In this paper the effect of diffusion formation of supersaturated solid solution in the Al-Ge system is discussed. It was shown that at relatively low temperatures of diffusion annealing, Ge concentration in Al-based solid solution became higher than the solubility limit at given temperatures. The maximal concentration of Ge was determined by extrapolation of the diffusion profile on the Ge/Al interface. Analysis of diffusivity of Al in Ge allowed to suggest that slow diffusion in Ge restricts the formation of Ge-based solid solution. Qualitative approach confirmed this suggestion.

In this work, the interdiffusion features in multicomponent (high-entropy) alloys of refractory metals were studied. The following pairs were chosen as the diffusion study objects: titanium–equiatomic alloy (Hf–Nb–Ta–Ti–Zr–Mo) and titanium–tantalum for the sake of comparison. The article covers the issues of sample preparation, microstructure study, sample preparation methodology for diffusion research, and experimental results. Diffusion annealing was carried out for 12 h in a vacuum at a residual argon pressure of 6.65·10–3 Pa and a temperature of 1200 °С. Particular attention was paid to the method of combining diffusion pairs (titanium with tantalum, titanium with alloy) by thermal cycling near the polymorphic transformation temperature in titanium (882 °C) within ± 50 °C. The behaviour of the most characteristic elements (Ta, Zr, Ti) in the weld area after the titanium and alloy diffusion pair joining was demonstrated. This is the first time that data on the dependence of the intensity of the corresponding spectral line for titanium and elements of a multicomponent alloy on the penetration depth were obtained. A change in the signal intensity for system elements was observed at a depth of 150–200 μm, whereas a sharp drop in the signal intensity was seen to occur at depths of about 50 μm. The effective value of the coefficient of diffusion of elements into titanium averaged over all elements of the alloying system (except for titanium) at a temperature of 1200 °C was calculated. The obtained value was compared to reference data: the self-diffusion coefficient in β-titanium and diffusion coefficients in titanium pairs with alloy doping elements.

The peculiarities of Ni and Fe diffusion in polycrystalline Cu and Cu-Fe alloys at a 650–750 °C temperature range were studied. It was shown that the bulk diffusion coefficients were in a good agreement with the available literature data obtained for different temperature concentration ranges. The obtained values of the Ni GB diffusion triple product could be described as sδDb=8.8×10−13×exp(−165 kJmol−1RT)m3s−1. The obtained values were an order of magnitude less than the values obtained by the radiotracer method. This fact was explained by the negative segregation of Ni at the Cu GB. A stronger negative segregation of Fe in the copper GB reduced the penetration depth of iron along the GB because of an additional (negative) “driving” force; this explained why there was no advanced grain boundary diffusion. Another peculiarity of the Fe diffusion that was confirmed was the significant supersaturation of the Cu-based solid solution near the Fe/Cu interface.

The microstructure and phase composition of a nickel -based heat -resistant alloy samples doped with Cr, Co, Ti, W and Mo (alloy VZh171) in the nitrided state were studied using methods of autoemission high -resolution scanning electron microscopy. The change in the particle sizes of titanium nitrides during isothermal annealing at a temperature of 1300 degrees C for 1.5, 2 and 3 hours was studied. It is shown that the evolution of particle sizes under the studied conditions corresponds to the Lifshitz-Slezov-Wagner model of diffusive coalescence of particles.

The analysis of grain boundary (GB) diffusion in metallic systems based on Cu, Ni, Ag and Al was made to set demonstrate the common behavior. It was shown that the slow penetration for 11 systems can be connected with negative segregation or specific interatomic interaction. Two energetic parameters such as energy of interaction with GB and energy of interatomic interaction are proposed as main characteristics. The analysis of a tendency toward segregation and tendency of intermediate phase formation in these terms allows us to divide the systems on four groups and formulate a qualitative way to predict the behavior of the diffusing elements in a non-dilute solution. Mathematical formulation of GB diffusion problem and typical solutions are presented.

Interdiffusion of the elements in a diffusion pair consisting of Ti and an equiatomic high-entropy alloy (HEA) TiZrHfNbTaMo in the temperature range of 1473–1673 K has been studied. A calculated results phase diagram of the alloy by Thermo-Calc 2021-B software as used to determine the temperature stability range of the β-phase in the alloy. Ti–HEA diffusion pairs were obtained by low = temperature welding and then diffusion annealing was carried out at temperatures of 1473, 1573, and 1673 K during 12, 9, and 6 h, respectively. The interdiffusion zone was profiled using electron probe microanalysis (EPMA). The diffusion parameters of the HEA’s elements were obtained using Hall’s method. An experimental results discussion is given.

Изучена кинетика высокотемпературного азотирования, а также изменение структуры и свойств в зависимости от его продолжительности для жаропрочного никелевого сплава ВЖ171 системы Ni - Co - Cr - W - Ti. Проведены испытания на кратковременное растяжение и длительную прочность. Исследована микроструктура азотированного слоя. Представлено математическое описание процесса. Даны рекомендации по определению оптимальных режимов азотирования сплава ВЖ171 для достижения наиболее высоких характертстик кратковременной и длительной прочности. Установленные в работе зависимости позволяют определить время азотирования при изготовлении изделий различной толщины из сплава ВЖ171.

