Plastic strain localization in Fe-3%Si single crystals and polycrystals under tension

Plastic flow localization in siliceous iron single crystals and polycrystals under identical stretching conditions is considered. The localization patterns are analyzed at the stages of linear and parabolic deformation hardening, as well as at the stages of necking and plastic fracture. The localization patterns observed in the alloy in the single-crystalline and polycrystalline states are compared.     

Plastic behaviour of Fe-3% Si alloy single crystals

Fe-3% Si alloy single crystals of single slip and double slip orientation have been tested in tension at temperatures between 113 K and 473 K. The stress-strain curves exhibit a yield drop followed by inhomogeneous yielding (yield propagation stage), a parabolic and an approximately linear parts. The slip line observations carried out in various stages of deformation show that only at the beginning of the parabolic part of stress-strain curve the specimen is completely filled out with slip bands and the deformation becomes relatively homogeneous. With both single slip and double slip orientations deformation takes place predominantly in one slip system only. At higher temperatures ageing occurs during deformation.Na Slovance 2, Praha 8, Czechoslovakia.The authors would like to thank Dr. B. esták for suggestion of the problem and for his interest in discussion of the results. We are also grateful to Mr. J. Poucha for help with some experimental work and to Miss G. Výborná for help with specimen preparation. To Dr. S. Libovický and Dr. F. Kroupa we thank for helpful discussions.     

Dislocations in plastically deformed Fe-3% Si alloy single crystals

The plastic deformation of Fe-3%Si alloy single crystals made from the melt is studied by the method of etching of dislocations. At a room-temperature and at static stress deformation by slip occurs in the 1/2〈111〉 directions along planes of maximum resolved shear stress. The plastic properties are determined by the motion of screw dislocations which cause the broadening of slip bands.     

Phase composition at surface of Fe-3%Si alloy

The structure, phase and chemical compositions of surface layers in different depths of Fe-3%Si alloy were investigated. According to the X-ray Photoelectron Spectroscopy (XPS) spectrum (penetration depth of up to ∼ 1nm) of the as-prepared sample, a layer of SiO₂ was present on the top. After the subsequent Ar⁺ sputtering (removing the SiO₂ layer), a segregation of Si atoms and two other phases were observed. The phases were described as the cubic c-FeSi and Fe₃Si. The emission⁵⁷Fe M?ssbauer spectra confirmed a presence of these phases. The α-Fe and solid solution of α-Fe + 1wt.%Si were recognized in the Conversion Electron M?ssbauer spectra (penetration depth ∼ 300nm) while the M?ssbauer spectra taken in scattering geometry with detection of 14.4 keV gamma radiation (scanning depth of ∼ 30 μm) indicate Fe-3wt.%Si solid solution as a main phase. Presented at International Colloquium “M?ssbauer Spectroscopy in Materials Science”, Všemina, Czech Republic, June 1–4, 2004. This work was supported by the Grant Agency of the Academy of Sciences of the Czech Republic (Contract No. IAA1041404).     

Dislocations in Fe-3% Si alloy single crystals deformed at a higher rate

The method of etching dislocations is used to study the distribution of dislocations and twins in Fe-3% Si alloy single crystals prepared from the melt after plastic deformation with higher speed. The crystals are deformed by twinning in the 〈111〉 directions along the {112} planes and by slip in the 〈111〉 directions along the {110} planes. The results prove that the dislocations causing plastic deformation move in the {110} planes during both fast and slow deformation. The difference in the slip surfaces during fast and slow deformation is explained by the different number of cross slips per unit dislocation path.     

Discontinuous deformation of Ni3Fe alloy single crystals in various states of atomic order

The conditions conducive to discontinuous deformation of alloy single crystals in various states of order were studied in experiments. An equation defining the minimum temperature for deformation discontinuities to develop was obtained. The possible reasons for the influence of order upon discontinuous deformation were analyzed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 65–71, December, 1977.     

The distribution of dislocations in slip bands of Fe-3% Si alloy single crystals deformed by bending

The distribution of dislocations at the ends of slip bands was studied by etching on surfaces parallel to the slip plane. In these places the slip band is formed by groups of asymmetric dislocation loops several hundred microns wide. The long mixed-type parts of these loops running nearly equidistantly and lying in near planes, are the equilibrium arrangement of dislocations of the same sign in the shear stress gradient. From the results we can judge that the dislocation sources are at larger distances from the ends of the slip bands and that the dislocation groups at the ends of the slip bands are sources of large stress fields.     

Morphologies of Fe-66.7 at.%Si alloy solidified in a drop tube

Solidification of 0.1–1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center.     

