Investigation of low-temperature electron relaxation by zero sound attenuation

We develop a new method of investigation of low-temperature electron relaxation \in metals, based on the analysis of the temperature dependences of the attenuation of zero sound excited by ultrasonic pulses. We have discovered that these dependences obtained in the temperature region about of 1–8 K reproduce directly the temperature behavior of the electron scattering rate. The main features of our method are its insensitivity to small-angle scattering and the additivity of contributions of various relaxation processes to the total scattering rate. Both the theoretical analysis of zero-sound propagation in various damping regimes and special experiments produced for gallium confirm the validity of our consideration. We have identified the considerable contribution of electron-electron collisions in all investigated metals (gallium, aluminum, molybdenum, and tungsten) in the whole studied temperature interval and established the dominating role of Umklapp processes in the zero-sound damping at T >- 4 K for gallium and most probably for tungsten. We interpret the latter result as the first experimental observation of Peierls' exponent in polyvalent metals in zero magnetic field. The values obtained for electron-electron and electron-phonon scattering rates are compared with known experimental data and theoretical estimations.     

Measurement of density,sound velocity,surface tension,and viscosity of freely suspended supercooled liquids

Noncontact methods have been implemented in conjunction with levitation techniques to carry out the measurement of the macroscopic properties of liquids significantly cooled below their nominal melting point. Free suspension of the sample and remote methods allow the deep excursion into the metastable liquid state and the determination of its thermophysical properties. We used this approach to investigate common substances such as water,v-terphenyl. succinonitrile, as well as higher temperature melts such as molten indium, aluminum, and other metals. Although these techniques have thus far involved ultrasonic, eletromagnetic, and more recently electrostatic levitation, we restrict our attention to ultrasonic methods in this paper. The resulting magnitude of maximum thermal supercooling achieved has ranged between 10% and 15% of the absolute temperature of the melting point for the materials mentioned above. The methods for measuring the physical properties have been mostly novel approaches, and the typical accuracy achieved has not yet matched the standard equivalent techniques involving contained samples and invasive probing. They are currently being refined, however, as the levitation techniques become more widespread and as we gain a better understanding of the physics of levitated liquid samples.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–34, 1994, Boulder, Colorado, U.S.A.     

Structure, properties, and applications of ceramic composite produced of nanostructured powders of composition ZrO2 + 3% Y2O3

The results of the investigations of a ceramic composite sintered from ZrO₂-based powders produced by ultrasonic spray pyrolysis have been considered. The scratch tests and microcutting with a single diamond grain have been used to evaluate the strength and deformation properties of surface layers of the resultant composite. The possibility to apply these composites in finishing products of non-ferrous metals has been discussed.     

Higher order elastic constants of rare earth metals: gadolinium,dysprosium and erbium

The expressions for the second and third order elastic constants of the rare earth metals, gadolinium dysprosium and erbium have been worked out and their values have been determined. The present theoretical values are compared with the experimentally observed results. It is also suggested that the third order elastic constants of these metals may be measured using ultrasonic technique under high pressures.     

面向电子制造的功率超声微纳连接技术进展

为满足电子制造与封装对新材料与工艺的迫切需求,尤其是高功率、高温服役、高集成度以及高可靠性等新型器件的连接难题,开发了面向电子制造的功率超声微纳连接技术。从固相键合、超声复合钎焊和超声纳米连接3个方面,综述了面向电子制造的功率超声微纳连接技术的原理方法、优势与应用场合。功率超声由于其表面清洁、声流和空化作用,将大幅提升冶金反应速率,有效解决了传统TLP反应温度高时间长,以及Cu和Al等金属的易氧化等问题,甚至攻克了Al2O3,AlN,SiC等陶瓷基板的难润湿以及低温纳米颗粒烧结驱动力不足的难题。综述了该领域多年来的研究成果,聚焦电子制造中的功率超声微纳连接技术,从固相连接领域的引线键合、室温超声金属连接和超声增材制造,到钎焊领域的超声低温软钎焊、超声中高温连接以及超声瞬态液相连接,最后针对第三代半导体高功率器件简述了超声纳米连接,探讨了功率超声微纳连接技术的研究进展及趋势。     

