Cu bicrystals were doped with different amounts of Bi and annealed at various temperatures. The segregation at the grain boundary (GB) was analyzed by energy dispersive X-ray analysis (EDX) in the scanning transmission electron microscope (STEM). It is found that with both increasing temperature and increasing Bi content the amount of faceting of the GB increases, finally reaching complete faceting. This final state is distinguished by brittle behavior. By analyzing the shape of pores at the GB we found that the Cu surface energy anisotropy is probably increased by Bi surface segregation.

The nucleation, growth and dissolution of lamellar precipitates formed due to discontinuous solid state reactions like: discontinuous precipitation, coarsening and dissolution, are reviewed. Emphasis is given on recent studies based on analytical electron microscopy in describing the microchemistry, and in situ electron microscopy for revealing the morphological features of the reactions.

We consider the problem of solute diffusion and segregation in the grain boundaries moving during a phase transformation in the framework of Cahn’s impurity drag model. The concept of a dynamic segregation factor for the diffusion along moving grain boundaries is introduced. The difference between static and dynamic segregation factors may cause the apparent difference of the triple product of the segregation factor, grain boundary width and grain boundary diffusion coefficient for stationary and moving grain boundaries. The difference between static and dynamic segregation is experimentally verified for the Cu(In)-Bi system, for which the parameters of static segregation are well-known. It is shown that the complications associated with the dynamic segregation may be avoided during the study of the discontinuous ordering reaction. From the kinetics of this reaction, the activation energy of the grain boundary self-diffusion can be determined.

The effect of pressure on the kinetics of grain boundary (GB) segregation in the Cu–50 at. ppm Bi alloy has been studied. It was found by means of Auger electron spectroscopy that at a temperature of 1173 K the segregation level decreases from 2 to 1.5 monolayer as the pressure increases from 0.01 to 1.2 GPa. This behavior was explained by considering the physical parameters controlling kinetics and thermodynamics of GB segregation. A simplified model based on dislocation pipe diffusion, proposed previously and discussed in more details in this work, was used to calculate the non-equilibrium GB segregation during cooling under high pressure. The pressure effect on bulk diffusion is responsible for the suppression of GB segregation, while the pressure effect on the phase stability in Cu–Bi alloys provides a negligible contribution on GB segregation in the pressure range studied.

The bulk diffusion of Ga in single crystals of Ge has been studied over a wide temperature range, 827-1189 K. The evaluation was performed using secondary-ion mass spectrometry (SIMS). The diffusion coefficients obtained ranged between the very low value of 9·6 × 10−23 and 1·5 × 10−16m2s−1. The results are expressed in the Arrhenius representation by the pre-exponential factor D0=(1·4±0·7) × 10−2 m2s−1 and the activation energy Q = 319·5±3·4kJmol−1. Secondary-ion mass spectrometry measurements also yielded the isotope effect of Ga in Ge, whose mean value was found to be E=0·240±0·045. This value is nearly equal to, or slightly lower than, the isotope effect of self-diffusion in Ge.

The grain boundary segregation in an Cu–50at.ppm Bi alloy annealed at two temperatures and under various hydrostatic pressures in a hot isostatic pressing apparatus was investigated by means of Auger electron spectroscopy. It was found that high pressures have only little effect on grain boundary segregation. At a temperature of 973K the segregation level remained approximately constant at 2 monolayers of Bi for all pressures studied. Some decrease of the grain boundary segregation with increasing pressure was observed at 1173K. It was also demonstrated that the segregation level in the alloy treated at 0.01GPa depended on the sample cooling rate after annealing. The observed pressure dependence of Bi segregation to the grain boundaries was interpreted in terms of non-equilibrium segregation during specimen cooling.

A new technology for fabrication of joints based on the principle of isothermal solidification is presented. Diffusion soldering has a relatively low cost since a small amout of material is used and a small energy consumption is involved due to the low fabrication temperature. This preliminary study contributes to the search of new alternatives technically and economically viable to replace the use of aggressive materials for the environment such as lead as solder material and fluxes and solvent constituted by CFC. Indium as joint material is used to interconnect Cu pieces. The features of the intermetallics formed make possible the fabrication of thermally and mechanically stable bonds.

