Temperature-dependent 2-D to 3-D growth transition of ultra-thin Pt films deposited by PLD

During the growth of thin metal films on dielectric substrates at a given deposition temperature T_d, the film’s morphology is conditioned by the magnitude and asymmetry of up- and downhill diffusion. Any severe change of this mechanism leads to a growth instability, which induces an alteration of the thin film morphology. In order to study this mechanism, ultrathin Pt films were deposited via pulsed laser deposition onto yttria-stabilized zirconia single crystals at different deposition temperatures. The morphological evolution of Pt thin films has been investigated by means of scanning electron microscopy, atomic force microscopy and standard image analysis techniques. The experimentally obtained morphologies are compared to simulated thin film structures resulting from a two-dimensional kinetic Monte Carlo approach. Two main observations have been made: (i) thin Pt films deposited onto ZrO₂ undergo a growth transition from two-dimensional to three-dimensional growth at T_d > 573 K. The growth transition and related morphological changes are a function of the deposition temperature; and (ii) a critical cluster size of i¹ = 4 in combination with an asymmetric Ehrlich–Schwoebel barrier favoring the uphill diffusion of atoms allows for a computational reproduction of the experimentally obtained film morphologies.     

Image processing and analysis of 3-D microscopy data

While there are many microstructural parameters that can be measured from a planar two-dimensional (2-D) section through a material, there are many measurements that require knowledge of the full three-dimensional (3-D) microstructure, such as true size and shape of individual objects, connectivity and interfacial curvatures. Serial sectioning and reconstruction can reveal the 3-D microstructure but are often considered to be time consuming and labor intensive. However, what is not often realized is that the majority of the time invested in serial sectioning is spent in the image segmentation, wherein individual objects are digitally identified. This article reviews the current state of image segmentation and novel analysis within 3-D materials science. We will also briefly discuss the future possibilities for more efficient segmentation of digital images for a broader range of materials.     

Elastic-plastic collapse of 3-D damaged cylindrical shells subjected to uniform external pressure

Hoo Fatt’s model was modified to obtain analytical solutions of plastic collapse for 3-D damaged cylindrical shells. To assess the effective wall thickness of a damaged pipeline, we used ASME B31G and its burst test results with Hauch and Bai’s approach. The effective thickness represents the corroded region of a pipe; it helps to transfer the response of the undamaged area near the damaged area. We propose solutions for the buckling of a damaged shell subjected to uniform external pressure. In these solutions, we extended Timoshenko’s solutions for the elastic-plastic buckle of linear elastic in a perfectly plastic cylindrical shell. The plastic collapse of a damaged shell is based on a modification of the interaction formula of the fully plastic membrane forces and bending moments in the nonuniform cylinder.     

三维模型重建中点云ICP拼接算法的改进

提出一种以不同视野下的点云为处理对象,自动进行点云配准的拼接算法.该算法首先利用点云的曲率、法矢量等几何信息,计算出初次拼接变换,并用几何哈希的方法筛选出最优的变换,完成初次拼接.然后改进最近点迭代法(iterative closest point,ICP)中最近点的选取方法:对点云A中的测点,先求出另一点云B中与其最近的3个点,并由这3个点构成一个三角形,把测点到三角形的垂足作为测点的最近点.并用该算法对点云进行再次拼接.最后基于该算法实现了对车头模型的配准.结果表明,该算法具有较高的配准精度.     

Kinetics of Pit Initiation at Passive Iron

Pit initiation at passive iron in borate and phthalate buffer solutions was investigated by separately measuring dissolution rates of Fe(III) and Fe(II) at rotating ring-dis electrodes. The rate of Fe(III) dissolution grow linearly with the chloride concentration. Fe(II) appears simultaneously with the first pits. At a constant electrode potential positive to the critical pitting potential a stage of pit initiation is observed ending at the time t_i of incubation after addition of chloride to the solution. The time t_i is independent of the time of prior passivation. The potential dependence of t_i described by a relation known from the theory of two-dimensional nucleation. The physical meaning of this formal analogy is discussed. According to the dependence of t_i on pH and chloride concentration the observed mechanism of pit initiation is possible only above a critical chloride concentration c=0.3 _mM and below a critical _pH 10.4. The absolute values of critical pitting potentials and the dependence of the critical pitting potentials on chloride concentration were found to be a function of the nature and the concentration of the supporting electrolyte. The influence of the supporting electrolyte on the time of incubation was also investigated.     

