Papers by Keyword: Interphase Boundaries

Abstract: Electric current has a significant effect on the transfer of matter in liquid layers that grow during contact melting. Depending on the direction of the current, both an increase and a decrease in the rate of contact melting can be observed. In this case, the growth of liquid interlayers does not obey the well-known parabolic law, in contrast to the usual (current-less) contact melting in a nonstationary diffusion mode and other diffusion processes. The paper considers the question of the influence of direct electric current on the concentration distribution in the melt formed during contact melting, as well as on the process of movement of interphase boundaries. A solution is obtained for the diffusion equation for a liquid layer growing in the process of contact melting in the presence of a constant electric current in the system. It is shown that the concentration distribution curves and their gradients for the two modes of the process under consideration (accelerating and decelerating) will have a rather different form, while the movement of the interphase boundaries occurs according to a complex law.

Abstract: Interfacial microstructure of TiN-TiB2 composite, which was synthesized by hot shock compaction combined explosively shock condolidation and self-propagating high-temperature synthesis, was investigated by transmission electron microscopy (TEM). In the TiN-TiB2 composite included 60mol% TiN, an experimentally measured average grain size of the both TiN and TiB2 was approximately 500nm, and it decreased rather than those of the raw powders. By the conventional TEM observations, we clarified that there was a specific orientation relationship between cubic TiN and hexagonal TiB2. The high resolution electron microscopy (HREM) observations revealed that the TiN/TiB2 interphase boudnaries were atomically flat. We also observed grain boundaries of the composite and found that no secondary phases such as amorphous phase and precipitates were observed at the grain boundaries in the composite.

Abstract: A model of discontinuous precipitation in binary polycrystalline alloys at low temperatures is presented. The proposed approach allows independent determination of the main parameters, including the interlamellar distance, the maximum velocity of the phase transformation front, and the concentration step at this boundary. This is achieved by using a set of equations for: 1) the mass transfer in the moving interphase boundary; 2) the balance of the entropy fluxes at the phase transformation front, and 3) the maximum rate of the free energy release under constraint of entropy balance. Concepts of mobility and linear interrelation between the driving force and velocity are not used explicitly. Comparison of the model calculation with the experimental results for the Pb-Sn system at different supersaturations is provided.

Abstract: A model of alloying in the three-layer thin-film system at the low temperature is constructed. Solid solution formation takes place as a result of the diffusion-induced grain boundary migration (DIGM). The unknown parameters are determined from the set of the equations for: (1) grain boundary diffusion along the moving planar phase boundary; (2) the entropy balance in the region of the phase transformation moving with constant velocity; (3) the maximum rate of the free energy release. We consider the model system with complete solubility of the components. The main parameters are self-consistently determined using thermodynamic and kinetic description in the frame of the regular solution model. The model allows determining the concentration distribution along the planar moving phase boundary, its velocity, the thickness of the forming solid solution layer and the limiting average concentration in this layer.

Abstract: In this communication we present the results of study of new contact systems to GaN epitaxial layers grown on sapphire and n-type 6H-SiC monocrystals. The TiBx nanostructure phase has been used during manufacturing Ti – Al – TiBx – Au and TiBx contact systems. The n-GaN epitaxial layers of 1 µm thickness were grown on [0001] sapphire substrate by vapor-phase epitaxy. The n-type 6H-SiC monocrystals were grown by Lely method with the donor concentration of 2x1018 cm3. The layers of Ti, Al, TiBx and Au were deposited by magnetron sputtering followed by high-temperature annealing.

Abstract: A method of the determining of the mutual diffusion coefficients in ternary intermediate phases is suggested. Methodology for determination of the interdiffusion coefficients of phases formed in a ternary diffusion couple in T-sample configuration is presented. The method requires only one annealing of the T-sample and makes it possible to calculate the matrix of the diffusion coefficients in the (CuNi)6Sn5 and Cu3Sn ternary intermediate phases under low temperature. The concentration profiles and electron micrograph of the diffusion zone was obtained in the ternary Cu-Ni-Sn system annealed for 64 hours under 200°C. Phase competition in this ternary system with special configuration of T-sample leads to lateral diffusion of Cu, to formation (CuNi)6Sn5 compound between Ni-Sn side and to suppression of other NixSny intermediate phases.