The kinetics of high-temperature nitriding and changes in the structure and properties of heat-resistant Ni – Co – Cr – W – Ti nickel alloy VZh171 depending on its duration were studied. Short-term pulling and long-term strength tests were carried out. An analysis of the microstructure of a nitrided case is presented along with a mathematical description of the process. Recommendations are given for determining the optimal nitriding conditions of the VZh171 alloy in order to achieve the highest short-term and long-term strength. The established dependencies allow the nitriding time during the course of manufacturing items of various thicknesses from the VZh171 alloy to be determined.

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.

Abstract—The results of the density functional theory calculation of the segregation energy of refractory metals at grain boundaries (GBs) in the alloys based on nickel (fcc solid solutions), chromium (bcc), and titanium (hcp) are analyzed. The influence of segregation on the cohesive strength of GBs is estimated using the Rice–Wong model, in which the mechanical strength of GBs is characterized by the boundary splitting energy. Refractory metals are shown to contain “useful” elements, which enrich GBs and increase their cohesive strength in alloys of all types. The calculated data are used to design experimental high-temperature alloys (HTAs), the alloying system of which contains useful elements in the form of a package of low-alloy additives in HTAs, namely, nickel (Zr, Nb, Hf, Ta), chromium-based (Nb, Ta), and titanium (W, Ta, Re) alloys. The results of testing the mechanical properties of these experimental alloys are presented. The low-alloy additives are shown to increase the creep resistance of all alloys at elevated temperatures.

Spectra of grain boundaries existing in the polycrystalline copper-silver system (positive enthalpy of mixing) have been studied in comparison with those of the copper-indium system (negative enthalpy of mixing). Spectra of grain boundaries are formed spontaneously upon an increase in the temperature, occurrence of eutectic and peritectic reactions, and subsequent relaxation of structures in the two-phase solid/liquid region of phase diagrams. It has been shown that the rate of grain growth and the relation between different grain boundary types in the total spectrum depend on the enthalpy of mixing.

Present work is dedicated to the investigation of grain boundary (GB) wetting phase transition on different types of grain boundaries in the Cu-Ag system. The character of GBs in the samples was determined by the electron backscattering diffraction. GB character distribution was based on the coincidence site lattice (CSL) model and on the values of the misorientation angle of GBs. Experimental results show that only the low angle GBs and the Sigma 3 CSL GBs do not reach complete wetting by the melt. Random high misorientation angle (HA) GBs reach complete wetting at 895 degrees C. Only Sigma 11, Sigma 5 and Sigma 13 CSL GBs have a higher wetting temperature than the HA GBs, so their GB energy should be lower than the energy of HA GBs. (C) 2020 Elsevier B.V. All rights reserved.

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.

Lack of plasticity is one of the main disadvantages of metallic glasses. One of the solutions to this problem can be composite materials. Diffusion bonding is promising for composite fabrication. In the present work the diffusion process in glassy multilayer films was investigated. A combination of advanced transmission electron microscopy (TEM) methods and precision sputtering techniques allows visualization and study of diffusion in amorphous metallic layers with high resolution. Multilayered films were obtained by radio frequency sputter deposition of Zr-Cu and Zr-Pd. The multilayers were annealed under a high vacuum (10(-5) Pa) for 1 and 5 h at 400 degrees C, that is, well below the crystallization temperatures but very close to the glass-transition temperatures of both types of the glassy layer. The structural evolution in the deposited films was investigated by high-resolution transmission electron microscopy. It was observed that, despite the big differences in the atomic mass and size, Pd and Cu have similar diffusion coefficients. Surprisingly, 1 h of annealing results in formation of metastable copper nanocrystals in the Zr-Cu layers which, however, disappear after 5 h of annealing. This effect may be connected with nanovoid formation under a complex stress state evolving upon annealing, and is related to the exceptionally slow relaxation of the glassy layers sealed with a Ta overlayer. (c) 2019 The Authors. Published by Elsevier Ltd.

Sn grain boundary diffusion (GBD) in dilute (up to 2% at Sn) Cu-based alloys was investigated in the temperature range from 560 to 650 degrees C by the EPMA method. 3-layer samples Cu/Cu-Sn alloy/Cu were prepared. Experimental values of the triple product P = s delta D-b were obtained in the frame of Fisher-Gibbs model: P= 10(-13).exp(-89 kJ/mol/RT) m(3) s(-1). The effective activation energy comprises approximately 0.5 from the bulk value. In the chosen temperature range the path of the bulk diffusion was equal about 10 mu m and the path of GBD (Fisher length) varied in the range 20-30 mu m. The accelerated GBD was observed only for the part of investigated GBs. (C) 2019 Elsevier B.V. All rights reserved.

The paper is devoted to some properties of grain boundaries: Segregation and concentration phase transitions – two important consequences of atomic interactions in grain boundaries. Except of a short description the Gibbs method of surface excesses and grain boundary segregation isotherms with the limited number of segregation sites in grain boundary, the paper concentrates on the effects of complexes formation, including thermodynamic and computer modeling, and concentration phase transition in the grain boundaries in systems with restricted solubility and intermediate compounds.

•Grain boundary diffusion is a complicated phenomenon which includes different effects.•We must take into account different fact and measure carefully both diffusion parameters and segregation parameters.•At large concentration the grain boundary diffusion rate can be so small that we can hardly see it.