Copper embrittlement by Bi atoms is a typical example of a severe detrimental phenomenon in materials science. It has recently been proposed that the strong Bi segregation in Cu can cause a liquidlike film at the grain boundaries (GBs), when the alloy is in the single-phase (solid solution) region of the equilibrium phase diagram [L.-S. Chang, E. Rabkin, B. B. Straumal, B. Baretzky, and W. Gust, Acta Mater. 47, 4041 (1999)]. However, a direct experimental confirmation of a liquidlike state of GBs in such a case is missing. If a liquidlike GB phase is indeed formed, the GB diffusivity should dramatically be enhanced. Radiotracer GB diffusion of Cu-64 and Bi-207 radioisotopes were measured in a set of well-characterized Cu-Bi alloys in the single-phase (solid solution) region of the equilibrium phase diagram as well as in the two-phase (solid+liquid) region. An abrupt increase of the GB diffusivities of both Cu and Bi by about two orders of magnitude was observed at certain Bi contents which are unequivocally in the single-phase region and are definitely less than that associated with the bulk solidus concentration. This critical Bi concentration was the same for self- and solute GB diffusion. With further increase of the Bi content and after exceeding the bulk solidus concentration, only marginal changes in the diffusivities of Cu as well as Bi were observed. The present results convincingly showed the occurrence of the premelting phase transition in GBs of the Cu-Bi system.

A novel environment-friendly process based on diffusion soldering for Ni/Ni interconnections using Al as the joint material is developed. The interconnections formed can be thermally stable up to 1133-1638 °C due to the high melting point of the intermetallics formed. This feature is a very important requirement which is not possible to satisfy using conventional soldering process. This joints find application in high service temperature sensors and contacts like in hot plates and between resistive heaters and electrical leads.

The faceting of R3 and R9 tilt grain boundaries (GBs) has been studied in bicrystals of pure Cu and Cu–Bi alloys containing 2.5 · 10 , 10 · 10 3 and 16 · 10 3 at.% Bi. The R3(100), R9(100), R9( 110), and R9( 120) facets and non-CSL R3 82 9R facet were observed, where R is the inverse density of coincidence sites. The ratio between GB energy, rGB, and surface energy, rsur, was measured by atomic force microscopy using the GB thermal-groove method. The GB energy and thermal-groove deepening rate increased slightly between 0 and 10 · 10 3 at.% Bi for all facets studied. However, between 10 · 10 3 and 16 · 10 3 at.% Bi the GB energy increased dramatically [from a factor 2 for the R9(110) facet to 15 times larger for the R3(100) facet]. The thermalgroove deepening rate also increased by a factor of 10 in this concentration range. This change corresponds well with the GB solidus line (i.e., the formation of a stable layer of a liquid-like GB phase called GB prewetting) observed previously. Wulff diagrams were constructed using measured rGB/rsur values. 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The morphology and kinetics of the discontinuous precipitation reaction in a Cu-4.5 at.-%In alloy were studied by means of analytical electron microscopy. A grain boundary movement was experimentally observed before the precipitation reaction at this grain boundary started. Subsequent development of the discontinuous precipitation reaction led to the formation of an alpha/delta(Cu7In3)) lamellar two phase microstructure, where alpha is the In depleted solid solution and delta the precipitate phase. By application of energy dispersive X-ray microanalysis a solute depletion in the a lamellae in the wake of the advancing reaction front was observed. Indium concentration profiles were determined parallel to the moving reaction front for individual a lamellae. These concentration profiles fall into two categories, namely symmetrical and asymmetrical with respect to the central axis of the a lamella, which were attributed to regular morphology and irregular morphology of the discontinuous precipitates, respectively. A local analysis was applied to characterise the kinetics of the discontinuous precipitation reaction. The local grain boundary diffusivity was determined.

