Depth Dependence of Nanoindentation Pile-Up Patterns in Copper Single Crystals

A study of the dependence of nanoindentation pile-up patterns on the indentation load and crystallographic orientation is presented. Three different orientations—(001), (011), and (111)—of single crystal copper were investigated. Experiments were conducted on a CSM ultra-nanoindentation tester using a Berkovich tip. The topographic images were obtained using an atomic force microscope. The evolution of pile-up patterns with different applied loads was observed. The results show that for applied loads equal to 0.45 mN and smaller the pile-up patterns do not depend on the crystallographic orientation of the indented surface; instead, they depend on the tip’s geometry. On the other hand, in the case of indentation loads bigger than 2 mN, pile-up patterns on the surfaces of (001)-, (011)-, and (111)-oriented single crystals have fourfold, twofold, and sixfold (or threefold) symmetry, respectively. An intermediate state was also reported. Furthermore, a detailed analysis of residual impressions with maximal applied loads equal to 2 mN and bigger reveals that both pile-up and sink-in patterns are present.     

Constitutive Modeling for CdTe Single Crystals

To understand the role of thermal stresses in the generation, multiplication, and propagation of dislocations in CdTe single crystals produced by directional solidification, constitutive models which accurately reflect the elastic-viscoplastic behavior of CdTe over a wide range of temperatures are needed. In this article, the relevant reported mechanical behavior of CdTe is reviewed and discussed. Constitutive equations developed for single slip, isothermal behavior of elemental semiconductor crystals by Haasen and co-workers, which include dislocation density as the important internal variable, are then extended to include an additional dislocation arrangement internal variable as well as a high-temperature, time-dependent recovery behavior. The constitutive framework is incorporated in a continuum slip framework to include the possibility of multiple slip and to relate slip system shear strain rates to the macroscopic plastic strain rate. Comparison of the model with available experimental data for the small strain case over a wide range of temperatures is presented. Slip system interaction is included. These constitutive equations can then be used in computational analyses of thermal stress generation for comparison with characterized crystals grown in microgravity and ground-based experiments. This article is based on a presentation made in the symposium entitled “Microgravity Solidification, Theory and Experimental Results” as a part of the 1993 TMS Fall meeting, October 17-21, 1993, Pittsburgh, PA, under the auspices of the TMS Solidification Committee.     

Mo-Nb合金单晶的高温力学性能

研究了晶向为111Mo-Nb合金单晶的高温力学性能。实验结果表明,随着少量溶质原子Nb的加入,Mo-Nb合金单晶的高温强度获得了明显的提高。在1873K和Nb含量在0～6%范围内时(文中合金元素Nb含量均为质量百分比,下同),Nb含量每增大1%,材料的高温屈服强度就增加约16～25MPa,当Nb含量在0～3%范围内时,随着Nb含量的增加,塑性急剧下降,而在3%～6%范围内时其下降幅度趋于平缓;同时,随着Nb浓度的增大,更多的Nb溶质原子增大了原子间扩散阻力,使材料高温稳态蠕变率减小,大大提高了材料的高温抗蠕变性能;在1773K/10MPa时Mo-Nb合金单晶的稳态蠕变率较纯Mo单晶的降低了3～4个数量级,分析认为其蠕变机制为扩散蠕变。     

Microstructure and Mechanical Properties of CMSX-4 Single Crystals Prepared by Additive Manufacturing

Currently, additive manufacturing (AM) experiences significant attention in nearly all industrial sectors. AM is already well established in fields such as medicine or spare part production. Nevertheless, processing of high-performance nickel-based superalloys and especially single crystalline alloys such as CMSX-4^® is challenging due to the difficulty of intense crack formation. Selective electron beam melting (SEBM) takes place at high process temperatures (~?1000 °C) and under vacuum conditions. Current work has demonstrated processing of CMSX-4^® without crack formation. In addition, by using appropriate AM scan strategies, even single crystals (SX SEBM CMSX-4^®) develop directly from the powder bed. In this contribution, we investigate the mechanical properties of SX SEBM CMSX-4^® prepared by SEBM in the as-built condition and after heat treatment. The focus is on hardness, strength, low cycle fatigue, and creep properties. These properties are compared with conventional cast and heat-treated material.     

