Materials Science Forum Vol. 749

Abstract: The Sn-3.5Ag based lead-free electronic solder doped with element In /Ce were prepared respectively using a smelting method with protection by molten salt (SMPMS). The effects of In addition and Ce addition on microstructure, melting point and wettability of Sn-3.5Ag solder were investigated comparatively. And the effects of addition on the intermetallic compound (IMC) layer formed at solder/Cu substrate interface and the shear strength of solder joint were also studied. The results showed that appropriate In or Ce addition can refine Ag₃Sn grains and improve the shear strength of solder joint. Element In can significantly reduce the melting point, narrow the melting range of the solder alloy and improve wettability on Cu substrate. When the content of In was 3%, the spreading area was the largest and the wettability was the best. The addition of Ce can efficiently reduce the thickness of the IMC layer grown at the solder/Cu substrate interface and improve the shear strength of solder joint. When the content of Ce was 0.5%, the solder joint had the minimum average IMC thickness and the maximum shear strength.

Abstract: Cu/nanoTiO₂/PBO composite fiber with low density, high strength, toughness and conductivity was prepared with a photocatalysis electroless plating method by reduction depositing Cu²⁺ on the surface of nanoTiO₂/PBO composite fiber. The process parameters on the preparation of Cu/nanoTiO₂/PBO composite fiber were optimized by the characterization of surface morphology, phase, composition, pull-out strength and resistivity of Cu/nanoTiO₂/PBO composite fibers using SEM, XRD, EDS, electronic tester of tensile strength and multimeter, respectively. The mechanism of Cu coating nanoTiO₂/PBO composite fiber was also discussed in this study. The results showed that Cu/nanoTiO₂/PBO composite fibers were well prepared under the bath composition of CuSO₄5H₂O 16gL^-1, KNaC₄H₄O₆4H₂O 15 gL^-1, Na₂EDTA2H₂O 24 gL^-1, HCHO 16 mlL^-1, NaOH 14 gL^-1, C₁₀H₈N₂ 24 mgL^-1 and K₄Fe (CN)6H₂O 12 mgL^-1 by the UV-light irradiated for 30 min. The diameter, pull-out strength and resistivity of Cu/nanoTiO2/PBO composite fiber were 20.2 μm, 2.25 GPa and 0.02864 Ωmm²m^-1, respectively. Cu²⁺ ions on the surface of nanoTiO₂/PBO composite fiber were reduced to Cu by photo-electrons which were generated of nanoTiO₂ under the UV-light irradiated, and the primary Cu layer as a catalytic center promoted the reduction reactions of producing Cu/nanoTiO₂/PBO composite fiber further.

Abstract: Oleic acid-modified zinc phosphate nanoparticles with about 15nm particle size were synthesized by chemical deposition method. The tribological properties of the prepared nanoparticles as lubricant oil additives on MSR-10D four-ball tribotest were investigated. Results indicated that the lubricant oils adding oleic acid-modified zinc phosphate nanoparticles exhibited a good friction-reduction and anti-wear property. The zinc phosphate nanoparticle as lubricant oil additive had the optimum concentration. Friction coefficient decreased 14.2% maximally, and the wear-scar width reduced to 36.5% correspondingly, as compared to the base oil without nanoparticles. The results of the worn surface analysis with SEM and AFM showed that the zinc phosphate nanoparticles could deposit on the worn surface and separate the direct contact between the asperities of the worn surface, which was effective in the reduction of the plough and adhesion between asperities.

Abstract: Lotus-type porous silicon is a promising micro-channel heat sink material in cooling of high powered electronic devices. Lotus-type porous silicon with elongated pores has been successfully fabricated by unidirectional solidification at different velocities. The average pore diameter and inter-pore spacing all increase whether along the height direction of the ingot or with increasing the thickness of graphite sheet (lower solidification velocity). The calculated porosity is in good agreement with the experimental results which almost keep as constant at different solidification velocities. The penetration ratio or the pore length increases with decreasing solidification velocity. The bigger pores are more likely to grow longer than smaller ones. In addition, the microstructure observation shows that the pores mostly distribute at the grain boundaries.

