Metals Property Changes Under Effect of Vacancy-Cluster Structures
Viktor Novikov,
Mark Levin,
Vyacheslav Pevgov,
Viktor Ulyanov
Issue:
Volume 8, Issue 1, January 2019
Pages:
1-11
Received:
11 April 2019
Accepted:
30 May 2019
Published:
12 June 2019
Abstract: The experimental results analysis of a metals property changes under vacancy-cluster structure effects are shown. Two technological approaches of such structures obtaining are considered. The first is a nanopowders compaction under high (up to 5GPa) hydrostatic compression, on example of a Ni nanopowder (70nm). The second is the Al and Pb crystallization under the high-intensity plastic deformation [ε¢ = (102-104) sec-1] (НIPD) conditions on the "solid-liquid" boundary in the centrifugal casting machine with rotary speed up to 2000 rpm. Using the method of atomic force microscopy (AFM), vacancy cluster tubes (VCT) with average diameters of 39 nm for Al and 25 nm for Pb have been detected in the crystallized volume of Al and Pb metals. Discussed the physical model of a new substructure formation within the metals in the form of vacancy cluster tubes, obtained in the process of high-intensive plastic deformation (HIPD) during the process of mass crystallization of Al and Pb and the changes in the mechanical, magnetic and superconducting properties of the above metals, which followed this process. During Al and Pb crystallization under high-intensive plastic deformation (HIPD) range about [ε′ = (102–104) sec-1] with specially selected modes of metals crystallization in high-speed centrifugal casting machine the special conditions are being created to achieve the dimensional effect of dynamic (shifting) re-crystallization. Shifting deformation during centrifugal crystallization caused primarily by a large incline of the temperature field from the periphery (relative to the cold wall of the rotor) to the molten central part of the rotor. The difference in the angular velocities of the already-frozen part of the metal (adjacent to the outer surface of the rotor wall) and the central part, where the metal still remains in the molten state, leads to a high-intensity deformation [ε′ = (102–104) sec-1] of the crystallized metal melt solidified phase. Since the grain sizes at the crystallized phase initially comprise around tens of nano-meters (approximately crystal nucleation size), it becomes possible to achieve the dimensional effect of the dynamic re-crystallization of a «nanocrystalline» solidified metal at high shift of strain velocities. The ≪non-equilibrium vacancies≫ formed this way condense into vacancy clusters, which are formed in the centrifugal force field in the form of vacancy-shaped cluster tubes stretched out to the center of rotation of the rotor. The process proceeds under conditions far from the equilibrium in comparison with the usual crystallization of the metal from the melt. Such processes can lead to the formation of highly ordered non-equilibrium statescharacteristic of non-equilibrium open systems. Discussed the physical model of a metals vacancy-cluster structures formation at high hydrostatic nanopowders compression (up to 5 GPa) and high-intensity plastic deformation (HIPD) at the stage of Al and Pb alloys mass crystallization during centrifugation. Conclusion of the article is that the high-intensity plastic deformation (НIPD) at the melt crystallization stage against a background of high stationary nonequilibrium vacancies concentration brings to the new type of the elements structure formation - vacancy cluster tubes (VCT). A comparative analysis of mechanical, magnetic and superconducting properties changes for structured metals introduced.
Abstract: The experimental results analysis of a metals property changes under vacancy-cluster structure effects are shown. Two technological approaches of such structures obtaining are considered. The first is a nanopowders compaction under high (up to 5GPa) hydrostatic compression, on example of a Ni nanopowder (70nm). The second is the Al and Pb crystalli...
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Dielectric and Ferroelectric Properties of Ho2O3 Doped Barium Strontium Titanate Ceramicsq
Mengyuan Zhang,
Congyu Li,
Fangxu Chen,
Long Chen,
Jianhua Liu,
Tianyu Chen,
Chen Zhang
Issue:
Volume 8, Issue 1, January 2019
Pages:
12-20
Received:
16 July 2018
Accepted:
2 August 2018
Published:
26 June 2019
Abstract: The crystalline structure, surface morphology, dielectric and ferroelectric properties of 0~10wt% Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics prepared by conventional solid state method were studied using X-ray diffractometer, scanning electron microscopy, LCR measuring system and ferroelectric property test systems aiming for ceramic capacitor applications. It is found that proper amount of Ho2O3 can refine grains of the system. With the increase of Ho2O3 doping content, the average grain size of (Ba0.75Sr0.25) TiO3 ceramics decreases. When Ho2O3>8 wt%, (Ba0.75Sr0.25) TiO3 based ceramic samples are multi-phase compounds with typical perovskite structure accompanied by the appearance of cylindrical grains. The Ho3+ ions substitute the host A sites and B sites of (Ba0.75Sr0.25) TiO3 perovskite lattice, resulting in the lattice distortion of the system and the change of the relative dielectric constant and dielectric loss at room temperature. With the increase of Ho2O2 doping content, the relative dielectric constant at room temperature of the system increases first and then decreases. The maximum of relative dielectric constant at room temperature can be found in the 1 wt% Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics. When Ho2O3＞1 wt%, the maximum of relative dielectric constant εrmax decreases and the temperature corresponding to the maximum of relative dielectric constant Tm shifts toward lower temperature with the increase of Ho2O3 doping content. The (Ba0.75Sr0.25) TiO3 ceramics with high Ho2O3 content show relaxor-like behavior which is characterized by the typical diffuse phase transition and frequency dispersion of dielectric constant. However, the (Ba0.75Sr0.25) TiO3 ceramics with low Ho2O3 content do not exhibit permittivity frequency dispersion. According to the P-E hysteresis loops of Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics, the ferroelectricity was increased and then decreased with the increase of Ho2O3 doping content. With the increase of Ho2O3 doping content, the P-E relationships turn out to be straight lines, implying the paraelectric phase for (Ba0.75Sr0.25) TiO3 ceramics with high Ho2O3 content.
Abstract: The crystalline structure, surface morphology, dielectric and ferroelectric properties of 0~10wt% Ho2O3 doped (Ba0.75Sr0.25) TiO3 ceramics prepared by conventional solid state method were studied using X-ray diffractometer, scanning electron microscopy, LCR measuring system and ferroelectric property test systems aiming for ceramic capacitor applic...
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