Cyclic Deformation Behaviors of $$ [\bar{5}79] $$-Oriented Al Single Crystals

During the cyclic deformation of [[`5]79] [\bar{5}79] , Al single crystals with a high stacking fault energy produced slip bands that were characterized by wavy slip. Its cyclic stress response curve demonstrated that the specimen experienced hardening–softening–secondary hardening in sequence with repeated fluctuation stresses usually less than 10 MPa, which is far lower than those of Cu, Ni, and Ag single crystals. Finally, the whole surface of the Al single crystals was covered with intense intrusion and extrusion, and the cell structure is the most typical dislocation arrangement. These cells mainly comprise loose clusters of dislocations, which move more freely. In the center of the cell, the dislocation density is relatively low, and most dislocations concentrate in the cell wall. At room temperature, compared with cyclically deformed Cu, Ni, and Ag single crystals, the cyclic deformation behaviors of Al single crystals show significant differences, which are highlighted in this study.     

单嘴精炼炉真空处理过程钢液流动行为模拟研究

根据相似理论,以国内某厂80t单嘴精炼炉1:4的水模型模拟了单嘴精炼炉吹气流量、吹气位置等工艺参数对混匀时间的影响.在水模型研究的基础上,通过数学模型仿真计算分析了不同吹气流量、吹气位置对单嘴精炼炉内流场的影响,数值计算结果与试验结果吻合较好.研究结果表明:吹气流量为6L/min、吹气位置γ/R为0.5范围内有利于缩短...     

Thermally Activated Deformation of Gold Single Crystals

A study of the thermally activated tensile deformation of gold single crystals has been conducted between 4.2 and 473 K. The activation energy in terms of a single process analysis, AG₀, at zero effective stress was found to be 1.5 eV and was sensitive to the effective stress. From the strain dependence of the zero temperature effective stress it was concluded that the barriers giving rise to the thermally activated deformation process increase in density during deformation and are probably the forest dislocations. ROBERT B. HERRING, Formerly of the Department of Materials Science, Northwestern University, Evanston, Illinois     

Constitutive Modeling of Inherently Anisotropic Sand Behavior

A plasticity constitutive framework for modeling inherently anisotropic sand behavior is presented within a modified form of critical state soil mechanics. A second-order symmetric fabric tensor, Fij, describes the material inherent anisotropy, and a scalar-valued anisotropic state variable A is properly defined in terms of a joint invariant of Fij and the stress tensor. The location of the critical state line in the plane of void ratio and effective mean normal stress is not fixed but depends on A, rendering the soil dilatancy also a function of A. In addition, the plastic modulus is made a function of A. The incorporation of these two modifications in terms of A in an existing stress-ratio bounding surface model, achieves the successful simulation of both the contractive and dilative responses of sand over a wide range of variations in stress and density as shown by experimental data. Of particular significance are the results which exhibit the drastic effect of different principal stress orientations in reference to the material axes of anisotropy.     

On the Ductility of Magnesium Single Crystals at Ambient Temperature

Magnesium single crystals were loaded in plane-strain compression at ambient temperature, parallel, and normal to the c-axis. In the latter configuration, compression was applied along the 〈 \( 11\overline{2}0 \) 〉 as well as 〈 \( 10\overline{1}0 \) 〉 directions, whereby extension was confined to the c-axis owing to the plane-strain geometry. Out of the three tested orientations, only specimens compressed along the 〈 \( 11\overline{2}0 \) 〉 axis were able to deform up to a remarkable strain of ?1 demonstrating a surprisingly high ductility for pure magnesium at ambient temperature. The other two specimen orientations have depicted failure at two different low strains. The final microstructure of the ductile specimen was a polycrystalline mix of large deformed grains adjoining recrystallized regions of much finer grains, developed by means of extensive dynamic recovery. The corresponding final texture was relatively weak, and showed two orientation peaks with appreciable scatter around them.     

