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The temperature field, flow field and solidification structure of Ag–28Cu–2Ge–0.4Co alloy during solidification under water cooling, air cooling and slow cooling conditions were investigate...

As a new type of vacuum filler metal, the effect of heating temperature and holding time on the interfacial microstructure evolution and brazing properties of 4J29 kovar alloy (Fe–29Ni–17Co)/Ag–27Cu–4Ga filler/4J29 kovar alloy brazed joint was observed. The typical interfacial microstructure corresponding to joint brazed at 900 °C/10 min could be divided into three different types of regions including 4J29 substrate (γ phase)/Diffusion zone (Fe (s.s)+Ag (s.s)+Cu(s.s))/residual filler metal region (Ag (s.s)+Cu(s.s)). Block-shaped β-Cu solid solution (s.s) extensively scatter in brazing alloy and played a large part in dispersion reinforcement. Owing to Cu and Ga elements diffuse to the interface between the substrate and the filler metal, β-Cu (s.s) layers generated at brazing interfaces and intensified brazing interface. The shear strength of joint increased from 830 °C to 870°/10 min and 5min to 10 min/870 °C due to the interfacial reinforcement effect of β-Cu(s.s) layers. The shear strength decreased from 900 °C to 960 °C/10 min and 10 min–25 min/870° because of weakened dispersion reinforcement of block-shaped β-Cu (s.s) phases. The brazed joints obtained a maximum shear strength of 339.6 MPa at optimal brazing parameters.

Ag–28Cu–8Sn (wt%) alloy is a widely used brittle silver-based brazing filler metal. The wire of brazing filler metal was prepared by continuous casting process and dieless drawing technology. The phase structure was measured by X-ray diffraction (XRD), and the microstructure of wetting interface, cast states, processing states and fracture morphologies were characterized by the optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The electrical conductivity, hardness, tensile strength and elongation rate were tested as well. Furthermore, the solid–liquid phase temperature was measured by a differential scanning calorimeter (DSC), and the wettability of brazing filler metal was tested by spreading method. The outcomes obtained show that the as-cast microstructure is a typical three-zone structure, including region of surface fine grain, zone of columnar grain and region of center equiaxed crystal. Ag–28Cu–8Sn alloy is mainly composed of Ag-rich α-phase, Cu-rich β-phase and intermediate compounds. Grain refinement appears in the cross section, as for grains of the longitudinal section, the shape is changed from ribbon to fiber to form a silk texture. The strength and hardness improve with the increase in the true strain, while the conductivity and elongation are reduced. Furthermore, the solid-phase temperature is 605.9 °C, and the liquid-phase temperature is 725.1 °C. The spreading area of Ag–28Cu–8Sn brazing filler metal is 174 mm2, and the metallurgical bonding occurs between Ag–28Cu–8Sn brazing filler metal and Cu matrix. In addition, compared with cold drawing process, there are not any microcracks at the fracture morphology for the alloy fabricated by dieless drawing. The dieless drawing process overcomes some processing defects of traditional cold drawing, and the processing performance of Ag–28Cu–8Sn alloy is improved.

The electrical contact–high-speed imaging experimental system was developed to investigate the molten bridge phenomena of AgNi10 electrical contact material. The dimension of molten bridges was measured along with the measurement of waveforms in the contact voltage under the load of direct current (DC) 6 V (8–20 A) and breaking speed of 50.0 mm·s−1. A part of the observed results was presented as well as surface morphology of the contacts after electrical contact behavior, which shows some interesting and new phenomena. Molten bridges and arc could exist simultaneously. The stable molten bridge looks like cylindrical shape and then becomes needle tip at its rupture, the diameter and length of molten bridges both increase with the increase in current and the growth gradient of the diameter is larger than that of the length. The morphology and elemental distribution of the contact surface are changed by the behavior of electrical contact.

The phase stability of Zr and Ru doped Pd system has been studied using the virtual crystal approximation (VCA) in density functional theory (DFT). Three possible VCA models have been set up for Zr and Ru doped Pd system, and elastic constants and tetragonal shear constant, bulk modulus and shear modulus, Young modulus and Cauchy press, density of states in Zr and Ru doped Pd system were also analyzed. The results show that Pd-5Ru-1Zr[T(3)] is the most stable phase in Pd-Ru-Zr system according to tetragonal shear constant, and Pd-10Ru-1Zr[T(2)] is the most brittle phase and has more directional bonding according to Cauchy press. Along with replacing Pd with Ru and Zr in the solution, the structure becomes unstable both energetically and geometrically, and the increase of Ru and Zr content can improve the strength of the chemical bonding and enhance the hardness of Pd-Ru system, but reduce their phase stability.

The stability and the thermal as well as mechanical properties of AuxCuy intermetallic compounds were investigated by density functional theory (DFT). The calculated cohesive energy and the formation enthalpy of AuxCuy phases show that they are thermodynamically stable structures and the calculated lattice constants are in good agreement with those of the experiments. The heat capacities of the compounds were calculated by a quasi-harmonic approximation (QHA) method. The Debyes temperature as a function of strength of chemical binding for each compound was also discussed. The elastic properties such as bulk modulus and Young's modulus were evaluated by Viogt-Reuss-Hill approximation. The phonon spectrum and the density of phonon states of AuCu compounds were calculated to determine the stability of two AuCu phases. The new knowledge from this study will be used for future development of Au-Cu alloy system.

Reusing Historical testcases play a crucial role in ensuring software testing quality. However, the diversity of historical testcases limits their potential uses. As a result, large amounts of human effort is required to write testcases for complex functional testings. In this paper, an effective framework is proposed to integrate and retrieve historical testcase bases with semantic analysis technologies. Firstly, semantic similarity is calculated to integrate the metadata of the inputted semi-structured testcases. Then, testcases are clustered by using similarity measures to eliminate heterogeneity existed in the contents of the testcases. The clustering results are added to the testcases as semantic annotations for the later semantic query. Using the semantic query interface, testers can easily obtain useful testcases without ambiguity. Finally, a case study demonstrates the effectiveness and scalability of this method for testcases retrieval for bank information systems testing.

Au-Pd alloys doped with Zr, Mo and Y, respectively, were prepared in a vacuum high frequency melting furnace. The effects of rare metal doping on Microstructure and mechanical, electrical properties of the binary alloy was investigated. X-ray diffractometer and metallographic microscopy were employed to detect the microstructures. Electric bridge and eddy current conductive instrument were employed to test the electrical resistivity and the mechanical properties of alloys were tested by AG-X100KN type tensile testing machine. The results show that adding rare metal elements into Au-Pd system could refine microstructure effectively, increase the melting point, density and electrical resistivity of the alloy, and improve mechanical properties, but the processing property of the alloy is decreased.