Energy dispersive X-ray spectroscopy is used to obtain concentration curves and calculate the coefficients of bulk and grain boundary diffusion in copper–tin solid solutions at tin concentrations of less than 13.9 wt % in the temperature range of 500 to 650°C. A qualitative explanation of the results is proposed.

The influence of the segregation energy on the diffusion of second-component atoms in copper is studied by molecular statics and dynamics methods. A number of modified potential is considered. The segregation energy of atoms in a grain boundary is calculated. The number of second-component atoms involved in a diffusion process is found to decrease because of desorption, which leads to a decrease in the grainboundary diffusion coefficient.

Electron probe microanalysis (EPMA) has been used to obtain concentration curves and calculate the bulk diffusion coefficients of Sn in solid solutions of the copper–tin system in a tin concentration range of less than 13.9% weight (7.96 at %) and temperature range from 500 to 650°C. Diffusion couples are made from pure Cu (99.995%) and a two-component alloy of Cu with chemically pure Sn by direct alloying metallic Cu with Sn in an Ar–H2 atmosphere at 1100°C for 2 h. Diffusion coefficients were calculated using the Matano–Boltzmann and Grube methods from the upper part of the concentration curve (from 6 to 8 at % (D1)) and the lower part (from 2 at % to zero (D2)). It is shown that Sn diffusion coefficients in a concentrated solution were several times greater than Sn diffusion coefficients in dilute solution. Both values of diffusion activation energy, especially the second, coincide with isotope data on Sn diffusion in a pure copper (187 kJ/mol). A qualitative interpretation is proposed of the effect of accelerating the diffusion of tin in a concentrated solid solution of the copper–tin system.

Electron probe microanalysis (EPMA) was used to obtain concentration curves and calculate bulk diffusion coefficients in solid solutions of the copper-tin system in the tin concentration range of less than 13.9 wt.% (7.96 at.%) and temperature range of 500 to 650 ° С . Diffusion couples were made of pure copper (99,995 %) and two-component alloy obtained by direct alloying of metallic copper with chemically pure tin in Ar—H atmosphere at 1100 °C in the quartz reactor during 2 hours. Diffusion coefficients were calculated using the Matano-Boltzmann method and the method proposed by Grube, i.e. in the tin concentration range from 6 to 8 at.% ( D 1 ) on the top of the concentration curve, and from 2 at.% to zero ( D 2 ) on the bottom of the concentration curve. It is shown that tin diffusion coefficients in the concentrated solution were several times greater than in the diluted one. It is shown that diffusion activation energy values virtually coincide with isotope measurement data on tin diffusion in pure copper (187 kJ/mol). A qualitative interpretation is proposed for the tin diffusion acceleration effect in the concentrated solid solution of the copper-tin system.

The influence of the segregation energy on the diffusion of second-component atoms in copper is studied by molecular statics and dynamics methods. A number of modified potential is considered. The segregation energy of atoms in a grain boundary is calculated. The number of second-component atoms involved in a diffusion process is found to decrease because of desorption, which leads to a decrease in the grain-boundary diffusion coefficient.

Processes of interdiffusion have been studied in the Ni-Re system. The method of electron-microprobe analysis was used to measure the interdiffusion coefficients D̃ in Ni4.4Re/Ni, Ni7Re/Ni Ni9Re/Ni, and Ni9Re/Ni4.4Re (wt %) diffusion pairs in the temperature range of 1050–1350°C. The averaged values of the preexponential factor and the activation energy for interdiffusion were found to be D 0 = 1.16 × 10−4 m2/s and Q = 317 kJ/mol, respectively. The value D 0 ∼ 10−4 m2/s is typical of substitutional alloying elements in fcc metals; the value of Q is determined to be close to that for W and is significantly higher than those that correspond to other alloying elements in nickel superalloys. No clearly pronounced concentration dependence of the coefficients of interdiffusion has been revealed at a rhenium concentration of 4.4–9 wt %.

типично для легирующих элементов замещения в ГЦК-металлах, а Q близко к таковому для W и значительно выше, чем для других легирующих элементов в никелевых жаропрочных сплавах. Явной концентрационной зависимости коэффициент взаимной диффузии в интервале исследованных концентраций Re 4.4–9 мас. % не обнаружено. в диффузионных парах Ni4.4Re/Ni; Ni7Re/Ni; Ni9Re/Ni и Ni9Re/Ni4.4Re (мас. %) в интервале температур 1050–1350°С. Усредненные значения предэкспоненциального множителя и энергии активации взаимной диффузии соответственно составляют D0 = 1.16 ? 10-4 м2 и Q = 317 кДж/моль. Данное значение D0 10-4 м2 типично для легирующих элементов замещения в ГЦК-металлах, а Q близко к таковому для W и значительно выше, чем для других легирующих элементов в никелевых жаропрочных сплавах. Явной концентрационной зависимости коэффициент взаимной диффузии в интервале исследованных концентраций Re 4.4–9 мас. % не обнаружено.

Thermodynamic modeling of the interaction of the yttrium ceramics with Nb-Si-based melts alloyed with Ti, Cr, Hf, and Al is performed. It is shown that the result of their chemical interaction is the formation of a solid solution of hafnium oxide (HfO2), while other elements almost do not participate in the interaction. It is revealed in the course of modeling that the main interaction mechanism is the reduction of yttrium oxide upon its dissolution from ceramics into the metallic solution, in which the Y content depends on the temperature, composition, and amount of the metallic phase.

