基于晶体变形的压电石英测试理论研究与应用

对基于晶体变形的压电效应的研究现状和应用进行阐述和讨论。介绍了压电弯曲、扭转效应理论的研究进展,给出了在弯矩、扭矩作用下的束缚电荷和极化电场的分布规律;在理论研究的基础上,对所研发的新型微雕笔式执行器、扭矩传感器、钻削测力仪进行了介绍。基于晶体变形的压电效应的探索与开发对压电学体系的发展与完善以及工程应用都有重要的实用价值。

锐钛矿TiO2溶胶成膜过程中的晶体变形研究

采用溶胶-凝胶工艺,在60℃水浴下制备出含有正方体型锐钛矿晶体的氧化钛溶胶,并对溶胶的成膜过程进行了研究。研究发现,锐钛矿溶胶成膜过程中,正方体型的锐钛矿晶体会解体成片状等新的晶体形状。不同的成膜方式、不同的基材种类、稀释与否等因素对成膜后的晶体形状有较大影响,可通过这些因素对晶体变形过程进行一定程度的调整和控制。

抽运光分布对圆截面激光晶体热变形的影响

为了简化激光晶体中热变形量的求解过程,分析抽运光分布对激光晶体热变形的影响,采用圆截面激光晶体热变形量的简便计算方法,并取抽运光束为超高斯光束,通过理论推导和数值计算,研究了抽运光强度分布对圆截面激光晶体热变形的影响。结果表明,晶体端面热变形量与半径为3次多项式关系,当抽运光阶次大于2时,随着阶次的增大,晶体端面的热变形量逐步减小。这一结果对全固态激光器的设计有一定帮助。

金属切削过程中晶体塑性变形的有限元分析

基于金属材料塑性变形理论,利用有限元分析软件,建立了金属切削过程中的晶体变形模型,对二维正交金属切削过程中的晶体塑性变形进行了数值模拟。将仿真结果与实验数据进行了对比,验证了相关理论和模型的有效性。

变形晶体X射线分光性能的数值模拟

通过有限元软件计算同步辐射晶体单色器分光晶体的变形,确定晶体倒格矢的改变量,按变形晶体光学理论预测变形晶体的Darwin宽度,建立一套预测直接水冷却晶体单色器分光性能的方法。算得直接水冷晶体子午方向Darwin宽度展宽为4.12μrad,与采用晶体表面变形倾斜误差计算值(3.89μrad)相比更接近实验值(5.0μrad)。

薄膜多层滚压的表面粗糙度晶体学分析

提出了晶体学模型来研究多层薄膜滚压的表面粗糙度。研究了单层滚压模型,提出滚压的三维模型和二维模型(平面应变),讨论了晶粒大小和应力状态的影响。把单个单层滚压和多层滚压模型、三维模型和平面应变模型进行了比较,发现对于所涉及的二维和三维模型来说,单层滚压和多层滚压模型并无明显的差别。因此在这些情况下,可以用单个单层滚压模型来代替多层滚压模型从而节省CPU时间。

β-锡单晶的变形行为

从β-锡单晶晶体结构各向异性着手,研究总结了其变形行为:①拉伸性能及温度的影响;②蠕变性能与蠕变机制;③在一定载荷下,β-锡单晶的位错运动和滑移系开动情况。与和体心、面心立方金属相比,具有体心四方结构的β-锡单晶基本性能的研究还不完善;对于β-锡单晶的研究不仅有助于对β-锡多晶力学行为的机理性认识、细观尺度的力学模拟,而且对工业界新系列无铅焊料的开发有一定指导意义。

多晶纯铝轧制变形晶粒局部取向的演变

本文采用SEM-EBSD检测技术研究了高纯铝多晶体内(011)[100]和(210)[001]两个相邻柱状晶粒在轧制变形前、后的微取向分布.结果表明,经65%压下量后,虽然两晶粒靠近晶界部分的转动要慢于晶内的转动,但转动趋势是一致的, 两个晶粒都显示{110}∥ND(α取向线)转动.运用Taylor晶体塑性变形理论,考虑靠近与远离晶界部分具有不同程度的附加强制剪切变形(de13≠0),模拟计算的两晶粒轧制变形时局部取向演变结果与实测微取向分布图具有较好的一致性,且考虑了附加强制剪切变形的Taylor模型预测结果优于经典FC和RC-Taylor模型.

变形体心四方点阵特殊点集的计算

给出了变形的体心四方点阵的若干组特殊点 ,描述了推导这些特殊点的方法 .这些特殊点可用于计算晶体中波矢的周期性函数过布里渊区的积分 .

