Defect and Diffusion Forum Vols. 309-310

Abstract: Processes involved in the structure and phase formation in the thin film systems Sn(4 nm)/Cu(14 nm) and Сu(14 nm)/Sn(8 nm) in the temperature range 130-500 оС were studied using “in situ” electron imaging and Transmission Electron Microscopy methods (TEM). Solubility of Sn α – solid solution Cu-Sn has been determined from the changes in the lattice parameter. This work was performed in the framework of the Swedish Institute supported cooperative research project “Thin metal films – the interplay of structure diffusion and boundaries” (SI dnr 00699/2009).

Abstract: The application of interference microscopy (IFM) and infrared microscopy (IRM) to monitor the evolution of the concentration of guest molecules in nanoporous host materials opens a new field of diffusion research in condensed matter. It combines the methodical virtues of the profiling methods of solid-state diffusion studies with the benefit of the mobility enhancement in fluids. We are going to illustrate the rich options of diffusion studies provided by this novel experimental approach.

Abstract: Diffusion-Induced Recrystallization (DIR) is investigated in size mismatched thin film interdiffusion couples. New grains formed in the diffusion zone are characterized by distinctive composition levels which seem to be characteristic to the interdiffusing materials. In this paper, we analyzed sputter-deposited Ni/Pd films. The lattice mismatch and the driving force are varied by pre-alloying one side of the diffusion couples. Recrystallization was detected after heat treatment by transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. We determined characteristic concentrations from XRD data. Remarkably, the difference between the concentration inside newly formed grains and that of the parent layers remains practically constant, when initial layer concentration is varied. Also, the characteristic compositions are nearly independent of temperature. A thermo-mechanic model has been derived, which demonstrates that the observed concentration differences are such that the stress in front of the moving grain boundary reaches a maximum close to the ideal strength of the host material.

Abstract: High strength steels for automotive industry undergo recrystallization annealing in N2-H2 gas atmosphere prior to hot dip galvanizing. Segregation and selective surface oxidation of the alloying elements (Al, Mn, Si, Cr etc.) depending on their extend, can be a serious problem for subsequent galvanizing as the wettability of these oxides with zinc is poor. Moreover, the H2 uptake from the annealing atmosphere majorly depends on the surface evolution during recrystallization annealing. In order to understand the surface phenomena during annealing of multicomponent alloy (i.e. steel), a systematic approach on model alloys is needed. In this work, selective surface oxidation of Mn, Al and the reduction of native Fe oxides in Fe 2 wt. % Mn and Fe 3 wt. % Al binary model alloys have been investigated by interrupting the recrystallization annealing cycle at the desired temperature. The specimens were annealed to various temperatures (200-800 °C) in N2-5%H2 gas atmospheres with a dew point of 30 °C. It has been found that the segregation and selective oxidation of the alloying elements starts at 300 °C whereas the significant reduction of native Fe oxides takes place at 400 °C. Further increase of temperature, increases the surface coverage by forming the oxide islands.

Abstract: Temperature and amplitude dependent internal friction (TDIF and ADIF) in ultrafine-grained copper (99.95% Cu) specimens processed by equal channel angular extrusion by route BC in 1, 4, and 8 passes and then subjected to annealing is investigated by means of dynamical mechanical analyzer DMA Q800 in the temperature range from -100 to 550 °C, amplitude range from 10-6 to 10-3, and frequency range from 0.05 to 100 Hz. Two IF peaks were registered and explained by structural relaxation due to the recrystallisation process and by thermally activated grain boundary relaxation with broad distribution of relaxation times. Increase in amplitude dependent damping in ultrafine-grained copper is due to dislocation but not grain boundary contribution.

Abstract: Rate of SHS (self-propagating high-tеmperature synthesis) reactions in solid nano-sized multilayers is controlled by the time and temperature dependent vacancy concentration. The increase of reaction temperature is typically faster than the rate of vacancy generation. Therefore, the finite relaxation rate of vacancies leads to drastic slowing down of SHS. On the other hand, as-prepared vacancy supersaturation due to fast deposition on the cold substrate may lead to a certain acceleration of SHS. Influence of (1) vacancy mean free path and (2) initial vacancy supersaturation on the SHS rate is investigated numerically. In wide region of parameters the front velocity appears to be inversely proportional to the square root of vacancy mean free path length.

Abstract: We performed molecular dynamics simulation of diffusion along symmetric <100> 5 and <111> 7 and one non-symmetric <100> 5 tilt grain boundaries in Al in the presence of Fe impurities. The simulation results are in reasonable agreement with available experimental data. The addition of Fe considerably decreases both Al and Fe diffusivities and increases the activation energy for diffusion. The simulation data indicate that the mechanism of diffusion is different in different grain boundaries. The diffusion along <100> 5 grain boundaries reminds that in liquid alloys.

Abstract: The interaction between liquid and solid metals where the liquid-solid interface contains three grain boundary lines which meet in triple junction point is considered. The assumption that the liquid grooves may be formed not only along grain boundaries but along triple junctions is presented. The variation of Gibbs energy during the formation of triangle pyramidal groove along triple junction is determined. The dependence of Gibbs energy variation from groove dimensions shows that the wetting of triple junctions occurs by lower temperatures than the wetting of grain boundaries. This result allows to take into account the existence of grain size effect on the liquid phase penetration depth into the polycrystalline sample. The proposed mechanism of wetting in polycrystalline metal contains two stages: the outstrip melt penetration along triple junctions and the liquid grooving on grain boundaries forming the triple junctions. One of the processes – triple junction diffusion or liquid diffusion – may control the wetting in the polycrystalline sample.

Abstract: The main parameter which shows the space distribution of the emitted gas components is the rate of concentration decrease by the increase of the distance from the point where the emitted gas appears in the atmosphere. It is considered three different driving forces leading to the spreading of the emitted gas components from the centre of the metallurgical region to its periphery:  diffusion factor – the appearance of the emitted substance is the reason of the local concentration increase, it correlates with the diffusion process;  wind load factor – the wind movement acts always in advantage direction, wind force is not space homogeneous as the diffusion force is;  chemical factor – the intensity of chemical interaction of emitted components with the atmospheric ones influences the space distribution of the interaction products (secondary emissions). The proposed method allows to predict the space-time distribution of the emitted metallurgical gas by various external conditions.

Abstract: During the exploitation of the atomic power stations the tubing metal is exposed to the influence of temperatures in the range of 290-320С. It can lead to thermal ageing and to the decrease of the embrittlement resistance. The critical embrittlement temperature is the main value which is needed to calculate the embrittlement resistance of materials. The metal properties degradation is taking into account by introduction of the shift of critical embrittlement temperature. The presented data ensure the prognosis of tube steels properties and shift of the critical embrittlement temperature for 60 years resource.