SiC/SiC mini-composites with multilayer ZrSiO4 interphase: Room-temperature properties and toughening mechanism

SiC/SiC mini-composites reinforced with SiC fibers coated with different numbers of ZrSiO₄ sublayers prepared via a non-hydrolytic sol-gel process were fabricated. The tensile strength and work of fracture of the prepared SiC/SiC mini-composites were determined, and the relationship between their mechanical properties and fracture morphologies was discussed. The toughening mechanism and the variation tendency of their mechanical properties were further elaborated by analyzing the interfacial debonding morphologies of the SiC/SiC mini-composites with 1 and 4 layers of ZrSiO₄ interphase as well as the results of prior studies. A relatively rare phenomenon—the delamination of the multilayer ZrSiO₄ interphase in the SiC/SiC mini-composites but not on the SiC fibers—was observed, which clearly demonstrated the weak bonding between the ZrSiO₄ sublayers in the SiC/SiC mini-composites. The ZrSiO₄ sublayer delamination mechanism was then explained based on the high-magnification morphologies found in and beside the ZrSiO₄ interphase.     

Liquid-state interfacial reactions in Sn–Zn/Pd couples and phase equilibria of the Sn–Zn–Pd system at 260 °C

This study investigated the effects of Zn contents on the reaction products and microstructural evolution in the liquid/solid Sn–Zn/Pd interfacial reactions at 260 °C. A uniform Pd₂Zn₉ layer was formed at the Sn–9 wt.%Zn/Pd interface. The reaction phase transited from Pd₂Zn₉ to PdSn₄ when the Zn content decreased from 2 wt.% to 1 wt.%. The most striking feature is that the PdSn₄ growth was greatly suppressed with only 0.5 wt.% Zn addition in solders. Additionally, a drastic microstructural evolution was observed in the Sn–1.5 wt.%Zn/Pd reaction. The Pd₂Zn₉ layer was initially formed and then it was detached from the interface due to the decrease in the Zn content. Subsequently, the dominant phase changed to the PdSn₄ phase. Furthermore, a partial isothermal section in the Sn–Zn–Pd ternary system (less than 20 at.%Pd) at 260 °C was experimentally determined. The liquid apex of the liquid + PdSn₄ + Pd₂Zn₉ tie-triangle was located at Sn–2.7 at.%Zn–1.0 at.%Pd. The phase transition from Pd₂Zn₉ to PdSn₄ in the interfacial reactions was in good agreement with the phase equilibria relationship.     

Residual strain in cadmium telluride/gallium arsenide (001) heterostructures as a function of temperature

Optical studies of residual strain in cadmium telluride (CdTe) films grown using molecular beam epitaxy on gallium arsenide (GaAs) substrate have been performed using photoreflectance techniques. Measurements have been conducted to determine the fundamental transition energy, heavy-hole and light-hole transition energy critical-point parameters in a range of temperatures between 12 and 300 K. There are problems inherent in the fabrication of optoelectronic devices using high-quality CdTe films, due to strain effects resulting from both the lattice mismatch (CdTe: 14.6%) and the thermal expansion coefficient difference. The CdTe film exhibits compressive stress causing valence-band splitting for light and heavy holes. We have used different models to fit the obtained experimental data and, although the critical thickness for the CdTe has been surpassed, the strain due to the lattice mismatch is still significant. However, the strain due to the thermal expansion is dominant. We have found that the fundamental transition energy, E₀, is affected by the compressive strain and the characteristic values are smaller than those reported. In addition, the total strain is compressive for the full measured range, since the strain due to the lattice mismatch is one order of magnitude higher than that calculated from the thermal expansion.     

Strong coupling effects during Cu/In/Ni interfacial reactions at 280 °C

The substantial heat generated in three-dimensional integrated circuits and high-power electronics has made thermal management a critical challenge for reliability in the electronics industry. Pure indium solder has been used as a thermal interface material to minimize the contact thermal resistance between a chip and its heat sink. Indium and indium-based alloys are potential lead-free solder for low-temperature applications. Heat sinks in the heat dissipation system as well as substrates of electronic joints are usually made of copper, with nickel being the most commonly used diffusion barrier on the chip side. Therefore, the Cu/In/Ni sandwich structure would be encountered in electronic devices. The soldering process for forming the Cu/In/Ni structure crucially determines the reliability of devices. In this study, Cu/In/Ni interfacial reactions at 280 °C were investigated. Intermetallic compounds were identified and the microstructural evolution was observed. A strong coupling effect between Cu and Ni was found, which caused several peculiar phenomena: (1) the formation of a Cu–In compound (the Cu₁₁In₉ phase) at the In/Ni interface; (2) the formation of two sub-layers of the Cu₁₁In₉ phase at the Cu/In interface; (3) the formation of faceted rod-like Cu₁₁In₉ grains; and (4) the formation of a half-Cu₁₁In₉, half-Ni₃In₇ microstructure after prolonged reactions. The mechanism of phase transformations is elucidated based on the calculated Cu–In–Ni ternary phase diagram using CALPHAD thermodynamic modeling.     

