Sergey N. Zhevnenko

Cross Diffusion-Stresses Effects

Three cross diffusion-stresses effects are considered: mobility-stress effect, flux-stress effect and vacancy-stress effect. The value of the migration volume for vacancies in Al is found from atomistic computer simulation. A cross vacancy-stress effect is applied to the process of the pores growth and dissolution in Ni-based superalloys.

Embrittlement of Cu and Cu-Based Alloys by Bi and Bi2Te3

Degradation of the mechanical properties of copper and copper based alloys after the treatment with telluride bismuth (Bi2Te3) at 570oC has been studied in the present work. The experiments were performed in a H2 deoxidizing atmosphere. The kinetics of embrittlement of pure copper has been shown to be parabolic. Bi2Te3 was in the solid state and was not in direct contact with the copper specimens during the experiments, i.e. the plating was performed through the gas phase. The brittle fracture along the GB was observed after 3 point bending test. The surface of fracture was investigated with the use AES. It was shown that intergranular penetrations of liquid bismuth and bismuth from Bi2Te3 have different mechanisms.

Isothermes of Surface and Grain Boundary Tension of Cu-Based Alloys with Sb, Sn, In

Grain boundary and surface tension for pure copper and copper-based alloys with Sb, Sn and In are measured by zero creep method. On the base of these and literature data, using the Shyshkovsky equation for a dilute solution, the isothermes of surface tension and grain boundary tension are constructed in Cu-based alloys with Sb, Sn, In and also Bi and Au. It is shown that all solutes are active on the surface tension of copper. The free energies of adsorption are negative and decrease in a following consequence: Bi, Sb, Sn, In, and Au.

Determination of Copper Self-Diffusion Coefficients on the Base of High-Temperature Creep Data

Indirect method is used for determination of copper self-diffusion coefficient on the base of high-temperature creep data. These data are obtained by the use of the new measuring device and assuming that Nabarro-Herring mechanism acts.

The Liquid Bismuth Penetration from Solid Bi2Te3: Grain Boundary Embrittlement and Effect of Impurities

The liquid bismuth penetration from solid bismuth telluride (Bi2Te3) into grain boundaries of copper and copper-based solid solutions was studied. The experiments were performed at 570 oC in hydrogen atmosphere. The copper specimens were annealed from 10 to 90 minutes. Solid Bi2Te3 didn’t contact with copper specimens during experiments, so copper was covered by the decay products of Bi2Te3 through the gas phase. Liquid Bi penetration leads to grain boundary embrittlement of copper. We assumed that the depth of penetration is equal to the length of cracks which are formed after sample bending. It was shown that there is only bismuth at the grain boundaries while on the surface tellurium also exists. Bismuth concentration in the grain boundaries measured by Auger spectroscopy was about 10-20 at. % and the width of penetration channel was less then 10 nm. Bismuth covered the grain boundaries uniformly. Time dependence of the penetration depth was approximately parabolic. In the present work the effect of impurities (silver, iron) on grain boundary liquid bismuth penetration was studied also. It was shown that silver accelerates the penetration in contrast to iron. The probable reasons were discussed.

Interface Controlled Diffusional Creep of Cu + 2.8 at.% Co Solid Solution

High-temperature creep experiments were performed on a Cu-2.8 ат.% Co solid solution. Cylindrical foils of 18 micrometers thickness were used for this purpose. Creep tests were performed in a hydrogen atmosphere in the temperature range of about from 1233 K to 1343 K and at stresses lower than 0.25 MPa. For comparison, a foil of pure copper and Cu-20 at.% Ni solid solution were investigated on high temperature creep. Measurements on the Cu foil showed classical diffusional creep behavior. The activation energy of creep was defined and turned out to be equal 203 kJ/mol, which is close to the activation energy of bulk self-diffusion of copper. There was a significant increase in activation energy for the Cu-20 at.% Ni solid solution. Its activation energy was about 273 kJ/mol. The creep behavior of Cu-Co solid solution was more complicated. There were two stages of diffusional creep at different temperatures. The extremely large activation energy (about 480 kJ/mol) was determined at relatively low temperature and a small activation energy (about 105 kJ/mol) was found at high temperatures. The creep rate of Cu-Co solid solution was lower than that of pure copper at all temperatures. In addition, the free surface tension of Cu-2.8 ат.% Co was measured at different temperatures from 1242 K to 1352 K. The surface tension increases in this temperature range from 1.6 N/m to 1.75 N/m. There were no features on the temperature dependence of the surface tension.

The Formation of Liquid Metal Channels Network under Grain Boundary Wetting in the Cu-Bi System

Grain boundary liquid grooving process takes place during the contact of solid metal phase with the metal melt. The liquid bismuth network formation along grain boundaries (GB) and triple junctions (TJ) was investigated in copper polycrystalline samples. The experimental observation in situ technique of Bi penetration through the Cu plate was used. Microscopic images of the liquid channels network were obtained. The temperature dependencies of GB and TJ effective penetration depths were determined. The effect of the GB and TJ diffusion on the liquid channels growth mechanism was discussed.

Grain Boundary Diffusion of Silver in Copper-Iron Alloys

Grain boundary (GB) diffusion of Ag in Cu-based alloys with Fe (0, 0.14, 0.29, 0.43, 0.55 and 0.99 at. % Fe) was investigated. The experiments were performed at 600, 650 and 700 °C, which corresponded to B-regime. It was proved by the presence of diffusion wedges. The triple product of silver GB diffusion was obtained by measuring of angle at the top of isoconcentration profiles which was detected by electrochemical etching. It was shown that iron decreased the triple product at higher temperatures and didnt affect significantly at lower temperatures. SEM investigation showed the presence of small (10-100 nm) precipitates on the copper grain boundaries. Analysis of particles composition by Auger electron spectroscopy indicated higher concentration of iron comparing with the alloy composition.

Grain Boundary Surface Tension, Segregation and Diffusion in Cu-Sn System

Grain boundary and free surface tension 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. Grain boundary diffusion coefficients of copper were calculated by using the relation of Borisov et. al. for copper and copper-tin alloys.

Isothermes of Grain Boundary Tension and Grain Boundary Adsorption in Cu-Sn System

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.