铸件充型凝固三维数值模拟软件SRIFCAST的研制及其应用

铸件充型凝固过程数值模拟软件SRIFCAST在确定了金属液在充型和凝固冷却过程中的湍流和层流流动模式以及三维速度场和温度场数值模拟计算方程及数值求解的基础,编制了网格单元的剖分、三维速度场和温度场计算、二维等温线图、速度矢量图和三维温度场显示等程序;在Windows 9x操作平台上,设计了方便、快捷的各种鼠标操作主界面和分界面;建立了铸铁、铸钢、高温合金、铸造有色合金等金属材料,以及石英砂等造型材料的热物性参数数据库。SRIFCAST软件在汽车铸件和重大装备铸件上进行了生产应用,获得了优质铸件,证明了它的先进性、实用性和易操作性。     

In?Situ Three-Dimensional Reciprocal-Space Mapping of Diffuse Scattering Intensity Distribution and Data Analysis for Precursor Phenomenon in Shape-Memory Alloy

Diffuse scattering contains rich information on various structural disorders, thus providing a useful means to study the nanoscale structural deviations from the average crystal structures determined by Bragg peak analysis. Extraction of maximal information from diffuse scattering requires concerted efforts in high-quality three-dimensional (3D) data measurement, quantitative data analysis and visualization, theoretical interpretation, and computer simulations. Such an endeavor is undertaken to study the correlated dynamic atomic position fluctuations caused by thermal vibrations (phonons) in precursor state of shape-memory alloys. High-quality 3D diffuse scattering intensity data around representative Bragg peaks are collected by using in situ high-energy synchrotron x-ray diffraction and two-dimensional digital x-ray detector (image plate). Computational algorithms and codes are developed to construct the 3D reciprocal-space map of diffuse scattering intensity distribution from the measured data, which are further visualized and quantitatively analyzed to reveal in situ physical behaviors. Diffuse scattering intensity distribution is explicitly formulated in terms of atomic position fluctuations to interpret the experimental observations and identify the most relevant physical mechanisms, which help set up reduced structural models with minimal parameters to be efficiently determined by computer simulations. Such combined procedures are demonstrated by a study of phonon softening phenomenon in precursor state and premartensitic transformation of Ni-Mn-Ga shape-memory alloy.     

Accurate 3-D cutting force prediction using cutting condition independent coefficients in end milling

The instantaneous uncut chip thickness and specific cutting forces have a significant effect on predictions of cutting force. This paper presents a systematic method for determining the coefficients in a three-dimensional mechanistic cutting force model—the cutting force coefficients (two specific cutting forces, chip flow angle) and runout parameters. Some existing models have taken the approach that the cutting force coefficients vary as a function of cutting conditions or cutter rotation angle. This paper, however, considers that the coefficients are affected only by the uncut chip thickness. The instantaneous uncut chip thickness is estimated by following the movement of the position of the center of a cutter. To consider the size effect, the present method derives the relationship between the re-scaled uncut chip thickness and the normal specific cutting force, K_n with respect to the cutter rotation angle, while the other two coefficients—frictional specific cutting force, K_f and chip flow angle, θ_c—remain constant. Subsequently, all the coefficients can be obtained, irrespective of cutting conditions. The proposed method was verified experimentally for a wide range of cutting conditions, and gave significantly better predictions of cutting forces.     

Stress-assisted martensitic transformations in steels: A 3-D phase-field study

A 3-D elastoplastic phase-field model is developed for modeling, using the finite-element method, the stress-assisted martensitic transformation by considering plastic deformation as well as the anisotropic elastic properties of steels. Phase-field simulations in 3-D are performed by considering different loading conditions on a single crystal of austenite in order to observe the microstructure evolution. The thermodynamic parameters corresponding to an Fe–0.3% C steel as well as the physical parameters corresponding to commercial steels, acquired from experimental results, are used as input data for the simulations. The simulation results clearly show the well-known Magee effect and the Greenwood–Johnson effect. The results also show that even though the applied stresses are below the yield limit of the material, plastic deformation initiates due to the martensitic transformation, i.e. the well-known transformation-induced plasticity (TRIP) phenomenon. It is concluded that the loading conditions, TRIP as well as autocatalysis play a major role in the stress-assisted martensitic microstructure evolution.     

Mechanical Behavior of fcc Crystal Simulated by 3-D Discrete Dislocation Dynamics

To simulate the mechanical behavior of the FCC crystal with the lower Peierls stress, the stiff property and physical meaning of the differential equation group consisting of dislocation evolution and mechanical state was investigated based on the 3-D discrete dislocation dynamics; the results indicate that the differential equation group is serious stiff, namely the external stress changes more quickly than dislocation evolution. Using the established numerical algorithm, the mechanical behavior of FCC crystal was simulated with the dislocations located in the parallel slip planes, and the effect of strain rate on the dislocation configuration and mechanical behavior, and the sat- uration process of mobile dislocation were discussed. The simulation results indicate that the numerical algorithm can efficiently simulate the dislocation dipole and the low strain rate loading.     