Morphologies of Fe-66.7 at.%Si alloy solidified in a drop tube

Because of their unusual optical, thermoelectric, and magnetic properties, iron sili- cides have attracted considerable attention in recent years. Among them, particular at- tention has been paid to the orthorhombic semiconducting iron disilicide β-FeSi2 due to its direct band gap of about 0.85 eV at room temperature, which makes it a candidate material to be used in optoelectronic devices in near-infrared light sources and detectors. In addition, β-FeSi2 has good physical and chemical sta…     

Grain Boundary Migration in Fe-3wt.%Si Alloys

The studies of three different laboratories on grain boundary migration in Fe-3wt.%Si alloys are presented. In all cases bicrystal techniques employing capillarity as driving force were used. [100] tilt boundaries were studied in the temperature range from 1223 K to 1373 K, and [110] tilt boundaries in the range from 1220 K to 1625 K. Proportionality between grain boundary velocity and driving force was confirmed. All data fulfil a linear relation between activation enthalpies and logarithms of the pre-exponential factors, corresponding to a compensation temperature of 1386 K where all boundaries theoretically should possess the same mobility. A considerably lower activation enthalpy was found in one case for an asymmetrical grain boundary compared to the symmetrical boundary of the same misorientation. High values of activation enthalpy of migration were found for special [100] boundaries compared to general ones although an opposite tendency was also observed for [100] boundaries.     

The effect of carbon content on the beginning of slip in single crystals of Fe-3·2 wt%Si alloy

Specimens with 18 ppm and 100 ppm carbon of different orientations were deformed by compression (?～1·1×10^?4 s^?1) at the temperatures 150 °K, 195 °K, 293 °K, 393 °K and 483 °K. The measuredΨ(χ) andτ(χ) curves are presented. The changes of the curves caused by increased carbon content are discussed from the point of view of the low temperature induced cross-slip. Deviations from the Schmid law of critical resolved shear stress are found for both carbon contents. The dependence of the CRSS on temperature for specimens of standard purity has a slightly different course for orientationχ=?30° than for orientationsχ=0° andχ=+30°. These deviations are discussed in terms of the influence of normal stress on the slip. The course ofΔτ (difference between the CRSS in the MRSS plane for specimens with 100 ppm and 18 ppm of carbon) onχ is discussed using different models of lattice hardening due to interstitial impurities. These models can also be applied to the explanation of deviations ofτ(χ) curves from the Schmid law.     

Thermally activated mechanisms of plastic deformation of single crystals of the disordered alloy Ni3Fe

On the basis of experiments on the variation of temperatures in the process of deformation and relaxation of stresses, we make an analysis of the temperature dependence of the yield stresses of single crystals of the disordered alloy Ni₃Fe and of the nature of the processes determining it.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 109–113, July, 1978.     

Dislocations in deformed and annealed Fe-3 wt.% Si single crystals

Changes of the dislocation arrangement during isothermal anneal in the temperature range 593 K–823 K of Fe-3 wt.% Si single crystals previously deformed 40% in tension are studied by TEM. From the observed decrease in dislocation densities it is concluded that bundles of dislocations which are the main component of the dislocation arrangement consist predominantly of edge dipoles of primary dislocations. The maximum height of the dipoles is about 16 nm.     

Plastic deformation of single nanometer-sized crystals

We report in situ electron microscopy observations of the plastic deformation of individual nanometer-sized Au, Pt, W, and Mo crystals. Specifically designed graphitic cages that contract under electron irradiation are used as nanoscopic deformation cells. The correlation with atomistic simulations shows that the observed slow plastic deformation is due to dislocation activity. Our results also provide evidence that the vacancy concentration in a nanoscale system can be smaller than in the bulk material, an effect which has not been studied experimentally before.     

Stress relaxation in cadmium-silver alloy single crystals

A series of cadmium — silver alloy single crystals containing up to 0·25 at % Ag were deformed in tension at a strain rate of 1×10^?4s^?1. The tensile tests were carried out at temperatures between 77 and 199 K. Stress relaxation experiments were performed to investigate the concentration dependence of the activation volume. Over the temperature range investigated, the activation volume at beginning of deformation decreases proportionally toc ^?2/3 wherec is the atomic concentration of silver as solute. The results are discussed on the basis of the interaction between dislocations and solute atoms.     

Distribution of slip tracks in single crystals of Ni3Fe alloy

The results of an experimental investigation of the distribution of slip tracks in a primary system in single crystals of Ni₃Fe alloy, oriented for a single slip, are presented. Investigations were carried out over a range of scales which differed by three orders of magnitude. Histograms of the distances between slip tracks at different scale levels are constructed. Self-similar track distributions in the primary slip system over the range of scales investigated are established. Tomsk State Architectural-Construction University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 51–56, April, 1998.     

Hydrogen-induced localized vibrational mode in proton implanted ZnSe single crystals

Infrared transmission spectra of proton implanted ZnSe single crystals exhibit a localized vibrational mode at 2116 cm^-1 which is ascribed to Se-H bond vibrations. The dependence of the integrated absorption A of this mode on the proton fluence D follows the relation A ∼ Dⁿ with n = 0.46. The results for ZnSe are compared with previous measurements on proton implanted III–V compounds.     

The growth of AlAgCu alloy single crystals

The present paper describes the preparation of AlAgCu (20% wt. Ag; 3.5% wt. Cu) alloy single crystals by the strain-anneal method. The effect of the following variables upon the growth of single crystals of alloys with limited solid solubility is discussed: the history of the specimen, the critical strain, the temperature gradient, the temperature and the rate of growth.     

Elastic constants of iron-silicon alloy single crystals

The adiabatic elastic constants of single crystals of Fe-Si alloys in the composition range from 6.3 at.% Si to 25 at.% Si have been determined by the ultrasonic pulse echo method at room temperature. The values of the elastic constants depend significantly on the silicon content, and their composition dependences are influenced by ordering.