Surface-interface analysis of InxGa1-xAs/InP heterostructure in positive and negative mismatch system

The change of In content in the InxGa1-xAs/InP system leads to the variation of the lattice constant and thereby to the negative mismatch between the base InP and the positive mismatch. Here, we studied the surface morphology and dislocation relationship of In_xGa_1-xAs/InP (100) in the positive and negative mismatch system by different characterization techniques. Under the same mismatch, the surface morphology and mass effect of negative mismatch were greater than those of positive mismatch. The reason was that in the negative mismatch system, during the film growth, the disorder degree at the interface increases, leading to an increase in dislocation density, meanwhile, the dislocation in the substrate more easily moved into the film, thus increasing the film and the dislocation density in it. Moreover, the mechanism of the buffer layer was also clarified. The addition of the buffer layer first limited the dislocation movement in the substrate, and secondly reduced the mismatch between the epitaxial layer and the substrate, thereby reducing mismatch dislocation.     

A constitutive model coupling irradiation with two-phase lithiation for lithium-ion battery electrodes

When lithium-ion batteries serve in extreme environments like space, severe irradiation might induce significant decay of the electrochemical performances and mechanical properties. In this paper, an electrochemical-irradiated constitutive model is proposed to explore the evolution of dislocation, defect and stress in electrodes during a two-phase lithiation process. The results from the analytic formulation and finite difference calculations show that, as Li intercalation proceeding, the hoop stress in the surface of a spherical particle converts from compression into tension because the large lithiation strain and plastic yielding at the front pushes out the material behind it. And the plastic flow resistance continuously increases with increasing irradiation dose result from the impediment of a defect to dislocation glide. There is a clear peak in the distribution of stress at yielding locations due to the competition between dislocations multiplication and defects annihilation. The model is meaningful for thoroughly understanding the micro-mechanism of lithiation deformation and provides a guideline for predicting their mechanical behaviours of lithium-ion batteries in unconventional environment.     

蓝宝石晶体的生长方向研究

本实验采用提拉法,在中频感应加热单晶炉内,进行了不同生长方向蓝宝石晶体的生长工作,分别取[11-20]和[0001]生长的晶体c面(0001)的晶片.通过应力仪、显微观测和X射线衍射等方式对晶片的位错密度等微观缺陷以及晶体结构进行了检测.实验表明:不同的生长方向生长得到的蓝宝石晶体的质量存在一定的差别,一般情况下,[11-20]方向生长的蓝宝石晶体质量优于[0001]方向生长的晶体.     

等径角挤压Al-4.25;Cu多晶材料的裂纹产生与扩展

本文使用内角为90°、外角为30°的模具对2A12铝合金进行了等径角挤压实验,并采用HitachiS-800透射电镜(TEM)研究了材料内部裂纹的产生和扩展.结果表明:挤压两次后的试样内部没有产生微裂纹,挤压三次后的试样中观察到了微裂纹的出现,而位错塞积是裂纹产生和扩展的主要因素.所以,2A12铝合金等径角挤压过程中,应该在两次挤压后进行退火处理,保证后续挤压的顺利进行.     

中子辐照铝的微观结构变化

研究了中子辐照后铝的微观结构和力学性能的变化。发现中子辐照使铝的硬度有了一定的提高,同时在铝的内部产生了大量细小的位错环。The change of microstructure and mechanical property in neutron irradiated aluminum was studied. It is found that neutron irradiation increased the hardness of the aluminum and caused the formation of many small dislocation loops in the aluminum.     

FeCrNi合金静动态物理本构模型研究

以金属材料塑性变形的位错动力学为基础,将FeCrNi合金的流动应力分解为非热应力和热激活应力两部分.通过对该合金屈服应力随温度变化特性、屈服应力的应变速率特性、孪晶组织的温度特性及位错组态的应变速率特性进行分析,认为非热应力不只是应变的函数,还与温度和应变速率相关,因此对Johnson-Cook模型方程形式进行修正以描述非热应力. 同时认为影响热激活应力的微结构参数主要为位错阻碍间距\Deltal, 定义并推导出表征\Delta l演化的g函数的表达式,将其引入Kocks的热激活方程,从而建立FeCrNi合金的物理型本构模型.该模型初步实现了对FeCrNi合金从室温到高温、从准静态到动态塑性变形行为的描述.      

二维声子晶体同质位错结缺陷态特性

利用平面波展开法结合超原胞的方法研究了二维声子晶体同质位错结的缺陷态.分别研究了横向位错和纵向位错两种情况，研究结果表明：横向位错效应与线缺陷相似，它可以使处于禁带频率范围内的声波沿位错通道进行传播，形成声波导；纵向位错效应则类似于点缺陷，位错线两边三个最接近的散射子形成腔，因而能够产生局域模.另外，横向位错距离和纵向位错距离的大小将影响缺陷带的位置和数量，因此，可以通过调节横向位错距离或纵向位错距离来人为的控制同质位错结中的缺陷带. 关键词： 声子晶体 同质位错结 缺陷态     

高速形变过程中运动螺位错的声子产生与能量局域

 从量子力学观点出发，研究了运动螺位错产生的声子场。结果证明了位错运动产生点阵微扰，使得在滑移面附近产生声子，声子的能量局域在这些平面里，使这些区域的温度升高，而成为热点。最后，考查了声子能谱，发现它是非波尔兹曼分布。     

氢对22－13－5不锈钢室温下力学行为的影响

２２－１３－５钢是一种高强度极稳定的奥氏体不锈钢，将它置于１０ＭＰａ（１００个大气压）纯氢气中在３００℃充氢１４天，含氢量为６５±１ｐｐｍ。室温下力学性能测试表明：充氢后钢的强度提高，塑性指标不变；但室温下瞬态蠕变和短期应力弛豫行为，在可比条件下，变得更为强烈。用Ａｌｄｅｎ的可动位错密度理论，对实验结果作了定性分析，并对瞬态蠕变结果进行了定量的计算。结果证明，氢原子阻碍位错运动，使材料强度增加，同时也使材料的粘滞性增大。