Guanhu He

Reversing effect of electropulsing on damage of 1045 steel

The influence of electropulsing on the damage of 1045 steel was studied, The results show that electropulsing can substantially increase the strength and ductility of the damaged material, with a little decrease of the Martensite hardness. After the treatment of electropulsing, the microstructure around the crack is modified, and the new structure can prevent the crack from growing, The healing effect of electropulsing on crack is discussed. It is thought that the temperature and thermal compressive stress caused by electropulsing are the main factors causing the healing effect.

Recrystallization in fatigued copper single crystals under electropulsing

Fatigued copper single crystal was treated by electropulsing, it leads to the formation of two kinds of recrystallized grain with finer-grain size, Due to the homogeneous distribution of the vein structures, the recrystallized grains formed in this region have no preferential direction. However, the recrystallized grains formed around persistent slip bands show bigger grain size along slip direction

Formation of a Nanostructure in a Low-carbon Steel Under High Current Density Electropulsing

The microstructure of a low-carbon steel after high current density electropulsing treatment was characterized by high-resolution transmission electron microscopy. It was found that nanostructured gamma-Fe could be formed in the coarse-grained steel after the electropulsing treatment. The mechanism of the formation of a nanostructure was discussed. It was thought that change of the thermodynamic barrier during phase transformation under electropulsing was a factor that cannot be neglected. It was reasonable to anticipate that a new method might be developed to produce nanostructured materials directly from the conventional coarse-grained crystalline materials by applying high current density electropulsing.

Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing

High current electropulsing was applied to a low-carbon steel in the solid state. The relationship between grain size and experimental conditions was revealed. It was found that the ultrafine-grained (UFG) microstructure could be formed when electric current density, heating rate, and cooling rate all were high. The UFG samples prepared by applying electropulsing were free of porosity and contamination, and had no large microstrain. Also, their tensile strength was dramatically enhanced over that of their coarse-grained counterparts, without a decrease in ductility. The mechanism for grain refinement and formation of the UFG microstructure was discussed. It is proposed that the effect of a decrease in thermodynamic barrier and enhancement of nucleation rate in a current-carrying system cannot be neglected.

Effect of electric current pulse on tensile strength and elongation of casting ZA27 alloy

The ZA27 alloy cast in the sand mould was treated with strong electric current pulse during the solidification. The experimental results indicated that the electric current pulse can restraint the growth of the dendrite in the alloy and enhance the tensile strength and the elongation (C) 2002 Elsevier Science B.V. All rights reserved.

Influence of electropulsing on nucleation during phase transformation

Phase transformation about precipitation in a Cu-Zn alloy was studied. It was found that with an electropulsing treatment the number of nuclei during phase transformation could be dramatically enhanced and nucleation of precipitates was more homogeneous. The phenomena did not result from the effect of rapid heating or rapid cooling during electropulsing but resulted from the electric current itself. The results were in good agreement with the theoretical model that electric current can increase nucleation by decreasing the thermodynamic barrier during phase transformation.

Diffusive phase transformation in a Cu–Zn alloy under rapid heating by electropulsing

Electropulsing with a damped oscillating waveform was employed to heat cycle a Cu–Zn alloy containing α and β′ phases. It was found that significant long-range diffusion and then a diffusive phase transformation α + β′→β can occur in the alloy during the course of heating, even when the heating rate during the electropulsing treatment is very high (106 K s−1). The phenomenon is different from the common cases of rapid heating and rapid cooling. It implies that electropulsing can dramatically enhance diffusion in the alloy.

Suspension effect of nanocrystalline grain growth under electropulsing

The effect of electropulsing on nanocrystalline grain growth in amorphous material is considered. A size-dependent growth rate of a nanoscale grain is revealed, which is due to the size-dependent electrical resistivity. A suspension effect is found when the density of electric current is at a critical value j(c). The formed grain may shrink when the density of applied electric current is higher than j(c). Numerical calculation shows that j(c) is about 2.59 x 10(3) A/mm(2) for nanocrystalline Ni80P20 alloy with grain size of 13 nm

Formation of nanoscale alpha-Al in a superdralumin under high current density electropulsing

Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Zhang, W (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, 72 Wenhua Rd, Shenyang 110016, Peoples R China

Investigation of thermal expansion measurement of brass strip H62 after high current density electropulsing by the CCD technique

chinese acad sci, int ctr mat phys, shenyang 110015, peoples r china. chinese acad sci, met res inst, shenyang 110015, peoples r china.;he, gh (reprint author), chinese acad sci, inst met res, 72 wenhua rd, shenyang 110015, peoples r china