氧和铝在氧化铝中的自扩散参数评估

评估了氧和铝在Al₂O₃中的自扩散参数,分析了其扩散机理.得出:(1)在1770~2100K 温度范围内,氧分压不超过1.0×105Pa时,杂质总含量为30×10^-6~500×10^-6,Mg,Ti含量低于30× 10^-6的未掺杂Al₂O₃单晶中,氧的自扩散系数与温度的关系式,氧分压和扩散方向对该扩散系数 值影响不明显.(2)在1943~2178K范围,多晶Al₂O₃中铝的自扩散系数在10^-15到10^-14m²/s之间, 扩散活化能为 477 kJ/mol.(3)单晶Al₂O₃中主要杂质为TiO₂和 MgO,掺Ti将降低氧的自扩散系 数,增加铝的自扩散系数;掺Mg使氧的自扩散系数略有增加;其他杂质对氧和铝在Al₂O₃中的 扩散系数影响不大.(4)氧和铝均通过空位扩散.     

Size of Defect Clusters in Lithium Niobate Single Crystals

On the basis of the Li-site vacancy model, the non-stoichiometric defects in LN crystals, i.e., anti-site defects NbLi and corresponding lithium vacancy defects VLi, were investigated by the bond valence model. According to the valence sum rule, 4 VLi sites must emerge in the nearest lattices of NbLi, and thus form a neutral cluster with the center, NbLi(VLi)4Nb5O15. The bond graph of the defect cluster was given, which reveals the ideal chemical bonding characteristics of defect clusters. Combining the possible configuration of defect clusters and the ideal bond lengths in the bond graph, the size of defect clusters in the LN crystallographic frame is estimated as 0.9～1.2 nm in diameter.     

掺锌（100）GaSb单晶的生长

采用LEC方法研制出掺锌(100)GaSb单晶;用霍尔测量法算出的锌掺杂浓度计算得出锌的有效分凝系数keff约为0.84±0.01,沿晶体生长方向随着锌浓度的提高,位错密度缓慢增加,数值约为(2～3.2)×103cm-2,当掺锌浓度大于3×1019cm-3以后,GaSb发生简并,载流子浓度随掺锌浓度的增加缓慢提高.采用重掺锌母合金作掺杂剂,可减少锌的损失,较好地控制掺杂浓度.     

Loading Rate-Dependent Mechanical Properties of Bulk Two-Phase Nanocrystalline Al-Pb Alloys Studied by Nanoindentation

Bulk samples (dia. = 20 mm) of various nanocrystalline (nc) Al-Pb alloys with Pb content varying from 1 to 4 at. pct are fabricated using spark plasma sintering of ball-milled powders. Al matrix in Al-2 at. pct Pb alloy had a grain size of 53 nm, and Pb particle size was 6 ± 2 nm. High angle annular dark-field image obtained in STEM mode of TEM indicates the presence of Pb along the nc Al grain boundaries as well as dispersion of smaller Pb particles in the intra-granular regions. Hardness studies are carried out using microindentation and nanoindentation with load varying over three orders of magnitude (100 ? 0.1 g). Microindentation yielded slightly smaller hardness values in comparison to nanoindentation possibly because of indentation size effect. Nevertheless both microindentation and nanoindentation resulted in the same trend of hardness for various nc Al-Pb alloys. Hardness of Al-Pb alloys increased with increase in Pb content up to the additions of 2 at. pct Pb, beyond that the hardness is decreased for higher Pb additions of 3 and 4 pct. The initial hardening behavior is explained based on the Orowan particle strengthening. Strain rate sensitivity (SRS) has increased with increase in Pb content reaching a value of 0.1 for Al-4 at. pct Pb alloy. Activation volumes measured are between 2.84 and 6.15 b ³. Higher SRS and lower activation volume suggest that grain boundary-mediated processes are controlling the deformation characteristics.     