Pinning effect of second-phase particles on grain growth in polycrystalline films studied by 3-D phase field simulations

Three-dimensional simulations of grain growth in thin films containing finely dispersed second-phase particles were performed using a phase field model. The simulations show that although the growth behavior of the columnar grain structures in thin films is essentially two-dimensional, the interaction between the particles and the grain boundaries is three-dimensional. Grain boundaries can therefore more easily break free from the particles than in purely two-dimensional systems, resulting in fewer grain boundary–particle intersections and a larger final grain size. For a given volume fraction f_V and size of the particles r, the final grain size ${\overline{R}}_{\text{lim}}$ increases with film thickness. Moreover, it was found that particles located in the middle of the film are most efficient in pinning grain boundaries. A classical Zener type relation ${\overline{R}}_{\text{lim}}/r=K(1/f_{\text{V}}^b)$ cannot describe these effects.     

Dielectric and magnetic properties of 0.7Bi(Fe1−xCrx)O3–0.1BaTiO3–0.2PbTiO3 solid solutions

0.7Bi(Fe_1−xCr_x)O₃–0.1BaTiO₃–0.2PbTiO₃ (x = 0, 0.1, 0.2, 0.3) solid solutions were prepared by the traditional ceramic process. X-ray diffraction results revealed that the samples with x = 0–0.3 showed pure perovskite structure. Frequency and temperature dependences of dielectric constants and dielectric loss of the samples were investigated. Both dielectric constant and the loss tangent increased at given frequencies (100 Hz–1 MHz), while the Curie temperature of the solid solutions decreased with increasing Cr content. Room temperature magnetic hysteresis loops indicated that an appropriate amount of Cr could improve magnetization of the solid solutions.     

Variational derivative equations for the partition functions of the Hubbard and Anderson models

The method of a generating functional of Green’s functions was further developed within the framework of the Hubbard model and single-impurity Anderson model. In contrast to the earlier proposed works, the equations in the variational derivatives for the partition functions are presented here in the closed form, i.e. the role of variables is played by the physical matrix parameters of the systems rather than by the external local fluctuating fields. The solutions to these equations are the generating functionals of different Green’s functions. It is shown that the simplest iterative solutions in terms of the parameters U/W and W/U in the case of the Hubbard model or U/Δ and Δ/U for the Anderson model, where U is the Coulomb repulsion on a site, W is the width of a free electron zone, and Δ is the width of an impurity level, lead to the well-known results of the weak and strong coupling limits.     

Studies on the anodic polarization of amalgams. The behaviour of manganese amalgams in alkaline solutions

Manganese amalgams of varying concentrations were anodically oxidized galvanostatically in 0·1, 1·0, 2·0 and 4·0N NaOH solutions at 25°C. For each amalgam and solution composition a number of constant polarizing currents were used. The anodic polarization curves in 1·0 and 2·0N NaOH solutions showed potential arrests corresponding to discharge of sodium amalgam formed during the pre-cathodization treatment, dissolution of Mn as Mn²⁺ followed by precipitation of Mn(OH)₃, formation of MnO₂ and oxidation of mercury before oxygen evolution. In 4·0N NaOH, the development of a new step or steps at potentials intermediate between those for the formation of MnO₂ and the oxidation of mercury is noticed.The correlation between polarizing current, i, and time of passivation, τ, was found to follow the following relation: log T = A – n log i where A and n are constants. The results indicate that the passivation of manganese amalgams in alkaline solutions is governed by the rate of diffusion of metal atoms (or ions) at the electrode solution interface and by the physical and chemical properties of surface oxide film.     

C-diffusion during hot press in the Al2O3-Cr2O3 system

Alumina is an important technological material due to its excellent physical and thermomechanical properties. Binary compositions enhance some of these properties; especially Cr additions significantly increase the mechanical behaviour of pure alumina. It is well known that the sintered bodies of chromium oxide doped-alumina do not become dense when sintering in air because vaporisation and condensation of Cr₂O₃ during the high temperature densification process. The aim of this work is to assess the hot press sintering as an adequate processing method to obtain full dense sintered bodies from well homogeneous powders on chromia-alumina system. Using solutions of the desired nitrates, powders were prepared by the Pechini process in the range 0–6 Cr₂O₃ wt% and hot-pressed at 1500 C. C-diffusion and microstructure of the final densed bodies were studied in order to evaluate synthesis process feasibility.     

