Density and surface tension of the Pb-Sn liquid alloys

The maximum bubble pressure method and the dilatometric method were used, respectively, in measurements of surface tensions and densities of Pb-Sn liquid alloys. The experiments were carried out in the temperature range from 573 to 1200 K for the pure Pb, pure Sn, and 7 alloys of the compositions 0.1, 0.2, 0.26, 0.36, 0.5, 0.7, and 0.9 mole fraction of Pb. A straight-line dependence on temperature was observed and fitted by the method of least squares both for the densities and the surface tensions. The calculated density isotherm at 673 K showed a positive deviation from the linearity over the entire range of composition, and the same tendency was seen at 1173 K for compositions higher than X _Pb=0.26. At the lower concentration of Pb, a nearly linear character of 1173 K isotherm was noted. In the case of surface tensions, both at the lowest and the highest temperatures (673 and 1173 K), the deviation from linearity with composition was negative, but deviation decreased with increasing temperature. The isotherms of the compositional dependence of surface tension calculated from the Butler model exhibit good agreement with experimental data.     

Density and surface tension of the Pb-Sn liquid alloys

The maximum bubble pressure method and the dilatometric method were used, respectively, in measurements of surface tensions and densities of Pb-Sn liquid alloys. The experiments were carried out in the temperature range from 573 to 1200 K for the pure Pb, pure Sn, and 7 alloys of the compositions 0.1, 0.2, 0.26, 0.36, 0.5, 0.7, and 0.9 mole fraction of Pb. A straight-line dependence on temperature was observed and fitted by the method of least squares both for the densities and the surface tensions. The calculated density isotherm at 673 K showed a positive deviation from the linearity over the entire range of composition, and the same tendency was seen at 1173 K for compositions higher than X _Pb=0.26. At the lower concentration of Pb, a nearly linear character of 1173 K isotherm was noted. In the case of surface tensions, both at the lowest and the highest temperatures (673 and 1173 K), the deviation from linearity with composition was negative, but deviation decreased with increasing temperature. The isotherms of the compositional dependence of surface tension calculated from the Butler model exhibit good agreement with experimental data.     

Dynamic surface tension measurements on molten metal-oxygen systems: model validation on molten tin

A theoretical model on oxygen transport at the surface of liquid metals has been validated by dynamic surface tension measurements performed on liquid tin as test metal. The oxygen contamination conditions have been obtained at different oxygen partial pressures under low total pressure conditions (Knudsen regime), confirming that an oxide removal regime occurs under an oxygen partial pressure much higher than the equilibrium one (the “Effective Oxidation Pressure”). Experimental results are reported which give a new insight on the relative importance of the various processes due to the oxygen mass transport between the liquid metal and the gas phase. The critical aspects involved in surface tension measurements of liquid metals, related to the problem of liquid metal–oxygen interactions, are also carefully underlined.     

Wetting behavior of Al alloys on a TiH2 substrate

The wetting behavior of Al–Ge alloys on TiH₂ substrates was investigated by an improved sessile drop method under high vacuum and in a temperature range of 773–818 K. Results indicate that the equilibrium contact angles of Al–Ge/TiH₂ increase linearly with temperature according to the following formula: θ = 0.2882T ? 85.04, and decrease linearly as the Ge content increases from 25.2% to 36.2% according to the formula: θ = 214 ? 200Ge (wt.%). The worst wetting behavior was obtained for a pure Al/TiH₂ system at its foaming temperature (973 K). TiH₂ particles were prone to aggregate and were thus difficult to disperse. This could be one of the reasons for closed-cell aluminum foam products having non-uniform pores.     

Emissivity measurements on aeronautical alloys

The emissivity of three Ni and Co based aeronautical alloys is analyzed in this paper. These alloys are employed in high temperature environments whenever good corrosion resistance, high temperature resistance and high strength are essential. Thus, apart from the aeronautical industry, these alloys are also used in other technological applications, as for example, aerospace, nuclear reactors, and tooling. The results in this paper extend the emissivity data for these alloys available in the literature. Emissivity dependence on the radiation wavelength (2–22 μm), sample temperature (200–650 °C) and emission angle (0–85°) has been investigated. In addition, the effect of surface finish and oxidation has also been taken into consideration. The data in this paper have several applications, as temperature measurement of a target by pyrometry, low observability of airplanes and thermal radiation heat transfer simulation in airplane nozzles or furnaces.     

The rapid prediction of the modification level of Al-Si alloys by surface tension

Both the theoretical analysis and experiments on Al-Si alloys have shown that a relationship between the surface tension and the modification of Al-Si alloys exists. A new method for the rapid prediction of the the modification level of Al-Si alloys by surface tension has been introduced. The quantity of the modifier is found to have the greatest effect, followed by the time of the modif cation and then the temperature. In Al-Si alloys, when the surface tension is above 530 mN/m, the modification level is partial. When the surface tension is between 400 mN/m and 530 mN/m, the modification level is moderate. When the surface tension is below 400 mN/m, the modification level is perfect.     

