Mesoscale modeling and simulation of microstructure evolution during dynamic recrystallization of a Ni-based superalloy

Microstructural evolution and plastic flow characteristics of a Ni-based superalloy were investigated using a simulative model that couples the basic metallurgical principle of dynamic recrystallization (DRX) with the twodimensional (2D) cellular automaton (CA). Variation of dislocation density with local strain of deformation is considered for accurate determination of the microstructural evolution during DRX. The grain topography, the grain size and the recrystallized fraction can be well predicted by using the developed CA model, which enables to the establishment of the relationship between the flow stress, dislocation density, recrystallized fraction volume, recrystallized grain size and the thermomechanical parameters

The great jerboa (Allactaga major) in the North Azov Region (Ukraine): distribution and abundance

The analysis of the species historical spread in Ukraine was conducted. The dependence of preservation of its localities on the availability of more or less large areas of virgin steppe unsuitable for arable farming was showed. The original data for the past 20 years on the great jerboa’s distribution within the Northern Pryazovia were reported, as well as the conditions of existence of its stable populations in the Azov Upland area. The reasons of further reduction in number and fragmentation of its range are the destruction of virgin steppe because of plowing and afforestation, alongside with increasing the projective vegetation cover due to reduce of grazing. To protect jerboa and other rare steppe species we proposed moratorium on plowing and other kinds of destruction of the virgin steppe and creation of a new environmental legislation on conservation, restoration and sustainable use of the steppe, the National Heritage of Ukraine

Investigation of the Crystallization Kinetics in Ge-Sb-Te-Bi Thin Films for Phase Change Memory Application

In this work the mechanism and kinetics of crystallization of the Ge₂Sb₂Te₅+Bi thin films were investigated using differential scanning calorimetry. Ge₂Sb₂Te₅ with different amounts of Bi (0, 0.2, 0.5, 0.8, 1, 3, 5 wt.%) was synthesized using quenching technique. Thin films were prepared by thermal evaporation of synthesized materials. X-ray diffraction has shown that synthesized materials had trigonal modification of Ge₂Sb₂Te₅. Introduction of Bi led to the appearance of trigonal modification of Bi₂Ge₂Te₅, which indicates on the replacement of Sb by Bi. As-deposited thin films were amorphous up to 3% of Bi. Higher concentrations of Bi led to the appearance of crystalline phases. Composition of thin films was verified by Rutherford backscattering, and was found to be close to that of the synthesized materials. The joint application of model-free Ozawa-Flynn-Wall and model-fitting Coates-Redfern methods allowed to estimate kinetic triplet for crystallization process of GST225+Bi thin films, and to predict data processing and storage times of the phase change memory cells. It was shown that GST225+0.5 wt.% Bi thin films have the most promising kinetic characteristics among the investigated materials, due to the predicted smallest data processing and largest storage times