Effective temperature rise during propagation of shock wave and high-speed deformation in metals

Two theoretical models are developed for the calculations of temperature rise during high-speed deformation and shock wave propagation. In the first model the calculations of the temperature distribution in metals during high-speed deformation are based on a model where the stationary high-speed deformation is considered as a propagation of shock wave with some fixed velocity in these metals. In this model the self-consistent system of equations describing the equation of state of metals and the conservation laws for momentum, energy and flow of energy is used for the determination of the temperature profile in the front of shock wave. The numerical calculations of the temperature distribution profile in shock wave front have been performed using the microscopic Thomas–Fermi–Dirac model for such metals as Al, Cu and Fe. In the second theoretical model the process of high-speed deformation is considered as an adiabatic process where a fraction of plastic deformation is converted into heat. The results of the numerical calculations of temperature rise during high-speed deformation in the dependence of strain to fracture are presented for metals: Al, Cu, Ni and Fe. It was shown that using these models the temperature during high-speed deformation can increase in different metals up to 1000 K.     

Green synthesis of colloidal silver nanoparticles by sonochemical method

A facile sonochemical method was developed for preparing colloidal silver nanoparticles (Ag-NPs) in aqueous gelatin solutions. The effect of the reducing agent and Ag⁺ concentrations, ultrasonic time, and ultrasonic amplitude on the particle size has been investigated. The size of the Ag-NPs decreases with the ultrasonic amplitude and increases with ultrasonic time. Well-dispersed spherical Ag-NPs with a mean particle size of about 3.5 nm have been synthesized under ultrasonic process. The use of gelatin as an eco-friendly stabilizer provides green and economic attributes to this work. This preparation method is general and may be extended to other noble metals, such as Au, Pd and Pt, and may possibly find various additional medicinal, industrial and technological applications.     

Characterization of solutionizing behavior in VT14 titanium alloy using ultrasonic velocity and attenuation measurements

VT14 titanium alloy (Ti–4.5Al–3Mo–1V) was subjected to a series of heat treatments consisting of solutionizing for 1 h at the selected temperatures in range of 923–1323 K at an interval of 50 K, followed by water quenching. Hardness and optical microscopy results are correlated with ultrasonic longitudinal and shear wave velocities and attenuation in these specimens. Ultrasonic velocities and hardness decrease with solution annealing temperature (SAT) in the 923–1123 K range. Beyond 1123 up to 1223 K, they increase slightly. Beyond 1223 K, ultrasonic velocities become constant, whereas hardness increases up to 1323 K. Ultrasonic attenuation exhibits an opposite behavior to velocity and hardness. Further, for the first time, authors have shown that ultrasonic velocity can be used to identify the β-transus temperature in this alloy. Because of non-monotonous variation of velocity and attenuation with solutionizing temperature, it was not possible to identify the SAT using any one of these parameters. Hence, a new parameter, ratio of normalized differential of ultrasonic attenuation to normalized differential of ultrasonic velocity (RNDAV) has been used, which is found to increase monotonously with SAT and hence enabling unambiguous characterization of SAT in solution annealed VT14 alloy.     

超声波在金属凝固中的应用与发展

简要介绍了超声波及其基本特性，综述了高能超声对金属凝固过程作用方面的研究和应用状况，提出超声处理是改善金属凝固组织，提高力学性能的有效方法，并对21世纪超声凝固细晶技术的前景进行了展望。     

Ultrasonic Torsion Welding of Sheet Metals to Cellular Metallic Materials

One of the most important requirements for finding new applications for cellular metals is to integrate them in complex technical structures. The metal foams have to be joined to each other, or to sheet materials, by suitable joining techniques. The main topics of this paper are the ultrasonic torsion welding of cellular metallic materials to sheet metals and the investigation of the mechanical properties of the joints. The basic materials of foams and sheet metals were different aluminum and iron alloys. Depending on the materials used, weldings with tensile shear strengths of up to 25 MPa were realized. Using aluminum foam sandwich (AFS) and sheet metals, successful weldings were performed before and after the foaming process. Furthermore, it was possible to perform a successful foaming process with the unfoamed AFS/sheet metal joints. Microscopic investigations showed that the ultrasonic welding technique allows the joining of the metal foams with sheet metals without significant deformation of the joining partners. The temperatures during the welding process in the interface were below the melting point of the foams and the sheet metals.     

