The results of a study on the geometric shape of the damper on the efficiency of the ultrasonic piezoelectric transducer are presented. In particular, a damper in the form of a truncated cone is ...considered, the generatrix of which has an inclination angle α relative to the diameter of the piezoceramic plate. The shape of the damper in the form of a truncated cone is chosen based on the a priori assumption that this helps to increase the path of the wave in the damper material due to numerous reflections in it. A criterion for the efficiency of damper operation is proposed. The optimal (from the point of view of the damper efficiency) value of the angle α was determined theoretically and experimentally. The technology of its production is described. Satisfactory agreement between the results of theoretical and experimental studies was noted.
The influence of static compressional stress on the anisotropy of piezoelectric ceramics of BaTiO3 and PZT types is considered theoretically and experimentally. Static compression changes the domain ...structure of piezoceramics. These changes occur due to the reorientation of mostly 90° domain axes. As a result, all the parameters of the material change—elastic, piezoelectric, and dielectric. Some of them increase, and some, on the contrary, decrease. Changes occur in a nonlinear way, and higher-order parameters appear. The relationship between the total volume of the reoriented domains and the change in elastic moduli and piezomoduli is theoretically considered. The corresponding theoretical dependences are obtained. To confirm these theoretical dependences, experimental measurements were performed using the ultrasonic pulse-interference method at a frequency of 8 MHz. There is practically no oscillation movement of domain boundaries at this frequency, therefore, the change in the system of elastic and piezoelectric moduli is structural, not dynamic. The possibility of predicting changes in the structure of modules as a result of static compression is shown.
The objective of this paper is presenting a review of high-entropy alloys and traditional alloys fabricated by laser cladding. In this paper, recent developments of different material system are ...summarized, and the developments in laser cladding for functional coatings with high wear resistance, good corrosion and oxidation resistances, and better medical biocompatibility are reviewed. By summarizing the analysis of microstructure, mechanical properties, corrosion resistance of high-entropy alloys and traditional alloys’ coating fabricated by laser cladding, it stated that laser cladding treatment can improve corrosion resistance, homogenize grain size, and increase microhardness and other properties. Laser cladding is considered as the potential method to ameliorate mechanical properties, improve microstructure and repair broken parts. Therefore, laser cladding has the successful applications in automobile and aerospace productions, and shipbuilding due to those advantages.
The objective of this paper is to present a review of a new developing manufacturing technology based on welding of metallic materials. Additive manufacturing (AM) is based on robot welding and it ...has showed the high flexibility, efficiency, fast output, good quality and low cost. This paper explores several common welding materials and manufacturing technologies include the shield gas, materials engineering, processes and most concerned commercial interests. AM has the potential to revolutionize the global parts manufacturing and industrial tendencies with the rapid development of increasing material manufacturing technology. AM based on arc welding has the big advantages of high efficiency and low cost, which makes it possible to use in many industries although it has a little bit poor surface qualities compare to AM based on laser and electron beam manufacturing.
•Co25.4Cr15Fe37.9Mn3.5Ni16.8Si1.4 alloy was produced by wire arc additive technology.•The microstructure consists mainly of FCC phase but also has CoCr nano phase.•The alloy has good mechanical ...properties.•The chemical are distributed homogeneously.
This study employed wire arc additive manufacturing (WAAM) to fabricate non-equiatomic Co25.4Cr15Fe37.9Mn3.5Ni16.8Si1.4 high-entropy alloy (HEA). Microstructure, elemental distribution, and mechanical properties were investigated. The fabricated HEA has a dendrite structure composed mainly of the FCC phase and CoCr nanoparticles with 1.5–2.5 nm sizes. Energy-dispersive X-ray spectrometry analysis showed that elements are distributed homogeneously in the alloy. Transmission electron microscopy demonstrated the presence of randomly oriented residual dislocations with the density of 1.2∙1010 cm−2. Compressive and tensile tests showed ductile deformation behavior. The yield strength of the alloy is ∼ 279 MPa; ultimate tensile strength is ∼ 500 MPa, and elongation is ∼ 63%.
•Al2.1Co0.3Cr0.5FeNi2.1 high entropy alloy was obtained by additive manufacturing.•The microstructure consists of dendrite grains and interdendrite areas.•The key phases detected at the submicro-and ...nano-levels are Al3Ni and (Ni, Co)3Al4.•Content of Al and Ni atoms are prevalent above other elements in the alloy.
The Al2.1Co0.3Cr0.5FeNi2.1 high-entropy alloy was a product of wire arc additive manufacturing. The feeding material was a three-core cable with different element compositions: Al – 99.95%; Cr – 20%, Ni – 80%; Co – 17%, Fe – 54%, Ni – 29%. Optical microscopy techniques were applied to study the microstructure of the produced material, which comprised dendrite grains varying from 4 to 15 µm and interdendritic regions. Scanning electron microscopy demonstrated the dendrite grains were generally made of Al and Ni atoms; the interdendritic regions contained Cr and Fe, whereas Co was distributed quasi-homogenously in the material. Transmission electron microscopy detected main phases to be Al3Ni and (Ni, Co)3Al4. An Al3Ni phase is cubic, and a (Ni, Co)3Al4 phase is spherical. 7 to 10 nm (Ni, Co)3Al4 particles were found along the boundaries of submicron (40–100 nm) Al3Ni phases.
