点状籽晶法生长KDP晶体的(100)面位错分布

通过光学显微镜对点状籽晶法生长的KDP晶体（100）面位错蚀坑的观察和分析，发现柱区的位错线走向不同于片状籽晶法生长的晶体。晶体的位错主要来自籽晶的位错。通过籽晶成锥-微溶-生长的过程可以减少籽晶锥区位错向晶体中的延伸，在晶体内部，当两条夹角很小的位错线相交时会合并成一条位错线。     

统一框架下的柱面和锥面教学

在直纹曲面的框架下统一了柱面、锥面方程的求法,统一了柱面、锥面判别定理的证明方法,统一了二次柱面、锥面的判别形式,从而把柱面和锥面放在统一的框架下进行教学。     

金属镁非共面位错相互作用强度的位错动力学模拟

采用位错动力学方法模拟金属镁在塑性变形过程中的基面、柱面及一阶锥面位错非共面相互作用,利用扩展Taylor硬化方程计算潜硬化系数,探讨位错相互作用强度及其影响因素。研究结果表明,位错相互作用强度随滑移机制以及主滑移系与林滑移系的交换而变化,表现出显著的各向异性和非对称性。共线基面/柱面相互作用最强,非共线柱面/基面相互作用最弱,相应的潜硬化系数分别为0.43和0.11。共线相互作用下主位错长度由于位错湮灭明显比非共线相互作用下的小,非共线作用下则形成大量位错交结或交叉态位错。虽然共线相互作用总体上略强于非共线作用,但特定主位错-林位错相互作用对的共线与非共线作用相对强弱随非共线作用下形成的交结性质而变化。当非共线相互作用形成固着交结或交叉态时,非共线作用强度高于共线作用强度,而当形成的交结为可动交结时则弱于共线作用强度。充分考虑位错可动性及摩擦阻力的差异是有效预测位错相互作用强度及其各向异性的重要前提。     

用二维编程实现线切割机床三维型面加工

对线切割机床能加工的零件进行了分类，分析了各类零件构成的特点，给出了柱面，锥面，锥台和上下异形面不同的加工策略，总结了直纹面工件加工程序编制的2个步骤，提出了一种不需将工件加工轨迹线性化，只用简单的二维编程实现复杂三维型面加工的直接插补法；使加工精度提高，编程工作简单。     

反演变换图解法

在生产实践中,热风管路及其它输送气体或液体的管路,在它们的拐弯处或由主干线通往分配管路的连结部分,我们经常遇见环面管和锥、柱面管相交的结构,这种结构是由钣金工下料焊接而成。为了得到准确的环面、锥面、柱面展开形状,应当求出这些曲面间的相贯线。本文将通过分析如图1所示在分配管路的连结处园环面和斜椭园锥面交线的求法,以介绍一种新的反演变换作图法。     

AZ31镁合金轧制板材各向异性行为的晶体塑性研究

室温下,镁合金的主要变形机制是滑移和孪生相互竞争。为了从介观尺度准确描述这种变形机制,晶体塑性本构关系需要考虑滑移和孪生的耦合作用。基于滑移-孪生耦合的晶体塑性本构关系,本文采用代表体积单元法建立了多晶模型,并对AZ31镁合金沿RD和TD方向进行拉伸模拟分析。结果表明:沿RD方向的变形机制为基面滑移、柱面滑移、锥面滑移,沿TD方向为柱面滑移和锥面滑移。沿不同方向基面滑移对变形的贡献不同,造成AZ31镁合金轧制薄板沿RD方向的屈服强度小于TD方向,表现出强烈的力学性能各向异性。     

密排六方金属锆及锆—4的疲劳变形机理及寿命预测

研究了锆及锆－４室温、４００℃和６００℃下疲劳机理,结果表明：室温下为｛＾－１０１０｝柱面滑移和｛＾１０１２｝,｛＾－１１２１｝,｛＾１１２２｝孪生变形;４００℃和６００℃下分别出现了锥面和基面滑移,首次建立了密排六方金属锆及锆－４的闰错组态与试验温度和循环应变幅之间的演化规律图,微观分析表明：有序分布的位错花样是疲劳位错稳态分布,是耗散结构自组织的表现。疲劳是不可逆能量耗散过程,循环塑性耗散应变     

