Effect of plastic deformation on the electronic properties of the Cu<Subscript>60</Subscript>Pd<Subscript>40</Subscript> alloy

The effect of severe plastic deformation by torsion under Bridgman anvil pressure (SPDT) on the electrical, magnetic, and optical properties of the Cu₆₀Pd₄₀ alloy was studied. It is shown that, after the alloy is disordered, the Curie-Weiss constants of the paramagnetic component are changed insignificantly. In this case, the temperature-independent negative component of the magnetic susceptibility decreases more than fivefold. The electrical resistance and negative thermopower, on the contrary, increase severalfold as a result of SPDT. The character of the optical conductivity is discussed using the band structure calculation results.     

Effect of deformation of diamond anvil and sample in diamond anvil cell on the thermal conductivity measurement

Studies show that the sample thickness is an important parameter in investigating the thermal transport properties of materials under high-temperature and high-pressure (HTHP) in the diamond anvil cell (DAC) device. However, it is an enormous challenge to measure the sample thickness accurately in the DAC under severe working conditions. In conventional methods, the influence of diamond anvil deformation on the measuring accuracy is ignored. For a high-temperature anvil, the mechanical state of the diamond anvil becomes complex and is different from that under the static condition. At high temperature, the deformation of anvil and sample would be aggravated. In the present study, the finite volume method is applied to simulate the heat transfer mechanism of stable heating DAC through coupling three radiative-conductive heat transfer mechanisms in a high-pressure environment. When the temperature field of the main components is known in DAC, the thermal stress field can be analyzed numerically by the finite element method. The obtained results show that the deformation of anvil will lead to the obvious radial gradient distribution of the sample thickness. If the top and bottom surfaces of the sample are approximated to be flat, it will be fatal to the study of the heat transport properties of the material. Therefore, we study the temperature distribution and thermal conductivity of the sample in the DAC by thermal-solid coupling method under high pressure and stable heating condition.     

Numerical study of stress and plastic strain evolution under compression and shear of a sample in a rotational anvil cell

The large-strain problem on the evolution of distribution of the components of stress tensor and plastic strain in a sample under compression and torsion in a rotational anvil cell was formulated and studied in detail using the FEM. Results are obtained for compression by different axial forces and torsion under two different constant axial forces. The effects of redistribution of the friction radial and torsional stresses and the load on a sample and gasket on the resultant fields are elucidated. Small pressure self-multiplication effect is revealed during torsion after compression below some critical force, and significant heterogeneity of all fields is found. Strong shear strain localization near the contact surface between sample and anvil is quantified. Results are compared with the simplified solution and available experiments. The results obtained are important for the determination of elastic and plastic properties of materials under high pressure and for the interpretation of kinetics of strain-induced phase transformations and chemical reactions.     

The mechanical property of single-walled carbon nanotube under combined electromechanical loading

The mechanical properties and failure process of single-walled carbon nanotube (SWCNT) under combined electric field and tensile loading are investigated using the semi-empirical quantum mechanical method. The local and global structural deformation and variation of mechanical properties of SWCNT under different directions and intensity of external electric field are discussed systematically. It is shown that the electric field induced deformation in the radial and axial directions of the SWCNT are strongly dependent on the direction of electric field. The analysis of mechanical properties shows that the structure stiffness, tensile strength and failure strain of the SWCNT all decrease with the increase of the field intensity, which is particularly evident under the longitudinal electric field. The Young's modulus of SWCNTs vary with the tube diameter and are affected by the electric field. The increase of the length of the tubes intensifies the charge concentration at the tube ends under the electric field and lead to the decrease of mechanical properties of SWCNTs. The failure process of SWCNTs under the coupling effect of electric field and tensile loading is found to be controlled by the field strength and also affected by the electric charge accumulation.     

变形及电场作用对石墨烯电学特性影响的第一性原理计算

利用基于密度泛函理论的第一性原理方法,系统研究了变形、电场及共同作用对石墨烯电学特性影响的电子机理.研究表明,本征石墨烯的能隙及态密度值在费米能级处均为0,呈现出半金属特性;在一定的变形量下对石墨烯施加剪切、拉伸、扭转及弯曲变形作用,发现剪切和扭转变形对打开石墨烯能隙的作用明显;对本征石墨烯施加不同方向的电场,可知010电场方向对打开石墨烯能隙的作用效果最强.这是因为该电场方向下石墨烯C-C原子间的布居数正值较大,成键键能较高,而负值数值较小,反键键能较低;线性增加电场强度,石墨烯的能隙呈线性增长势;变形及电场共同作用下,外加电场提高了变形对打开石墨烯能隙的作用效果,但不及两种外场叠加的作用效果.     

