Retardation of grain growth and cavitation by an electric field during superplastic deformation of ultrafine-grained 3Y-TZP at 1,450–1,600 °C

The influence of a continuous dc electric field applied orthogonal to the tensile direction on the flow stress, grain growth, and cavitation during superplastic deformation (SPD) of ultrafine-grained 3Y-TZP at 1,450–1,600 °C was determined. The field gave a significant reduction in the level of the stress-strain curve, and reduced grain growth and cavitation. The decrease in flow stress by the field was attributed mainly to the retardation of grain growth. The decrease in cavitation correlated with the retardation of grain growth and was attributed largely to the reduction in flow stress by the field.     

Thermally activated plastic flow of metals and ceramics with an electric field or current

The effects of high density electric current pulses (10³–10⁶ A cm⁻²) on the flow stress of metals at low homologous temperatures and of a modest external electric field on the flow stress of fine-grained oxides at high temperatures is presented. The results in both cases are evaluated in terms of thermally-activated plastic deformation processes. In the case of the metals, the influence of an electron wind on each of the parameters in the equation for the thermally-activated motion of dislocations was determined, the largest effect being on the pre-exponential. The derived electron wind push coefficient was one or more orders of magnitude larger than the value normally accepted for the electron drag coefficient. In the case of the oxides, the substantial effect of an applied electric field on the flow stress was evaluated in terms of its influence on the electrochemical potential of vacancies in the space-charge cloud adjacent to the grain boundaries. Both the derived space-charge cloud width and the electric potential/stress parameter Δ∅/Δσ are in reasonable accord with theoretical predictions.     

Risk analysis of fracture and failure

 This paper is inspired by the work of Professors Heinz Wilsdorf and Doris Kuhlmann-Wilsdorf on fundamental aspects of ductile fracture mechanism. Risk – a measure of the probability and severity of adverse effects – is introduced and related to the consequences associated with elastic (reversible) deformation, plastic (irreversible) deformation, and catastrophic deformation (total failure). Cost-benefit-risk trade-off analysis is discussed. Received: 25 February 1998 / Accepted: 10 March 1998     

Superplasticity by internal frictional heat under biased cyclic loading

A new damping method was developed not only as a testing tool to investigate in situ deformation under stress, but also as a processing method to superplastically deform ceramics. The specific damping capacity (SDC) at low frequencies (<0.2 Hz) decreased with increasing frequencies, which matched previous internal friction results. However, at higher frequencies (0.2–5 Hz) SDC increased with frequencies, which was explained by a new internal frictional heat mechanism. Three different ceramics: a non-superplastic one and two superplastic ones with different activation energies, showed the same behavior at the high frequency damping tests (1–5 Hz). From these results, it was deduced that a cyclic load at high frequencies, superimposed on a static one, has a great potential to enhance superplasticity by specifically heating up grain boundaries from internal frictional heat.     

Nanostructure formation in the surface layer of metals under influence of high-power electric current pulse

The possibility to tailor the microstructure of metals is explored utilising a skin-effect for surface treatment. The theoretical simulation of the electric and magnetic fields in a metallic cylinder shows that melting followed by rapid quenching can occur in a skin layer of 5–10-μm thickness if the amplitude of a single electric pulse of several nanoseconds duration is of the order of hundreds kiloamperes. The experiments using the SUS304 stainless steel show that besides a thin amorphous layer, a specific nano-twin structure can form at the near-surface region. The appearance of nano-twins is explained considering the stress components arising at the surface layer and in the bulk of the specimen during shock wave propagation caused by temperature gradients and the Lorentz force. It is shown that the high stress amplitudes can arise locally, furnishing the required conditions for twin nucleation and resulting in intensive plastic deformation of the sub-surface layer.     

Equilibrium states of an ion-beam plasma with magnetized electrons at low pressures

Results are presented of an experimental investigation of an ion-beam plasma with magnetized electrons in the cathode channel of an ion accelerator with an anode layer. New data are reported on the spatial distributions of the local plasma parameters (plasma potential, electron temperature, electron and ion densities) as functions of the external parameters of the discharge (magnetic field strength, anode voltage, and working gas pressure) in regions with strong, nonuniform electric and magnetic fields. Pis’ma Zh. Tekh. Fiz. 24, 33–38 (March 12, 1998)     

Field Emissions Caused by Fracture and Yielding

Two effects, magnetic and electric emission, have been observed and used in fracture tests to detect and analyse onset and progress of plastic deformation and fracture. While magnetic emission (ME) occurs only in ferromagnetic materials, electric emission (EE) can be found with any material, metals as well as plastics, ceramics, glass, and others. In ferromagnetic materials the two effects supplement each other. In steel, for example, electric emission is produced by plastic deformation but not by fracture; magnetic emission, on the other hand, is produced by fracture but not by plastic deformation. This paper describes the effects, demonstrates their application in Charpy tests, and shows how to derive fracture parameters, for instance the instants of the onset of plastic deformation and fracture. ME and EE, therefore, yield an attractive, inexpensive and fast supplement to conventional fracture test methods.     

