Void initiation,growth, and coalescence in ductile fracture of metals

Ductile fracture in metals and alloys occurs through the coalescence of voids in the necked region of the specimen. While considerable information exists on the propagation of cracks, the mechanism of their initiation is still unclear. This paper reports onin situ electron microscope investigations aimed at an elucidation of crack initiation and the enlargement of crack nuclei to final rupture. Single crystal ribbons of silver 0.5 − 7.0 μm thick were pulled to fracture inside of a high voltage electron microscope (HVEM). After considerable necking, cracks initiated at the edges; their propagation occurred by the formation of microcracks ahead of the macrocrack, followed by the growth of the microcracks and finally their coalescence. Thesein situ experiments were complemented by stress-strain data obtained from fractured austenitic 304 stainless steel foils; subsequent examination of fracture surfaces in a scanning electron microscope allowed the accurate measurement of intervoid spaclngs. Inter-particle spacings were determined by HVEM. It was found that the average void density is 100 times larger than the average particle density. The combination and analysis of all experimental data led to a detailed model of void initiation and growth, which is based on a dislocation-vacancy mechanism and crystal plasticity.     

Zr-Sn-Nb合金的碘致应力腐蚀断口分析

为进一步提高压水堆燃料元件包壳材料锆合金的抗腐蚀能力，以满足新型核动力反应堆高燃耗和长寿期的要求，我国开发了属Zr．Sn．Nb系的两种新锆合金。碘致应力腐蚀开裂(I-SCC)是锆合金燃料包壳的失效形式之一。本文对I-SCC断口形貌及腐蚀产物进行分析，可加深对新型锆合金的应力腐蚀     

A mechanism of low-temperature stimulated processes in plasma anodization of metals and semiconductors

A mechanism of stimulation of low-temperature plasma anodization using a catalyst or ultraviolet radiation in the case of the formation of oxide films of metals and semiconductors is suggested. The stimulating effect of a catalyst or ultraviolet radiation on the process of plasma anodization is attributed to the appearance of an additional concentration of antibonding quasiparticles (electrons and holes) that weaken the chemical bonds in the anodized material. The conditions for implementing the stimulated processes are reported.     

Nature of impurity centers of rare-earth metals and self-organization processes in a-Si:H films

The existence of self-organization processes in a-Si:H:Er films and the appearance of an ordered structure of [Er-O] crystallites in the unordered structural network of a-Si:H:Er were ascertained. The principal parameter of the self-organization process was shown to be the control parameter, which is the [Er-O]-complex content in the a-Si:H:Er films. A decrease in the sizes of crystallites and an increase in the particle density leads to an increase in the photoluminescence intensity for λ=1.54 μm, i.e., to an increase in the optical activation of Er ions in the a-Si:H:Er films.     

受激布里渊散射和超声空化

激光场诱导介质电致伸缩，结果受激布里渊散射和超声波同时产生，由超声空化引起液体击穿．     

液体物质中的空化现象实验研究

采用自行研制的光偏转测试系统对强激光诱导液体物质的空化现象进行了实验研究。实验得到了激光等离子体冲击波传播规律和空泡的动力学特性。结果表明,激光等离子体冲击波在其传播过程中迅速衰减为声波;激光空泡的最大泡径随脉动次数增加依次减小,而收缩的最小泡径则由腔内含气量决定。     

Microstructural characteristics and vibration fracture properties of Sn-Ag-Cu-TM (TM=Co, Ni, and Zn) alloys

This study investigated microstructure thermal behavior, and mechanical properties of Sn-3.3Ag-0.5Cu alloys (SAC) with the addition of transition metals (TM, Ni, Co, and Zn). Results show that alloying with TM elements was able to reduce the degree of undercooling and strengthen SAC alloys. Among these elements, only Zn can raise the ductility. CoSn and Cu-Ni-Sn intermetallics appeared, respectively, in the Co-containing and Ni-containing samples while coarse Sn dendrites and a large area of eutectic phases could be observed in the specimens with Zn. These microstructural changes led to an inferior vibration fracture resistance under resonant vibration with a constant pull force.     

Thermochemistry of alloys of transition metals: Part III. Copper-silver, -titanium, -zirconium,and -hafnium at 1373 K

The enthalpies of mixing of liquid copper with liquid silver and with solid titanium, zirconium, and hafnium have been measured by high temperature reaction calorimetry at 1371 to 1373 K. A least squares treatment of the data for copper-silver alloys yields the following expression for the molar enthalpy of mixing: δH_mix = x_Agx_Cu(17.66-5.46 x_Ag) kJ mol^-1. The enthalpies of solution of solid titanium, zirconium, and hafnium in dilute solutions in liquid copper are all exothermic; the following values were found: -2.0 kJ mol^-1 for Ti, -52.5 kJ mol^-1 for Zr, and -46.3 kJ mol^-1 for Hf. These values are all significantly less exothermic than predicted by the semiempirical theory of Miedema. The enthalpies of formation of congruent melting intermetallic phases in the systems Cu-Ti, Cu-Zr, and Cu-Hf were measured by drop calorimetry or by solution calorimetry in liquid copper. The enthalpies of formation of the solid alloys have been compared with corresponding data for the liquid alloys.     

