Gaohui Wu

Co-enhanced SiO2-BN ceramics for high-temperature dielectric applications

Abstract Two typical high-temperature dielectric materials, fused silica and BN, have been used to form a composite with an attempt to overcome their own drawbacks. In the resultant BN–SiO 2 composites, BN platelike grains were preferentially orientated by hot pressing and homogeneously distributed in the fused silica matrix. An evident co-operative enhancement has been achieved by the combination of the constituents. The sinterability and the thermal shock resistance of the BN materials were increased and the ablation surface temperature was decreased by the involvement of the fused silica. On the other hand, the strength, fracture toughness, and flame ablation resistance of the fused silica were increased due to the addition of BN. Furthermore, an amorphous Si–B–O–N structure was identified in the surface layer of the ablated composites, to which attention should be further paid in the development of new elevated temperature dielectric materials.

Property characteristics of a AlNp/Al composite fabricated by squeeze casting technology

TiB_(2p )/Al 合成成功地被制作由压榨扔技术。它的机械并且 tribological 性质被评估。Ti-Alintermetallic 化合物的消除被衍射(XRD ) 学习的 X 光检查证实。在 45% 体积部分，在周围的温度的弯曲强度是 934 MPa。并且破裂模式包括了艾尔矩阵的可锻的失败和 TiB_2 粒子的易碎的骨折。在干燥滑动穿模式，严重塑料变丑和粘合剂穿在 SiC_p/Alcomposite 的穿的表面上被发现。但是粘附或磨耗(量) 的明显的特征都没在 theTiB_(2p ) 的上被观察 /Al composites。在稳定的阶段， SiC_p/Al 的磨擦系数合成是大约 0.6。当时 TiB_(2p )/Al 的合成仅仅关于 0.16-0.17。

The thermal expansion and mechanical properties of high reinforcement content SiCp/Al composites fabricated by squeeze casting technology

Abstract With mixing different sized SiC particles, high reinforcement content SiCp/Al composites ( V p =50, 60 and 70%) for electronic packaging applications were fabricated by squeeze casting technology. The composites were free of porosity and SiC particles distributed uniformly in the composite. The mean linear coefficients of thermal expansion (20–100 °C) of SiCp/Al composites ranged from 8.3 to 10.8×10 −6 /°C and decreased with an increase in volume fraction of SiC content. The experimental coefficients of thermal expansion agreed well with predicted values based on Kerners model. The Brinell hardness increased from 188.6 to 258.0, and the modulus increased from 148 to 204 GPa for the corresponding composites. The bending strengths were larger than 370 MPa, but no obvious trend between bending strength and SiC content was observed.

Mechanical properties of Cf/Mg composites fabricated by pressure infiltration method

The carbon fibers and the woven reinforced magnesium matrix composites were fabricated by pressure infiltration method. Effects of fiber species, fiber arrangement, hybrid particles and environment temperature on microstructures and properties of the composite were studied. Results showed that the mechanical properties at ambient temperature were affected by interfacial reaction. The magnesium matrix composites reinforced with graphite fibers showed higher strength and elastic modulus due to less interfacial reaction. During loading, the fibers were pulled out and the load was transferred through the interfaces, then the fiber bundles were fractured, finally the whole specimen failed. The introduction of hybrid SiC particles during fabrication can improve the mechanical properties of the magnesium matrix composites. Moreover, taking orthogonal carbon fiber woven as reinforcement can modify the anisotropy and reliability of materials.

Coating of Y2O3 additive on Al2O3 powder and its effect on the wetting behaviour in the system Al2O3p/Al

Abstract Al 2 O 3 powder was coated with Y 2 O 3 percursor generated by in situ precipitation of Y(NO 3 ) 3 ·6H 2 O in aqueous solution. After calcining at high temperature, the precursor was completely transformed into a crystalline Y 2 O 3 , and Y 2 O 3 -coated Al 2 O 3 powder was obtained. Transmission electron microscope (TEM), high resolution electron microscope (HREM) observation and elemental analysis clearly showed that the Y 2 O 3 was successfully coated on the surface of the Al 2 O 3 particles. The coated powders were also characterized by energy dispersive spectrum (EDAX) and X-ray diffractometry (XRD). The wetting behaviour of molten aluminum on the coated Al 2 O 3 powders was investigated by the sessile drop method. Due to the introduction of Y 2 O 3 , the wettability of the coated-Al 2 O 3 powders by liquid aluminum was dramatically improved in comparison with that of the as-received powders.

Study on properties of high reinforcement-content aluminum matrix composite for electronic packages

Aluminum matrix composites reinforced by a high volume fraction of ceramic particles provide a novel solution to electronic packaging technology, because of their high thermal conductivity, compatible and tailorable coefficient of thermal expansion (CTE) with chips or substrates, low weight, enhanced specific stiffness, and low cost. In this paper, SiC-particle-reinforced aluminum matrix composites are fabricated by the cost-effective squeeze-casting technology, and their microstructure characteristics, thermo-physical, and mechanical properties are investigated. The reinforcement volume fraction is as high as 70% and composites with linear CTE of 6.9–9.7×10−6 °C−1 and thermal conductivity of 120–170 W m−1 °C−1 are produced. The composites can be electric-discharge machined, ground, and electric-spark drilled. An electroless nickel layer is plated on the composite by the conventional procedures. Finally, their potential applications in electronic packaging and thermal management are illustrated via prototype examples.

Micro-yield property of sub-micron Al2O3 particle reinforced 2024 aluminum matrix composite

Abstract The microstructure and micro-yield strength of sub-micron Al2O3 particle reinforced 2024Al composites and the effect of the thermal-cold cycling treatment on the microstructure and properties were studied. The results show that the dislocations are rare in the microstructure of the sub-micron Al2O3p/2024Al composite in the squeeze casting condition. Aging and thermal-cold cycling treatment does not change this phenomenon. The Al2O3 particles are fine, so the thermal misfit between particles and the matrix is very small during the temperature change, resulting in decreased dislocations. The tiny and uniformly dispersed S′ precipitates and sub-micron particles can effectively pin dislocations, therefore, the micro-yield strength of the composite increases. Depending on the condition of the thermal-cold cycling treatment after aging, both the size and distribution of the S′ precipitates in the composite change, and they have great effect on the micro-yield strength of the composite.

Effect of Mg Content on the Thermodynamics of Interface Reaction in Cf/Al Composite

The interface of carbon-fiber-reinforced aluminum matrix (Cf/Al) composites fabricated by the pressure infiltration method with different Mg contents (0, 3.2, 4.5, 6.5, and 8.5xa0wt pct) was observed by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The Gibbs free energy of Al4C3 and Al3Mg2 was calculated by an extended Miedema model and a Wilson equation. The effect of Mg on the critical nuclear size of Al4C3 was discussed also. The size and number of Al4C3 decreased and transformed from needle-like to blocky with Mg content, and no Al4C3 but blocky β phase (Al3Mg2) was observed at the C-Al interface in the Cf/Al-8.5Mg composite. Increased Mg content in the Al matrix would increase the Gibbs free energy of Al4C3 but decrease that of the Al3Mg2 phase. The critical value of the Mg content, above which the formation of Al3Mg2 would be easier than Al4C3, was 8.8xa0wt pct when the C activity was 0.0013, which agreed well with the TEM observation. The critical nucleation size of Al4C3

Fabrication of in situ Ti2AlN/TiAl composites by reaction hot pressing and their properties

left( {t_{{{text{Al}}_{4} {text{C}}_{3} }}^{*} } right)