Effect of electropulsing on anisotropy behaviour of cold-rolled commercially pure titanium sheet

The specimens cut from the cold-rolled pure titanium sheet at 0°,45°and 90°to the rolling direction were treated by high density electropulsing(maximum current density J=(7.22-7.96)×10^(3)A/mm^(2),pulse period t_(p)=110μs).The mechanical properties and microstructures of the cold-rolled,electropulsed and conventional annealed commercially pure titanium sheet were examined by using uniaxial tension test machine and optical microscope(OM),respectively.The results show that the deformation behavior of the electropulsed pure titanium sheet is significantly different from that of conventional annealed pure titanium sheet.The difference of the mechanical properties between the 0°,45°and 90°direction specimens is almost diminished.It is mainly due to the increase in dislocation mobility and formation of lamellar microstructure after the electropulsing.

Dynamic Electropulsing Induced Phase Transformations and Their Effects on Single Point Diamond Turning of AZ91 Alloy

The effects of dynamic electropulsing on microstructure changes and phase transformations of a rolled Mg-9Al-1Zn alloy were studied by using optical microscopy, X-ray diffraction, back-scattered scanning microscopy and transmission electron microscopy techniques. The decomposition of β phase was accelerated under dynamic electropulsing, compared with the conventional thermal processes. Dynamic electropulsing was less effective in affecting the phase transformations, but more effective in reducing residual stress than the static electropulsing. Dynamic electropulsing improved machinability of single point diamond turning, the mechanism of which is discussed from the point of view of dislocation dynamics.

Effects of Electropulsing Induced Microstructural Changes on THz-Reflection and Electrical Conductivity of Al-Doped ZnO Thin-Films

Electropulsing induced phase transformation and crystal orientation change and their effects on electrical conductivity, THz reflection and surface roughness of thin-films of Al2O3 (2 wt%) doped ZnO were studied using XRD, SEM, AFM and Thz spectroscopy techniques. AZO-2 thin-films showed an effective response in THz spectroscopy under electropulsing. Electropulsing induced circular preferred crystal orientation changes and phase transformations were observed. The preferred crystal orientation changes accompanying decrease in stress and the secondary phase precipitation favored enhancing conductivity and THz reflection of the AZO-2 thin-films. After adequate electropulsing, both THz reflection and electrical conductivity of the thin-films were enhanced by 22.8% and 6.8%, respectively;meanwhile surface roughness reduced. The property responses of electropulsing are discussed from point view of microstructural change and dislocation dynamics.

Introducingωand O'nanodomains in Ti-6Al-4V:The mechanism of acceleratingα→βtransformation kinetics via electropulsing

Conventional kinetics theory for diffusion-controlled phase transformation shows that the reverse transition should lag behind the temperature rise through rapid heating,i.e.,overheating is required.In this work,we found that theβ-transus temperature decreased by∼50°C during studying theα→βtransformation in Ti-6Al-4V alloy via electropulsing treatment(EPT).The calculation suggests that the acceleration of transformation kinetics cannot be fully explained by Joule heat and athermal effects of the electromigration effect and electron wind theory.The microstructural evolution during EPT was systematically investigated utilizing scanning electron microscope(SEM),electron backscattered diffraction(EBSD),X-ray diffraction(XRD),transmission Kikuchi diffraction(TKD),and transmission electron micro-scope(TEM).Microscopic analysis shows that the nano-sizedωand O'phases formed in theβphase,which causes large numbers of lattice distortion regions.The defects are conducive to accelerating the bulk diffusion of alloying elements inβ.Moreover,the nanodomains limited the growth of martensite,therefore nanocrystalline martensite formed after quenching.These findings develop the understanding of the destructive effect of current on metallic crystal,which will help to guide microstructural regulation in titanium and other alloys.

Crystallization of a Ti-based Bulk Metallic Glass Induced by Electropulsing Treatment

The effect of electropulsing treatment(EPT)on the microstructure of a Ti-based bulk metallic glass(BMG)has been studied.The maximum current density applied during EPT can exert a crucial role on tuning the microstructure of the BMG.When the maximum current density is no more than 2 720A/mm^2,the samples retains amorphous nature,whereas,beyond that,crystalline phases precipitate from the glassy matrix.During EPT,the maximum temperature within the samples EPTed at the maximum current densities larger than 2 720A/mm^2 is higher than the crystallization temperature of the BMG,leading to the crystallization event.

Rapidly modifying microstructure and mechanical properties of AA7150 Al alloy processed with electropulsing treatment

Studies show that the proper solid solution treatment(SST)is a key step in the precipitation strengthening of AA7150 Al alloy.Despite the superior characteristics of the fully dissolved phase,it has major drawbacks,including high consumption of energy and low efficiency.Recently,electropulsing treatment(EPT)has been proposed to study dissolved precipitations and modify microstructures of AA7150 Al alloy faster than conventional SST.Experiments have been conducted in the present article,and the obtained results show that EPT can promote the rapid dissolution of theη’phase at relatively low temperatures in only 20 s.Meanwhile,the strength and ductility of electropulsed samples decrease drastically.Compared with conventional SST,EPT accelerates recrystallization and obtains relatively fine grains after 20 and 50 s electric pulses.Moreover,as the EPT time increases,the corresponding non-uniform local heating and the electron force promote dislocation generation and annihilation.

