Defect and Diffusion Forum Vol. 249

Abstract: Spreading of liquid and solid Ga over the surface of thin polycrystalline Ag film is accompanied by fast penetration of Ga through the film. The penetration process between +60°C and –10°C has likely a common mechanism with the spreading. The activation energies of the process responsible for spreading/penetration are EL = 0.3±0.05 eV and ES = 0.5±0.1 eV for liquid and solid Ga, respectively. The common mechanism is attributed to grain boundary (GB) grooving with diffusion of Ag out of the groove either via liquid Ga or along GBs in solid Ga. A possible formation of intermetallic compound between Ag and Ga is considered as the secondary process, which does not control the kinetics. The model reproduces the spreading/penetration rates that are observed, and gives reasonable estimates of the experimental activation energies ES and EL.

Abstract: The interaction of liquid metals with solid polycrystalline metal leads to the appearance of liquid grooves at grain boundaries. The shapes of these grooves may be of a very wide variety. In this paper the typical features of different liquid grooves are presented, classified and analyzed on the base of our experimental data. The developed models confirm the dominant role of diffusion mechanisms.

Abstract: The effects of compressive stress and undercooling of Ga to liquid gallium penetration along grain boundaries (GBs) of aluminum were investigated. It was shown that the penetration rate does not change with the temperature if gallium is in liquid state. The effect of compressive stress applied to Al samples was demonstrated. The time to wetting of all aluminum GBs increased several orders of magnitude if the compressive stress was between 0.1 and 6 MPa. It was proved that solid-liquid transformation does not take place during penetration process.

Abstract: The kinetics and morphology of the grain boundary grooving of Zn bicrystals with 16° <1010> tilt GB by Sn(Zn) melt has been studied at 325°C in equilibrium conditions in vacuum. It is shown that grooving process is interface controlled at least on the first stage. Groove walls mobility is evaluated. Changing of GB grove shape from “faceted walls” corner for annealing time < 78 h to concave “Mullins type” groove for annealing time > 78 h at the same experimental temperature was observed for the first time.

Abstract: The kinetics and morphology of the grain boundary grooving of Zn bicrystals with 16° <1010> tilt GB by Sn(Zn) melt has been studied at 325°C in equilibrium conditions in vacuum. It is shown that grooving process is interface controlled at least on the first stage. Groove walls mobility is evaluated. Changing of GB grove shape from “faceted walls” corner for annealing time < 78 h to concave “Mullins type” groove for annealing time > 78 h at the same experimental temperature was observed for the first time.

Abstract: The cavity growth behavior in a polycrystalline LSI conductor is investigated on the basis of diffusion along grain boundary (GB) and interface (IF) induced by stress and electric current. The of GB and IF, which strongly affects the characteristics of the atom migration. Numerical analysis is conducted for a polycrystalline conductor with GB/IF network after a discussion on a specialized FEM for the diffusion. Results obtained are as follows. (i) In a conductor, the atom migration is eminently activated near a cavity along GBs while there is little flow without the defect. (ii) IF diffusion between the conductor and the surrounded passivation activates the atom migration along GBs inside of a conductor. This implies that the cavity grows under the interaction between GB diffusion and IF one. (iii) Under an external stress, the cavity growth is fast in the early stage while it is decelerated by the constraint of the triple junction ahead of the cavity. (iv) The complex branches of the atom migration due to electric current (EM) amplifies the stress evolution and the stress-induced atom migration (SM) takes place. The cavity grows under the interaction between EM and SM, which stems from the GB/IF network.

Abstract: Ionic conductivity and phase transitions of lithium-zirconium phosphates, Li1±XZr2- XMX(PO4)3 (M = Ta, Nb, Y, Sc, In), with NASICON structure were studied using X-ray powder diffraction, calorimetry, 31P and 7Li NMR and impedance spectroscopy. Triclinic-rhombohedral phase transition in these materials occurs in a wide temperature range at coexistence of both phases. Unusual change of LiZr2(PO4)3 lattice parameters with temperature increase was found. During heating of this compound parameter “a” significantly decreases.

Abstract: Properties of interfaces in solid state metal/oxide joints (Al/SiO2, Al/MgO, Al/glass, Mg/MgO, Mg/SiO2, In/glass etc.) are reported. The interfaces were formed by plastic deformation of metal on the oxide surface at room temperature. Their structure, chemical composition, and micromechanical properties were studied by the AFM, XRD, SIMS, optical microscopy, and precision microindentation techniques. A noticeable adhesion was observed for metals with high affinity for oxygen and only in the regions of the maximum shear stress. Formation of an interfacial reaction zone with an oxygen concentration gradient is detected. In this zone metals are nanostructured and noticeably hardened. The effect of mechanoactivation is considered as a result of physical and chemical interaction and formation of nanostructures in deformed metal/oxide systems.

Abstract: Diffusion effects of alloying elements on the structure and phase transformation during thermo-chemical treatment in AISI M2 high-speed steel additionally alloyed with vanadium, titanium and niobium have been investigated. The results of metallographic, X-ray diffraction, and electron microprobe analyses of the steels after casting, annealing, hot plastic deformation, carburising, quenching and tempering are discussed. The redistribution of alloying elements between the metallic matrix and carbide phases upon high-temperature treatment due to diffusion was shown to result in the structure and phase transformations in the steels studied.

Abstract: The composition and microstructure of historic tongues and shallots from reed pipes of various Baroque organs has been studied. They contain Cu-Zn solid solution (α-brass with 23-29 wt. % Zn) and lead particles. Lead is mainly present as spherical bulk or lens-like grain boundary (GB) inclusions. However, in two samples Pb wets the brass GBs. In this case Pb forms the branched root-like structures. Grain size in brass scatters from 10 to 200 µm. Around 50% of all GBs in brass are Σ=3 twin GBs. The high-indexed coincidence site lattice facets were observed in twin GBs. The increase of number of various facets roughly correlates with decreasing grain size. It may indicate the variation in annealing temperature used by organbuilders in Baroque Era. The annealing temperature has been estimated using the faceting phase diagram for twin GBs in Cu.