Effect of wire diameter compression ratio on drawing deformation of micro copper wire

A crystal plasticity finite element model was developed for the drawing deformation of pure copper micro wire,based on rate-dependent crystal plasticity theory.The impact of wire diameter compression ratio on the micro-mechanical deformation behavior during the wire drawing process was investigated.Results indicate that the internal deformation and slip of the drawn wire are unevenly distributed,forming distinct slip and non-slip zones.Additionally,horizontal strain concentration bands develop within the drawn wire.As the wire diameter compression ratio increases,the strength of the slip systems and the extent of slip zones inside the deformation zone also increase.However,the fluctuating stress state,induced by contact pressure and frictional stress,results in a rough and uneven wire surface and diminishes the stability of the drawing process.

A new rhombohedral phase and its 48 variants inβtitanium alloy

A new rhombohedral phase(termed R′)in a solution-aging-treated titanium alloy(Ti-4.5Al-6.5Mo-2Cr-2Nb-1V-1Sn-1Zr,wt.%)was identified.Its accurate Bravais lattice parameters were determined by a novel unit cell reconstruction method based on conventional selected-area electron diffraction(SAED)technique.The orientation relationship between R'phase and BCC phase was revealed.The results show that the R′phase is found to have 48crystallographically equivalent variants,resulting in rather complicated SAED patterns with high-order reflections.A series of in-situ SAED patterns were taken along both low-and high-index zone axes,and all weak and strong reflections arising from the 48 variants were properly explained and directly assigned with self-consistent Miller indices,confirming the presence of the rhombohedral phase.Additionally,some criteria were also proposed for evaluating the indexed results,which together with the Bravais lattice reconstruction method shed light on the microstructure characterization of even unknown phases in other alloys.

Crystal anisotropy of AZ31 magnesium alloy under uniaxial tension and compression

To investigate the deformation twinning and the plastic anisotropy of the hexagonal-close-packed（HCP） single crystal, the crystal plastic constitutive model including slip and twinning deformation was established with finite element method based on crystal plasticity theory. The model was verified by test data. Newton-Raphson iteration method was developed with the stress components directly as the basic variables of iteration. The plastic deformation behavior of single crystal AZ31 alloy was analyzed numerically under monotonic tension and compression, respectively, in four different strain paths（i.e. along 〈2110〉, 〈 0110〉, 〈0001〉 and 〈0111〉） with this model. The stress-strain curves were obtained in the above paths. The numerical calculation results show that this crystal model is feasible to predict the activity of slip/twinning system and to describe the number of active twin variants, the types of dominant twin variants and twin intersection. Due to the polar nature of mechanical twinning in inelastic deformation of the material, the plastic behavior of the single crystal material is demonstrated to be notably anisotropic and high asymmetry.

Polycrystalline model for FE-simulation of micro forming processes

A new polycrystal model was presented from the viewpoint of polycrystal structure of the billets considering free surface effects.In the model,the billet was divided into three portions,such as free surface portion,transition portion and internal portion.The grains in free surface portion were considered the single grains,and the anisotropy of the grains was taken into account by introducing grain orientation to explain the inhomogeneous deformation.In the transition portion,the effects of the neighbouring grains were adopted in the model.The grains in the internal portion were considered the polycrystalline material.With the developed model,the upsetting deformation process was simulated by the MSC Superform software.The scatter of the flow stress and inhomogeneous deformation was observed by analysis of the model.The comparisons show that the computational results are good agreed with the experimental results.This means that the presented model is effective.

Grain statistics effect on deformation behavior in asymmetric rolling of pure copper foil by crystal plasticity finite element model

The grain statistics effect was investigated through asymmetric rolling of pure copper foil by a realistic polycrystalline aggregates model and crystal plasticity element finite model.A polycrystalline aggregate model was generated and a crystal plasticity-based finite element model was developed for each grain and the specimen as a whole.The crystal plasticity model itself is rate dependent and accounts for local dissipative hardening effects and the original orientation of each grain was generated based on the orientation distribution function（ODF）.The deformation behaviors,including inhomogeneous material flow,decrease of contact press and roll force with the increase of grain size for the constant size of specimens,were studied.It is revealed that when the specimens are composed of only a few grains across thickness,the grains with different sizes,shapes and orientations are unevenly distributed in the specimen and each grain plays a significant role in micro-scale plastic deformation and leads to inhomogeneous deformation and the scatter of experimental and simulation results.The slip system activity was examined and the predicted results are consistent with the surface layer model.The slip band is strictly influenced by the misorientation of neighbor grain with consideration of slip system activity.Furthermore,it is found that the decrease of roll force and the most active of slip system in surface grains are caused by the increase of free surface grain effect when the grain size is increased.The results of the physical experiment and simulation provide a basic understanding of micro-scaled plastic deformation behavior in asymmetric foil rolling.