Investigation on Corrosion Behaviors of Anti-Corrosion

从互感器误差校验、电能计量统计和电能计量系统整体校验3个方面对光学电流互感器的现场运行性能进行客观评价。投运前和运行中期的误差校验数据显示,变差小于0.1%,满足0.2S级要求。建立2套独立计量系统,在实际现场运行条件下进行长期数据比对,反映数字电能计量系统在各种环境因素影响下的长期运行稳定性。通过对数字电能计量系统的整体校验,在额定功率条件下不确定度达到9.0×10-5,置信概率达到97.15%,系统综合误差为1.013%,满足规程要求。     

Bonding Energy and Growth Habit of Lithium Niobate Single Crystals

On the basis of crystallographic structure of lithium niobate (LN), the bonding energy was quantitatively calculated by the bond valence sum model, which was employed to investigate the crystal growth. A possible relationship between the crystal growth habit and chemical bonding energy of LN crystals are found. It is found that the higher the bond energy, the slower the growth rate, and the more important the plane. The analytical results indicate that (012) plane is the most influential face for the LN crystal growth, which consists well with the standard card (JCPDS Card: 20-0631) and our previous experimental observation. The current work shows that the chemical bond analysis of LN crystals allows us to predict its growth habit and thus to obtain the expected morphology during the spontaneous growth.     

The Thermal Effect in Pseudoelastic Single Crystals of β-CuZnSn

The thermal effect associated with the formation and reversion of stress-inducedβ2 martensite has been studied in single crystals of β2-CuZnSn. The martensite in this system forms as isolated plates of β2 which increase in number and ultimately coalesce. The maximum temperature pulse obtained increased with fraction of specimen undergoing transformation and reached a maximum for complete transformation. The temperature pulse was the same for the forward and reverse transformations and the same at different points on the specimen. The maximum temperature change increased with increasing strain rate and reached a constant at high strain rates. Calculations showed that heat loss to an air environment was negligible at high strain rates and the transformation could be considered adiabatic. In tests in water there was always a significant heat loss to the environment and corrections were necessary to allow for this. The temperature rise under adiabatic conditions was used to calculate the entropy change of the transformation and gave ΔSβ2 - β2 = - 1.03 ± 0.07 J/mol K, in excellent agreement with tke value of - 1.00 ± 0.17 J/mol K found from the Clausius-Clapeyron equation. The variation of the entropy change with specimen temperature was small and could be considered constant within experimental error.     

Laser Repair of Superalloy Single Crystals with Varying Substrate Orientations

The casting and repair of single-crystal gas turbine blades require specific solidification conditions that prevent the formation of new grains, equiaxed or columnar, ahead of the epitaxial columnar dendrites. These conditions are best determined by microstructure modeling. Present day analytical models of the columnar-to-equiaxed transition (CET) relate the microstructure to local solidification conditions (temperature gradient and interface velocity) without taking into account the effects of (1) a preferred growth direction of the columnar dendrites and (2) a growth competition between columnar grains of different orientations. In this article, the infiuence of these effects on the grain structure of nickel-base superalloy single crystals, which have been resolidified after laser treatment or directionally cast, is determined by experiment and by analytical and numerical modeling. It is shown that two effects arise for the case of a nonzero angle between the local heat flux direction and the preferred dendrite growth axis: (1) the regime of equiaxed growth is extended and (2) a loss of the crystal orientation of the substrate often occurs by growth competition of columnar grains leading to an “oriented-to-misoriented transition” (OMT). The results are essential for the definition of the single-crystal processing window and are important for the service life extension of expensive components in land-based or aircraft gas turbines. This article is based on a presentation made in the symposium entitled “Solidification Modeling and Microstructure Formation: In Honor of Prof. John Hunt,” which occurred March 13–15, 2006, during the TMS Spring Meeting in San Antonio, Texas, under the auspices of the TMS Materials Processing and Manufacturing Division, Solidification Committee.     

浅析砷锑在铜电解过程中的行为

通过对铜电解过程中阳极铜、阳极泥、砷锑渣、电解液悬浮物、电铜中杂质元素存在形态的分析 ,探讨砷锑在铜电解过程中的行为 ,以寻求稳定铜电解生产过程和提高电铜质量的方法