Yttrium effect on the structural-phase state in situ of Mo – 15.3 V – 10.5 Si composite

The effect of yttrium on the structural-phase state of the Mo – 15.3 V – 10.5 Si hypereutectic alloy has been investigated using X-ray phase analysis and scanning electron microscopy with energy-dispersive X-ray analysis. It has been established that the main phases of Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys obtained under nonequilibrium crystallization are the metal solid solution (Mo1 – xVx)ss-matrix, silicide solid solution (Mo1 – xVx)3Si and silicide Y5Si3. In alloys doped with yttrium up to 1.0 at. %, the space between the dendrites of the (Mo1 – xVx)ss metal phase is filled with (Mo1 – xVx)3Si solid solution, and Y5Si3 is located at the boundaries of the metal solid solution. At a concentration of yttrium in alloys above 3.0 at. % the space between (Mo1 – xVx)ss dendrites is filled with Y5Si3 silicide, inside which (Mo1 – xVx)3Si grains are formed. Triple or quaternary compounds containing yttrium were not detected. Elemental composition of alloy phases of the Mo – (14.3 – 15.4) V – (9.8 – 10.6) Si – (0.3 – 5.3) Y alloys is almost identical and is characterized by non-stoichiometry with respect to silicon. According to well-known literature data, the silicon contents in the (Mo1 – xVx)ss and (Mo1 – xVx)3Si phases are within the acceptable limits of the homogeneity region, and the silicon concentration in Y5Si3 (≈ 35.4 at.%) is beyond the established limits. Doping of the Mo – 15.3 V – 10.5 Si alloy with yttrium increases the dispersion of the structure. Particles of the main structural components become close in size. Wherein the volume ratio of the metallic phase to the silicide with increasing yttrium content in the alloys increases. The density of alloys varies between 8.7 – 9.0 g/cm3.

Structure Diagnostic of Iron-Based Out-of-Peritectic Alloys during Nonequilibrium Crystallization

The effect of the contribution of basic components (silicon, manganese, chromium, and nickel) in multicomponent iron-based alloys on critical point position of the peritectic reaction was studied by using the POLYTHERM software package. Obtained temperature and concentration values of critical points of peritectic transformation, depending on the content of iron-based alloy components (Si, Mn, Cr, Ni) were used to build summary equations, represented the change in temperature and concentration of critical points by variation of binary, ternary and quaternary alloy composition. Investigation of nonequilibrium crystallization of out-of-peritectic casting steels was performed by using a system of computer models describing thermodynamic, thermophysical, diffusion and capillary processes during solidification under coalescence of dendritic branches. The nonequilibrium crystallization regime was specified by suppression of diffusion in the solid phase, reflected by adding the inverse diffusion parameter to the system of the computer model. The application of these computer models not only allows to make calculations of the temperature course, the solid phase fraction and the composition of the components in the liquid phase but also the calculation of secondary arm spacing during crystallization with taking into account the coalescence process.

Features of the influence of thermal modes of cooling on processes of nonequilibrium crystallization of materials from the liquid state

The quantitative estimation of maximum level of cooling rates in the process of casting microwires in glass insulation is given. The shown possibility of nonequilibrium formation of microwire substance is due to the influence of an amorphous substrate in the form of glass insulation. The amorphous state in the case of thin microwires with cast iron vein Fe‒20 at.% C confirms the implementation of an increased (compared to splat-quenching) level of nonequilibrium formation of microwires in combination with updated rates of cooling and increased degree of supercooling of liquid microwire vein.

DIAGNOSTICS OF DENDRITE STRUCTURE OF MULTICOMPONENT ALUMINUM ALLOYS

Stages of system analysis and mathematical models for predicting the dendritic structure of multicomponent aluminum alloys are considered. Computer diagnostics of nonequilibrium crystallization is realized by the joint use of the apparatus of computational thermodynamics and means of computational heat transfer for solving problems of computational materials science. The results of modeling the evolution of the dendritic structure are presented with a change in the diffusion intensity in the solid phase from equilibrium conditions to complete suppression.