[011]多滑移取向铜单晶体的循环形变行为──Ⅰ.循环应力-应变响应

本文在一个较宽的塑性应变幅范围（γpl=1.1×10-4-7．2×10-3）内研究了[011]多滑移取向铜单晶体的循环形变行为.结果表明,[011]晶体的循环形变行为明显不同于[011]和[111]多滑移取向的铜单晶体.[011]晶体具有较低的初始硬化速率,即使在较高的塑性应变幅下,初始硬化速率也无明显变化.［011］晶体的循环应力-应变曲线（CSSC）在所研究的塑性应变幅范围内呈现平台区.CSSC上是否存在平台区,主要由晶体本身的滑移特点和相应的位错反应所决定.疲劳滞后回线形状参数VH在某种程度上可用于确定[011]多滑移铜单晶体的PSB萌生应力     

循环变形铜单晶体的滞后回线形状变化与驻留滑移带的萌生

本文系统测量并总结了不同类型双滑移取向铜单体循环变形中滞后回线性形状参数ＶＨ随循环周次Ｎ的变化关系,结果表明,与单滑移晶体不同晶体取向双滑移晶体的滞后回线形状变化趋势有显著的影响,ＶＨ与驻留滑移带（ＰＳＢ）的形成有无明业对应关系与该取向单晶体的循环应力－应变（ＣＳＳ）曲线有无平台区或准平台区出现密切相关,ＶＨ随Ｎ的变化关系反映了晶体在循环变形中的微观组织结构的不同变化,通过ＶＨ确定了不同类型双滑移     

不锈钢在循环形变中的Bauschinger效应及其位错结构

两种处理的Cr-Mn-N不锈钢在室温下进行了对称的拉压循环形变试验,所使用的应变范围从0.008到0.024,测量了不同循环周次后的拉半周和压半周的屈服应力σ_(0.2f)和σ_(0.2r),峰值应力σ,并记录了应力-应变滞后回线。从σ_(0.2f)和σ_(0.2r)计算出不同循环周次后的Bauschinger效应强度差别因子(BSDF),从滞后回线计算出各种周次的能量损耗△E。结果指出,两种制度处理的试样在不同的循环应变幅下,三个参量σ,△E和BSDF都表现出明显不同的两个阶段. 在应变范围0.012下经受不同循环周次的试样做了透射电镜观察,表明位错主要堆积在晶界,并存在大量的形变孪晶.合金中的氮含量有效地降低了合金的层错能,位错的交滑移和攀移受到一定程度的抑制,因而循环形变的稳态位错结构,即位错胞和驻留滑移带中的位错墙,只有在接近寿命或断裂后的试样中才能观察到.     

垂直晶界钢双晶体的循环形变行为

本文通过对取向近垂直晶界铜双晶体进行塑性应变控制循环变形,在表面滑移形貌及饱和位错组态观察的基础上,研究了其循环应力－应变响应．结果表明该铜双晶体循环应力－应变（CSS）曲线具有两个饱和轴向应力基本不变的平台区．即在塑性应变范围1．80×10-4－1．35×10-3对应于饱和应力幅62—64MPa及在塑性应变范围2．04×10-3—2．56×10-3对应于饱和应力幅70—71MPa．讨论了组元晶体的相对取向对其滑移形貌、饱和位错组态及CSS曲线的影响。     

垂直晶界铜双晶体的循环形变行为

本文通过对取向近垂直晶界铜双晶体进行塑性应变控制循环变形,在表面滑移形貌及饱和位错组态观察的基础上,研究了其循环应力－应变响应．结果表明该铜双晶体循环应力－应变（CSS）曲线具有两个饱和轴向应力基本不变的平台区．即在塑性应变范围1．80×10-4－1．35×10-3对应于饱和应力幅62—64MPa及在塑性应变范围2．04×10-3—2．56×10-3对应于饱和应力幅70—71MPa．讨论了组元晶体的相对取向对其滑移形貌、饱和位错组态及CSS曲线的影响。     

滑移取向对循环形变Al单晶的应力响应,内耗和超声衰减的影响

本文报道了不同取向Al单晶体在循环形变过程中的应力响应、内耗和超声衰减的变化及它们之间的关系,试验结果表明,循环应力σ、内耗Q~(-1)和超声衰减△α对晶体取向有明显的依赖性,单滑移取向和多滑移取向晶体之间,上述三量的差别很大,对同一取向晶体,σ增加对应着Q~(-1)减少和Δa增加,但Δa达到最大值需要的循环周次少于σ达到最大值所需的循环数,而Q~(-1)与σ则基本上同时达到最低值和最大值。     

CYCLIC DEFORMATION OF FCC CRYSTALS AND ITS DISLOCATION INTERACTION MODEL Ⅱ. DISLOCATION INTERACTION MODEL OF CYCLIC DEFORMATION

运用位错之间的交互作用理论,对各种轴向Cu晶体的循环形变行为进行了分析和比较,确认晶体循环形变的应力-应变响应以及形成的位错组态是由各滑移系统的位错反应的模式和强度决定的,根据晶体轴向在标准取向三角形中的位置,可以推断其循环形变行为.     

