高取向聚乙烯的形态与晶体形变

采用ＳＥＭ 和ＷＡＸＤ分析了高取向ＨＤＰＥ的形态、晶粒尺寸及结晶度。ＨＤＰＥ经口模拉伸，形态由初始材料的微球状结构转变为纤维结构。随着拉伸比的提高，晶粒沿拉伸方向（ｃ轴）的尺寸增大、横向（ａ，ｂ轴）尺寸减小、有序性提高，结晶度增大。口模温度提高，晶粒沿ａ，ｂ，ｃ轴的尺寸均增大，有序性和结晶度提高。表明口模拉伸过程中既存在应力诱导的结晶过程，又存在温度诱导的二次重结晶过程。

二维X射线衍射光谱原位检测单轴拉伸过程中等规聚丙烯晶体的结构演变

聚合物制品在使用过程中,人们最关心的是它的使用失效条件,失效的重要体现就是材料的屈服。目前为止,人们普遍利用位错理论来解释聚合物材料的屈服现象,该理论关注的是晶体的取向和破坏现象,而忽略了晶体的形变和受力情况。事实上,晶体的取向和破坏只是屈服的结果,晶体承受应力的能力才是屈服的直接原因。因此,从晶体的受力和非均匀形变入手研究了聚合物制品的屈服行为,期望为理解聚合物材料的失效行为提供新思路。这里选取被人们广泛使用的等规聚丙烯(iPP)材料作为研究对象,将iPP熔体在不同温度下等温结晶制备出具有不同片晶厚度iPP样品,利用二维广角X射线衍射光谱原位监测了拉伸过程中iPP样品的晶体破坏和晶体取向过程。首次利用“覆盖法”对二维X射线衍射图进行了处理,原位观察了(110)晶面在拉伸过程中的2θ角的变化,区分出了两个方向上(平行于拉伸方向和垂直于拉伸方向)晶体形变的非均一性。结果表明:对于不同片晶厚度的iPP晶体,在单轴拉伸过程中,晶体在不同方向上的受力和形变均是不同的,即晶体的非均一形变是一种普遍现象;晶体的破坏和取向总是同时发生,都是从屈服点位置处开始,这和片晶厚度无关;而晶体破坏时对应的临界应力和晶体厚度有关,片晶越厚,晶体越稳定,需要的临界应力就越大。以上结果表明,原位X射线衍射光谱技术可以实时观测晶体结构在拉伸过程中的变化情况,从而将晶体结构演化和宏观力学性能直接关联。

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.

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.

Morphological evolution and growth kinetics of Kirkendall voids in binary alloy system during deformation process-Phase field crystal simulation study

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated byphase field crystal model.The simulation results show that Kirkendall voids nucleate preferentially at the interface,and the averagesize of the voids increases with both the time and strain rate.There is an obvious coalescence of the voids at a large strain rate whenthe deformation is applied along the interface under both constant and cyclic strain rate conditions.For the cyclic strain rate appliedalong the interface,the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is largerthan1.0×10-6,while it increases initially and then decreases when the strain rate is smaller than9.0×10?7.The growth exponent ofKirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-waveform constant strain rate.

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.

Simulation of strain induced abnormal grain growth in aluminum alloy by coupling crystal plasticity and phase field methods

A mesoscale modeling methodology is proposed to predict the strain induced abnormal grain growth in the annealing process of deformed aluminum alloys. Firstly, crystal plasticity finite element(CPFE) analysis is performed to calculate dislocation density and stored deformation energy distribution during the plastic deformation. A modified phase field(PF) model is then established by extending the continuum field method to consider both stored energy and local interface curvature as driving forces of grain boundary migration. An interpolation mapping approach is adopted to transfer the stored energy distribution from CPFE to PF efficiently. This modified PF model is implemented to a hypothetical bicrystal firstly for verification and then the coupled CPFE-PF framework is further applied to simulating the 2D synthetic polycrystalline microstructure evolution in annealing process of deformed AA3102 aluminum alloy.Results show that the nuclei with low stored energy embedded within deformed matrix tend to grow up, and abnormal large grains occur when the deformation is close to the critical plastic strain, attributing to the limited number of recrystallized nuclei and inhomogeneity of the stored energy.