界面结构对Cu/Ni多层膜纳米压痕特性影响的分子动力学模拟

金属多层膜调制周期下降到纳米级时,其力学性质会发生显著改变. Cu-Ni晶格失配度约为2.7%,可以形成共格界面和半共格界面,实验中实现沿[111]方向生长的调制周期为几纳米且具有异孪晶界面结构的Cu/Ni多层膜,其力学性质发生显著改变.本文采用分子动力学方法对共格界面、共格孪晶界面、半共格界面、半共格孪晶界面等四种不同界面结构的Cu/Ni多层膜进行纳米压痕模拟,研究压痕过程中不同界面结构类型的形变演化规律以及位错与界面的相互作用,获取Cu/Ni多层膜不同界面结构对其力学性能的影响特征.计算结果表明,不同界面结构的样品在不同压痕深度时表现出的强化或软化作用机理不同,软化机制主要是由于形成了平行于界面的分位错以及孪晶界面的迁移,强化机制主要是由于界面对位错的限定作用以及失配位错网状结构与孪晶界面迁移时所形成的弓形位错之间的相互作用.     

Crystallization Features of Rapidly Quenched Ti50Ni20Cu30 Amorphous Alloys after High-Pressure Torsion

Physics of the Solid State - The effect of severe plastic deformation under high-pressure torsion (HPT) on the structural properties of rapidly quenched alloys belonging to the quasi-binary...     

Deformation textures produced in diamond anvil experiments, analysed in radial diffraction geometry

Diamond anvil cells may not only impose pressure upon a sample but also a compressive stress that produces elastic and plastic deformation of polycrystalline samples. The plastic deformation may result in texture development if the material deforms by slip or mechanical twinning, or if grains have a non-equiaxed shape. In radial diffraction geometry, texture is revealed by variation of intensity along Debye rings relative to the compression direction. Diffraction images (obtained by CCD or image plate) can be used to extract quantitative texture information. Currently the most elegant and powerful method is a modified Rietveld technique as implemented in the software package MAUD. From texture data one can evaluate the homogeneity of strain in a diamond anvil cell, the strain magnitude and deformation mechanisms, the latter by comparing observed texture patterns with results from polycrystal plasticity simulations. Some examples such as olivine, magnesiowuestite, MgSiO(3) perovskite and ε-iron are discussed.     

Axial-strain-induced torsion in single-walled carbon nanotubes

Using classical molecular dynamics and empirical potentials, we show that the axial deformation of single-walled carbon nanotubes is coupled to their torsion. The axial-strain-induced torsion is limited to chiral nanotubes-graphite sheets rolled around an axis that breaks its symmetry. Small strain behavior is consistent with chirality and curvature-induced elastic anisotropy (CCIEA)-carbon nanotube rotation is equal and opposite in tension and compression, and decreases with curvature and chirality. The large-strain compressive response is remarkably different. The coupling progressively decreases, in contrast to the tensile case, and changes its sign at a critical compressive strain. Thereafter, it untwists with increasing axial strain and then rotates in the opposite direction, i.e., the same sense as under tension. This suggests that the response is now dictated by a combination of nonlinear elasticity and CCIEA.     

Increase in the Saturation Magnetization in a Fe<Subscript>3</Subscript>Al Superstructure under Large Plastic Deformations

The effect of large plastic deformations at room temperature in a Bridgman anvil cell on the specific saturation magnetization of the DO₃-type ordered (Fe–24 at % Al) alloy has been revealed. It has been found that torsion at high pressure and certain deformation parameters results in the complete suppression of long-range order in the alloy and in the corresponding increase in the specific saturation magnetization by 11% with respect to the equilibrium state. A theoretical model qualitatively describing the revealed phenomenon has been proposed.     

