加工对难熔金属高应变速率行为的影响——评述

对结构难熔金属，如钨、钽、铪及其合金的高应变速率行为进行了评述。钨、钽及其合金有显著的速率敏感性，而铪很少有或没有速率敏感性。单晶及（１００）取向织构钨具有极佳延性，而（１１０）取向织构钨则以典型的脆性方式断裂。钨重合金（ＷＨＡ）具有中等延性，而且在高应变速率下发生应变局部化。钽具有中等到上等的延性但其变形高度依赖于初始加工织构。铪的延性极佳且在很宽的应变速率范围易于局部化。难熔金属的宏观高应变速     

应变速率对Fe-20Mn-3Al-3Si钢的力学性能及其微观组织的影响

分别采用分离式Hopkinson压杆和MTS Landmark电液伺服疲劳试验机对冷轧退火态Fe-20Mn-3Al-3Si相变诱导塑性(transformation induced plasticity, TRIP)钢进行900 s^-1～3 500 s^-1范围内的动态冲击实验和应变速率为3×10^-3 s^-1准静态压缩实验。采用X射线衍射技术(X-ray diffraction, XRD)、电子背散射衍射技术(electron backscatter diffraction, EBSD)和透射电镜(transmission electron microscope, TEM)等对变形试样的微观组织结构进行表征。结果表明,该TRIP钢表现出正应变速率敏感性,且动态冲击变形的屈服强度明显高于准静态变形的屈服强度。无论是在动态冲击样品还是准静态压缩样品中,都可以观察到大量的ε-马氏体和α′-马氏体,且动态冲击样品中ε-马氏体和α′-马氏体的体积分数明显低于准静态变形样品中ε-马氏体和α′-马氏体的体积分数。在...     

Influence of the dislocation density on the performance ofheteroepitaxial indium phosphide solar cells

The authors point out that heteroepitaxial indium phosphide solar cells developed to date have low efficiency due to misfit dislocations. Dislocations act as recombination centers and strongly influence the solar cell performance. Calculations have been made to study the dependence of heteroepitaxial InP solar cell efficiency on dislocation density. The effects of surface recombination velocity and cell emitter thickness are also considered. Calculated results are compared with the available experimental results on representative InP solar cells. It is shown that heteroepitaxial InP cells with over 20% AM0 efficiency could be fabricated if dislocation density can be reduced to <10⁵ cm^-2 and the surface recombination velocity reduced to <10⁵ cm/s     

Influence of microstructure size on the plastic deformation kinetics, fatigue crack growth rate, and low-cycle fatigue of solder joints

The influence of microstructure size on the plastic deformation kinetics, fatigue crack growth rate and low-cycle fatigue of eutectic Sn-Pb solder joints is reviewed. The principal microstructure feature considered is the average eutectic phase size d=(d_Pb+d_Sn)/2. The effect of an increase in reflow cooling rate (which gave a decrease in d) on the flow stress and on fatigue life was irregular at 300K, depending on the stress or strain level and cooling rate. In contrast, a consistent increase in fatigue life with decrease in d occurred for thermomechanical cycling between −30° and 130°C. Constitutive equations for plastic deformation and fatigue crack growth rate are presented which include the microstructure size. It appears that the rate-controlling deformation mechanism is the intersection of forest dislocations in the Sn phase. The mechanism for both static and dynamic phase coarsening appears to be grain boundary diffusion with a t^1/4 time law. Some success has been achieved in predicting the cyclic stress-strain hysteresis loops and fatigue life, including the influence of the as-reflowed microstructure size and its coarsening. Additional definitive studies are however needed before we can accurately predict the fatigue life of solder joints over the wide temperature range and conditions experienced by electronic packages.     