Cavitation erosion of laser quenched Fe--Aluminum bronze

Samples of C62500 aluminum bronze were treated by a continuous wave CO2laser to rapidly melt and quench the surface. This processing transformed the surface layer from multiphasebeta' + gamma_{2} +primary and secondary iron-rich δ to homogeneous, supersaturated single-phasebeta'solid solution. The cavitation erosion resistance of the laser quenched material far surpassed that of untreated C62500. The physically detrimental effect of the processing, i.e., roughening of the surface, appears to have been overridden by the positive microstructural changes in the surface layer.     

The Correlation Between Bubble-Enhanced HIFU Heating and Cavitation Power

It has been established that while the inherent presence of bubbles increases heat generation due to scattering and absorption, inertial cavitation is responsible for elevated heating during high-intensity focused ultrasound (HIFU) application. The contribution of bubble-induced heating can be an important factor to consider, as it can be several times greater than the expected heat deposition from absorption of energy from the primary ultrasound field. The temperature and cavitation signal near the focus were measured for 5.5-s continuous-wave 1.1-MHz HIFU sonications in tissue mimicking phantoms. The measured temperature was corrected for heating predicted from the primary ultrasound absorption to isolate the temperature rise from the bubble activity. The temperature rise induced from cavitation correlates well with a measurement of the instantaneous “cavitation power” as indicated by the mean square voltage output of a 15-MHz passive cavitation detector. The results suggest that careful processing of the cavitation signals can serve as a proxy for measuring the heating contribution from inertial cavitation.      

Maximum entropy fracture model and its use for predicting cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys

Appropriate constitutive, damage accumulation and fracture models are critical to accurate life predictions. In this study, we utilize the maximum entropy fracture model (MEFM) to predict and validate cyclic hysteresis in Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys through a damage enhanced Anand viscoplasticity model. MEFM is a single-parameter, information theory inspired model that aims to provide the best estimate for accumulated damage at a material point in ductile solids in the absence of detailed microstructural information. Using the developed model, we predict the load drop during cyclic fatigue testing of the two chosen alloys. A custom-built microscale mechanical tester was utilized to carryout isothermal cyclic fatigue tests on specially designed assemblies. The resultant relationship between load drop and accumulated inelastic dissipation was used to extract the geometry and temperature-independent damage accumulation parameter of the maximum entropy fracture model for each alloy. The damage accumulation relationship is input into the Anand viscoplastic constitutive model, allowing prediction of the stress–strain hysteresis and cyclic load drop. The damage accumulation model is validated by comparing predicted and measured load drops after 55 and 85 cycles respectively for Sn3.8Ag0.7Cu and Sn3.0Ag0.5 solder alloys. The predictions agreed to within 10% and 20% of the experimental observations respectively for the two alloys. The damage enhanced Anand model developed in this study will enable the tracking of crack fronts during finite element simulations of fatigue crack initiation and propagation in complex solder joint geometries.     

Heat-transfer phenomena in alloys

The phonon heat conductivity k _ph in Bi_{1 − x} Sb _x (x = 0.04–0.12) alloys is investigated in the temperature range of 6–60 K. The results are compared with the theory of solids at low temperatures, and the basic sources of phonon scattering are revealed. It is shown that phonon scattering at local mass changes dominates over other sources. The dependences of k _ph on composition are considered at temperatures of 60 and 90 K, and it is found that the normal N processes substantially affect the phonon scattering under these conditions. The donor-impurity effect on heat conductivity of Bi_0.88Sb_0.12 is considered, and the heat resistance caused by the phonon scattering at impurity centers is singled out.     

Passive Spatial Mapping of Inertial Cavitation During HIFU Exposure

A novel method for mapping inertial cavitation activity during high-intensity focused ultrasound (HIFU) exposure is presented. Inertial cavitation has been previously shown to result in increased heat deposition and to be associated with broadband noise emissions that can be readily monitored using a passive receiver without interference from the main HIFU signal. In the present study, the signals received passively by each of 64 elements on a standard diagnostic array placed coaxially with the HIFU transducer are combined using time exposure acoustics to generate maps of inertially cavitating regions during HIFU exposure of an agar-based tissue-mimicking material. The technique is shown to be effective in localizing single-bubble activity, as well as contiguous and disjoint cavitating regions instigated by creating regions of lower cavitation threshold within the tissue phantom. The cavitation maps obtained experimentally are also found to be in good agreement with computational simulations and theoretical predictions. Unlike B-mode imaging, which requires interleaving with the HIFU pulse, passive array-based mapping of cavitation activity is possible during HIFU exposure. If cavitating regions can be directly correlated to increased tissue damage, this novel cavitation mapping technique could enable real-time HIFU treatment monitoring.      

