Electroplastic Effect in Cast Polycrystalline NaCl with Various Orientations of the Electric Field

Abstract

The influence of various orientations and configurations offlat with SiC abrasion papers down to 1000 grit, as were also the surfaces of the holes drilled in the specimens for configuraan electric field on the flow and fracture stresses in compression of cast polycrystalline NaCl was determined at room tions B-a, and B-b. The specimens were then polished in distemperature. An electric field of }0.1 MV/m reduced the tilled water to give smooth internal and external surfaces. flow and fracture stresses by }50%, relatively independentThe external electrodes for all configurations were of stainof the orientation of the field. This field is one to two orders less steel sheet. For configuration A in Fig. 1, 6.5 cm diam of magnitude lower than those previously reported to stainless steel sheets were placed at the top and bottom ends of enhance {110} ͗110͘ dislocation motion in NaCl single crysthe compression specimen and connected to the positive and tals. It is concluded that in the present tests on polycrystals negative terminals of the power supply. The geometry and the electric field enhanced cross slip. Several mechanisms dimensions pertaining to configurations B-a, B-b, and C are by which this might occur are proposed.shown in Fig. 2. The internal electrodes in B-a and B-b were a copper tube and wire, respectively. For configuration C, the two stainless steel sheet electrodes (4 cm ϫ 5 cm high) were placed I. Introduction parallel to, and equidistant from (2 cm), the cylindrical speci-I N PRIOR work by the authors, 1 it was found that an electric men. The more complex electrode configurations D and E repfield of 0.1 MV/m reduced by ϳ50% the flow and fracture resented combinations consisting of electrodes at one or both stresses of cast polycrystalline (2 mm grain size) NaCl in comends of the specimen and an external cylindrical electrode (6 cm pression at room temperature. These field strengths are one to diam). An example of the specimen arrangement during comtwo orders of magnitude lower than those which had been pression testing (that for electrode configuration C) is given in previously reported to enhance dislocation multiplication and Fig. 3. That for A was previously shown in Ref. 1. motion in halide single crystals. [2][3][4][5][6][7][8][9][10][11][12] It was proposed by the The electric field in the NaCl specimen for configuration A present authors that the reduction in the flow and fracture was taken to be stresses in the case of their polycrystals resulted from an E ϭ V 0 /h (1) enhancement of cross slip by the electric field.In the previous paper, 1 the electric field was applied along the where V 0 is the applied voltage and h the specimen height. The compression axis. In view of the relatively large effect of elecaverage field in the NaCl in the case of B-a and B-b was tric field that was observed, the present study was undertaken to determined from 13 determine whether similar behavior occurs with other orientations and configurations of the field. It was found that the(2) reductions in flow and fra...

Flash sintering of ceramics

“…Moreover, rapid stress relaxation can be associated with the superplastic behavior observed in some ceramics under DC-electric field. This phenomenon was deeply studied by Yang and Conrad on NaCl [150][151][152] and some oxides (YSZ, MgO, Al 2 O 3 ) [153][154][155] and it was observed also at room temperature in NaCl polycrystals using field of 10 3 V/cm. Such field is one-two orders of magnitude lower than that needed for inducing dislocation mobility in alkali halides single crystals: accordingly, the mechanism for electroplasticity in polycrystalline NaCl was proposed to be different with respect to that involved in single crystals, typically based on the field-induced electrostatic force on charged dislocations or on the defect dipoles reorientation which hinder dislocations motion [155].…”

Influence of Externally Imposed and Internally Generated Electrical Fields on Grain Growth, Diffusional Creep, Sintering and Related Phenomena in Ceramics

“…If this were the reason for the lower flow stress then the direction of the electric field would have an effect on the deformation behavior. However, experiments ruled out any effect of the direction of the electric polarity on the electromechanical effect A second explanation may be that the electric field produces additional defects in the volume of the material, regardless of field orientation.…”

“…However, experiments ruled out any effect of the direction of the electric polarity on the electromechanical effect. 35 (2) A second explanation may be that the electric field produces additional defects in the volume of the material, regardless of field orientation. This higher defect concentration enhances the effective self-diffusion coefficient.…”