Important progress in the development of high-temperature superconductors (HTSC) of the second group made it possible to design the quasi-stationary tokamak with reactor technologies (TRT) with the ...high magnetic field (
B
t0
= 8 T). The high magnetic field will ensure the achievement of plasma fusion regimes in the tokamak with the fusion energy gain
Q
> 1 at the considerably reduced size of the facility (
R
0
= 2.15 m,
a
= 0.57 m), and, consequently, at its reduced cost. TRT will be capable of operating in the quasi-stationary regimes (≥100 s) with hydrogen, helium, and deuterium plasmas (with the densities
n
e
of up to 2 × 10
20
m
–3
) and in the regimes with short (duration Δ
t
< 10 s) deuterium–tritium plasma shots with the fusion energy gain
Q
> 1 limited by the radiation heating of toroidal coils. TRT is being designed as a plasma prototype for both the pure fusion reactor and the fusion neutron source for the hybrid (fusion–fission) reactor. The TRT missions are the development of the key fusion technologies and their integration in one facility. These technologies are as follows: the HTSC electromagnetic system operating at the extremely high magnetic fields; the metal and liquid-metal (lithium) first wall and innovative divertor; the unique advanced systems for the auxiliary plasma heating and non-inductive current drive, including the systems for atomic beam injection with energy of 0.5 MeV and power of several tens of megawatts, the electron cyclotron heating system based on the megawatt-power gyrotrons with a frequency of 230 GHz and a total power of ~10 MW, and the ion cyclotron heating system at frequencies of 60–80 MHz with a power of several megawatts; the tritium fuel cycle; the remote control technologies; the technologies for diagnostics capable of operating under the fusion reactor conditions; the technologies for maintaining quasi-stationary plasma discharges; and the technologies for the tokamak operation in the fusion ignition regime, in which the heating by alpha particles is the dominant heating mechanism at the axis of the plasma column, in the deuterium–tritium experiments limited by the radiation heating of the toroidal coils. The results are presented from the conceptual design of the basic TRT components, as well as the expected characteristics of its operation. It is shown that TRT has a wide window of working parameters suitable for studying the reactor operating regimes. The high magnetic field provides the necessary margins of the pressure, MHD stability, and plasma controllability variation. Implementation of the advanced divertor and first wall concepts, including those using the liquid-metal technologies, will provide the optimum choice of design options in order to reliably control the heat and particle fluxes under the reactor conditions. The advanced systems for the auxiliary heating and current drive will make it possible to implement both the pulsed and stationary regimes of the reactor operation. Calculations of the TRT discharge scenarios show that, for the DT mixture with equal content of components, the long discharges (with duration exceeding 100 s) can be realized with a neutron flux of more than 0.5 MW/m
2
onto the wall, as well as the stationary discharges with a flux of approximately 0.2 MW/m
2
. Thus, TRT can be a real prototype of the fusion neutron source for the hybrid reactor.
Using wire-arc additive manufacturing (WAAM), we produced samples of Al–Co–Cr–Fe–Ni high-entropy alloy (HEA) with a grain size of 4–15 µm. Inclusions of the second phase were found along the ...boundaries and in the volume of the grains. The near-boundary volumes of the alloy (volumes located along grain boundaries) are enriched in chromium and iron atoms, the volume of grains is enriched in nickel and aluminum atoms, and cobalt is quasi-uniformly distributed in the alloy. The inclusions of an elongated shape are enriched in chromium, iron, and oxygen atoms and may be carbides. Microhardness, modulus of elasticity, and tribological properties of the alloy are determined and the stretch curves are analyzed. Irradiation of the HEA with a pulsed electron beam is accompanied by the release of grain boundaries from precipitates of the second phase, which indicates the homogenization of the material. High-speed crystallization of the molten surface layer of HEA samples is accompanied by the formation of a columnar structure with a submicrometer-nanocrystalline structure. The electron-beam processing decreases the microhardness of the surface layer of the alloy with a thickness of up to 90 µm, which may be due to the relaxation of internal stress fields formed in the initial material during its manufacture. Irradiation of a high-entropy alloy with an intense pulsed electron beam improves the strength and plasticity of the material, increasing the compressive strength by 1.1–1.6 times.
Abstract
Piezoelectric transducers (PET) are widely used as emitters and receivers of acoustic signals to solve a great number of problems related to the study of the World Ocean. Providing the ...ability to operate the PET in the mode of short-sounding pulse radiation allows increasing the resolution of the remote sensing equipment of the aquatic environment. At the same time, a number of tasks require the use of non-directional emitters, for example, in the form of a thin-walled sphere. It is of interest to study the possibility of obtaining a short probing signal at the output of this type of PET. The paper considers the pulse mode of operation of a non-directional thin-walled spherical emitter excited by a short electrical signal. The research is based on the application of the method of equivalent circuits of the PET and the Fourier spectral method. The durations and amplitudes of the probing pulses emitted by the PEP are estimated. The results obtained may be applied to the design of equipment for underwater research.
A coating of high-entropy Cantor alloy FeCoCrNiMn of nonequiatomic composition was formed on a 5083 aluminum alloy substrate by wire-arc additive manufacturing (WAAM). The methods of physical ...materials science were applied to analyze the structure, elemental composition, microhardness, and wear resistance of the coating–substrate system. The deposition of the FeCoCrNiMn high-entropy coating on the 5083 alloy surface is accompanied by the formation of microhardness and elemental composition gradients. Microcracks and micropores were revealed in the cross section of the coating. Microhardness in the volume of the coating is 2.5–3.5 GPa and increases to 9.9 GPa at the boundary with the substrate. In the middle part of the coating, the wear factor is 2.3 × 10
–4
mm
3
/N m; the friction coefficient is 0.7. A transition layer up to 450 µm thick is formed at the interface between the coating and the substrate. We analyzed the elemental composition gradient of the transition layer and noted a high level of chemical homogeneity of the coating. The found doping of the coating with substrate elements (aluminum) leads to the formation of a FeC-oCrNiMnAl high-entropy coating, causing a lamellar structure at the interface between the transition layer and the substrate.
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