High Strain Rate Deformation Behavior of Zirconium at Elevated Temperatures

High temperature mechanical behaviors of zirconium at high strain rate of 103 s-1 were studied by split Hopkinson pressure bar (SHPB).The influences of strain rate and temperature on the micro-structural evolution,as well as the occurrence of shear localization and subsequent fracture,were also investigated.It s found that the compressive stress-strain response depends sensitively on the applied strain rate and test temperature.Micro-structural observations revealed that the density of the twinning grains r...     

FeAl金属间化合物的高温变形行为

对Ｆｅ－３６．５ａｔ％Ａｌ金属间化合物进行了高温拉伸试验研究。结果表明，变形温度在６００－１０００℃范围内，这种ＦｅＡｌ合金的延伸率随温度的升高不断增加，在１０００℃时延伸率最高，达１１５％。经透射电镜分析，该合金高温变形后不仅有大量的滑移位错线，而且有一定数量的位错绻线存在。     

Ti60合金热变形行为与应变补偿型本构模型

目的 确定Ti60合金在高温下的应变行为,促进材料性能的优化和工程应用的发展。方法 在变形温度为900、950、990、1 020、1 050℃,应变速率为0.001、0.01、0.1、1、5 s^-1,最大变形量为60%条件下,利用Gleeble-3800热模拟实验机对Ti60试样进行不同应变速率的热压缩实验。结果 Ti60合金的高温流变应力-应变规律如下：当温度一定时,随着应变速率的升高,峰值应力上升,当温度和应变速率一定时,随着应变的升高,应力表现为先上升后下降的趋势,而在1 020℃、0.01s^-1条件下,表现反常,这可能与第二相的动态析出有关。不同真应变下的变形激活能Q=838.996 201 9 kJ/mol,相应的本构方程相关系数n=2.889 582,α=0.013 182 009,A=1.335 7×10³³,建立了Ti60合金热变形Arrhenius本构关系模型■,用于预测和优化Ti60合金在高温条件下的峰值应力。采用应变补偿方法计算了五次多项式的各个系数和其他应变对应的应力。通过比较由模型计算得到的流...     

Cyclic Creep Deformation and Fracture of a Cr-Mo Rotor Steel at Elevated Temperatures

Static creep and cyclic creep tests were carriedout on a Cr-Mo rotor steel from 0.5 to 0.6 T_m.Cyclic creep retardation occurred under the testconditions.With an increase of stress frequency,cyclic creep strain rate decreases and rupture timeincreases.The cyclic creep strain rate for the stresswave of a square shape is higher than that of a tri-angle shape.The apparent stress exponent of cycliccreep and the apparent activation energy of cycliccreep are both higher than those of static creep.Theminimum strain rate is inversely proportional torupture time for both static and cyclic creeps at dif-ferent stresses,temperatures,frequencies and waveshapes.The cyclic creep retardation mechanism wasexplored by the observation and analysis of the dis-location structure and fracture surface.     

Verification of Dislocation Density and Dynamic Recrystallization in Deformed Pure Copper

Strength of Materials - The mechanisms of dynamic recovery and dynamic recrystallization significantly affect the mechanical behavior and microstructure of the materials deformed at high...     

金属塑性变形的本构模型研究

根据位错动力学理论,忽略动态应变时效因素,将塑性变形的流变应力分解为非热应力、热激活应力和粘拽阻力3部分,建立了一个基于物理概念的本构模型。对HSLA-65结构钢的力学行为进行了研究,试验温度为77～700K,应变率为0.001～0.1s-1,真实塑性应变超过60%。结果表明,塑性流变应力随温度的降低、应变和应变率的增加而增大;在一定的温度和应变率范围发生动态应变时效现象,并且随应变率的提高,该现象将移向更高的温区。通过模型预测与试验结果的比较可知,所给本构关系能很好地描述较宽的温度与应变率范围内的塑性流变应力。     

Interface Interactions of Dissimilar Materials at Elevated Temperatures

This paper reviews some of the chemical interactions that occurred at the interface of ceramic/molten metal liquids. Control of interfacial reactions between dissimilar materials is an important issue in numerous technological applications, such as brazing of ceramics to metals, design of ceramic–metal composites, coatings of ceramics on metal substrates, and development of crucibles for melting of refractory metals. In ceramic/metal systems, wetting of the ceramic surface by the liquid metal is typically accompanied to some extent by interfacial reactions. The chemical incompatibility between the metal and non‐metallic materials can result in the formation of undesirable phases, due to the chemical and metallurgical reactions that take place during processing or in service. There is a need, therefore, to characterize the governing factors and reaction pathways at these interfaces. So, when the reaction products obtained during interdiffusion processing are not favorable, the diffusion pathway can be modified to control their formation.     