Abstract: The microstructures of AA6111 automotive aluminum alloy were investigated by optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), differential scanning calorimetry (DSC), X-ray diffraction analysis (XRD) and transmission electron microscope (TEM). The results indicated that as-cast AA6111 alloy has a complex microstructure. There were many kinds of intermetallic phases, such as lath-shaped β-Al₅FeSi, Al₁₅(FeMn)₃Si₂ and Mg₂Si on the grain boundaries. The Al₅Cu₂Mg₈Si₆ precipitates presented non-equilibrium eutectic morphology in the grain interiors. After homogenization treatment (6h at 470), the low melting point Mg₂Si phase began dissolving. The eutectic Al₅Cu₂Mg₈Si₆ phase were dissolved completely after 530/24h homogenization treatment. The Al₁₅(FeMn)₃Si₂ phase started to be spheroidized at 560. Increasing treatment temperature will promote Mn to substitute for Fe in this phase.

Abstract: Surface heat transfer coefficient is a key parameter for accurately predicting the extrusion product temperature near the die exit and then achieving isothermal extrusion by speed controlling. Based on the heat transfer characteristics of extrusion product during cooling process, a dynamic loading method of heat transfer boundary conditions was proposed. The surface heat transfer coefficient model of 7075 Al-alloy extrusion product was established using the dynamic loading method and inverse calculation comprehensively. The model indicated the relationship among surface heat transfer coefficient h, surface temperature T and initial temperature T₀ as h=1.16T-0.97T₀. Its accuracy is high enough for calculating the surface temperature of 7075 Al-alloy extrusion product. According to the model and the experimental data, the relationship between the product and the measured temperatures can be established. It provides an effective way to solve the problem that the extrusion product temperature near the die exit cannot be directly measured.

Abstract: In this work, the bainite transformation during isothermality of aluminium bearing TRIP steel was studied by dilatometric experiment on a pushrod Formastor-F highspeed dilatometer with radio frequency induction heating. The aluminium bearing TRIP steel consisted of the microstructure of austenite, ferrite and bainite in the form of laths which produced by intercritical annealing and isothermal transformation followed by rapid cooling. The effect of intercritical annealing temperature and isothermal transformation temperature were studied by dilatometric experiment and JEOL JXA-8530F Electron Probe Microscopic Analyzer (EPMA).

Abstract: Based on ultra fast cooling, effects of cooling paths on microstructure and mechanical properties of vanadium bearing microalloyed steel were investigated by the observation of optical microscope and scanning electron microscope and the testing of mechanical properties, moreover, the work-hardening exponent was determined based on stress-strain curves. The results show that using ultra fast cooling can effectively refine ferrite grain size and the ferrite grain size is decreased as the final temperature of ultra fast cooling is decreased. In addition, the microstructure and mechanical properties can be controlled by cooling paths. The ferrite-perlite microstructure with lower strength and higher n-value of approx. 0.2 and the ferrite-bainite microstructure with higher strength and lower n-value of approx. 0.16 can be gained at the higher and lower final temperature of ultra fast cooling, respectively. And the yield ratio are all lower than 0.85.

Abstract: The diversities and relations of microstructures and properties between the center and surface layer in thick-plate 7150 alloy were investigated by means of OM, TEM, SEM and tensile tests. The results indicated that the average width of elongated grains with fewer substructures in the center of hot-rolling thick plate is about 2 times larger than that in the surface layer. The coarser second phases are massed up at the grain boundaries of the center layer while those are crushed into smaller particles in the surface layer. By aging, the strengthening precipitates in the center are mainly GP zone and η' phase, while in the surface layer η' and η phases play the main roles. Consequently, the strength is about 80Mpa (15%) higher in the center than in the surface, with lower elongations (26% lower).

Abstract: Bulk glasses of xNb₂O₅(1-x)La₂O₃ (NL) with high refractive index were prepared by aerodynamic levitation method. Only when x ranges from 0.62 to 0.72, NL glasses can be obtained. The effect of compositions on the thermal property and refractive index was investigated. The results indicated that the glass transition temperature ranged from 733 to 767 with the increasing of La₂O₃ in NL glasses, while the crystallization peak ranged from 811 to 837 . The glasses had high refractive index ranging from 2.26 to 2.31. According to the Drude-Voigt relationship, the Abbe number of the glasses was calculated to be about 20. This type of glass was colorless and transparent in the region from visible to infrared region. Thus, the niobate glass system has promising application in lenses, next-generation optical disk, and endoscopes.