Influence of high-energy impact actions on the elastic and anelastic properties of martensitic Cu–Al–Ni crystals

The influence of high-energy impact shock-wave loading on the microplasticity and macroscopic performance of the Cu–Al–Ni crystals in the β₁′ martensitic phase has been studied. Elastic and anelastic properties of quenched and aged polyvariant single crystals before and after impact shock-wave loading were measured in the temperature range 80–300 K, at a frequency of about 100 kHz in the strain amplitude-independent and amplitude-dependent ranges by means of the composite oscillator technique, and in the MHz frequency range using the pulse–echo technique. High-velocity impact loading of the specimens was realised by plane shock-waves with stress pulses with a duration of 2·10⁻⁶ s and stress amplitudes up to 5 GPa. A pronounced influence of impact shock-wave loading on the elastic and anelastic properties of the β₁′ martensite has been observed. A strongly marked softening of the material and an enhancement of damping properties are revealed up to the highest stress pulse amplitudes. This behaviour differs fundamentally from the one observed in ‘ordinary’ fcc metals. Changes of the defect structure induced by shock-wave loading, which may be responsible for the observed phenomena, have been discussed.     

Magnetic held dependence of elastic modulus and resistance in La2/3Ca1/3MnO3

We have measured the magnetic field dependence of the anelastic modulus and the electric resistance of a ceramic sample of the magnetoresistant perovskite La_2/3Ca_1/3MnO₃ around the metal–insulator transition by the vibrating reed technique (2.5 KHz). Previous work [1] showed that the modulus becomes higher while the internal friction has a peak at the transition temperature (T_c=262 K). In this work, improvements made on the equipment allowed us to measure at constant deformations (<10⁻⁵) and magnetic fields up to 4500 Gauss. We made isothermal measurements of internal friction, modulus and resistance as a function of an applied magnetic field. We found that most of the changes induced by the magnetic field take place in a few degrees (almost 5 K) near the transition temperature where the changes in resistance are more important. Up to the highest magnetic field applied, we found 3% maximum variations of the modulus and no hysteresis while cycling the magnetic field. We suppose that the experiment is placed in the linear response of the inverse Wiedemann effect [2], due to the small deformations used, and that the ferromagnetic domain structure is responsible for the observed effects. Some additional measurements are needed (magnetic hysteresis loops) to be compared with our results.     

Measurement of elastic modulus and evaluation of viscoelasticity of foundry green sand

Elastic modulus is an important physical parameter of molding sand; it is closely connected with molding sand's properties. Based on theories of rheology and molding sand microdeformation, elastic modulus of molding sand was measured and investigated using the intelligent molding sand multi-property tester developed by ourselves. The measuring principle was introduced. Effects of bentonite percentage and compactibility of the molding sand were experimentally studied. Furthermore, the essential viscoelastic nature of green sand was analyzed. It is considered that viscoelastic deformation of molding sand consists mainly of that of Kelvin Body of clay membrane, and elastic modulus of molding sand depends mainly on that of Kelvin Body which is the elastic component of clay membrane between sands. Elastic modulus can be adopted as one of the property parameters, and can be employed to evaluate the viscoelastic properties of molding sand.     

Elastic behavior of La0.67Ca0.33MnO3:ZrO2 composites

A series of Colossal Magneto Resistance materials, with compositional formula (1 − x) La_0.67Ca_0.33MnO₃ + xZrO₂ (where x = 0%, 10%, 20%, 40%, 60%, 80%) were prepared by sol–gel technique. When characterized structurally by X-ray diffraction they are found to have cubic structure. After measuring their bulk densities, the ultra sonic longitudinal (V_l) and shear velocities (V_s) were measured at room temperature using the pulse transmission technique. Using the ultrasonic data, the values of Young's and rigidity moduli along with Poisson's ratio and Debye temperatures have been calculated. As the materials are porous, zero porous elastic moduli have also been arrived at using a well-known model. The observed variation of elastic moduli with varying ZrO₂ concentration has been explained qualitatively.     

Towards understanding anelasticity of the β1′ martensitic phase of Cu–Al–Ni

The present work continues the series of experimental investigations undertaken in order to elucidate the mechanisms controlling elastic and anelastic properties of the β₁′ martensitic phase of Cu-based shape memory alloys. The paper reports an attempt to distinguish between ‘dislocation’ and ‘interface’ mechanisms of the internal friction in the β₁′ martensitic phase of Cu–Al–Ni single crystals. Two types of experiments have been performed. First, the ultrasonic strain amplitude-independent and amplitude-dependent internal friction (ADIF) of a monovariant specimen for temperatures 90–300 K is carefully re-examined. Second, in situ measurements of the ADIF and of the influence of ultrasonic oscillations on the plastic deformation (acoustoplastic effect) were carried out during quasistatic deformation of a quenched polyvariant specimen. Experimental results support a dislocation rather than an interface mechanism of anelasticity, at least at ultrasonic frequencies and moderate strain amplitudes.     

