祝庆勋
,
徐勇
,
张士宏
,
张贵杰
,
宋鸿武
材料科学与工艺
通过XRD衍射及不同方向单向拉伸试验验证,经过多道次拉拔生产出的304奥氏体不锈钢管材存在有明显的各向异性现象.采用Mises各向同性、Hill1948和Barlat1991各向异性屈服准则对不锈钢弯管过程进行有限元模拟,分析弯曲后管材内外侧壁厚分布、弯曲角度及管坯截面椭圆度的变化规律,通过模拟与实验结果对比发现,当实验数据较少时,采用Hill1948各向异性屈服准则,能够很好预测304奥氏体不锈钢管材弯曲成形过程,而Barlat1991各向异性屈服准则中的一些参数经过近似后,对成形行为的预测精度明显降低.
关键词:
奥氏体不锈钢
,
管材弯曲
,
屈服准则
,
各向异性
Jing HAN
,
Hongtao CHEN
,
Mingyu LI
金属学报(英文版)
A small Pb-free solder joint exhibits an extremely strong anisotropy due to the body-centered tetragonal (BCT) lattice structure of β-Sn. Grain orientations can significantly influence the failure mode of Pb-free solder joints under thermomechanical fatigue (TMF) due to the coefficient of thermal expansion (CTE) mismatch of β-Sn grains. The research work in this paper focused on the microstructure and damage evolution of Sn3.0Ag0.5Cu BGA packages as well as individual Sn3.5Ag solder joints without constraints introduced by the package structure under TMF tests. The microstructure and damage evolution in cross-sections of solder joints under thermomechanical shock tests were characterized using optical microscopy with cross-polarized light and scanning electron microscopy (SEM), and orientations of Sn grains were determined by orientation imaging microscopy (OIM). During TMF, obvious recrystallization regions were observed with different thermomechanical responses depending on Sn grain orientations. It indicates that substantial stresses can build up at grain boundaries, leading to significant grain boundary sliding. The results show that recrystallized grains prefer to nucleate along pre-existing high-angle grain boundaries and fatigue cracks tend to propagate intergranularly in recrystallized regions, leading to an accelerated damage after recrystallization.
关键词:
Pb-free solder
,
null
,
null
,
null
,
null
张宝芹
,
于名讯
,
张伟
,
黄成亮
,
李永波
宇航材料工艺
介绍了各向异性吸波材料高频磁性能,对近年来研究较多的薄膜、纤维、片状磁性吸波材料及其研究进展进行了总结,并分析了在工程化应用中存在的问题,最后,对其发展趋势和方向进行了展望.
关键词:
各向异性
,
电磁性能
,
吸波材料
Yanxue CHEN
,
Shouguo WANG
,
Liangmo MEI
,
Kungwon Rhie
,
Sangjin Byeun
材料科学技术（英文）
A series of CoFe (4 nm)/ Cu(X nm) Al (Y nm)/ CoFe(6 nm) samples have been prepared at room temperature. An exponential decay of the GMR (Giant Magnetoresistance) with Y was observed for fixed X=2nm. The characteristic decay parameter of Al is obtained to be about 0.26nm, which is rather close to 1 monolayer for Al. A coexistant state of GMR and AMR (anisotropic magnetoresistance) was observed when Y=2 nm. As the Cu spacer is replaced by Al layer, only AMR effect dominates. The experimental data further underline the important role played by the nonmagnetic spacers.
关键词:
CoFe
,
null
,
null