Wetting behaviour of Cu based active brazing alloys on siliconised graphite

Abstract

The effects of Al and silicon additions to Cu based brazing alloy and the surface free silicon on siliconised graphite substrate on the wetting behaviour of the siliconised graphite by Cu–Al–Si–Ti alloys were investigated using the sessile drop technique at 1100°C. The contact angles were measured and the interfacial reactions were analysed. It was shown that surface free Si on siliconised graphite had a great positive effect on the contact angle. Furthermore, interfacial reactions could be controlled by adjusting the contents of Si and Al in brazing alloys.     

White gold alloys:

A numerical grading system has been established for white gold alloys using the ASTM Yellowness Index D1925, an existing colour quality standard. The Index is calculated from the CIE (International Commission of Illumination) Tri-stimulus values, X, Y and Z, and the scale is linear, so that as the number decreases, the alloy becomes whiter.     

Anomalous temperature dependence of the surface tension in liquid silver–lead alloys

The surface tension of liquid silver–lead alloys is discussed with special emphasis on the unusual temperature coefficients apparent at certain concentrations. In contrast to most other liquid alloys silver-rich mixtures of silver–lead adopt positive temperature coefficients. This anomalous behaviour is found to be well explained in terms of Butler's model of surface tension. The phenomenological approach of Bhatia and March was applied in semi-empirical manner in order to achieve agreement with the experimental findings. In view of the high concentration fluctuations of the system – expressed in terms of S_cc(0) – the anomalous temperature coefficients find a plausible interpretation. A short critical assessment of the model's general applicability to systems with demixing properties is presented. Qualitatively, both treatments indicate that the unusual temperature dependence of the surface tension is the mere consequence of the thermodynamics of the system.     

Diffusion in gold and Au-Ag alloys

The self-diffusion coefficients of gold in pure gold and alloys of gold and silver have been measured over a range of temperatures. Chemical interdiffusion coefficients have been measured on pure metal and incremental couples, but are of lower accuracy because of the development of porosity. The results are compared with earlier work and internally on the basis of Darken’s equations.     

Calorimetric measurements on some undercooled metals and alloys

Undercooling was achieved directly in the cell of a high temperature calorimeter (Setaram HTDSC) for Ni, Fe, Cu, Pd and several alloys, using cooling rates between 1 and 15 K min⁻¹. The samples were immersed in alumina powder inside a standard alumina crucible under flowing helium. Ag, Au and Al were not undercooled significantly. The reproducibility of the measurements was within 1.5%. The heat of solidification of Ni at an undercooling of ΔT = 220 K was −17.5 ± 0.2 kJ mol⁻¹, which is the same absolute value of the heat of fusion at the equilibrium melting point T_m. This implies that the specific heat of the undercooled liquid is very close to that of the crystalline solid in this temperature range. Fe appears to display a similar behavior at ΔT = 220 K. The difference between the heat of fusion at T_m and the heat of solidification at an average value of ΔT = 95 K is significant for a Pd_77.5Cu₆Si_16.5 glass-forming alloy. From these data, we calculated an average specific heat difference between the liquid and crystal phases of 7 ± 5 J mol⁻¹ K⁻¹. The enthalpy data for Pd₈₂Si₁₈ comply with those of the ternary Pd---Cu---Si.     

Surface tension of liquid Au-Bi-Sn alloys

The surface tension of a promising lead-free solder Au-Bi-Sn alloys was investigated both by the sessile-drop method and calculation. Experimental measurements were carried out for two cross-sections with the constant gold to bismuth ration of 1:1 and 1:2. For all the investigated compositions, decrease of the surface tension is observed with increasing temperature. Meanwhile, the surface tension values were also calculated based on Butler's equation, with using the newest research on thermodynamics data of...     

Property measurements on spray formed Si-Al alloys

A novel Si-Al alloy was prepared by spray forming process for electronic packaging. Property measurements on spray-formed Si-Al alloys after hot pressing were carried out. The results indicate that the alloys (Si-(30%-40%)Al) have advantageous physical and mechanical characteristics, including low coefficient of thermal expansion (6.9×10-6-8.7×10-6/K), high thermal conductivity (118-127 W/(m·K)), low density (2.421×103-2.465×103 kg/m3), high ultimate flexural strength (180-220 MPa) and Brinell hardness (162261). The alloys are easy to machine to tight tolerances using standard machine tools and they can be electroplated with gold finishes and soldered with Sn-Pb alloy without any difficulty.     