Nonlinear electromechanical behaviour of KDP near its phase transition

Potassium dihydrogen phosphate (KDP) undergoes a ferroelectric phase transition at 123 K. The linear elastic and electromechanical properties are well known. This paper deals with simultaneous measurements of the transit time and the attenuation variations of pulsed ultrasound in parallelepiped samples of KDP using a picosecond sampling oscilloscope. These variations are introduced by low frequency electric fields. The results can be used to determine complex nonlinear piezoelectric coefficients above and below the phase transition of KDP.     

Formation of Yb α-SiAlON whiskers by heat treatment of hot-pressed bulk samples

Novel α-SiAlON whiskers with various morphologies were produced at the surface of hot-pressed bulk samples by heat treatment at an elevated temperature of 1800 °C. Other than straight whiskers with or without nodules on their heads, curved bow-like and kinked whiskers were also observed. The growth mechanisms of different whiskers were discussed in detail, and it was proposed that the VLS (vapour–liquid–solid) mechanism was the predominant growth mode responsible for the formation of a majority of whiskers. With continuous vaporization and consumption by reactions, the liquid droplet necessary for VLS would be exhausted in some cases, and at this time VS mechanism could also become active.     

Effect of precipitation on elastic modulus of Al-Zn-Mg-Cu-Li alloys

Al-5.6Zn-3.0Mg- 1.6Cu- 1.1Li-0.24Cr alloys and Al-8.0Zn-2.4Mg-2.4Cu- 1.1Li-0.18Zr altoys （mass fraction, %） were aged by different processes. The microstructure and mechanical properties were determined by transmission electron microscopy（TEM）, tensile test and Vicker＇s hardness test. The experimental results show that the most signified hardening is obtained by double-ageing or multi-ageing for the Al-Zn-Mg-Cu-Li alloys. The yield strength and the elastic modulus of the Li-containing alloys have relationships with ageing processes. The elastic modulus of Li-containing alloys decreases with the increment of precipitates though it is higher than that of Al-Zn-Mg-Cu alloy.     

Further remarks on the modelling of elastic modulus of grinding wheels

A modified non-dimensional group for modelling the elastic modulus of grinding wheels is proposed and thoroughly discussed. Specific attention is paid to the temperature effect on the variations of the modulus. A new factor called processing parameter is successfully defined to reflect the behaviour of a wheel influenced by the manufacturing processes. The well constructed 3-D diagram shows that the variation of the non-dimensional elastic modulus is well represented by the present prediction and that the proposed method is convenient for both theoretical and engineering applications. In order to offer guidelines for engineers in drawing simple relations from the presented governing parameters, formulation procedures are clearly detailed through some illustrative examples.     

Internal friction and elastic properties of the high pressure-induced phases of solid C60

Solid C₆₀ is a new promising material made from giant high-symmetric carbon clusters. Though C₆₀ molecules are extremely stable at ambient conditions, heat treatment under high pressures induces transformations to other phases, in which some weak van der Waal-type bonding between C₆₀ molecules is replaced with covalent sp³ bonds. Many new C₆₀ high pressure phases (HP) demonstrate a set of unique physical properties including mechanical and elastic ones. This paper is an analytic review of the experimental measurements of the elastic and dissipative properties of solid C₆₀ (from C₆₀ single crystal to C₆₀ ultrahard phase).     

钢的高温弹性模量E值的测定研究

介绍了根据实际生产需要测试20#钢的高温弹性模量E值的方法和依据的原理、试件的设计、加热温度设定和试验结果。     

Internal friction and Young’s modulus of V–Ti–Cr alloy before, during and after proton irradiation

Using a composite oscillator, the Young’s modulus and the internal friction of annealed, plastically bent and bent–straightened V–4Ti–4Cr alloy specimens have been measured, in a wide amplitude range, before, during and after proton irradiation. The proton energy and flux were 8 MeV and 10¹² p cm⁻² s⁻¹. The in situ dependencies on the proton beam current and temperature have been obtained. Softening and overheating (which looks like softening–strenghtening of the alloy) effects, which arise due to radiation damage, have been revealed. The influence of beam heating and defect accumulation–annihilation on the acoustic properties of the annealed and pre-strained samples, during and after proton irradiation, are briefly discussed.     