Role of yttrium content in twinning behavior of extruded Mg−Y sheets under tension/compression

The influence of Y content on the grain-scale twinning behavior in extruded Mg−xY(x=0.5,1,5,wt.%)sheets under uniaxial tension and compression along the extruded direction was statistically investigated.An automatic twin variant analysis was employed,based on large data sets obtained by electron backscatter diffraction(EBSD),including 2691 grains with 977 twins.The{1012}tension twinning(TTW)dominance and prevailing anomalous twinning behavior(Schmid factor(m)<0)under both tension and compression were found.The anomalous twinning behavior was more pronounced as Y content increased under tensile loading,indicating a promoted stochasticity of twin variant selection for more concentrated Mg−Y alloys.However,the trend for the Y-content dependent anomalous twinning behavior was opposite in compression.The fractions of the anomalous TTWs were found to be well correlated with the maximum Schmid factor(m_(max))values of basal slip and prismatic slip in the corresponding parent grains for compression and tension,respectively,indicating that twinning and dislocation slip might be closely related in the present Mg−Y alloys.

Prediction of grain scale plasticity of NiTi shape memory alloy based on crystal plasticity finite element method

Grain scale plasticity of NiTi shape memory alloy(SMA)during uniaxial compression deformation at 400℃was investigated through two-dimensional crystal plasticity finite element simulation and corresponding analysis based on the obtained orientation data.Stress and strain distributions of the deformed NiTi SMA samples confirm that there exhibits a heterogeneous plastic deformation at grain scale.Statistically stored dislocation(SSD)density and geometrically necessary dislocation(GND)density were further used in order to illuminate the microstructure evolution during uniaxial compression.SSD is responsible for sustaining plastic deformation and it increases along with the increase of plastic strain.GND plays an important role in accommodating compatible deformation between individual grains and thus it is correlated with the misorientation between neighboring grains,namely,a high GND density corresponds to large misorientation between grains and a low GND density corresponds to small misorientation between grains.

The Preparation of Ultra-fine Calcium Carbonate and Its properties Study

This article adopts the double decomposition method, select the appropriate experimental conditions and operation process, respectively add appropriate amount of sodium carboxymethyl cellulose （CMC） as crystal control agent to study the influence of crystalline of ultrafine calcium carbonate. The experimental results show that the different concentrations of CMC as crystal control agent on the morphology and crystal structure of calcium carbonate have obvious effect, which emerge morphology change from square to spherical, crystalline transition from calcite to aragonite. Thus, the results provide experimental data and theoretical basis for the use of different additives, and provide experimental basis and feasible solution for this kind of reaction.

晶格形变能对GaAs－InAs固溶体溶解度的影响

由Ｇａ－Ｉｎ－Ａｓ三元系的热力学分析结果，计算了ＧａＡｓ－ＩｎＡｓ赝二元系相图，讨论了由外延法生成这类化合物时，外延产物发生的晶格弹性形变对ＧａＡｓ和ＩｎＡｓ互溶度的影响。计算结果表明，晶格弹性形变有使溶解度间隙区缩小，甚至消失的效应。

Effects of deformation parameters on formation of pro-eutectoid cementite in hypereutectoid steels

Brittle pro-eutectoid cementite that forms along prior-austenite in hypereutectoid steels is deleterious to mechanical properties. The optimum process parameters which suppress the formation of pro-eutectoid cementite in hypereutectoid steels with carbon content in the range of 0.8%-1.3% in mass fraction, were investigated. Pro-eutectoid cementite formation is effectively hindered by increasing the deformation temperature and decreasing the amount of strain. Transformation at lower temperatures close to the nose of the cooling-transformation diagram also reduces the tendency of the formation of pro-eutectoid cementite. Control of prior-austenite grain size and grain boundary conditions is important. Due to larger number of nucleation sites, finer prior-austenite grain size results in the acceleration of transformation to pro-eutectoid cementite. However, large prior-austenite and straight boundaries lead to less nucleation sites of pro-eutectoid cementite. The cooling rate and carbon content should be reduced as much as possible. The transformation temperature below 660 °C and the strain of 0.5 at deformation temperature of 850 °C are suggested.

晶态热力学第2版

热力学是一门非常成熟的传统经典物理学科，它研究物质在与其周围环境达到热平衡时的物理性质，特别是讨论均匀材料中能量的转换过程。当将其应用于凝聚态特别是晶体时，一些热力学规律必然会结合晶格的各种结构细节而发生变化。在晶体热力学函数中会隐含着格点对称性。但是，当晶体形变时，这些对称性受到扰动，使得晶体不再是稳定的和均匀的。这时晶体会显示出一些介观性质，