Excitons and polaritons in AlGaAs semiconductor alloys

For Al_xGa_1?x As semiconductor alloys with x = 0.15 and 0.21 at temperatures T = 1.7?380 K, the band-edge absorption spectra are measured and the temperature dependence of the integrated absorption coefficient is obtained. The results are analyzed in the context of two mechanisms of the exciton-polariton energy transfer that can lead to the variation of the integrated absorption in systems with random excitonic potential at low temperatures. In one case, the temperature anomaly in the absorption results from the competition between the excitonic and electromagnetic mechanisms of the energy transfer in a quasi-homogeneous medium (a virtual crystal) with spatial dispersion. In the other case, the effect is related to the reemission of light by resonance localized excitons along finite chains of quantum wells in the absence of excitonic transfer. The observation of a characteristic temperature dependence of the integrated absorption supports the existence of exciton polaritons in the samples under study. It is found that integrated absorption in Al_0.15Ga_0.85As alloy saturates above the critical temperature T _c = 155 K. It is demonstrated that, in the temperature range from 1.7 to 60 K, the inhomogeneous broadening due to the fluctuating potential is responsible for the dominant contribution to the width of the excition line in the alloys investigated and considerably exceeds the homogeneous broadening caused by the interaction of excitons with phonons and charged impurities.     

高功率激光空化气泡声辐射特性研究

研究了水下高功率激光击穿水介质形成单空泡及空泡辐射声波的特性,推导了激光空泡辐射声波信号在击穿近场、远场的特性模型.利用调Q Nd:YAG激光聚焦水下击穿水介质产生空泡,采用高速摄像机、高频测量水听器对激光空泡的生长过程及辐射的声波信号进行了测量.实验结果与理论模型吻合,可为相关研究提供参考.     

New horizons in semimetal alloys

A small number of free carriers, a small cyclotron mass, a very high mobility at superconducting temperatures?these are among the properties that make bismuth, along with its alloys, the subject of intensive research efforts. The ``cleanness' of these materials, for example, makes them ideal for new kinds of plasma experiments in solids. Results so far could be described as intriguing to the scientist and promising to the engineer.     

Persistent photoconductivity in MgZnO alloys

The electrical characteristics and persistent-conductivity effects in MgZnO:P alloys grown by the method of pulsed laser deposition on undoped n-ZnO substrates are systematically investigated. It is shown that the pronounced persistent conductivity and the persistent photocapacitance related to the presence of high-barrier electron traps for electron capture are observed in initial unannealed layers. These traps are located in the lower half of the band gap and have the optical ionization threshold of 2.8 eV and the electron-capture barrier height of ～0.4 eV. Alongside such centers, the hole traps with the ionization energy of 0.14 eV are also observed. The annealing at 850°C transforms the material into that of p-type conductivity with the depth of dominant phosphorus-related acceptors close to 0.2 eV. The conductivity compensation and the formation of hole traps with the activation energy of 0.14 and 0.84 eV in the n-ZnO substrate are also observed, and these traps are associated with the acceptor-defect diffusion into the substrate at annealing.     

Apple iMac MA199LL台式电脑拆解分析

iMacMA199LL是苹果电脑Mac系列中第一个采用Intel处理器的成员。它采用1440×900宽屏17英寸LCD显示器,内置1.83GHzIntelCoreDuo双核处理器,该处理器带有2MB二级缓存,其FSB(前端总线)频率为667MHz。iMacMA199LL的其他特点包括:512MBRAM、ATIRadeon×1600显卡(带128MBGDDR3内存)、160GB串行ATA硬驱,内置以太网、Wi-Fi和蓝牙接口。下面的拆解统计了不同集成部分在总成本中所占的比例,并在下面的列表中给出了部分器件的一些详细信息,包括产品型号、生产厂商、封装形式、引脚及数据手册的网站链接地址等,希望能给国内的电子…     

Surface cracking in gold-silicon alloys

Cast gold-silicon specimens containing Au₃Si were examined after room temperature aging for eight to nine years. Dissociation of Au₃Si in a surface layer had caused extensive surface cracking. Such cracking might, in some circumstances, be responsible for failures of gold-silicon eutectic bonds in solid state circuits.     

Structure and properties of glassy metals

Glassy metals exhibit short range order which is almost as well developed as, but is topologically distinct from, that in crystalline metals. Their “defectiveness” is due only to the absence of long range spatial correlations of the local configurations. The mechanical and magnetic behavior of glassy metals will be interpreted in terms of current structural models, in conjunction with hypotheses concerning dilatational and flow disordering and softening.