三维地震作用下板锥柱面网壳结构的力学性能

以两纵边支承的板锥柱面网壳结构为研究对象,基于几何非线性有限元法,运用时程分析法计算板锥柱面网壳结构在三维地震作用下的地震响应,研究了板锥柱面网壳结构在动力作用下的位移和内力分布规律,同时分析了此结构在地震作用下的支座反力特点,并且得出了一些有价值的结论,为板锥柱面网壳结构的应用和设计提供理论指导。     

Mg2Ca相对镁合金形变和失效机理的影响

采用分子动力学(MD)模拟方法,在分析Mg-Ca合金中Mg基质和Mg_2Ca稳定相机械性能基础上,对比揭示了Mg_2Ca对多晶镁合金形变和失效机理的影响.特定方向的单轴载荷下,单晶Mg伴随着活跃的锥面c+a和柱面a位错,有显著塑性形变.单晶Mg_2Ca无明显塑性形变,高刚度且脆性强烈.对比多晶Mg/Mg_2Ca复合材料的微观结构,在塑性形变过程中,Mg_2Ca晶粒因其高刚度能减少合金位错并阻断相邻Mg基质中活跃的基面a和锥面c+a位错的传播,从而锚定周围原子.而较弱的Mg/Mg_2Ca界面容易产生裂缝,引起晶间断裂,最终使多晶镁合金失效.     

板锥柱面网壳结构地震响应的动力时程分析

基于有限元法,以两纵边支承的板锥柱面网壳结构为研究对象,运用时程分析法分别计算板锥柱面网壳结构在水平地震和竖向地震作用下的地震响应,分析研究了板锥柱面网壳结构在动力作用下的位移和内力分布规律,结果表明,其竖向地震反应要大于其在水平向地震作用下的地震反应。同时分析了此结构在地震作用下的支座反力特点。在此基础之上,得出了一些有价值的结论,为板锥柱面网壳结构的应用和设计提供理论指导。     

Optical homogeneity of ADP crystals from rapid growth

ADP (NH₄H₂PO₄) crystals were grown through the traditional method and rapid growth technology. The optical homogeneity of rapid grown ADP crystals was analyzed by laser interferometry and X-ray topography. Laser interferometry revealed sector boundaries at which optical homogeneity decreased dramatically. The main defects that seriously reduced the optical homogeneity of the rapid grown ADP crystal were sector boundaries, growth bands and inclusions. The concentration of Fe and Cr impurities was tested by a plasma emission spectrometer. It was found that the preferential incorporation of metallic impurities into the prismatic faces resulted in high density of growth bands and inclusions, thus reducing optical homogeneity of the prismatic sector.     

Ultrahigh-quality silicon carbide single crystals

Silicon carbide (SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for next-generation electronic devices. Careful consideration of the thermal conditions in which SiC [0001] is grown has resulted in improvements in crystal diameter and quality: the quantity of macroscopic defects such as hollow core dislocations (micropipes), inclusions, small-angle boundaries and long-range lattice warp has been reduced. But some macroscopic defects (about 1-10 cm(-2)) and a large density of elementary dislocations (approximately 10(4) cm(-2)), such as edge, basal plane and screw dislocations, remain within the crystal, and have so far prevented the realization of high-efficiency, reliable electronic devices in SiC (refs 12-16). Here we report a method, inspired by the dislocation structure of SiC grown perpendicular to the c-axis (a-face growth), to reduce the number of dislocations in SiC single crystals by two to three orders of magnitude, rendering them virtually dislocation-free. These substrates will promote the development of high-power SiC devices and reduce energy losses of the resulting electrical systems.     