Microwave processing of WC-Co composities and ferroic titanates

 The innovations in microwave processing of ceramics have been dominated to date by serendipitous discovery, because the interaction between such radiation as delivered via available tools and the materials of widely varying properties, sizes, and shapes is so complex that it has defied quantitative analysis. For over 10 years a wide variety of inorganic ceramic and semiconducting materials have been synthesized, sintered, and reacted in our own labs, including microwave hydrothermal synthesis of metals, ferrites, and electroceramic phases. These local results are summarized and used as the reference point for reporting on two different new advances: sintering of WC-Co composite tool bits and other similar objects in under 15 min, while retaining extremely fine microstructures, without any grain growth inhibitors; using reduced TiO₂ or Ta₂O₅ for the synthesis of phases such as BaTiO₃, Ba3MgTa₂O9, and Pb(Zr.Ti)O₃ in a few minutes in a 2.45 GHz field at the astonishing temperatures of 300–700 oC. Received: 2 January 1997 / Accepted: 27 March 1997     

Towards a new model of crack tip stress fields

This work introduces a novel mathematical model of the stresses around the tip of a fatigue crack, which considers the effects of plasticity through an analysis of their shielding effects on the applied elastic field. The ability of the model to characterize plasticity-induced effects of cyclic loading on the elastic stress fields is assessed and demonstrated using full-field photoelasticity. The focus is on determining the form of the shielding stress components (induced by compatibility requirements at the elastic–plastic interface along the crack flank and via the crack tip plastic zone) and how they influence the crack tip elastic stress fields during a load cycle. The model is successfully applied to the analysis of a fatigue crack growing in a polycarbonate CT specimen.     

Effect of electromagnetic fields on integrated microcircuits

We consider the results of investigations on the effect of external electromagnetic fields on integrated microcircuits. We have determined the stability thresholds for microcircuits as a function of the electric field strength, the number of pulses to which they are exposed, and the relative orientation of the integrated microcircuit and the electromagnetic field. We have determined the reasons for local degradation of the metallization and we present data on the threshold values for degradation processes. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 65–67, April, 1998.     

Achieving high strain rate superplasticity via severe plastic deformation processing

In this study, a thermomechanical process consisting of general precipitation and severe plastic deformation through equal channel angular extrusion (ECAE) was applied to a Zn-22 wt.% Al alloy to produce a microduplex structure for high strain rate (HSR) superplasticity studies. Microstructures, hardness, and superplastic properties of the Zn–Al alloy were studied by using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), recordable hydraulic press, and a tensile test with a hot stage. A work-softening phenomenon due to the occurrence of a grain boundary-sensitive dynamic recrystallization (DRX) was observed during the ECAE processing of the Zn–Al alloy at the extrusion temperatures investigated from −10 °C to 50 °C. An important discovery regarding the grain boundary-sensitive DRV was realized in this study such that through a progressive work-softening process the Zn–Al alloy will eventually exhibit HSR superplastic properties.     

Superplastic power-law creep of Sn–40%Pb–2.5%Sb peritectic alloy

The power law-creep behavior of superplastic Sn–40Pb–2.5Sb alloys with different grain sizes has been investigated at room temperature. Stress exponent values for these alloys have been determined by indentation creep, conventional creep and uniaxial tension tests in order to evaluate the correspondence of indentation creep results with conventional tests. In all cases, the indentation results were in good agreement with each other and with those of the tensile and conventional creep tests. The average stress exponent values of about 2.6 and 3.0 corresponding to the strain rate sensitivity (SRS) indices of 0.33–0.39, depending on the grain size of the materials, indicate that the grain boundary sliding is the possible mechanism during creep deformation of Sn–Pb–Sb alloys. Within limits, the indentation tests are thus considered useful to acquire information on the creep behavior of small specimens of these soft tin–lead–antimony alloys at room temperature. It is also demonstrated that the indentation creep test provides a convenient method to measure SRS and thereby to assess the ability of a material to undergo superplastic deformation.     