面心立方晶体的循环形变及其位错反应模型 Ⅱ 循环形变的位错反应模型

运用位错之间的交互作用理论,对各种轴向Cu晶体的循环形变行为进行了分析和比较,确认晶体循环形变的应力-应变响应以及形成的位错组态是由各滑移系统的位错反应的模式和强度决定的,根据晶体轴向在标准取向三角形中的位置,可以推断其循环形变行为.     

面心立方晶体的循环形变及其位错反应模型 Ⅰ Cu晶体的循环形变

系统地观察了各种不同轴向Cu晶体的循环应力-应变响应及其饱和位错结构.实验结果表明,晶体的宏观循环形变行为和微观位错组态的演变都与晶体的轴向紧密相关.在一些轴向位于标准取向三角形内的单滑移晶体中观察到明显的多滑移现象;其循环形变行为和饱和位错结构都与相邻的双滑移或多滑移晶体有许多相似之处.     

[■12]双滑移取向铜单晶体的循环应变硬化及饱和

本文在塑性分切应变幅（γpl）为1．3×10-4－7．2×10-3范围内研究了双滑移取向铜单晶体的循环形变行为当γpl＜2×10-3,晶体的初始硬化速率θ0.2较低,几乎与应变幅大小无关。当γpl＞2×10-3,θ0．2随γpl的增加而显著增大．　晶体的循环应力－应变（CSS）曲线在5×10-4＜γpl＜4×10-3范围内呈现一个明显的平台,平台区的范围与单滑移晶体相比明显缩短,但平台区对应的饱和应力相近．和晶体虽然同处于标准取向三角形的001／边上．但其循环形变行为存在明显的差异,可归结为各个滑移系相对于晶体轴的几何位置不同,从而造成不同的滑移形变特征     

EFFECT OF ORIENTATION ON STRESS RESPONSE,FRICTION STRESS AND BACK STRESS DURING CYCLIC DEFORMATION IN Al SINGLE CRYSTALS

The symmetrical push-pull fatigue tests at strain amplitude of 2×10~3 with different sliporientation of Al single crystals,were carried out at room temperature in air.The peakstresses of various cycles were measured and the stress-strain hysteresis loops for selected cy-cles were recorded.The energy losses.friction stresses,back stresses and shape     

EFFECT OF SLIP ORIENTATION ON STRESS RESPONSE,INTERNAL FRICTION AND ULTRASONIC ATTENUATION DURING CYCLIC DEFORMATION IN Al SINGLE CRYSTALS

The variation of cyclic stress,internal friction and ultrasonic attenuation during cyclicdeformation and relations among them have been investigated with different slip orientationAl single crystals.The results indicate that the value of cyclic stress σ,internal frictionQ~(-1)and ultrasonic attenuation △α depend obviously on the slip orientation.There are largedifferences in above three parameters for different slip orientation Al crystals.In early stageof fatigue life,σ and △α increase and Q~(-1)decreases with cycles N,and △α reached maxi-mum before σ,while Q~(-1)and σ get the valley and the peak,respectively,at same cycles.     

Investigation of the tensor character of mesoscopic internal stresses in tensile-deformed nickel single crystals by X-ray diffraction

X-ray diffraction profiles of tensile-deformed nickel single crystals with two different orientations of the loading axis were investigated. To characterize the internal elastic strain state on a mesoscopic scale, the profile shapes of different Bragg reflections were analysed. The asymmetric profile broadening is interpreted on the basis of a two-component model for internal stresses in a dislocation cell structure. A least-squares method was applied to determine the stress tensor for the cell interior from the asymmetry parameters of at least six independent reflections. Furthermore, this method was advanced to evaluate the distribution of the plastic deformation across the slip systems. Taking into account an inclusion approximation, by this way the calculated internal stresses were correlated with the plastic strain in the cells. The orientation of the principal axes of the stress tensor and the heterogeneity of slip in the slip systems found agree with model assumptions for the tensile deformation.     