一种新型5轴执行机构末端定位算法

针对一种5轴执行机构末端建立二维、三维的定位模型,使之定位到给定目标点处。采用向量积方法确定关节实际旋转角度的取值范围。二维模型中,分别旋转大臂、小臂和腕部关节点,进行二维平面定位;三维模型中,分别旋转腰部、大臂、小臂和腕部关节点,进行三维空间定位。逆运动学求解时,对大臂俯仰角度进行迭代,解出所有的有效解,并用正运动学分析方法对所有解进行验算。按照执行机构运行效率最高原则,从所有有效解中计算最优解。最后,给出二维模型和三维模型最优解的各关节点运动轨迹、各关节点角度-时间关系曲线。仿真结果表明:定位精度在毫米级,能够满足定位需求。     

A thermometric study of the reaction between Fe and HNO3

The reaction between Fe and HNO₃ is studied under a wide variety of conditions by the thermometric technique. Up to 4N HNO₃ ΔT varies linearly with the normality of HNO₃, while in solutions from 6 to 10N HNO₃ it is independent of the concentration. Passivity sets in solutions ≥ 10·8N HNO₃. Calculations of the reaction number (R.N.) reveal that the maximum rate of metal dissolution occurs in 7·3N HNO₃. Fe dissolution in dilute HNO₃ is promoted by additions of NO₃⁻ and NO₂⁻. That the rate-determining step of the autocatalytic process involves HNO₂ is supported by the results of addition of urea to the solution. This additive lowers the maximum measured temperature, without affecting the corresponding time necessary to reach it.Additions of HCI, NaCl, H₂SO₄ and Na₂SO₄ to dilute HNO₃ reduce the dissolution rate of Fe. The effect produced by the salts exceeds that of the acids.In contrast to its action in dilute solutions, the Cl⁻ion induces pitting corrosion in concentrated HNO₃. The attack starts after an induction period which decreases in length as the concentration of HCI is increased. Concentrated HNO₃ can tolerate a certain amount of the aggressive agent before attack starts. The concentration “N_HCl” which can be tolerated depends on that of the passivator according to logN_HCl=a+blog(N−N°)_HNO3 where a and b are constants, and N^o is the least concentration of HNO₃ necessary to cause passivity. Pitting corrosion in concentrated HNO₃ can be initiated also through NaCl. In one and the same acid solution more of NaCl is needed to cause the attack than of HCI.     

3-D finite element modelling of ribbed strip rolling

A main feature of the rolling of ribbed strip is local residual deformation, which affects the pulling down of rib height when the ribbed strip is rolled. Using a 3-D “slightly-compressible” rigid visco–plastic finite element method, the hot rolling of ribbed strip is analyzed in this paper. The results show that the distribution of rib height along the width of strip is not uniform, and the pulling down of rib height increases when the reduction and thickness of base strip increase. The variation of rib height is smaller with a higher rolling temperature. If the friction factor in the backward zone increases, the rib height and forward slip increase. Friction variation is found to affect the convergence of simulation. Results of simulation from the rolling of ribbed strip and experimental values have been found to be in good agreement.     

3-D surface analysis of worn spherical roller thrust bearings

Wear of boundary lubricated spherical roller thrust bearings has been characterised with 3-D surface measurements and analysis. Due to the curved contact surface in a spherical roller thrust bearing, the rollers will undergo sliding in the contact. For an unskewed roller there will be two points along each contact where the sliding velocity is zero. At all other points along the contact, sliding is present. Previously presented results from measurements of the contacting surfaces show that outside the zero sliding points there is a significant change in the washer surface profile due to wear. In order to study how the wear depends on the number of revolutions ten tests were performed. After the tests, 3-D surface roughness measurements were performed. The results from these measurements show that there are different wear mechanisms involved. Initially, the surfaces are run in by possible plastic deformation and two-body abrasion. After running-in, the surfaces are subjected to mild wear probably caused by two-body abrasion and/or delanunation wear. For the long term tests, three-body abrasion clearly influences the amount of wear. A 3-D parameter set was used to characterise the different wear mechanisms. Three amplitude parameters (S_a, S_q S_z) and three of the functional Abbot curve parameters (S_pk, S_k, S_vk) were able to characterise all the wear mechanisms.     

Thermodynamic evaluation of phase equilibria in NaNO3-KNO3 system

The binary phase diagram of NaNO₃-KNO₃ was studied by differential scanning calorimetry (DSC) and high-temperature x-ray diffractometry. The solid solutions in the intermediate concentration phase appeared to be a mixture of the NaNO₃-based solid solutions and KNO₃-based solid solutions. This behavior below the solidus suggests that NaNO₃-KNO₃ might well be regarded as a system with limited solid solubilities instead of a continuous series of solid solutions. The temperatures for the solidus and liquidus have been determined with consideration of limited terminal solid solutions. Two models, the Henrian solution and regular solution theory for NaNO₃-based phase and the KNO₃-based phase, respectively, were used to reproduce the solidus and liquidus of the phase diagram. The results are in good agreement with the DSC data. The thermodynamic properties for the NaNO₃-based and KNO₃-based solid solutions have been derived from an optimization procedure using the experimental data. The calculated phase diagram and optimized thermodynamic parameters are thermodynamically self-consistent. Thus, the limited solid solution model seems to be more consistent with the phase diagram obtained by DSC than the continuous solid solution model.