高温预熔化晶界位错的结构组态转变的探究

晶体材料的性能受其内部晶界特性的影响。在高温下,晶体材料在晶界上易发生预熔化。本研究采用晶体相场(PFC)方法模拟高温二维六角晶体的晶界预熔化区在双轴加载作用下的结构演化情况。结果显示,晶界位错会发生配对,形成具有对称结构的位错团,一对位错上下排列,另一对位错左右排列,构成4个位错的组合。随着施加的应变增大,晶界位错预熔化区域横向扩展,其形状最初为棒状,逐渐转化为六边形,再转变成“V”形,最后又收缩为六边形。晶界预熔化区的形状变化伴随着内部位错结构的转变,从而发生位错芯扩展,原来上下配对的位错转变为并行排列的位错,左右排列的位错发生扩展滑移,并在左右两端萌生出一对新的位错。当预熔化区域扩展达到横向最宽时,该区域发射一对位错,随后预熔化区域开始收缩,最后又恢复到初始的形状。上述结果表明,位错结构的组态转变对晶体材料的高温变形机制能产生强烈的影响。     

The impact of nanoporous SiN x interlayer growth position on high-quality GaN epitaxial films

The impact of nanoporous SiN x interlayer growth position on high-quality GaN epitaxial film was elucidated from the behavior of dislocations. The best quality GaN film was achieved when a nanoporous SiN x interlayer was grown on a rough layer, with the high-resolution X-ray diffraction rocking curve full width at half maximum for ( 1102 ) reflection decreasing to 223 arcs, and the total dislocation density reduced to less than 1.0×10 8 cm 2 . GaN films were grown on sapphire substrates by metal organic chemical vapor deposition. The quality of these films was investigated with high-resolution X-ray diffraction, atomic force microscopy, and cross-sectional transmission electron microscopy. A preference for the formation of half-loops to reduce threading dislocations was observed when an SiN x interlayer was grown on a rough layer. A growth mechanism is proposed to explain this preference.     

水热法KTP晶体生长及形貌特征

晶体宏观形态和表面微形貌特征是晶体生长机制的具体反映,通过对晶体形貌特征的研究,探寻晶体生长的规律,为进一步改善晶体的质量打下基础。通过对水热法KTP晶体(磷酸钛氧钾,KT iOPO4,KTP)宏观形态和表面微形貌的研究,首次发现了KTP晶体中高指数晶面和{100}单形晶面上的螺旋生长纹,探讨发现高指数晶面和{100}单形晶面上螺旋纹的形成原因主要是溶液的过饱和度偏低以及籽晶的悬挂方式,为生长高质量的KTP晶体,提出了增大原材料溶解区与晶体生长区的温度差、改变籽晶的切向和悬挂方向等建议。     

Dislocation multi-junctions and strain hardening

At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects called dislocations. First proposed theoretically in 1934 (refs 1-3) to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening, a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions that tie the dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed 'multi-junctions'. We first predict the existence of multi-junctions using dislocation dynamics and atomistic simulations and then confirm their existence by transmission electron microscopy experiments in single-crystal molybdenum. In large-scale dislocation dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication, thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in body-centred cubic crystals.     

Effect of pyrophosphate on the light scatter in KDP crystal

Pyrophosphate doped potassium dihydrogen phosphate (KDP) crystal was grown from aqueous solution by the temperature lowering method. Light scatter in KDP crystal was detected with the ultramicroscopic method. The light scatter in KDP crystal was aggravated when pyrophosphate was doped into the growth solution, which was distributed ununiformly in prism and pyramidal sectors of KDP crystal. Different effects of pyrophosphate on prism and pyramidal sectors of KDP crystal can explain this case. The transmission in this crystal was measured, showing that pyrophosphate affects the transmission evidently.     

Ⅲ-Ⅴ族半导体微重力生长研究进展

空间微重力环境为理解被地面重力场掩盖的晶体生长现象与规律、探索新的晶体制备工艺提供了独一无二的平台.我国学者在过去的30多年里进行了Ⅲ-Ⅴ族半导体晶体的空间生长研究,主要进展有:在微重力条件下得到了器件级的半绝缘GaAs,基于其制备的低噪声场效应晶体管和模拟开关集成电路性能明显超过地基器件;通过抑制熔体静压力的作用,实现了GaSb及InSb两种材料的非接触Bridgman生长,并大幅降低了材料的位错密度;深入研究了浮力对流、Marangoni对流及旋转磁场驱动的强制对流对组分微观偏析的影响规律;将垂直梯度凝固法应用于半导体合金生长,获得了组分均匀分布的GaInSb材料.本综述回顾了以上方面的研究进展,并对半导体空间材料科学的未来挑战进行了展望.