Band 95, Heft 3

An electrochemical cell * Zn | Zn 2+ in LiCl, KCl | Pb x Sn y Zn z has been made to measure the activity of zinc in the liquid phase of the ternary Pb–Sn–Zn and to determine the liquid miscibility gap. In this paper we present an assessment of the ternary Pb–Sn–Zn system. An optimization of the liquid phase based on the description of the Pb–Sn and Sn–Zn systems by Ohtani et al. [1], Lee [2], and ourwork on Pb–Zn [3], has been carried out taking into account available thermodynamic and phase diagram data. All ternary phases are described by the Redlich–Kister–Muggianu model. The optimized coefficients obtained and the calculated phase diagram are presented.

The thermodynamic properties of liquid Bi–Sn alloys were measured over the whole composition range by an electromotive force (emf) method using a liquid electrolyte. The basic thermodynamic functions were calculated from the corresponding excess functions by using the Gibbs–Duhem integration at 723 K. The liquid Bi – Sn system was classified as a subregular solution and an asymmetrical curve of enthalpy of mixing vs . composition was found.

Knudsen cell mass spectrometry has been employed to investigate thermodynamically the fcc solid ternary Fe–Ni–Co alloys over the entire range of composition. The “Digital Intensity-Ratio” method has been applied for the determination of the thermodynamic excess properties. The values of the molar excess Gibbs energies G E , the molar heats of mixing H E , the molar excess entropies S E , as well as the thermodynamic activities at 1600 K are presented.

A high-efficiency diffusion-multiple approach was employed to map the phase diagram of the Nb–Cr–Ti ternary system which is critical for the design of niobium silicide-based composites. These composites have high potential as a replacement for Ni-base superalloys for jet engine applications. The formation of the Laves phase and alloying with Ti are critical for the high oxidation resistance of the composites and the Nb–Cr–Ti system serves as the base for understanding the Laves phase formation and Ti alloying. Three isothermal sections at 1000, 1150 and 1200°C were constructed from the results obtained from diffusion multiples using scanning electron microscopy, electron probe microanalysis, and electron backscatter diffraction. The results help to define the relative stability of the C15 and C36 Laves phases in the Nb–Cr–Ti ternary system.

The thermal diffusivity of NiO pellets was determined by the photoacoustic technique. A NiO powder, with a purity of 99.95 %, was pressed into pellets 10 mm in diameter. The average agglomerate size of the NiO powder was 50 μm and the size of individual particles was between 1 and 10 μm. The pressing pressure was 1.5 GPa and the sintering temperature was 1100 °C. The sintering time was between 15 and 240 min. The photoacoustic phase and amplitude spectra of NiO were measured as a function of the modulating frequency, using a transmission detection configuration. Thermal diffusivity, D T , the coefficient of minority carrier diffusion, their mobility and life time, and front and rear recombinating velocities were calculated as a function of sintering time by comparing the experimental results with theoretical photoacoustic phase and amplitude signals. The thermal diffusivity increases from 0.67 · 10 −5 to 0.97 · 10 −5 m 2 /s when the sintering time was changed from 15 to 240 minutes.

The partial and integral enthalpies of mixing of molten, ternary Ag–Cu–Sn alloys were determined at 500, 700 and 900 °C using a Calvet-type microcalorimeter. Five sections in a compositional range from pure Sn to about 40 at.% Sn were investigated. The data were fitted using a Redlich–Kister–Muggiano polynomial, where the binary interaction parameters were taken from the literature. Additionally, the temperature dependence of the ternary interaction parameters was described analytically by a linear function. In the ternary Cu–Ni–Sn system, the enthalpies of mixing were determined at 1250 °C in five sections, starting from pure Sn to about 40 at.% Sn. Again, the ternary interaction parameters were fitted using the substitutional Redlich –Kister –Muggiano model. For both ternary systems and all mentioned temperatures, isoenthalpy curves were constructed for the integral molar enthalpy of mixing.

CoFe single and multi-layer systems are deposited by a radio-frequency sputter process. Thickness, roughness, morphology, texture and internal stress state of the layers are determined by X-ray reflectometry, transmission electron microscopy, and diffraction methods. The texture and the internal stress of the layers depend strongly on the parameters of the sputter process. The magnetic properties of the layers are determined from hysteresis curve measurements and magneto-optical Kerr microscopy. A strong correlation between the texture, the internal stress, and the magnetic properties of the CoFe layers is observed.

Samples made from AISI 1015 carbon steel grade have been subjected to warm-rolling (700 °C) with a deformation of 36.4 %. The microstructure and mechanical properties of the samples were then compared to normalized samples. The experiments showed that warm-rolling generates a very fine microstructure with mechanical properties similar to those obtained by normalizing. By considering technological and economical aspects, it is shown that warm-rolling offers important advantages as compared to both, hot and cold working.

Creep in copper dispersion-strengthened with fine alumina particles and reinforced with tungsten short fibres is investigated at three temperatures ranging from 923 to 1023 K. It is shown that creep is associated with a true threshold stress decreasing with increasing temperature more strongly than the shear modulus of copper. The true threshold stress in the composite is higher than that in the composite matrix by a factor K, by which the flow stress in the matrix is reduced due to the load transfer. The minimum creep strain rate is found to be lattice diffusion controlled and to depend on the fifth power of applied stress. The values of the apparent activation energy of creep are higher than that of the activation enthalpy of lattice self-diffusion in the composite matrix, which is fully explained in terms of the temperature dependence of the true threshold stress. The values of the apparent stress exponents are higher than the value of the true stress exponent since the true threshold stress is independent of the applied stress.

The present authors [1] and Ochoa et al. [2, 3] indicated that the creep and rupture strengths of a Sn-3.5% Ag lead-free solder alloy are very much affected by the variation of the microstructure formed under different solidification and cooling rates after casting. In the present research, the cooling effect and microstructural effect on the creep and rupture strengths of the Sn-3.5% Ag alloy is further investigated. The effect of the reflow and flow joining process on the rupture life is also discussed.