Measurement Interpretation and Uncertainty Resulting from Nonlinear Ultrasonic Wave Propagation

Nominally identical ceramic-element ultrasonic transducers, of the type used in the aerospace and metals industries for nondestructive evaluation (NDE), often have variability in the peak pressure of the generated ultrasonic pulses. The generated pressures are also high enough for nonlinear propagation to be present in the water medium, often used as coupling in these types of inspections. In this study, a measurement system for monitoring ultrasonic pulse pressure level and nonlinear propagation in water is presented. Several different industrial NDE measurement applications are examined to quantify the impact of variable pressure and nonlinear propagation with respect to test interpretation and measurement uncertainty. In particular, pulse frequency content, velocity measurements, reference block calibrations, and beam-width measurements are examined. In addition, an experimental demonstration of why nonlinear pulse distortion is not normally observed in practice is presented.     

Ultrasonic attenuation calculations for magnesium,zinc, and cadmium. I. Longitudinal waves

The ultrasonic attenuation due to conduction electrons has been calculated for the hexagonal metals magnesium, cadmium, and zinc using the real metal theory of Pippard and Fermi surfaces of these metals based on band structure calculations. For most cases when the calculations are compared with experimental data excellent agreement is obtained. Since the calculations assume isotropic deformation parameters, the ultrasonic attenuation is determined principally by strictly geometrical features of the Fermi surface.Supported in part by the NSF. Part of this work was carried out by J.T. at the University of Arizona under support of a Faculty Fellowship awarded by John Carroll University.     

Ultraschallverfahren zur Bestimmung der Anzahl von Einschlüssen in Materialproben — eine kritische Betrachtung empfohlener Methoden

Ultrasonic test procedure to determine the number of inclusions in material samples — a critical analysis of recommended methods. To judge the specific properties of metals one tries to determine the quantity and distribution of the non-metallic inclusions. But the microscopic procedures used so far are destructive and do further not refer to the volume, but rather to the surface of the micrograph sample. Contrary to these methods the inspection by ultrasound is non-destructive and wellsuited for the volumetric detection of inclusions. The possibilities of the ultrasonic pulse-echo-method for cleanliness rating are being checked. Based on the respective results there is a critical view on the ultrasonic test methods which have been recommended so far. Proposals will be made how to make the optimum use of the advantages of the ultrasonic inspection when determining the purity degree of a sample.     

Advanced technologies developed at the All-Russia Institute of Light Alloys (VILS) for production of materials with enhanced behavior

A number of innovative metallurgical processes and products developed by the All-Russia Institute of Light Alloys (VILS) are discussed. These include rapid solidification, advanced casting, innovative high temperature isostatic pressing, improved inspection techniques, mechanical alloying, diffusion bonding, composite materials, and ultrasonic processing. The latter applied to enhanced processing of molten metal and as a cleaning technique. Consideration is given to both metals, intermetallics and ceramics; and inspection techniques. Implementation into the commercial segment of the economy requires much greater concern over cost considerations than in the past.     

Properties of transverse ultrasonic transducers of ferroelectricpolymers working in thickness shear modes

Shear piezoelectric properties of poly(vinylidene fluoride) (PVDF) and copolymer of vinylidene fluoride and trifluoroethylene [P(VDF/TrFE)] have been studied precisely in a wide temperature range from 10 to 400 K. It was found that these polymers have the shear electromechanical coupling factors k₁₅ and k₂₄ large enough to be utilized for transverse ultrasonic transducers operating in a wide frequency range and in a wide temperature range below 400 K. Shear mode ultrasonic transducers of P(VDF/TrFE) were fabricated and their performances were studied both experimentally and theoretically. The shear polymer transducers are useful for generation and detection of transverse ultrasonic waves     

Ultrasonic assisted fabrication of particle reinforced bonds joining aluminum metal matrix composites