Measurement of Interface Free Energy in Polypropylene/Ethylene–Propylene Rubber Blends

Measurement of between ethylene–propylene rubber (EPR) and polypropylene (PP) is an important research subject in the study of rubber toughened PP. When the ethylene content in EPR is low, the EPR and the PP phases become optically indistinguishable due to their similar refractive indexes, and thus the measurements of interface free energy by conventional methods are impossible. In this study, we devised a new experimental technique that enables measurement of the interface free energy between two polymers having similar refractive indexes. When small amount of inorganic additives are incorporated to the PP phase, interface between PP and EPR phases are clearly seen and the measurements become attainable. Using the suggested method, the interface free energy between EPR and PPs were obtained and presented. Four different PPs were investigated, homo PP and three random PPs that contain small amounts of ethylene unit ranging from 1 to 3 wt%. It was found that the interface free energy decrease as the ethylene content in the PPs increases and the effect of the ethylene content on the interface free energy is unexpectedly large.     

Pure and Ni2O3-decorated CeO2 nanoparticles applied as CO gas sensor: Experimental and theoretical insights

In the present work, the structural, morphological and electrical properties of CeO₂ nanoparticles with spherical and rod-like morphologies and rods decorated with Ni₂O₃ were investigated. Morphological, structural and electronic analyses showed a relationship between the shape/size of particles and the respective surface types, number of carriers, density of vacancies and local structural atomic order, in addition to an influence on the electrical properties of the materials. Electrical analyses revealed that the rod-like morphology has a better CO sensor response than the spherical one. In order to complement and rationalize the experimental findings, simulations at the density functional theory (DFT) were carried out to investigate the two possible mechanisms (Langmuir?Hinshelwood and Mars-Van Krevelen) acting on the CO adsorption process and elucidate the behavior of the sensor in heterojunction-type samples.     

改性剂与矿物填料界面结合关系研究

本文通过对改性矿物填料的热稳定性，红外光谱以及比表面积测定研究，揭示了改性剂与矿物填料的界面结合关系。     

5083Al/1060Al/TA1/Ni/SUS304五层爆炸复合板退火组织演化及力学性能

为改善5083Al和304不锈钢爆炸焊接质量,提升隔热效果,本研究采用1060Al、TA1和Ni作夹层材料,制备了具有热传导梯度的五层爆炸复合板。为消除爆炸焊接后的残余应力,减少绝热剪切带和微裂纹等缺陷,采用550℃×60min退火工艺对五层爆炸复合板进行退火处理,并通过SEM、EBSD和万能试验机等手段,分析研究退火对其组织演化及力学性能的影响。结果表明：五层爆炸复合板的4个焊接界面均呈波形,且在界面处存在微裂纹、孔洞、绝热剪切带和漩涡区等缺陷。经退火处理,4个焊接界面均发生不同程度的再结晶,微裂纹、绝热剪切带等缺陷得到有效改善;5083Al/1060Al/TA1界面的β相和Al-Ti金属间化合物增多,TA1/Ni界面在原TiNi₃熔化层的基础上新增TiNi熔化层和Ti₂Ni熔化层。界面抗拉剪强度均有所降低,但均仍远高于相应国标使用要求;拉脱试样在5083Al/1060Al界面断裂分离。     

Towards Friction Stir Remanufacturing of High-Strength Aluminum Components

Volumetric defects in high-strength aluminum alloy components were repaired via friction stir remanufacturing (FSR). Various consumable pins made of AA7075-T6 were designed. Top diameters of the consumable pins affected material flow, which ensured that the materials at the repairing interface were forged to metallurgical bonding. Conical angles determined load transfer besides material flow, which affected the fracture of the pins before the dwelling stage. Sound repaired components were achieved when the conical angle of the consumable pin was 1° larger than that of the volumetric defect. The ultimate tensile strength and elongation of the repaired components reached 445.9 MPa and 9.6%, respectively. The design criteria of the consumable pin in the FSR was established, which provided valuable references to repair volumetric defects in high-strength aluminum components.