Key Engineering Materials Vol. 573

Abstract: In this paper, micro interfacial behavior for Sn3.5Ag0.5Cu (SAC305) lead-free solder on Cu-Ni-Au substrate has been carefully investigated. It is observed that the intermetallic compound (IMC) ingredients along the SAC305 solder on the Cu-Ni-Ag substrate are (Ni, Cu)₃Sn₄ and (Cu, Ni)₆Sn₅ after reflow process. Reliability analysis for IMC ((Ni, Cu)₃Sn₄ and (Cu, Ni)₆Sn₅) was conducted based on the measurement of IMCs thickness and ball shear force. Temperature effects were also included in the analysis. The ingredients of IMC remain un-change if the working temperature is below 400 ^OC. Diffusion rate of interfacial controlled reaction was found to be depended on the annealing temperature. The IMC layer thickness decreased as the ramp-up rate of reflow temperature was increased for all cases studies. Preliminary results demonstrated that the measured ball shear force slightly changed for all different IMC thicknesses.

Abstract: The purpose of this study is to measure contact angle and surface tension of liquid Fe-Si-B alloys at high temperature using sessile drop method. The surface tension and contact angle result is based on sessile drop method by use of a digital camera to take the drop profile and fit the profile by Youngs-Laplace equation. The surface tension of liquid Fe-Si-B alloy and its dependence on temperature has been studied. Contact angles of this liquid alloy on various refractories substrate have been determined using this instrument. The result showed that the contact angles and surface tension of Fe-4Si-3B alloy liquid drop on Al₂O₃ substrate have value of 134 to 127and 1575-1350 mN/m respectively. The result indicated also that increasing temperature can decrease contact angle and surface tension in Fe-Si-B alloy.

Abstract: Ionic/electronic performance of various cathodes in contact with solid electrolytes used for intermediate-temperature (500-750°C) solid oxide fuel cells (SOFCs) is investigated. Perovskite-type material, e.g. (La,Sr)(Co,Fe)O₃ as abbreviated LSCF, mixed with Gd-doped CeO₂ (GDC) particulates in various size ranges has been synthesized by Pichini and co-precipitation methods. The composites are assembled into multilayer cathode structure, which is arranged in a sequence of composite/GDC/ YSZ electrolyte. The microstructure of the interface, electrochemical performance, and interface conductivity of various cell combinations are investigated.

Abstract: In the design of runner systems, ceramic foam filters are used for reducing the velocity of liquid metal in order to avoid so called bifilm defect resulting from a high gating velocity (over its critical gating velocity) in aluminum gravity casting. In this study, two types of runner systems incorporated with the ceramic foam filters were designed. In order to observe the flow phenomena in these two runner systems with and without the filters, a water analogy experiment in a transparent plastic mold was utilized. Furthermore, in order to understand the effect of the filters used in these systems, an aluminum sand casting experiment was conducted. The quality of the cast metal in the outlet area of the filter for these systems was investigated. The defect content of this casting sample was measured by the re-melt reduced pressure test (re-melt RPT) and followed by measuring its bulk density. An optimized runner system with the filter was suggested in this study. Keywords: ceramic foam filter, runner system design, gravity casting, critical gating velocity, bifilm defect.

Abstract: The physical and optical properties of P₂O₅-Al₂O₃-ZnO glasses doped with different concentration of Yb³⁺ ions were investigated. The experimental results indicated that density, chemical durability, glass transition temperature (T_g) and glass softening temperature (T_d) of glasses increase with increasing the Yb₂O₃ content of glasses. However, the coefficient of thermal expansion (α) for glasses decrease with increasing the Yb₂O₃ content. From the results of Fourier transform infrared spectroscopy, the numbers of (-P-O-P-) bonds decrease and (-P-O-M⁺-) bonds increase with increasing the Yb₂O₃ content. Increase of non-bridge oxygen (-P-O-M⁺-) raise the refractive index of glasses. Moreover, the results of absorption spectra indicate that the absorption peak of glasses are observed at both wavelengths of 916nm and 977nm. As increasing the concentration of Yb₂O₃, the absorption efficiencies become stronger. In accordance with the results of fluorescence spectra, the fluorescence emission of glasses are detected at wavelengths of 970nm, 995nm, 1020nm and 1048nm, respectively. The intensity of the fluorescence emission peaks significantly decrease at wavelengths of 970nm and 995nm as the concentration of Yb₂O₃ increases. However, the intensity of the fluorescence emission peaks significantly increase at wavelength of 1048nm under the same condition.