This paper presents a method of producing uniform particle strengthened bonds between pieces of aluminum metal matrix composite (Al-MMCs), of strength equal to that of the substrate material. SiC particle reinforced Zn-based filler metals were fabricated by mechanical stir casting and ultrasonic treatment, and then used to join pieces of SiC_p/A356 composite with the aid of ultrasonic vibration. The filler metals made by mechanical stirring were porous and contained many particle clusters. Ultrasonic vibration was used to disperse the agglomerates and prevent further coagulation of SiC particles during joining, but the method failed to eliminate the porosity, resulting in a highly porous bond. The filler metal treated by ultrasonic vibration was free of defects and produced a non-porous bond strengthened with uniform particles between pieces of SiC_p/A356 composite. The presence of surface oxide films at the bonding interface significantly degraded the performance of SiC particle reinforced bond. Removal of this oxide film by at least 4 s of ultrasonic vibration significantly increased the bond strength, reaching a value equal to that of the substrate metal.     

Dynamic mechanical and ultrasonic properties of polyurea

Dynamic mechanical analysis (DMA) and ultrasonic measurements were carried out to study the temperature and frequency dependences of viscoelastic properties of polyurea. Master curves of Young’s storage and loss moduli were developed from the DMA data. Relaxation spectra were subsequently calculated by means of two approximate models, and the apparent activation energy of molecular rearrangements was also determined based on the temperature dependence of the time-temperature shift factor. Velocity and attenuation of longitudinal and shear ultrasonic waves in polyurea were measured in the 0.5-2 MHz frequency range between −60 and 30 °C temperatures. The complex longitudinal and shear moduli were computed from these measurements. Combining these results provided an estimate of the complex bulk and Young’s moduli at high frequencies. The results of the DMA and temperature and frequency shifted ultrasonic measurements are compared and similarities and deviations are discussed.     

Residual Stress Distributions in Glass/Metal‐Joints produced by Ultrasonic Torsion Welding

The development and industrial application of efficient methods to join glass with metals which combine the individual advantages of both material groups are a great technological challenge. One research field of the Institute of Materials Science and Engineering is the production of glass/metal joints by means of ultrasound. Industrial applications are for example the sealing of glass vessels, fixtures in the vacuum technique or lens mounts. For this reason an industrial ultrasonic torsion welding system normally used for metal weldings was modified to be suitable for the demands of high sensitive glass/metal‐joints. With the developed welding system helium‐tight joints of glass and metals can be realized. In comparison to the conventional welding techniques [1] for glass like diffusion welding or adhesive bonding, ultrasonic torsion welding is characterized by very short welding times (< 1s) as well as low welding temperatures (< 450°C). Further advantages of this joining technique are the high automation potential and the environmental compatibility. Furthermore this technique can be applied under normal or specific atmospherical conditions. In spite of the low joining temperatures thermal residual stresses occur during the cooling of the joints due to the different coefficients of thermal expansion of the used materials [2]. In the present paper the measurement and calculation of the temperature distribution and the development of thermal residual stresses are described.     

Temperature dependence of the Anderson-Grüneisen parameter δ of Co,Ru, and Er

The third-order elastic (TOE) constants of cobalt, ruthenium, and erbium have been calculated as a function of temperature using the nearest neighbor central-force model of Srinivasan and Ramji Rao, taking into account the temperature variation of the second-order elastic (SOE) constants of the metal. The Anderson-Grüneisen (AG) parameter has been evaluated at different temperatures using the respective TOE constants at each temperature for the three metals. It is found that the AG parameter for these metals does not vary markedly with temperature.     

Ultrasonic attenuation in commercial lead-silicate glasses

The ultrasonic attenuation of a range of commercial lead—silicate glasses has been studied over the temperature range 4.2 to 360 K. Measurements of shear-wave ultrasonic attenuation,A, over the frequency range 5 to 50 MHz have revealed peaks in the attenuation below room temperature and these are interpreted in terms of the resonant movement of oxygen ions in the silica networks. In some cases the effects of the peaks are seen to extend to room temperature in some of these glasses. Frequency dependence of the attenuation,A, can be fitted to a relation of the formA F ^N , whereF is the frequency andN is a constant. Shear-wave velocities are also measured to aid characterization of the glasses.