Action Of Pulse Current Research Articles

Calorimetric and Volumetric Studies of Dislocations During Martensitic Transformations in Shape Memory TiNi Alloy

Based on the use of appropriate approaches, methods and results of the analysis of a number of topical problems of physical materials science, an in-depth analysis has been done of calorimetric and volumetric data for direct, reverse and deformation martensitic transformations in a nanostructured Ti49.3Ni50.7 shape memory alloy obtained by cold rolling with simultaneous action of pulsed high-density current. For the first time, by applying a new technique for processing calorimetric spectra (peaks), the staging and “kinetics” of changes in heat content, as well as thermal effects (enthalpies of individual stages) during direct and reverse martensitic transformations during cooling or heating of samples at a constant rate (3 × K/ min) in the range 170–370 K has been done. It is shown, by processing volumetric data, using theoretical values of the dislocation density and elements of the classical theory of dislocations, that in the Ti49.3Ni50.7 shape memory alloy subjected to cold deformation accompanied by the action of a pulsed current, a deformation martensitic transformation occurs, leading to a positive volume effect (∆V/V) ≈ 3 × 10–3), which can be largely due to dislocations. It is shown, by applying the theoretical values of the dislocation density and elements of the classical theory of dislocations, that the possible contributions of dislocations to the enthalpies of direct and reverse martensitic transformations (in the Ti49.3Ni50.7 alloy) can and should be significantly lower in absolute value, but opposite in sign to the observed enthalpies of direct and reverse martensitic transformation in a given alloy. It is shown that the physics of the processes under consideration is contained to a certain extent in scientific discoveries No. 239 “The phenomenon of thermoelastic equilibrium during phase transformations of the martensitic type – the Kurdyumov effect” and No. 339 “The phenomenon of the formation of non-equilibrium grain boundaries in polycrystals when they absorb lattice dislocations”.

Purification of Cu–Zn melt based on the migration behavior of lead and bismuth under pulsed electric current

The recovery and regeneration of waste brass can alleviate the pressure of ore resource demand, and can also obtain considerable economic profits from the regenerated alloy products. However, excessive lead and bismuth residues in brass will lead to severe high temperature brittleness of the alloy, and chemical separation will complicate the separation process due to the difference in activity between elements. In this study, the physical separation of Pb and Bi from brass was realized by applying pulse current based on the electrical conductivity difference between Pb, Bi and brass melt, overcoming the limitation of using metal activity difference for oxidation refining. For 10 kg melt, the distribution of current line is adjusted by designing current intensity, frequency and electrode position to explore the migration behavior of Pb and Bi in brass melt under the action of pulse current. After pulse current treatment, Pb and Bi accumulate on the surface of the melt, especially at the bottom of the melt, forming a region rich in Pb or Bi. Based on the numerical calculation, Pb and Bi migrate in the direction perpendicular to the current line driven by the current density gradient, and the migration direction is the direction of the current density gradient decreasing. Pulse current separation technology has the characteristics of shortening the recovery steps, green energy saving, which provides a new solution for the difficult recycling of scrap copper and has great commercial value.

Improved forming capability of 7075 aluminum alloy using electrically assisted electromagnetic forming

7075 aluminum alloy has high strength but its formability is poor at room temperature. To improve its plastic deformation capability, a new forming method, electrically assisted electromagnetic forming (EAEMF), is introduced and investigated. Our results indicate that the major and minor strain (i.e. the forming limits) of the material following EAEMF increases by 42.3% and 40.0%, respectively, compared to (conventional) electromagnetic forming (EMF). The respective increase thanks to the new method is even higher (by 76.4% and 83.9%) compared to quasi-static (QS) deformation. Furthermore, the yield strength and tensile strength of the material are reduced by 3.6% and 2.6%, compared with conventional EMF, while the elongation can be increased by 21.6% using EAEMF. The texture and microstructure of the alloy were investigated by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that both grain size and texture strength decrease after EAEMF, while the brass and S textures become more dominant. The dislocation density of the material used for EAEMF is low, and directional alignment of dislocations occurs. This is related to the impulse current promoting the dislocation motion. In addition, Joule heating (by the electric current) enables a dynamic recovery during the deformation process, which reduces both the flow stress and the effect of work hardening. However, it also increases elongation. • The technology of electrically-assisted electromagnetic forming(EAEMF) is proposed for the first time, which is used to break through the limitation of EMF. • EAEMF process can improve the forming limit and energy efficiency. • Under the action of pulse current, the dislocation density decreases, and a part of dislocations show directional arrangement. • The pulse current did not change the types of texture, but changed the volume fraction of different textures.

