Papers by Keyword: Amorphous Alloy

Abstract: An amoprphous and nanocrystalline ribbon is produced applying the technology of rapid molten metal quenching. The chemical composition of the alloy is required to contain elements ensuring the amorphous structure formation in the course of quenching. A great number of various chemical elements in amorphous and nanocrystalline alloys contribute to the complex process of the structure formation in the course of heat treatment of the amorphous precursor. After heat treatment, the structure of the soft magnetic material can remain amorphous or partially crystallized or nanocrystalline. The results of an investigation into the melts’ property of iron-based amorphous and nanocrystalline alloys are presented in the paper. The structure has been shown to influence mechanical properties of the material in preparing the melt before casting.

Abstract: Plastic deformation after indentation of the metallic glass Cu₄₇Ti₃₅Zr₁₁Ni₆Si₁ at different loading conditions was examined. Discontinuities on the loading curves were observed, the magnitude of which depends on the loading rate. The presence of these discontinuities is influenced by the precise shape of the indentation tip. At lower loading rates and using a cube corner indenter tip the discontinuities on the loading curves are more pronounced. An increase of the loading rate tends to diminish instantaneous plastic deformation as appear by pop-ins. Using a Berkovich type indenter tip the plastic deformation is more steady. It is concluded that the final morphology of the pile-up area strongly depends on the geometry of the indenter tip, whereas no correlation between discontinuities in the loading part of the indentation curve and the formation of shear band patterns was observed.

Abstract: An amorphous metallic ribbon of Fe₄₀Ni₄₀B₂₀ was used for in-situ observation of the crack propagation and shear band formation during tensile tests. Prior to the tensile tests, two holes (with different positions with respect to the tensile axis) were made by laser ablation as stress concentrators. The nucleation and propagation of shear bands on the ribbon surface during tensile tests were analysed with scanning electron microscopy (SEM). At room temperature inhomogeneous plastic deformation of amorphous alloy occurs via the development of primary and secondary shear bands. The influence of the different loading geometry on the topology of shear bands and crack propagation was studied.

Abstract: In metallic glasses plastic deformation occurs via the creation and the propagation of a softened region in the shear bands. Some of the high strength metallic glasses (as Zr-based metallic alloys) exhibit complex shear band topography and the final failure respects the allocation of the shear bands. We studied the differences in the fracture surfaces of Zr-and Mg-based amorphous alloys. Ductile behaviour of the shear bands in Zr-based amorphous alloy tends to the dimple creation during the failure. On the fracture surfaces the vein pattern morphology manifestations were present. Conchoidal fracture was typical for Mg-based amorphous glass. Two different surface morphologies, plumes and rib marks ornament the fracture surfaces.

Abstract: Al-based amorphous materials are believed to be a promising light weight and high strength material, but the application has not yet been realized due to difficulties in fabricating bulk materials resulted from their quite weak glass forming ability. In order to overcome this difficulty, a solid state route was studied to fabricate bulk Al-based metallic glass. An amorphous Al₇₂Ni₈Ti₈Zr₆Nb₃Y₃ powder was first fabricated by mechanical alloying, and then the microstructure, glass-forming ability and crystallization behavior were characterized. The powder shows a wide supercooled liquid region (81K), and high activation energy for crystallization (312.6kJ/mol). By this powder, a bulk material was fabricated through high pressure (2GPa) sintering (673K and 723K). The microhardness of bulk sample is as high as 1215Hv, providing a solid basis for fabricating bulk materials and applications.

Abstract: Bulk metallic glasses are attractive materials for structural and functional applications when compared to crystalline materials. The Cu-based glasses exhibit particular interest due primarily to their relatively low cost and high fracture resistance. In this work the Cu_49.7Ti_31.8Zr_11.3Ni_7.2 alloy was prepared from the mixture of pure metals by arc melting and following the ingot was re-melted by centrifugal casting in wedge-section copper mould. The structure of wedge bulk sample was evaluated by a combination of X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The results show that the amorphous state is formed in the thinner region and it is maintained up to thickness of 3.5 mm in the wedge bulk-sample. The crystallization temperature was observed above 400 °C coinciding with the studies of thermal crystallization by XRD and DSC. Dynamical heating of the amorphous phase from room temperature up to 750°C showed the formation of CuTi, Cu₁₀Zr₇ e Cu₂TiZr crystalline phases.

Abstract: The paper describes results of testing of magnetic loss and saturation of magnetic system for superconductive electrical devices, manufactured of AMAG 225 AMAG 170 amorphous alloys produced by the Open Joint-Stock Company “Mstator”. Note that annealing of the cores was not carried out, since previous experience shows that annealing process makes steel crispy, and, furthermore, in case of thermal cycling, which occurs in cryogenic machines and devices, the destructive process is accelerating and results in the total destruction of amorphous tape. Manufacturing of the cores of different superconductive electrical devices requires testing with 2NSR, 5BDSR amorphous alloys, AMAG 200 nanocrystalline tape, (unannealed and annealed). The results of these investigations were published previously.

Abstract: The paper is devoted to testing of a brushless exciter intended for a 1 MVA high-temperature superconductive (HTSC) synchronous generator. It was decided to make a ambient-temperature version on the 1-st stage with a latter transaction to a cryogenically-cooled version. The exciter incorporates a number of nanomaterials: rare-earth Nd-Fe-B magnets and magnetic cores, manufactured of amorphous alloy tape.

Abstract: In this paper, the core losses of Fe₈₀Si₉B₁₁, Fe₇₈Si₉B₁₃ amorphous alloy cores were separated to investigate the behaviors of hysteresis loss, eddy current loss and additional loss in high frequency range. The results showed that the losses of amorphous alloy core were mainly composed of hysteresis loss in low frequency. With the increase of frequency, eddy current loss increased drastically compared with the hysteresis loss, the eddy current loss was greater than the hysteresis loss when the frequency was higher than 5 kHz and 6 kHz for amorphous alloy with the composition of Fe₇₈Si₉B₁₃ and Fe₈₀Si₉B₁₁, respectively. The eddy current loss proportion in total loss increased with the increment of frequency.

Abstract: We analyzed the failure characteristics of the metallic glass Co₄₃Fe₂₀Ta_5.5B_31.5 (at.%) deformed in bending. The nanoscale fracture surface morphology respects the micromechanisms of the failure of the amorphous structure. The fracture surfaces consist of nanosized dimples (40 nm) arranged in the lines respecting the periodic corrugation zones oriented perpendicular to the crack propagation direction. The corrugation topology exhibits the point nature of the generation site, the concentric form of the stress waves and their interference.