Casting effect on compressive brittleness of bulk metallic glass

An interesting phenomenon of cooling-rate induced brittleness in Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass （BMG） was reported. It was found that the as-cast BMG specimens exhibited a brittle-ductile transition when the larger specimens were machined into smaller specimens through removing the cast-softening surface layer by layer. After compression tests, the as-machined small specimens, owing to the absence of the cast-softening surface, displayed highly dense and intersecting shear bands, and extensive plastic deformation. This is in contrast to the catastrophic failure and low deformability in the as-cast large specimens. More free volume was detected in the smaller as-fractured specimens, by differential scanning calorimetry, which may be attributed to the occurrence of strain softening and increased plasticity. Compared with the relatively smooth fracture surface in the smaller specimens, the larger specimens showed more diverse features on the fracture surface due to their graded structures.

Simulation of mechanical behavior of AZ31 magnesium alloy during twin-dominated large plastic deformation

Experiments and visco-plastic self-consistent (VPSC) simulations were used to quantify the amount of twinning and the relationship to stress?strain behavior in a textured Mg?3Al?1Zn plate. Two different compression directions were utilized to favor{1012} extension or{1011} compression twinning.{1012} twins nucleate at the beginning of plastic deformation and grow to consume the parent grains completely. During compression along the normal direction,{1011} twinning and{1011}?{1012} double twinning start at strain of 0.05, and the number of twins increases until rupture, above strain of 0.15.{1011} and{1011}?{1012} twinning also occur during compression along the transverse direction, start at strain of 0.06 and then multiply in grains totally reoriented by{1012} twins. Using suitable parameters, the VPSC model can accurately predict the occurrence of extension, compression and double-twinning as well as the flow stresses and deformed textures. According to VPSC simulations, twinning and slip have the same latent hardening parameters.

Effect of rolling reduction on deformation mechanism and twinning behavior of WE43 magnesium alloy

The effect of rolling reduction of the last pass on the dislocation slip and twinning behavior during direct hot rolling of a cast WE43 magnesium alloy at 480℃ was investigated.The results showed that prismatic<á>slip was always the main deformation mode during rolling at 480℃.In addition,the activated twinning type was associated with rolling reduction.The{1012}extension twinning was activated at a slight rolling reduction(2%),while{1011}compression twinning and{1011}−{1012}double twinning were activated at larger rolling reduction(12%and 20%).Schmid factor calculation showed that the activation of{1012}extension twin variants followed the Schmid Law,whereas the activation of{1011}compression twin variants did not follow it.Even if the rolling reduction reached 20%,almost no dynamic recrystallization(DRX)grains were found,presumably because the amount of deformation required for DRX to occur was not reached.

Slip deformation mechanism of α-Zr at 700 °C

Mechanical properties, corrosion behavior and hydrogen absorption of zirconium alloys are related to the texture resulting from prior forming processes. In order to investigate the high temperature deformation behavior of α-Zr, compression tests at 700 ℃, microstructure measurements via EBSD, and visco-plastic self-consistent modeling were performed. Twinning activity was negligible at strain rates ε≤1s^-1. The strain rate sensitivity m=0.17 seemed to be the same for all slip modes. Material parameters were fitted to reproduce the mechanical anisotropy and deformed texture, and were validated by comparing the simulated and measured strain anisotropy. The best-fit simulation showed that at high temperatures prismatic slip was the easiest deformation mode and pyramidal <c+a> was the hardest, but basal slip and pyramidal slip operated easily and in large amount.

Thermal stability evaluation of nanostructured Al6061 alloy produced by cryorolling

Grain growth of nanostructured Al6061produced by cryorolling and aging process was investigated during isothermalheat treatment in100?500°C temperature range.Transmission electron microscopy(TEM)observations demonstrate that aftercryorolling and aging at130°C for30h,the microstructure contains61nm grains with dispersed50?150nm precipitates and0.248%lattice strain.In addition,an increase in tensile strength up to362MPa because of formation of fine strengtheningprecipitation and nano-sized grains was observed.Thermal stability investigation within100?500°C temperature range showedrelease of lattice strain,dissolution of precipitates and grain growth.According to the X-ray diffraction(XRD)analysis,Mg2Siprecipitates disappeared after annealing at temperatures higher than300°C.According to the results,due to the limited grain growthup to200°C,there would be little decrease in mechanical properties,but within300?500°C range,the grain growth,dissolution ofstrengthening precipitates and decrease in mechanical properties are remarkable.The activation energies for grain growth werecalculated to be203.3kJ/mol for annealing at100?200°C and166.34kJ/mol for annealing at300?500°C.The effect ofprecipitation dissolution on Al lattice parameter,displacement of Al6061(111)XRD peak and Portevin?LeChatelier(PLC)effect onstress?strain curves is also discussed.

Development of 3D crystallographic orientation measurement for grain deformation analysis in aluminum alloy

Development of inhomogeneous deformation is an interest matter in material engineering. Synchrotron radiation tomography provides 3D distribution map of local strain in polycrystalline aluminum alloy by tracking microstructural features. To perform further deep analysis on development of inhomogeneous deformation, crystallographic grain orientation is necessary. Three-dimensional X-ray diffraction technique was developed. A new crystallographic orientation measurement method was described in 3D space, utilizing grain boundary tracking （GBT） information.