Effect of temperature and reduction ratio on the interface bonding properties of TC4/304 plates manufactured by EA rolling

In this paper, a TC4/ 304 plate was successfully manufactured by electrically-assisted rolling (EA rolling). Under the constant pulse current, the effect of EA rolling on the interfacial structure and interfacial bonding strength of TC4/304 plates was systematically studied at different rolling reduction ratios of 19.5%, 38% and 58% at 750 °C and at reduction ratios of 58% when the rolling temperatures were 650 °C, 750 °C and 850 °C. The microinterface and shear fracture surface were analysed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) was employed to determine the formation of the phase. The interfacial bonding properties of the plates were tested by tensile shear. The results show that under action of pulse current, the tensile shear strength of the TC4/304 plate is the highest at 750℃×38%, reaching 286 MPa. Insufficient element diffusion caused by small reduction ratio and Kirkendall micro voids caused by diffusion acceleration with large reduction lead to the decrease of tensile shear strength. When the reduction ratio is 58%, the tensile shear strength reaches 239 MPa at 650 ℃. Kirkendall micro voids at 750 ℃ and the intermetallic compounds at 850 ℃ lead to the continuous decrease of shear strength. EA rolling is the primary factor that lead to the substantial increase in the interface bonding strength of the TC4/304 plate at low temperature and small deformation.

Effect of High Density Electric Current Pulse on Solidification of Cu-37.4 wt.%Pb Monotectic Alloy Melt

The effect of high-density electric current pulse (ECP) on the solidification of Cu-37.4 wt.%Pb monotectic alloy melt was investigated. The microstructure formation mechanisms of ECP were clarified according to liquid metal cluster theory. The results demonstrated that with ECP treatment, the microstructure of Cu-Pb monotectic alloy became finer, the distribution of Pb phase in the matrix was more even and the solute trapping was significantly apparent. Based on the metal liquid cluster theory under ECP, the solid solubility increase result might be due to the salvation clusters increase under the action of pulse current, leading to the binding force increase among solute atoms and solvent atoms. Simultaneously, the aforementioned results were verified through the Differential Scanning Calorimetry (DSC) curve analysis. The results of hardness test, anti-friction test and wear- resistance test show that the ECP can enhance the hardness, improve the properties of anti-friction and wear-resistance of the alloy.

Measurements of Vibrations Produced by Current Pulses in Elements of Electrical Equipment

The effects of vibration response of a conductor on the action of current pulses in the absence or presence of static loads have been studied. During the tests, three-component piezoelectric accelerometers were used to control the amplitude and time characteristics of vibration against a background of the effect of separate current pulses. The main characteristic used to determine vibrations was the acceleration of surface layers of metal. Single current pulses have no appreciable thermal effects on a sample. The experimental data that show that the main contribution, in the formation of mechanical oscillating processes, is made by an electrodynamic process determined by changes in the magnetic field and skin effect. It has been found that an increase in the static load leads to an increase in the decrement of oscillating process attenuations caused by the action of pulse current. A technique for measuring vibrations produced by the current pulses has been suggested. This technique of determining vibrations under the action of pulse current can be recommended for nondestructive testing of defects in structures, including in cases of their static load. The analysis of these results allows one to determine the service life of elements in windings of powerful energy equipment starting from normal operational modes to emergency conditions.

Investigation of Gyroscopic Stabilization for Single-Stage Saddle Sextupole Field Electromagnetic Launcher

This paper presents a novel single-stage saddle multipole field electromagnetic launching mode for the realization of projectile linear acceleration with gyroscopic stabilization. The hollow cylindrical projectile with three symmetrical vertical slots can change the eddy current and magnetic field density distribution on the projectile surface. When twisted an angle relative to saddle multipole coils along the circumference, the projectile will be linear accelerated with spinning motion under the action of pulse current. In this paper, analytical calculations and simulation methods were used to analysis this mode, the simulation results indicated that the axial acceleration force and circumferential torque acting on the projectile were generated simultaneously, and an optimal initial twisted angle was existed to make the muzzle rotation speed reach peak. To verify the conceptual feasibility, a single-stage saddle sextupole field electromagnetic launcher was built and tested. The experiment demonstrate that the mode is indeed possible to realize the projectile linear acceleration moving with the gyroscopic stabilization, launching performance can be adjusted by changing the initial voltage or twisted angle, and the experimental results are accordant with the simulation results.

Numerical simulation of pulsed current tungesteninert gas (TIG) welding arc

A two-dimensional axisymmetric model of free burning tangsten inert gas (TIG) arc under the action of pulsed current is developed. Using the FLUENT software and choosing appropriate boundary conditions and strongly coupling control equations, a pulsed TIG arc is simulated. The variations of arc form, temperature field, temperature and velocity on the arc axis and surface pressure distribution of the workpiece are obtained and analyzed in the periodic current process; under the action of different values of peak current, duty ratio and pulse frequency, the arc pressure distributions are obtained and analyzed. The results show that they lag behind the variation of pulse current, the variation from base current to peak current is faster, then eventually reaches a relativly stable state; with the increase of peak current, the arc pressure increase greatly; with the increase of duty ratio, the arc pressure increases slowly; with the increase of pulse frequency, the arc pressure cannot reach a stable state gradually, and the max arc pressure tends to decrease.