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ELECTRON BEAM REMELTING OF PLASMA SPRAYED ALUMINA COATINGS
Matějíček, Jiří ; Veverka, J. ; Čížek, J. ; Kouřil, J.
Plasma sprayed alumina coatings find numerous applications in various fields, where they enhance the properties of the base material. Examples include thermal barriers, wear resistance, electrical insulation, and diffusion and corrosion barriers. A typical structure of plasma sprayed coatings, containing a multitude of voids and imperfectly bonded interfaces, gives them unique properties - particularly low thermal conductivity, high strain tolerance, etc. However, for certain applications such as permeation barriers or wear resistance, these voids may be detrimental.\nThis paper reports on the first experiments with remelting of plasma sprayed alumina coatings by electron beam technology, with the purpose of densifying the coatings and thereby eliminating the voids. Throughout the study, several parameters of the e-beam device were varied - beam current, traverse velocity and number of passes. The treated coatings were observed by light and electron microscopy and the thickness, structure and surface morphology of the remelted layer were determined and correlated with the process parameters. Based on the first series of experiments, the e-beam settings leading to dense and smooth remelted layer of sufficient thickness were obtained. In this layer, a change of phase composition and a marked increase in hardness were observed.\n
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Diffusion of C and Mn in steel weldment Fe-0,3C/Fe-0,3C-15Mn
Král, L. ; Million, Bořivoj ; Čermák, Jiří
In the present paper, the results of measurements of C and Mn diffusion in steel weldments of ternary alloys Fe-0.3C/Fe-0.3C-15Mn are reported. Alloys were cast in induction furnace under protective Ar atmosphere. Ingots were hot-forged to rods of the diameter 15mm and homogenized. After annealing they were machined on diameter 12mm and cut into pieces of 4mm thickness. These cylindrical samples were ground and welded by electrical impulse. Diffusion couples were sealed into evacuated silica ampoules together with Ti-chips. They were annealed at 500-1100 °C for 1.5-96 hours. Measurement of carbon and manganese redistribution was done by means line segment microanalysis in normal direction to welded interface using electron scanning microscope Philips SEM-505WDS equiped with Microspec WDX-2A. Diffusion coefficients of C and Mn were obtained and the relations between them were found.
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Transient and Average Markov Reward Chains with Applications to Finance
Sladký, Karel
The article is devoted to Markov reward chains, in particular, attention is primarily focused on the reward variance arising by summation of generated rewards. Explicit formulae for calculating the variances for transient and average models are reported along with sketches of algorithmic procedures for finding policies guaranteeing minimal variance in the class of policies with a given transient or average reward. Application of the obtained results to financial models is indicated.
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XIVth Youth symposium on Experimental Solid Mechanics
Major, Z. ; Kytýř, Daniel
The Youth Symposium on Experimental Solid Mechanics traditionally brings together young researchers and engineers, students and PhD students, who are actively involved in the experimental solids mechanics, theoretically and practically, in order to exchange their experience, to report on the present state-of-art as well as on running research projects, to discuss due questions and problems and to promote the cooperation among individuals as well as among institutions. The XIVth symposium continues both, the long tradition of this conference series and introduces novel elements. The combination of the experimental mechanics with modern numerical methods was focused. This year, participants from 12 countries attended the symposium. Based on their presentations, 19 papers were selected for the publication in this issue of Acta Polytechnica CTU Proceedings.
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