Papers by Author: Savko Malinov

Abstract: Stainless steels can form a protective oxide layer when exposed to a high temperature oxidising environment, this protective layer forms a diffusion barrier and slows the oxidation of the alloys in harsh environments. This characteristic has made stainless steels one of the most commonly used alloys for high temperature industrial applications. In this work, a systematic testing procedure has been used to investigate the high temperature oxidation of two commonly used grades of stainless steel, 316 and 310. Samples of each alloy have undergone isothermal testing in air at 1050°C, 1150°C and 1250°C for a range of time periods up to 8h. The oxidation kinetics were also investigated using thermo-gravimetric analysis in air at the same temperatures for 8h. The oxide layers formed on the samples were characterised using X-Ray diffraction, Scanning electron microscopy and energy dispersive spectroscopy. Information derived from oxide layer characterisation was used to explain any differences between the two alloys in terms of oxidation rate and overall alloy performance in the high temperature environment.

Abstract: Chemical ordering kinetics in L10- and B2-ordered AB binary intermetallics was simulated by means of Monte Carlo (MC) technique implemented with vacancy mechanism of atomic migration. While vacancy concentration is usually much lower than the antisite defect concentration in L10-ordered systems, triple defects are generated in particular B2–ordered systems. The latter definitely affects the chemical ordering process and requires that full thermal vacancy thermodynamics is involved in B2-ordering simulations. The study on L10-ordered binaries was dedicated to FePt thin layers considered as a material for ultra-high-density magnetic storage media. Metastability of the L10 c-variant with monoatomic planes parallel to the layer surface and off-plane easy magnetization was revealed. Thermal vacancy formation in B2-ordered binaries was modelled by implementing a mean-field Hamiltonian with a specific formalism of phase equilibria in a latticegas composed of atoms and vacancies. It was demonstrated that for particular pair-interaction energetics, equilibrium concentrations of vacancies and antisites result mutually proportional in well-defined temperature ranges. The MC simulations of B2-ordering kinetics involved the modelled equilibrium vacancy concentration and reproduced the experimentally observed low rate of the process.