Optical and scanning electron microscopy, as well as electron microprobe analysis and electron backscatter diffraction, have been used to study diffusion processes that occur in a diffusion pair that consistsof a single-crystal CMSX-10 nickel-base superalloy and polycrystalline nickel, at temperatures of 1050–1250°C. It has been found that, in this system, the distributions of γ-stabilizing elements (Cr, Co, W, and Re) are described by the Boltzmann solution for diffusion between two semiinfinite plates of a binary alloy. The processing of these distributions has shown that the diffusion coefficients of Cr, Co, W, and Re in the multicomponent system are close to those in binary alloys of these elements with Ni. The diffusion redistribution of the elements leads to the dissolution of the γ′ phase in the nickel-base superalloy, growth of nickel grains toward the superalloy constituent of the diffusion pair, and the formation of porosity on both sides of the migrating interface, which is determined from a crystal misorientation of the alloy single crystal and nickel grains.

Методами оптической и растровой электронной микроскопии, а также микрорентгеноспектрального анализа и дифракции обратноотраженных электронов исследованы диффузионные процессы, происходящие в диффузионной паре монокристалл никелевого жаропрочного сплава CMSX-10 – поликристаллический Ni при температурах в интервале 1050–1250°C. Установлено, что в данной системе распределения -стабилизирующих элементов Cr, Co, W и Re описываются решением Больцмана для диффузии между двумя полубесконечными пластинами бинарного сплава. Обработка этих распределений показала, что коэффициенты диффузии Cr, Co, W и Re в многокомпонентоной системе близки к коэффицентам диффузии в бинарных сплавах этих элементов с Ni. В результате диффузионного перераспределения элементов происходит растворение -фазы в никелевом жаропрочном сплаве, рост никелевых зерен в сторону сплава и образование пористости по обе стороны мигрирующей поверхности раздела, определяемой по кристаллографической разориентации монокристалла сплава и никелевых зерен.

In a temperature range of 280–320°C, the mechanism and kinetics of segregation of impurities in steels have yet remained insufficiently studied. Under these conditions diffusion of impurities in the bulk of steel grains practically ceases, and for describing the kinetics of the process it is incorrect to use the Langmuir-McLean equation. In this work we put forward two new approaches to describe the mechanism and kinetics of phosphorus segregation in steels: a model of sequential changes in the state of phosphorus based on first-order reactions and a model of diffusion redistribution of phosphorus between boundaries of carbide precipitates, structure defects, and boundaries of steel grains. A comparative analysis of the suggested models has been conducted, and estimates of the kinetics of segregation based on them have been made; these estimates have been compared with the experimental results obtained in the temperature range of 280–320°C for test times to ∼20 years. It has been shown that these models fairly well describe the experimental kinetics of phosphorus segregation in boundaries of steel grains.

The process of grain-boundary segregation (GBS) has been considered under an assumption that the formation of associates (atomic complexes with a composition that corresponds to the nearest chemical composition in the phase diagram) is possible in a grain boundary (GB). The grain boundary is considered as a two-component mixture of A and B atoms, which can exist both in free and bound states (bound in a complex). The formation of complexes with an arbitrary composition and complexes of an AB type have been considered. It has been shown that, even in the absence of segregation (b = 1), the interactions of atoms in a GB that induce the formation of complexes leads to an enrichment of GBs in impurity atoms. It has been demonstrated that under certain conditions, a GBS isotherm can exhibit saturation corresponding to the chemical composition of the complex.

The wetting phase transition at low-angle intercrystallite grain boundaries has been experimentally observed. In contrast to the high-angle grain boundaries with the misorientation angels θ > 15°, the low-angle grain boundaries (θ < 15°) are not continuous two-dimensional defects, but constitute a discrete wall (network) of lattice dislocations (edge and/or helical). The theory predicts that, depending on θ, either a continuous layer of the liquid phase or a wall (network) of microscopic liquid tubes on wetted dislocation nuclei is formed at completely wetted low-angle grain boundaries. It has been shown that the continuous liquid layers at low-angle grain boundaries in the Cu-Ag alloys appear at the temperature T wminL = 970°C, which is 180°C higher than the onset temperature T wmin = 790°C and 50°C lower than the finish temperature of the wetting phase transition at high-angle grain boundaries, T wmax = 1020°C.

Grain boundary surface tension and surface tension of free surface for pure copper and copper-tin alloys are measured. On the base of these data isothermes of grain boundary tension, free surface tension and isothermes of adsorption are constructed in assumption of a dilute solution.

An investigation is made of the diffusion of antimony through the bulk and along grain boundaries in copper bicrystals containing a symmetric 〈100〉 misorientation boundary with misorientation angles from 20 to 37.2°. The bicrystals are grown by the method of horizontal zone recrystallization. The temperature range for these studies is 480–580 °C, where the solubility of Sb in Cu is about 6 atomic % and practically temperature-independent. The concentration profiles are obtained by x-ray spectral microanalysis, and the grain-boundary diffusion parameters are computed by the method of Whipple and Suzuoka. The orientation dependence of the triple product P=sδD b (where s is the segregation coefficient, δ the width of the grain boundary, and D b the grain-boundary diffusion coefficient) is nonmonotonic, with a maximum for the special ∑5 misorientation boundary (36.9°). The effective activation energy for grain-boundary diffusion ranges from ∼70 kJ/mol for ∑5 to140 kJ/mol for general boundaries.