Resonant absorption of energy accompanying phase transitions in NaKC4H4O6·4H2O

Resonant absorption of external electric field energy was detected experimentally in the presence of phase transitions in Rochelle salt. An external alternating electric field leads to the appearance of an anomalous increase in the signal intensity at frequencies typical of those of the pulsed electric signal induced by a phase transition in the material. Pis’ma Zh. Tekh. Fiz. 24, 46–49 (August 26, 1998)     

陶瓷超塑性的研究进展

本文综述了氧化锆及其复相陶瓷超塑性的研究现状，论述了陶瓷超塑性的变形机理，微观特征和断裂特性。同时，分析和对比了陶瓷超塑性与金属超塑性的特点。目前，对于正确理解超塑性陶瓷的变形机理，还需进行大量工作。     

Superplastic behavior of Zn–Al eutectoid alloy with 2?% Cu

The effects of deformation temperature and strain rate on the superplastic behavior of the Zn–21Al–2Cu alloy (Zinalco alloy) were investigated by uniaxial tensile tests. Results were compared with those of the Zn–22Al eutectoid alloy without Cu. It was observed that additions of 2 % Cu leads to a decrease of the maximum strain attainable from 2600 % to 1000 %. The maximum strain in Zinalco alloy is obtained at lower strain rates. The presence of Cu increases the values of flow stress up to 600 % compared with those reported in the Zn-22Al alloy. Grain size sensitivity (p), true activation energy (Q _t ), and constant A of the constitutive equation were not affected by presence of Cu unlike the stress exponent (n) which increased from 2.5 to 3.9. The main effect of Cu was to decrease the plastic flow stability of the Zn–22Al alloy. The results indicate that presence of Cu in the Zinalco alloy causes a hardening effect at low strain rates leading to a decrease in the strain rate sensitivity which promotes the formation and growth of sharp necks. Microstructural characterization suggests that the large deformations at necking could possibly be due to the substantial elongation capability of the Zn-rich phase (η).     

Seventy-five years of superplasticity: historic developments and new opportunities

On this seventy-fifth anniversary of the first scientific report of true superplastic flow, it is appropriate both to look back and examine the major developments that established the present understanding of superplasticity and to look to the future to the new opportunities that are made possible by new processing techniques, based on the application of severe plastic deformation, that permit the production of fully dense bulk materials with submicrometer or nanometer grain sizes. This review proposes a minor modification to the present definition of superplasticity, it provides an overview of the current understanding of the flow of superplastic metals and ceramics and then it examines, and gives examples of, the new possibilities that are now available for achieving exceptional superplastic behavior.     

Structural, mechanical, and frictional properties of titanium nitride films exposed to continuous ion beam bombardment

The influence of low-dose (10¹⁴–10¹⁵ cm⁻²) ion bombardment on the structural, mechanical, and frictional properties of titanium nitride films has been studied and results are presented. It is shown that at these doses plastic deformation processes take place in the target material, which change the degree of crystallinity. By selecting the bombardment conditions, the properties of TiN films can be varied fairly widely. Pis’ma Zh. Tekh. Fiz. 24, 64–68 (February 12, 1998)     

Optical properties of the polarized Dirac vacuum

An investigation is made of the propagation of laser radiation through the Dirac vacuum polarized by a strong electric field. Calculations are made of the refractive index of the vacuum and the angle of rotation of the plane of polarization of the radiation. The possibility of measuring strong electric fields is assessed. Pis’ma Zh. Tekh. Fiz. 24, 45–47 (July 26, 1998)     

Mathematical model of induction heating of a cylinder for computer-aided manufacturing (CAM)

The article contains computational algorithms for the parameters of induction heating of a long ferromagnetic cylinder in a longitudinal magnetic field. The algorithms can be used to determine the operating conditions of heating devices rapidly and accurately in computer-aided plastic working of metals on the basis of numerical solutions of the heat-conduction equation and the equation of electrodynamics. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 3, pp. 547–550, May–June, 1998.     

Electromechanical properties of lead zirconate titanate piezoceramics under the influence of mechanical stresses

In lead zirconate titanate piezoceramics, external stresses can cause substantial changes in the piezoelectric coefficients, dielectric constant, and elastic compliance due to nonlinear effects and stress depoling effects. In both soft and hard PZT piezoceramics, the aging can produce a memory effect that will facilitate the recovery of the poled state in the ceramics from momentary electric or stress depoling. In hard PZT ceramics, the local defect fields built up during the aging process can stabilize the ceramic against external stress depoling that results in a marked increase in the piezoelectric coefficient and electromechanical coupling factor in the ceramic under the stress. Although soft PZT ceramics can be easily stress depoled (losing piezoelectricity), a DC bias electric field, parallel to the original poling direction, can be employed to maintain the ceramic poling state so that the ceramic can be used at high stresses without depoling.