多晶体压剪试样静态加载有限元计算

基于晶体塑性理论研究了晶体织构对数值计算结果的影响,建立了带有织构的多晶体压剪试样(SCS)模型。从材料和试样结构两方面研究了静态加载条件下微观晶粒在有限变形过程中对试样宏观力学性能的影响。由于模型几何结构的特殊性,重点对模型斜槽部分的应力、应变及变形特点进行了分析。考虑到试样在压缩过程中受摩擦的影响,数值分析了不同摩擦系数对变形过程的影响,在此基础上计算了相同摩擦系数下不同晶粒数目、不同单元数目以及单元类型对多晶体压剪模型力学性能的影响,并对试件关键部位不同取向晶粒的应力状态进行了分析。     

Microstructural peculiarities of copper and mechanisms of its hardening after mechanical activation and torsion in Bridgman anvils

The paper presents the results of complex research on microstructural peculiarities of copper and mechanisms of its hardening after mechanical activation in planetary ball mills, high-pressure torsion, and combined treatment which includes mechanical activation and subsequent consolidation under high-pressure torsion in Bridgman anvils. The main structural factors responsible for the hardening mechanisms are discussed depending on the pattern and degree of deformation.     

基于马赫-曾德干涉的全光纤双参量传感器

提出一种基于S形-错位结构的全光纤马赫-曾德干涉仪（MZI）双参量传感器。该传感结构是采用单模光纤在光纤熔接机中通过简单的放电和熔接等步骤制备而成。顺时针扭转时, 传感器的传输光谱向短波长方向偏移; 逆时针扭转, 向长波长方向偏移。对传感器的实验研究结果表明,该传感器在光纤横截面上顺时针和逆时针两个旋转方向上的扭曲传感灵敏度分别为?223 pm/(rad·cm?1), 140 pm/(rad·cm?1),且可实现扭转方向的判别,在一定应变范围内的应变灵敏度为0.145×106 dB/ε(这里ε为应变),且温度交叉灵敏度极小,可忽略不计。因此,这种基于单模光纤的纤芯-包层MZI双参量传感器具有传感灵敏度高,体积小巧,工艺简单,成本低廉且可判别扭转方向的优点,有望成为众多双参量测量操作中良好的候选仪器之一。     

扭转形变对石墨烯吸附O原子电学和光学性质影响的电子理论研究

基于密度泛函理论的第一性原理方法研究了扭转形变对石墨烯吸附O体系结构稳定性、电子结构和光学性质,包括吸附能、带隙、吸收系数及反射率的影响.研究发现,吸附O原子后,距O原子最近的C原子被拔起,导致石墨烯平面发生扭曲.吸附能计算表明,扭转形变使石墨烯吸附O原子体系结构稳定性下降,而扭转程度对结构稳定性影响微弱.能带结构分析发现,O原子的吸附使石墨烯由金属变成半导体,扭转形变发生时,可实现其从半导体到金属、再到半导体特性的转变.扭转角为12°的吸附O原子体系为间接带隙,而其他出现带隙的体系均为直接带隙.与本征石墨烯受扭体系相比,吸附O原子体系的电子结构对扭转形变的敏感度降低,其中扭转角在10°—16°范围内变化时,带隙始终稳定在0.11 eV附近,即在此扭转角范围内始终对应窄带隙半导体.在光学性能中,受扭转形变的吸附体系吸收系数和反射率峰值较未受扭转形变石墨烯吸附O原子体系均减弱,且随着扭转程度的加剧,均出现红移到蓝移的转变.     

Effect of annealing on the microstructure and mechanical properties of ultrafine-grained commercially pure Al

The influence of annealing on the microstructure and mechanical properties of ultrafine-grained (UFG) commercially pure aluminum preliminarily subjected to severe plastic deformation by high pressure torsion has been studied. It is found that annealing of the UFG samples in the temperature range 363–473 K for 1 h leads to increases in the conventional yield strength and ultimate tensile strength, which attained maximum values (50 and 30%, respectively) after annealing at 423 K. A key role of nonequilibrium high-angle grain boundaries in the strengthening effect of UFG-Al due to annealing is discussed. The increase in the strength of UFG-Al is accompanied by a significant decrease in its ductility. A new approach of increasing the ductility of UFG-Al with retaining a high strength is proposed. It is an introduction of additional dislocation density to a UFG structure relaxed by annealing.     