Abstract: 50Si-50Al alloys were synthesized by the Spray Forming process, and were further deformed in the semi-solid state. The spray-formed microstructure consists of small equiaxed primary Si in 3-5 μm scale. For semi-solid deformation at 650°C at solid fraction (fs) of 0.4, the stress increases initially to reach the peak stress, then decreases to a plateau level, followed by last stage of stress climbing, and the effects of the deformation speeds on the stress level are significant, but not large. For deformation at 750°Cat fs of 0.31, the stress increases initially, then increases at a slower rate, followed by last stage of fast climbing, and the lower the deformation speed is, the higher the deformation stress. The average deformation stress needed at 650 °C was much higher that that needed at 750 °C. The deformation was inhomogeneous at 650°C to become pieces of connected semi-solid clusters, while the deformation was much more homogeneous at 750°C.

Abstract: In this study, the coating layers of IN625 and 301 stainless steel powders were deposited on the AZ80 magnesium alloy substrates by cold-spray technique. The crystal structures, cross-section of the coating layers and anti-corrosion capabilities were examined via XRD, SEM, potentio-dynamic polarization and salt spray test. Experimental results show that the coating layers have a few porosities. The AZ80 substratesexhibit a phenomenon of grain refining after the cold-spraying. Meanwhile, these coating layers could improve significantly the alloy’s corrosion resistance.

Abstract: A rapid and sufficient osseointegrating functions is obviously essential to the patients who suffered the bone reconstruction period. In order to perfectly target this issue, a single-stage micro-arc treated (MAT) coating beneficial from its inherent porous morphologies with controllable pore sizes, strong adhesive force between coatings and substrate and wide selections in electrolytes, is considered. Hydroxyapatite is extensively utilized and identified as mimic composition to human bone and an active bone ingrowth function. However, a controllable high-purity HAp phase via one-stage MAT has not yet been achieved. This study therefore prepares high-purity HAp coatings using one-stage MAT with the electrolyte combination of Calcium acetate and sodium biphosphate dihydrate on a titanium surface through a systematical evaluation of various MAT parameters, including Ca/P ratios of the electrolyte, electrolyte concentrations, working voltages, and treatment periods. Analytical results show that high-purity HAp can grow at a relatively high Ca/P ratio and electrolyte concentration when combined with a relatively high working voltage and long treatment time, which would otherwise grow with CaTiO₃ and/or anatase TiO₂ and/or rutile TiO₂ simultaneously. Additionally, CaTiO₃ acts a precursor phase for HAp formation. Ultimately, the highest purity of HAp coating is obtainable on metal titanium using a Ca/P ratio = 2.16 and applying a working voltage of 450 V for 10 min using one-stage MAT. This highest purity of HAp coating also presents excellent level of E_corr than that on raw Ti alloys. The high E_corr of HAp coating contributed from its thick and dense oxide layer by working voltage via one-stage MAT, consequently promises its satisfactory protection. The HAp coating demonstrated in this study not only provides the effective approach to produce the desired purity of HAp coatings but compromises its resistance to SBF. The bioactive HAp coating on Ti alloys via one-stage MAT, thus, considers as one significant surface modification for artificial hip joints and dental implants.

Abstract: A pack boriding technique was employed to obtain a hard coating on the surface of Ti6Al4V alloy in this paper. The microstructure, surface appearance, hardness depth profile and the cavitation erosion behavior of the borided samples in 3.5% NaCl solution were examined. The cavitation erosion resistance of the borided samples was significantly improved as compared with the untreated samples. Increasing in the surface hardness and the compact boride layer contribute to the significantly enhanced cavitation erosion performance of Ti6Al4V alloy.