Simplified prediction model for elastic modulus of particulate reinforced metal matrix composites

Some structural parameters of the metal matrix composite, including particulate shape and distribution do not influence the elastic modulus. A prediction model for the elastic modulus of particulate reinforced metal matrix Al composite was developed and improved. Expressions of rigidity and flexibility of the rule of mixing were proposed. A five-zone model for elasticity performance calculation of the composite was proposed. The five-zone model is thought to be able to reflect the effects of the MMC interface on elastic modulus of the composite. The model overcomes limitations of the currently-understood rigidity and flexibility of the rule of mixing. The original idea of a five-zone model is to propose particulate/interface interactive zone and matrix/interface interactive zone. By integrating organically with the law of mixing, the new model is found to be capable of predicting the engineering elastic constants of the MMC composite.     

Fracture of metallic glasses at notches: Effects of notch-root radius and the ratio of the elastic shear modulus to the bulk modulus on toughness

The Anand–Su theory for large elastic–plastic deformations of metallic glasses is modified to account for the strongly nonlinear and eventually softening dilatational volumetric elastic response of these materials. Using this theory, we have conducted finite-element simulations of fracture initiation at notch tips in a representative metallic glass under Mode-I, plane-strain, small-scale-yielding conditions. We show that our theory predicts three important experimentally observed phenomena: (a) fracture initiates ahead of the notch root, where the mean normal stress reaches a maximum value; (b) the fracture toughness increases linearly with the square-root of the notch-tip radius; and (c) the fracture toughness decreases as the ratio of the elastic shear modulus to the bulk modulus increases.     

Ag/Cu/Fe复合材料的界面研究

采用Ag／Cu／Fe层状预复合、热挤压工艺,制备了Ag／Cu／Fe系层状复合材料。使用电子探针技术研究了在热处理条件下,材料的界面结构变化和扩散过程,得出了扩散层厚度、扩散速度、扩散激活能与热处理条件的相互关系。     

Hardness and elastic modulus of amorphous and nanocrystalline SiC and Si films

Hydrogen-free amorphous and nanocrystalline films were prepared by magnetron sputtering of the SiC or Si targets. Mechanical properties (hardness, elastic modulus, intrinsic stress) and film structures were investigated in dependence on the substrate bias and temperature. It was found that both hardness and elastic modulus of all amorphous a-SiC films prepared at different substrate temperatures and biases are always lower than those for bulk α-SiC single crystal while the hardness of partially crystalline SiC films is higher and the elastic modulus lower than those for α-SiC one. In contrast, both hardness and elastic modulus of all amorphous Si films are always lower than those for nanocrystalline Si films which show approximately the same value as the Si single crystal.     

铸钢表面WC-高碳铬铁铸渗层冲击的磨损性能

采用铸渗工艺,在铸钢表面获得了一层均匀、耐磨且与母材为冶金结合的高铬铸铁基碳化钨粒子增强复合层.在MLD-10动载磨料磨损试验机上对不同质量分数WC的复合材料进行了冲击磨损性能的研究,并分析了磨损机理.结果表明,复合材料具有良好的抗冲击磨损性能.当WC的质量分数在20%～30%时冲击磨损性能最好.与ZG25相比,复合层的耐冲击磨损性能远远高于铸钢.     

The effect of dopant Cu, Fe, Ni or La on the structures and properties of mesoporous Co-Ce-O compound catalysts

A series of Co-Ce-O mesoporous catalysts doped with Cu, Fe, Ni or La and the undoped one were synthesized by using tri-block copolymer P-123 as the template. These catalysts show wormhole-like structures, high surface areas (144–167 m²/g) and uniform meso-pore size distributions (4.0–4.8 nm) after calcination at 500 °C. The activity for low-temperature CO oxidation and the thermal stability of the mesoporous Co-Ce-O catalyst are largely modified by the dopant Cu, Fe, Ni or La in different ways. It is revealed by in situ diffuse reflectance infrared spectroscopy that CO oxidation over all the samples except the Ni-doped one undergoes carbonates pathway. In this case, the oxidation activities of the catalysts are mainly determined by the mobility of surface lattice oxygen species, which is indicated by the temperature-programmed reduction and desorption results. Doping with Cu greatly enhances the oxidation activity of Co-Ce-O catalyst at the calcination temperatures of 500 °C and 650 °C, and doping with La significantly improves its activity at the calcination temperature of 800 °C. However, doping with Fe always decreases the activity of Co-Ce-O catalyst regardless of the calcination temperature. Largely different from other dopants, the addition of Ni induces a change of the mechanism for CO oxidation and results in a remarkable decrease in the activity.