Effect of the Temperature of Megaplastic Deformation in a Bridgman Chamber on the Formation of Structures and the Physicochemical Properties of Titanium (BT1-0)

The formation of regions corresponding to deformational fragments and dynamically recrystallized grains in the structure of the α-phase after torsion under high hydrostatical pressure at room and cryogenic temperatures is determined by means of transmission electron microscopy. Its applicability to describing defective structures of a two-phase mixture model is shown. In optimizing the results from mechanical and corrosion tests, it is found that two rounds of torsion treatment under hydrostatic pressure is sufficient to obtain the best possible properties.     

Influence of the number of passes under equal-channel angular pressing on the elastic-plastic properties,durability, and defect structure of the Al + 0.2 wt % Sc alloy

The regularities of the influence of the number of passes under equal-channel angular pressing on the mechanical properties and defect structure of an aluminum alloy have been elucidated. It has been established that the degradation of the mechanical properties (a decrease in the durability) is associated with the formation of nanoregions of an excess free volume in the course of severe plastic deformation under equalchannel angular pressing. A correlation between the nucleation of excess free volume regions and the formation of high-angle grain boundaries under equal-channel angular pressing has been revealed. The nature of the influence of severe plastic deformation on the elastic modulus, the vibration decrement, and the microplastic flow stress has been analyzed.     

Double-sided laser heating system at HPCAT for in situ x-ray diffraction at high pressures and high temperatures

An overview of a YLF:Nd laser heating system at the undulator x-ray diffraction station (16ID-B) of the high-pressure collaborative access team (HPCAT) of the Advanced Photon Source is presented. Based on the double-sided laser heating technique, the system is designed with considerable effort on the mechanical and optical stabilities, features for user-friendly operation, and the capability of accommodating diamond anvil cells of various heights up to 68?mm. This system has been used for x-ray diffraction studies of a wide range of materials to over 150?GPa and above 3000?K. Applying the laser heating technique to radial x-ray diffraction studies at simultaneous high-pressure and high-temperature (PT) conditions requires heating to be conducted at variable angles relative to the x-ray direction. A rotation laser heating design is discussed.     

复合型多晶金刚石末级压砧的制备并标定六面顶压机6-8型压腔压力至35GPa

通过分析二级6-8型大腔体静高压装置八面体压腔的受力状况, 研制了一种使用成本低、尺寸大且易于加工的多晶金刚石-硬质合金复合二级(末级)顶锤(压砧). 采用原位电阻测量观测Zr在高压下相变(α-ω, 7.96 GPa; ω-β, 34.5 GPa)的方法, 标定了由多晶金刚石-硬质合金复合末级压砧构建的5.5/1.5(传压介质边长/二级顶锤锤面边长, 单位: mm)组装的腔体压力. 实验表明, 自行研制的多晶金刚石-硬质合金复合末级压砧可使基于国产六面顶压机构架的二级加压系统的压力产生上限从约20 GPa提高到35 GPa以上, 拓展了国内大腔体静高压技术的压力产生范围. 应用这一技术, 我们期望经过末级压砧材料与压腔设计的进一步优化, 在基于国产六面顶压机的二级6-8 型大腔体静高压装置压腔中产生超过50 GPa的高压. 关键词： 二级6-8型大腔体静高压装置 多晶金刚石-硬质合金复合末级压砧 压力标定     

Effect of annealing under tensile loading on the structure of nanocrystals in the Finemet alloy

The effect of nanocrystallization annealing under tensile loading on the structure of nanocrystals in the soft magnetic alloy Fe-Si-Nb-B-Cu (Finemet) has been investigated. It has been shown that the body-centered cubic (bcc) lattice of α-FeSi nanocrystals is extended along the direction of the application of the load upon annealing and is compressed in the transverse direction. Nanocrystals in the Finemet alloy have a higher degree of anisotropy of mechanical properties as compared to bulk crystals of α-FeSi, so that agreement between the measured and calculated values of the elongation is achieved only with a significant increase in the elastic moduli. Substantial changes in mechanical properties of the crystals with a decrease in their size to the nanometer scale are caused by the influence of the rigid amorphous matrix of the Fe(Nb)-B phase surrounding the nanocrystals.