Calorimetric Study of Rubidium Hexafluoroarsenate at Elevated Temperatures

The heat capacity of rubidium hexafluoroarsenate, RbAsF₆, was measured from 300 to 700 K by differential scanning calorimetry. The results indicate that the structural transformation from the rhombohedral to the cubic phase occurs in the range 305–436 K through an intermediate stable phase and reaches isothermal completion in a narrow temperature range of 407–409 K. The enthalpy of the transformation is 10.90 ± 0.03 kJ/mol, and its entropy is 26.39 ± 0.08 J/(K mol) = Rln24, which suggests that this structural transition is of the order–disorder type. The heat capacity data are used to evaluate the thermodynamic properties of RbAsF₆ in the range 300–700 K.     

Search for New High-Tc Superconductors at Elevated Temperatures

Journal of Superconductivity and Novel Magnetism - One of the long-standing challenges in experimental superconductivity are the sustained efforts to achieve stable and cheap superconducting...     

Phonon Modes in CMR Manganites at Elevated Temperatures

Phonon modes of the colossal magnetoresistance manganites La_0.7Ca_0.3MnO₃ and La_0.8Li_0.2MnO₃ have been investigated by far-infrared (100–700 cm^–1) reflectivity spectroscopy at elevated temperatures (300–800 K). The three principal optical phonons all move systematically to lower frequency as temperature increases, in accordance with a Grüneisen relationship. The La(Ca,Li)–(MnO₃) vibration (170 cm^–1) varies with cation mass as expected. The Mn–O stretching mode (580 cm^–1) has a higher frequency in the Li-doped compound than in the Ca-doped, whereas the O–Mn–O bending mode )340 cm^–1) occurs at the same frequency in each, demonstrating that the cation strongly influences the Mn–O– length but not the bond angle.     

A New Analytical Model for the Flow Stress of Twin-roll Casting Magnesium Sheet at Elevated Temperatures

To evaluate the flow stress of the twin-roll casting magnesium sheet in high temperature forming processes,a new analytical model was proposed by analyzing stress-strain curves measured under various temperatures and strain rates.The model can be parameterized to reflect the volume fraction of semi-sold grain and sold grains undergoing twinning.By applying the new model,the result showed that the simulated stress-strain curves fit the experiment data very well.Such curve fitting can be employed for any magn...     

Thermal Expansion and Shrinkage of Unidirectional Composites at Elevated Temperatures

Strength of Materials - The model of multiphase media analyzes the effectiveness of describing thermal expansion and shrinkage of unidirectional polymer composites at their uniform heating by...     

Mechanisms of Fatigue in Cemented Carbides at Elevated Temperatures

Cemented carbides are mainly used as cutting tools in various fields of application. In nearly all industrial uses they have to resist wear and concurrent complex thermomechanical loading, often including alternating mechanical loads at high temperatures. It has been shown that cemented carbides suffer lifetime‐limiting fatigue under cyclic loads at 25 °C caused by subcritical crack growth. Present investigations show that strong, temperature‐dependent fatigue effects occur in cemented carbides at elevated temperatures. TEM investigations revealed temperature‐dependent processes that are responsible for the changes in the fatigue behavior: at low temperatures a phase transformation of the Co‐binder phase and at higher temperatures oxidation in the cracks and brittle–ductile transitions of cubic carbides.     

细颗粒掺杂石墨高温热导率的研究

通过球磨分散方法制备了具有优良热机械性能的细颗粒掺杂石墨.该掺杂石墨材料具有致密的结构,细小的碳化物颗粒均匀分布在石墨基体中.研究表明;球磨分散方法制备的掺杂石墨比常规方法制备的石墨材料具有更优良的高温热性能以及抗热震性能.同时,本文对材料的性能与其微观结构进行关联.     

Electrical Resistance of CdSe and CdTe at Elevated Temperatures and Pressures

The electrical resistance of polycrystalline CdSe and CdTe was measured as a function of temperature (up to 560 K) and pressure (up to 5.5 GPa). The resistance change across the phase transition and the transition onset pressure were found to decrease linearly with increasing temperature. The band gap of the low-pressure phases of CdSe and CdTe decreases with increasing pressure. The rapid reduction in the resistance change with increasing temperature restricts the use of CdSe and CdTe as high-temperature pressure calibration standards.     

纯钼薄板各向异性拉压不对称性本构建模研究

目的 对纯钼薄板的各向异性、拉压不对称性以及本构关系进行研究.方法 对纯钼薄板进行不同方向的单拉实验、中心带孔试样单拉实验,和纯钼薄板V形弯曲实验,同时结合有限元模拟反推材料力学性能以及对CPB06屈服准则及Swift强化模型进行参数标定,并进行模型可靠性验证.结果 纯钼薄板具有一定的面内各向异性、拉压不对称性以及显著...