SnAgCu-xTi在单晶硅表面的润湿行为

采用改良座滴法在高真空条件下研究了熔融Sn0.3Ag0.7Cu(SAC)-xTi(x为质量分数,%)在800 ~ 900 ℃与单晶硅表面的润湿行为. 结果表明,SAC-xTi/Si体系属于惰性润湿体系,钛的添加显著改善了润湿性. 在不添加钛时,SAC钎料在800 ℃与单晶硅润湿1 800 s后达到平衡,平衡接触角为63°;SAC-1Ti钎料在900 ℃润湿1 800 s后获得最小平衡接触角41°;SAC-3Ti钎料在900 ℃时达到平衡润湿的时间最短,仅为50 s,平衡接触角为48°. 润湿机制为钛加速了单晶硅表面氧化膜的去除. 在熔融钎料的铺展过程中,通过溶解?再析出机制和微掩膜机制,在固/液界面处形成了温度依赖的“金字塔”结构,温度越高,“金字塔”结构越稀疏且形貌越大. “金字塔”结构的出现并未改善体系的润湿性,由于其对三相线的钉扎作用,进而使得体系的润湿性变差.     

Superelastic tension and bending characteristics of shape memory alloys

The objective of this study was to develop a numerical model of the superelastic behavior of shape memory alloys (SMA) on a macro-scale level. Results from a study on this behavior under tension and pure bending tests are presented and discussed. Two SMA samples were used in the experimental work and subjected to various loading paths in tension and pure bending: a single crystalline CuZnAl alloy and polycrystalline NiTi wire. Bending tests were performed under a pure bending loading condition on a new testing apparatus designed for the specific needs of this study. The experimental part of this study focused mainly on the response of the SMA to the loading paths in a quasi-plastic domain where the deformation mechanism is dominantly governed by the stress-induced martensitic transformation. Experimental results obtained from the NiTi polycrystals by tensile tests indicate that the superelastic SMA exhibits sufficient repeatability useful enough for a modeling task, while similar results obtained from the single crystalline CuZnAl indicate that the same modeling approach is not easily feasible. The facts have been qualitatively verified by the experimental data from pure bending tests, and a further area as study is suggested.     

High temperature calorimetric measurements on liquid Pd---La and Au---Gd alloys

An improved method for the high temperature calorimetric determination of the mixing enthalpies of liquid alloys is presented. The method helps to avoid certain difficulties which are encountered in the process of treatment of calorimetric functions when the thermal equivalent of the calorimeter is unknown. The method was applied for measurement and calculation of the heats of mixing in Pd---La and Au---Gd melts, which show a large exothermic effect of alloy formation owing to the very high electron affinity of palladium and gold.     

Experimental and calculated liquid-liquid interfacial tension in demixing metal alloys

Liquid-liquid interracial tension in binary and temary Al-based monotectic systems has been determined experimentally with a tensiometric method in a wide temperature interval. The temperature dependence of the interfacial tension is well described by a power law function of the type σαβ - （1 - T/Tc）δ with the critical exponent δ= 1.3 and a critical temperature Tc. Theoretical models describing the liquid-liquid interface in monotectic alloys and their applicability for calculation of the interfacial tension and its temperature dependence in binary systems are considered.     

氧化铝表面粗糙度对熔融铅润湿性及表面张力的影响

表面粗糙度是高温下的液态金属/陶瓷润湿性的重要影响因素.在923～1123 K的温度范围内研究氧化铝表面粗糙度对铅液滴接触角、接触直径、液滴高度、表面张力的影响.在冷却后使用SEM观察铅/基底界面的微观结构.通过使用几何平均法计算氧化铝基板的表面自由能进而解释铅液滴润湿行为的机理.结果表明,在铅液滴/氧化铝陶瓷系统中,...     

Wetting and interfacial reaction characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys

Through the use of a wetting balance technique, the wetting characteristics of Sn-1.2Ag-0.5Cu-xIn quaternary solder alloys with respect to the In content and soldering temperature were investigated to validate the applicability of compositions with a low Ag content as solder material. It was found that a small addition (0.4–0.6 wt.%) of In significantly improved the wetting properties of the Sn-1.2Ag-0.5Cu-xIn composition at soldering temperatures ranging from 230 °C to 240 °C due to the excellent wetting property of In. In an observation of the interfacial reaction, it was found that the added In element did not participate in the interfacial reaction with a Cu or Ni pad, unlike in the Sn-Ag-Cu-In case, which has a high In content. The package or boardside IMC layers in Sn-1.2Ag-0.5Cu-0.4In joints were thinner than those of Sn-3.0Ag-0.5Cu, especially after aging.