Wydział Metali Nieżelaznych zaprasza na seminarium pt. „Mechanical and galvanomagnetic properties of FCC metals at low temperatures”, które wygłosi prof. Marek Niewczas (McMaster University, Hamilton, Kanada). Wydarzenie odbędzie się w 17 października 2019 r. o godz. 11.00 w bud. A-2, sali 101.
This work is concerned with the plasticity of pure FCC metals at low temperatures and the influence of material microstructure on galvanomagnetic properties. In-situ measurements of electrical resistivity during tensile deformation of single- and polycrystals were conducted at 4 K to follow the relationship between flow stress and density of deformation-induced defects. The data is assessed against general relationship τ = αμbρn, with n and α constants. The Taylor law, τ = αμbρ1/2, describes the flow stress adequately in monotonically deformed samples, however, it distorts this relationship in samples subjected to intermittent annealing, characterized by a higher rate of defect production and a lower rate of flow stress increase. Dislocations introduce a distortion to the Fermi surface, which influences the magnetoresistance. The degree of Fermi surface distortion can be assessed from De Haas Van Alphen measurements. Angular and field-dependent transverse magnetoresistance (TMR) has been studied in single- and polycrystals containing different density and distribution of dislocations. In the open-orbit orientation, TMR exhibits a quadratic variation with the applied magnetic field, which changes to the quasi-linear dependence, as the density of dislocations increases. In the closed-orbit orientations, TMR shows a linear dependence with the magnetic field; the slope of the characteristics decreases with increasing the density of dislocations. The magnetoresistance data are consistent with the two-band model and support the theory that the dislocation-induced relaxation time is anisotropic due to the non-sphericity of the Fermi surface. The presentation will provide framework for the discussion of the influence of dislocation microstructure on various physical properties of FCC metals.
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