin thickness increased. The Sn-40Al undergoes a dispersing effect which forms a fine overlapping structure, thereby improving the low frequency EMI shielding. In addition, the Sn-20Al powders possessed the properties of a small particle size, closed structure and higher electric conductivity which improved the high frequency EMI shielding. For the sputtering films, the annealed treatment not only had higher electric conductivity but also increased the high frequency EMI shielding.

Abstract: The bioactivity of materials was evaluated based on the ability to induce a bond-like apatite layer on the surface in simulated body fluid (SBF). The aim of this study was to investigate the coatings containing strontium on bioactivity after heat treatment. After the materials were soaked in SBF for 1 day, precipitates did not form on the surface of heat-treated MAO coating without strontium. The precipitates were observed on surface of heat-treated MAO coatings containing strontium. After 7 days, the surface of heat-treated MAO coatings containing strontium was completely covered with precipitates. The precipitates were found to be composed of fiber structures using scanning electron microscope (SEM). The phase was identified as the apatite phase using thin film X-ray diffraction (TF-XRD). The results show that heat-treated MAO coatings containing strontium can induce the formation of an apatite layer on their surface. All finding in this study indicated that heat-treated MAO coatings containing strontium have good bioactivity for clinical applications.

Abstract: Sn, Al and Cu not only possess electromagnetic interference shield efficiency, but also have the acceptable costs. In this study, sputtered Sn-Al thin films and Sn-Cu thin film were used to investigate the effect of the crystallization mechanism and film thickness on the electromagnetic interference (EMI) characteristics. In addition, the annealed microstructure, electrical conductivity and EMI of the Sn-xAl films and the Sn-xCu films were compared. The results show that Sn-Al film increased the electromagnetic interference (EMI) shielding after annealed. Sn-Cu films with higher Cu atomic concentration, the low frequency EMI shielding could not be improved. After annealing, the Sn-Cu thin film with lower Cu content possessed excellent EMI shielding at lower frequencies, but had an inverse tendency at higher frequencies.

Abstract: Experimental results showed that both of commercial pure titanium (CP-Ti) and yttria-stabilized zirconia (YSZ) intermediate layers significantly enhanced the bonding strength of HACs (one-way ANOVA test, p < 0.05). On the basis of fracture morphologies and bonding strength data fluctuation, the Weibull model provided a powerful statistical analysis for assessing the failure mechanism and the reliability of composite coatings. Plasma-sprayed HACs were reliable materials with a right-shift wear-out failure model (m > 3) of increasing failure rate (IFR). The HA composite coatings remained in tack on the substrate, which represented better reliability and less dissociation for further applications. The measured bonding strength of HACs was a combination of adhesive and cohesive strength of a coating layer. The area fraction of adhesive failure tended to decrease with introducing the reinforced intermediate layer, especially for the HA/YSZ composite coating. The decrease of adhesive failure area fraction represented good interlocking between the coating/substrate interfaces. The knowledge of fracture behaviour in HACs with reinforced intermediate layers will be very helpful for the understanding and prediction of the bonding strength.

Abstract: Plasma-sprayed HA coatings (HACs) on Ti-6Al-4V substrates with post-heat treatments were employed to improve the microstructural homogeneity, bonding strength and reliability of the HACs. A defect-healing effect can be recognized to diminish coating defects with the hydrothermal treatment, and 150°C hydrothermally-treated HACs shows a significant improved bonding strength than 600°C vacuum heating HACs because of its dense structure from the defect-healing effect. Low-temperature hydrothermal treatment demonstrates a more superior crystallization effect than vacuum heat treatment. Based on the statistical calculation by the Weibull distribution function, hydrothermally-treated HACs show a wear-out failure with a higher Weibull modulus than vacuum heating HACs. Hydrothermally-treated HACs possessed better reliability can be attributed to the suppression of defect content (about 2.6-3.2 volume %) and its smaller strength data fluctuation.

Abstract: In this study, stellite 6 alloy was overlaid on spheroidal graphite (SG) cast irons with various carbon contents (1.5wt%~3.8wt%) and a fixed silicon content (approximately 2.5wt%) using the plasma transferred arc (PTA) process at different overlaying current (140A~220A) while the travel speed of the PTA torch was maintained constant. Results indicated that the solidification structures of the stellite 6 overlayers were dendritic and had a large amount of interdendritic precipitates (M7C3 and M23C6 carbide) after the satellite 6 alloy had been overlaid on SG cast irons with different carbon contents (1.5wt%~3.8wt%) at a low overlaying current (I=140A). The partially melted zones of the substrates below the carbide-containing interfacial layers consisted of eutectic carbides (ledeburites) and fine pearlites. The amount of the carbide-containing interfacial layers and ledeburites increased following the increase in the overlaying current. The results of the tearing test reported that the occurrence of the carbide-containing interfacial layers was detrimental to the bonding strength between the overlayers and the substrates. The metallography of the fractured area of the tearing specimens after the bonding strength test revealed that fractures always occurred at the carbide-containing interfacial areas. On the other hand, the overlayers were rich in iron content when the overlaying currents were high (I=190A and 220A). Owing to the dilution effect, the matrices of the overlayers were α-Fe with lamellar M7C3 carbides. The results of the tearing test indicated that the bonding strength of the overlaid specimens was relatively low, and fractures always occurred in these highly diluted overlayers.

Abstract: Both Al-Zn alloy and Mg-Al-Zn alloy have been considered as high damping and light materials. For practical use, this study investigated the effects of the structure and the composition on the vibration fracture characteristics of the Al-xZn alloy and the Mg-xAl-Zn alloy under resonance. For Al-xZn (x=7, 11, 49, 83wt%) alloys, under both constant force and initial-deflection conditions, the 7Zn showed the greatest vibration life. For Mg-xAl-Zn (x=3, 6, 9wt%) alloys, experimental results indicate that the AZ31-F as-extruded samples showed a greater vibration life, while high Al fully-annealed samples (AZ91-O) had greater vibration fracture resistance under constant force conditions.