Effect of Electropulsing on Recrystallization and Mechanical Properties of Silicon Steel Strips

Electropulsing-induced recrystallization and its effect on mechanical properties of oriented silicon steel strips (Fe-3.0%Si) were studied by optical microscopy, scanning electron microscopy and electron back-scatter diffraction. The results indicated that electropulsing accelerated recrystallization, and decreased the temperature of recrystallization. Electropulsing favors refinement of the grain structure of the alloy. Effects of electropulsing on strength and elongation of the alloy were discussed from the point view of dislocation dynamics, microstructural changes, and electropulsing kinetics.

Hot Tensile Behaviors and Microstructure Evolution of Ti-6Al-4V Titanium Alloy Under Electropulsing

The effect of electropulsing on the mechanical behaviors and microstructures of Ti-6Al-4V titanium alloy was investigated by an uniaxial tensile test. Compared to the value measured in cold tensile test, the alloy exhibits lower ultimate tensile strength when the tensile deformation is assisted by electropulsing. The tensile elongation is found to vary non-monotonically with increasing root mean square(RMS) current density. Though decreasing at first, the tensile elongation increases with current density once the value exceeds 8.1 A/mm^2. Through applying current with RMS current density of 12.7 A/mm^2, the tensile elongation at strain rate 0.001 s^(-1) can be improved by 94.1%. In addition, it is observed that more remarkable electroplastic effect is induced by the higher peak current density under similar thermal effect. Microstructure analysis reveals that the low plasticity at 8.1 A/mm^2 is attributed to the micro-void easily formation near the tips of acicular β phases. The enhanced ductility at higher current densities, on the other hand, is attributed to the dynamic recrystallization.

Effect of electropulsing on austenite to ferrite transformation in low-carbon steel

We explore the application of electropulsing for the control of phase transformation in a low-carbon steel.The effect of electropulsing on the transformation from austenite to ferrite in continuous casting low-carbon steel slab has been studied through experimental and thermodynamic investigations.The results reveal that electropulsing promotes the precipitation of ferrite within austenite grain in the low-carbon steel.When the electropulsing intensity increases,the precipitation of ferrite increases within austenite grains,and ferrite omentum precipitates become thinner along the austenite grain boundary.The results provide a basis for controlling the austenite to ferrite transformation in low-carbon steel.

Electropulsing-Induced Microstructural Changes and Their Effects on Electrical Conductivity of Thin Films of an Al-doped ZnO

Electropulsing-induced phase decompositions and microstructural changes in AZO-5 thin films were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, Hall effect measurement and photoluminescence(PL)measurement techniques. It was found that the electropulsing induced phase decomposition started with spinodal decomposition, which was accompanied by discontinuous precipitation in the AZO-5 thin films. Both circular phase decompositions and the crystal orientation occurred. Inappropriate electropulsing might damage zones, which resulted in tremendous decrease in electrical conductivity. Circular changes in both the peak position and the width of the PL wavelength were observed in the EPT AZO-5 thin films. Formation of zones favored reducing the roughness of the thin film.

Effect of electropulsing treatment on solidification behavior of spring steels in a continuous casting mold simulator

An electropulsing-assisted mold simulator technique was developed to investigate the effects of a pulsed electric voltage on the quality of spring steels during continuous casting by analyzing the mold flux film,shell surface profile,shell micro-structure and inclusion distributions.The results revealed significantly increased crystallization fraction of the mold flux film from 61.2%to 75.3%and finer crystalline phase morphology in the case of electropulsing treatment.The surface of the initially solidified shell could be effectively healed,resulting in smoother shell surface profiles with higher pulsed voltage from 0 to 30V.Furthermore,an increase in the pulsed voltage from 0 to 30V resulted in finer dendritic structures during solidification with decreasing secondary dendrite arm spacing from the values of 17.6-32.2 to 9.7-15.0μm in the direction of shell side toward melt side.In addition,an area scan analysis of inclusions in the as-cast spring steel samples showed that the number of MnS inclusions in the size range of 2.0-4.0μm gradually decreased from 836 to 114 and the number of Al2O3 inclusions in the same size range decreased from 144 to 39,as the voltage increased from 0 to 30V.

Giant Magneto-Impedance Effect in Amorphous and Current Annealed Fe73.5Cu1Nb3Si13.5B9 Wire

The magneto-impedance (MI) effect in amorphous and current annealed Fe73.5Cu1Nb3Si13.5B9 wires has been measured to investigate the influence of DC annealing, high-current-density electropulsing annealing and tensile stress applied during annealing process. The results showed that the MI of DC annealed sample exhibits a sharp maximum. The Maximum MI ratio of 60 % was observed in the sample of high-current-density electropulsing annealed under applied tensile stress.