Grain boundary (GB) wetting phase transitions were studied, for the first time, in Al-Mg polycrystals (Mg contents of 5, 10, 15 and 20 wt.%; temperature range 490-630 degreesC). It was observed that above 598 degreesC all GBs in the solid Al-rich phase were wetted by a liquid phase. Below 540 degreesC no GBs wetted by a liquid phase were observed. The maximal and minimal temperatures of the GB wetting phase transitions, T-wmax and T-wmin, were determined. Between 540 and 598 degreesC the percentage of the wetted GBs gradually increases from 0 to 100 %. Grain boundary prewetting or premelting is given as an explanation for the hitherto not understood high-strain rate superplasticity observed for ternary Al-Mg-X alloys in a narrow temperature range just below the bulk solidus line.

The correlation between the geometry of the grain boundaries (GBs) and the kinetics of the discontinuous precipitation (DP) reaction in a Mg–10 wt.% Al alloy has been studied. The GBs were categorized as special or random by using the electron back-scattered diffraction (EBSD) technique and theoretical tables of the coincidence site lattice. The analysis showed convincingly the absence of low-angle GBs and no distinguished maximum on the GB misorientation angle distribution in this hexagonal system. The DP cells appeared predominantly at nonspecial (random) orientations, confirming that the initiation and growth of the reaction products occur at high-angle GBs. Generally, some orientations which are inactive after 20 min became active after 40 min of ageing at 500 K. For each rotation axis, there were several misorientation angles (no special ones) for which a maximum growth distance of DP reaction was observed.

This work describes a Pb-free solder alternative for the interconnection technology and its implementation in a diffusion soldering technique: In-48 at.% Sn solder (eutectic alloy), with a melting point of 120 degreesC. The system proposed has the advantages of both traditional soldering and diffusion bonding, i.e., good joint filling, high service temperature, and good mechanical properties. The diffusion reaction processes in Cu/In-48 at.% Sn/Cu joints were investigated between 180 and 400degreesC. Electron microprobe analysis revealed the presence of one or two intermetallic layers in the interconnection zone: a layer of the eta phase below 200degreesC, and layers of the eta and zeta phases above 200degreesC. The eta and zeta phases form through a solid-liquid and a solid-solid diffusion reaction, respectively. Below 200degreesC the eta phase exhibits two different morphologies: large coarse grains at the eta/(originally liquid)ln-48 at.% Sn interface and a fine-grained region at the Cu/eta interface. The thickness of the zeta layer shows a constant growth rate (linear growth) at constant temperature. The temperature dependence of the growth rate constant of the zeta layer is described by an Arrhenius relationship with an activation energy equal to 121 kJ/mol and a pre-exponential factor of about 57 m/s. (C) 2002 Published by Elsevier Science B.V.

Faceting is a well documented phenomenon known both for surfaces and interfaces, particularly, grain boundaries (GBs). Faceting can be considered as a phase transition when the original surface or GB dissociates onto flat segments whose energy is less than that of the original surface or GB. For the investigation of GB faceting a cylindrical Cu bicrystal with an island grain was grown by the Bridgman technique. Grain I in this bicrystal is completely surrounded by grain 2. The dissociation Sigma9 Sigma 3 + Sigma3 proceeds during the growth of the bicrystal. The twins appear instead of {111}(1)/{115}(2) or (110)(Sigma9CSL) facet. GB faceting was studied at 1293 K, 1073 K, and 873 K The profiles of the GB thermal groove were analysed by atomic force microscopy. Wulff-Herring plots and GB phase diagrams have been constructed for the Sigma3, Sigma9 and Sigma9+Sigma3 GBs. With increasing temperature the facets with low-density CSL-planes disappear in the GB shape. GB roughening phase transition can be responsible for this phenomenon.

A method of grain refinement which does not require plastic deformation is discussed. The refinement is obtained by a carefully designed thermal treatment in which the discontinuous precipitation (DP) reaction is followed by a dissolution process. Two different mechanisms of refinement were identified based on the investigations performed on Al–22at.% Zn and Ni–4at.% Sn alloys. The first one is associated with holding the orientation relationship of the former DP process. Such a behaviour was observed in the Al–22at.% Zn alloy in which the grains are refined by a factor of 7–8. If the small grains are created via recrystallisation within the area previously covered by a DP cell, like in Ni–4at.% Sn alloy, a refinement factor of 40 or even more can be obtained.