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Zhou Y.,Xian Jiaotong UniversityXian710049 China | Liu F.,State Key Laboratory of Solidification Processing | Wang H.,Electronic Materials Research Laboratory
Polymer Composites | Year: 2015

Significant progress has been made recently in developing the organic-inorganic composites with high thermal conductivity, low dielectric constant, and dielectric loss, for applications in the electronic packaging and substrates. Many studies have shown that some polymers filled with high thermal conductivity and low dielectric loss ceramics are suitable for electronic packaging for device encapsulation. Until now, extensive attentions have been paid to the preparation of polymeric composites with high thermal conductivity and low dielectric loss for the application in electronic packaging. In contrast, the thermal conductivities of these dielectric materials are still not high enough and that might restrict their serviceable range. Herein, we briefly reviewed recent progress in this field and introduced a kind of novel composites with surface insulation modified metal aluminum cores to form multilayer coating structures as fillers in polyimide matrix for electronic applications. This structure can significantly improve the thermal conductivity and dielectric properties of composites and give some insights into the effects of modified fillers of composite materials. Such multilayer core-shell structures should have great potentials for the improvement of nanoparticle-based fillers and applications of electronic packaging. © 2015 Society of Plastics Engineers.

Zhang M.-J.,Northwestern Polytechnical University | Li F.-G.,Northwestern Polytechnical University | Li F.-G.,State Key Laboratory of Solidification Processing | Wang S.-Y.,Aerospace Research Institute of Materials And Processing Technology
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2012

The finite element models of dies used for P/M superalloy disk forming were established, and the heating parameters were optimized based on the thermal-physical property of Ni-11Co-17W-6Al-8Ta alloy. The results show that stress peaks of the dies were lower when they were heated in heating rate range from 0.1°C/s to 0.5°C/s. The effect of holding time on thermal stress decreased when holding time was larger than 4h. This leaded to that the rate of decreasing stress became lower. According stress amplitude-holding time curve, the optimal holding time is between 2-4 h. Moreover, at the heating rate of 0.1°C/s and the holding time of 2 h, the outside surfaces and profile transition zones of dies exhibited stress concentration. The values of stress amplitudes were larger in these regions. However, the results of fatigue test at the temperatures of 1050°C and 1100°C show that the effect of thermal load on crack propagation in above-mentioned regions was slight.

Li Y.,Northwestern Polytechnical University | Xie F.,Northwestern Polytechnical University | Wu X.,Northwestern Polytechnical University | Li X.,Northwestern Polytechnical University | Li X.,State Key Laboratory of Solidification Processing
Applied Surface Science | Year: 2013

Si-Al-Y co-deposition coatings were prepared on a Ti-Al alloy by pack cementation process at 1050 for 4 h. The effects of pack Y2O 3content (from 0 to 5 wt%) on the microstructure and constituent phases of the co-deposition coatings were studied, the wear resistance of the substrate and the coated specimens were also compared at 600°C in air. The results showed that the pack Y2O3 content imposed strong influences on both coating structures and phase constituents. The coatings prepared with the pack mixtures con-taining 1 and 2 wt% Y2O 3were composed of an TiSi2out layer, an (Ti, X) 5Si4 and (Ti, X)5Si3(X represents Nb and Cr)middle layer, an TiAl2inner layer and an Al-rich interdiffusion zone. However, the constituent phases changed into TiSi 2,(Ti, X)5Si4and (Ti, X)5Si 3in the out layer of the coating prepared with the pack mixture containing 3 wt% Y2O3. Moreover, (Ti, X) 5Si4and (Ti, X)5Si3phases were observed in the outer layers of the coatings prepared with the pack mixtures containing 0 and 5 wt% Y2O3. The coating growth could be catalyzed obviously when the content of Y2O3in the pack mixtures increased from 1 to 2 wt%, but this phenomenon was not observed when further increased the pack Y2O3content to 3 or 5 wt%. Si-Al-Y co-deposition treatment improved the surface hardness and wears resistance of the Ti-Al alloy significantly. The wear resistance of the tested samples could be sorted in the following sequence: 1%Y2O 3-coating > no RE-coating > bare Ti-Al alloy. © 2013 Elsevier B.V. All rights reserved.

Chen Z.,State Key Laboratory of Solidification Processing | Zhang H.,State Key Laboratory of Solidification Processing | Zhao J.,Northwestern Polytechnical University
Advanced Materials Research | Year: 2011

Microstructure of A357 alloy modified by Sr has been investigated by the Electron Back Scattering Diffraction (EBSD) mapping technique using a Field Emission Gun Scanning Electron Microscopy (FEG-SEM). An appropriate sample preparation technique by ion milling was applied to obtain a sufficiently smooth surface for EBSD mapping. Results show that the eutectic morphology in microstructure of A357 alloy modified by Sr was changed to fine fibrous, and the grain size was refined. By comparing the orientation of the aluminum in the eutectic to that of the primary aluminum dendrites, the nucleation and growth mechanism of the eutectic solidification in A357 cast alloy was determined. The eutectic Si phase of the modified sample nucleates on the heterogeneous nuclei located in the region between primary α-Al dendrites and grows up, while the eutectic Si phase of the sample without modification nucleates on the primary α-Al dendrites and grows up.

Zhongwei C.,State Key Laboratory of Solidification Processing | Haifang Z.,State Key Laboratory of Solidification Processing | Ruijie Z.,Northwestern Polytechnical University
China Foundry | Year: 2010

Iron is the most deleterious impurity in the Al-Si-Mg casting alloys and can easily form inter-metallic compounds that can significantly affect the subsequent behavior of material properties. Using differential scanning calorimetry (DSC) and microstructural analysis, how the Be and Fe additions affect the iron-bearing phase in A357 alloys was investigated. The results show that the iron-bearing phase in A357 alloy comprises mainly the plate like β-AI 5FeSi and a small quantity of the script-type p{cyrillic}-AI 8FeMg 3Si 6; and that the plate-like β-AI 5FeSi proportion increases with increasing iron content in the alloy. The iron-bearing phase is mostly transformed from the plate-like β-AI 5FeSi to the script-type p{cyrillic}-AI 8FeMg 3Si 6 with the addition of Be in the alloy. The hardness of alloy samples was also tested. The results show that both the increasing iron content and Be content can increase the hardness of the alloy. This may be contributed to the change of morphology and distribution of the iron-bearing phase in A357 alloy with the addition of iron or Be to the alloy.

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