Extraordinary mechanical properties of AZ61 alloy processed by ECAP with 160° channel angle and EPT

AZ61 Mg alloy with homogeneous refined microstructure and exceptional mechanical properties was obtained by the combined technology of equal-channel angular pressing(ECAP)and electropulsing treatment(EPT)in this paper.Based on an ECAP die with an intersection angle of 160,the lower temperature is particularly adapted for AZ61 alloy to be deformed,in which accompanied by high accumulated defects density.The recrystallization of EPTed samples during different stages indicated that the recrystallization behavior of the deformed Mg alloy was mainly affected by the processing time and duration of EPT.Compared to those of the as-received samples,the average grain size of the EPTed samples was refined from 89μm to 1.0μm,accordingly the yields stress(YS)and ultimate tensile strength(UTS)were increased from 100 MPa and 260 MPa to 330 MPa and 448 MPa,respectively.The mechanisms of microstructure transformation and the reinforced mechanical properties were analyzed based on the strain of single ECAP,cumulative storage energy and the athermal effect of EPT.

A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation

Electropulse stimulation provides an energy-efficient means of excavating hard rocks through repeated application of high voltage pulses to the rock surface.As such,it has the potential to confer significant advantages to mining and drilling operations for mineral and energy resources.Nevertheless,before these benefits can be realized,a better understanding of these processes is required to improve their deployment in the field.In this paper,we employ a recently developed model of the grain-scale processes involved in electropulse stimulation to examine excavation of hard rock under realistic operating conditions.To that end,we investigate the maximum applied voltage within ranges of 120e600 kV,to observe the onset of rock fragmentation.We further study the effect of grain size on rock breakage,by comparing fine(granodiorite)and coarse grained(granite)rocks.Lastly,the pore fluid salinity is investigated,since the electric conductivity of the pore fluid is shown to be a governing factor for the electrical conductivity of the modeled system.This study demonstrates that all investigated factors are crucial to the efficiency of rock fragmentation by electropulsing.

Study on Improving Solidification Structure of Rare Earth Al-Si Alloys with Electropulse Acting on Liquid Alloy

Electropulse modification (EPM) process, a new physical field method for improving the solidification structure of metals was introduced.Different from other research, EPM is only acting pulse current on melt under liquid state.The solidification structure of Al-Si alloys, A1-Cu alloys,cast iron and steel can be modified obviously with this method: the solidification structure of ZL101 alloy presented the Na and Sr modification and the mechanical properties were enhanced; a large number of primary silicon appeared in the microstructure of ZL109 alloy; the equiaxed grain zone was expanded and the grains were fined in Al-5.0wt% Cu alloy; the graphitization took place in solidification process of molten cast iron; the grain sizes of solidification structure of T8 steel were reduced significantly and the shape of steel pearlites also changed; the equiaxed grain zone increased to 88% from original untreated 19%, the equiaxed grains were fined and the intercrystalline crack was avoided in concasting billet by continuously treating liquid electrical sheet steel in tundish.Effects of rare earths on casting Al-Si alloys were also summarized.The method of modifying the solidification structure of rare earth Al-Si alloys with EPM in producing the alloys was proposed.

Anisotropic Electroplastic Effects on the Mechanical Properties of a Nano-Lamellar Austenitic Stainless Steel

Effects of electropulsing treatment(EPT)on the microstructural evolution and mechanical properties of a cold-rolled 316 L austenitic stainless steel with nano-lamellar structure were investigated.The EPT experiments were carried out with the electric current direction along the rolling direction(RD)and the transverse direction(TD)of the samples,respectively.Significant anisotropic electroplastic effects for the RD and TD specimens,i.e.,reduced hardness/strength and enhanced ductility,were obtained owing to the different recrystallization behaviors of the RD and TD specimens during EPT.The RD specimens after EPT with larger recrystallized grain size and higher volume fraction of recrystallization show lower strength and higher elongation than that of the TD specimens.The main reason might be attributed to the change of the current direction in the two kinds of samples,which results in the different sensitivity of the microstructures to thermal and athermal effects during EPT.

Exceptional mechanical properties of AZ31 alloy wire by combination of cold drawing and EPT

A 0.66 mm-diameter AZ31 alloy wire with ultimate tensile strength of 400 MPa and elongation of 28.5%was successfully prepared via the combination of cold-drawing and electropulsing treatment processing(EPT).Microstructure observation showed that the grain size of EPTed samples was refined to about 1μm and the basal texture strength with maxima texture index was weakened to 7.18.EPT can significantly accelerate recrystallization by enhancing the mobility of dislocation and atomic diffusion due to the coupling of the thermal and athermal effects.Finally,uniform ultrafine-grained structure was obtained in the EPTed samples by static recrystallization completed in a very short time(30 s)at relatively low temperature(433 K).