铸态Mg-Zn-Gd合金中准晶相的应变速率敏感性研究

利用纳米压痕仪、原子力显微镜以及电子显微镜等性能与显微结构分析手段对镁基二十面体准晶的应变速率敏感性问题进行了研究.在室温下对铸态Mg79.4-Zn18.5-Gd2.1(at.%)合金中形成的网状准晶相进行纳米压入测试,比较了不同压入应变速率下压痕的压入曲线、表面形貌差异,并据此对准晶相的压入变形行为进行了研究.结果表明,准晶相的室温硬度对应变速率敏感,其变形行为与常规金属及合金相比具有特殊性.结合准晶原子团簇摩擦变形理论,对反映准晶特性的压入实验现象进行了分析和讨论.     

Mechanisms of strain induced roughening and dislocation multiplication in SixGe1-xthin films

We discuss the stress driven roughening transition of Si_xGe_1-x thin films. In the case of annealed films, nucleation effects dominate the nature of the surface ripple which formed by a cooperative nucleation mechanism. Individual islands appear to nucleate via multilayer fluctuations. Faceting can however be suppressed at high supersaturations, resulting in a transition with characteristics of the Asaro-Tiller-Grinfeld instability. The relationship between morphological evolution and dislocation nucleation and multiplication is considered.     

Influence of substrate on the high-frequency permeability of thin iron films

The ferromagnetic resonance (FMR) spectra of thin metallic films obtained by magnetron deposition on polymeric and ceramic substrates are investigated in the strip line at frequencies of 0.13–12 GHz via frequency and external magnetic field sweeping. The influence of mechanical stresses on the FMR spectra of films deposited on an elastic (polyethylene rephthalate) substrate is discussed. The magnetostriction contribution to the anisotropy field of a film, as well as the influence of tensile stresses on the quasi-static permeability and FMR frequency, is estimated. It is demonstrated that the microwave properties of a thin metallic film are also specified by the properties of the substrate with such a film. A distinction in the magnetic properties of films with the same composition, which are deposited on different substrates, is explained in terms of the magnetostriction effect.     

氮掺杂对于n型6H-SiC氧化速率的影响

本文研究了不同氮掺杂浓度对n型6H-SiC干氧氧化速率的影响。实验中,氮掺杂浓度从9.53×〖10〗^16 〖cm〗^(-3) 到 2.68×〖10〗^18 〖cm〗^(-3),氧化温度为1050 0C和1150 0C,氧化时间从2 h 到10 h。由修改的Deal-Grove模型结合阿伦尼乌斯方程,提取出了氧化的线性速率常数和抛物线速率常数以及它们分别对应的活化能。实验数据表明,氧化温度的增加会加速氧化;氮的掺杂浓度对SiC的干氧氧化速率有影响：线性和抛物线速率常数都随着掺杂浓度的增加而增大;抛物线速率常数对应的活化能从0.082 eV增加到0.104 eV,线性和抛物线速率常数对应的活化能都随着掺杂浓度的增加而增大;抛物线速率对应的指前因子从2.6x104 nm2/s 增加到 2.7x105 nm2/s,线性和抛物线速率对应的指前因子都随着掺杂浓度的增加而增大;而且,实验间接说明用提取出的Arrhenius活化能的变化来解释掺杂改变SiC氧化速率是不合理的。     

温度及应力变化对光纤光栅布喇格波长的影响

着重讨论温度对光纤光栅的稳定性和反射谱的影响。分析了温度变化引起光纤光栅布喇格波长漂移的机理,为提高光纤光栅稳定性,对布喇格波长的温度漂移进行应变补偿。     

CCN中基于替换率的缓存空间动态借调机制

针对内容中心网络(CCN, content centric networking)节点存储资源的有效利用和优化配给问题,在同质化缓存分配的基础上,提出了一种基于替换率的缓存空间动态借调机制。该机制从节点存储空间使用状态的动态差异性出发,首先对于缓存资源借调的合理性给予证明,进而,依据节点对于存储资源的需求程度,动态地执行缓存借调,将相对空闲的存储资源分配给需求程度更大的节点支配,换取过载节点缓存性能的提升。该机制减小了内容请求跳数,提高了缓存命中率,以少量额外的代价换取了内容请求开销的显著下降,提升了存储资源整体利用率,仿真结果验证了其有效性。