单晶Nb拉伸,压缩及恒应变疲劳后的滑移系和滑移特征

研究了单滑移位向和多滑移位向Ｎｂ单晶在拉伸，压缩及循环变形时的滑移系，根据试样表面滑移线的方向，在极图上确定滑移面，单滑移位向（［３２１］）的单晶，在拉伸时的滑移系为（１０１）［１１１］，在压缩时是（１０１）［１１１］和（２１３）［１１１］．根据ｂｃｃ晶体变形特点，分析了拉伸，压缩和循环变形的滑移系之间的关系，用光学显微镜和透射电镜复型观察了试样的表面形貌，确定了多滑移位向（［１１０］位向）单晶滑     

AZ31镁合金棒材循环扭转过程中的力学性能和织构变化

对AZ31镁合金挤压棒材在循环扭转变形过程中的力学性能和织构演化进行了研究。循环扭转变形分别在298,373,443,503和573 K下进行。镁合金循环变形的力学性能测试结果表明,循环扭转变形过程的应力应变滞回线呈现严格的对称性,意味着微观变形模式以滑移为主。变形过程的热效应使应力应变曲线中的峰值应力随着周期数的增加而降低。变形过程中柱面滑移系启动使晶粒取向发生改变,由变形前的{11■0}⊥ED织构转变为变形后的{10■0}⊥ED织构,变形过程中拉伸孪晶启动使晶粒取向产生两种变化。     

Cyclic deformation behaviors of Ti-46Al-2Cr-2Nb-0.15B alloy during thermo-mechanical fatigue tests

Thermo-mechanical fatigue tests were carried out on the gamma-TiAl alloy in the temperature range of 500-800 °C under mechanical strain control in order to evaluate its cyclic deformation behaviors at elevated temperature.Cyclic deformation curves,stress-strain hysteresis loops under different temperature-strain cycles were analyzed and dislocation configurations were also observed by TEM.The mechanisms of cyclic hardening or softening during thermo-mechanical fatigue(TMF) tests were also discussed.Results showed that thermo-mechanical fatigue lives largely depended on the applied mechanical strain amplitudes,applied types of strain and temperature.On the hysteresis loops appeared two apparent asymmetries:one was zero asymmetry and the other was tensile and compressive asymmetry.Dislocations configuration and slip behaviors were contributed to cyclic hardening or cyclic softening.     

Three Nb single crystals processed by equal-channel angular pressing—Part I: Dislocation substructure

Three high-purity Nb single crystals with different orientations are deformed by equal-channel angular pressing (ECAP) at room temperature for one pass. The microstructures of two different cross-sections are systematically characterized by means of electron backscatter diffraction on various length scales. The completely different microstructural features of the three single crystals provide clear experimental evidence that crystallographic orientation has a strong influence on orientation splitting and on microstructural heterogeneity. Lattice rotation is analyzed by comparing the crystal orientation before and after ECAP. The orientation evolution reveals that the three crystals tend to align in such a way that the primary slip plane and the primary slip direction overlap with the simple shear plane and direction, respectively. An in-depth analysis of the large misorientation bands is given in a companion paper.     

Evolution of compatible laminate domain structures in ferroelectric single crystals

The electromechanical properties and behaviour of ferroelectric single crystals are dominated by their domain structures. The domain structure can evolve according to the applied electrical and mechanical boundary conditions, but typically maintains a low energy state by adopting compatible configurations of microstructure in the form of multi-rank laminates. In this work, a model of domain structure evolution is developed, using a variational method to capture the dissipative nature of domain wall motion. The model describes the evolution of domain patterns with the constraint that they remain in low energy, compatible configurations. The electromechanical behaviour, such as microstructure evolution and hysteresis response, of periodic compatible laminate domain patterns in the tetragonal crystal system is studied. Estimates of the material response based on uniform field approximations are developed, and compared with a numerical model in which finite element analysis is used for accurate computation of the free energy. Microstructural transitions from one type of laminate domain pattern to another are included in the model by considering “pivot states”, which are the limiting states shared by more than one laminate pattern. The transition between distinct microstructural patterns at a pivot state is modelled as a bifurcation in which a material element notionally evolves along multiple paths simultaneously, representing sub-regions of the element evolving in different ways. The model is applied to study the hysteresis responses, such as dielectric hysteresis loops and butterfly strain loops, and switching mechanism of barium titanate (BaTiO₃) single crystals subjected to a variety of loads. The relationship between domain patterns and the behaviour of ferroelectric switching is discussed. The results show good general agreement with experimental data in the literature, reproducing several features such as the effect of stress on electrical hysteresis.     

Electrical characteristics and microstructures of Pr6O11-doped Bi4Ti3O12 thin films

Pr6O11-doped bismuth titanate (BixPryTi3O12, BPT) thin films with random orientation were fabricated on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering technique, and the structures and ferroelectric properties of the films were investigated. XRD studies indicate that all of BPT films consist of single phase of a bismuth-layered structure with well-developed rod-like grains. For samples with y=0.06 , 0.3, 1.2 and 1.5, I-E characteristics exhibit negative differential resistance behaviors and their ferroelectric hysteresis loops are characterized by large leakage current. Whereas for samples with y=0.6 and 0.9, I-E characteristics are of simple ohmic behaviors and their ferroelectric hysteresis loops are saturated and undistorted. The remanent polarization (Pr) and coercive field (Ec) of the BPT Film with y=0.9 are above 35 μC/cm2 and 80 kV/cm, respectively.