Investigation of the transition to superplastic behaviour by measurements of electrical resistivity annealing curves

Superplastic behaviour of the Zn-0·25 wt. % Cd alloy is studied by means of electrical resistivity measurements accompanied by dynamical tensile tests and optical metallography. Specimens of the alloy were deformed at various strain rates and temperatures and then step-by-step annealed up to 520 K, the electrical resistivity changes due to annealing being recorded. It is shown that the resistivity annealing curves are strongly influenced by the value of strain, strain rate and deformation temperature. A good correlation between the mechanical characteristics of the alloy and the resistivity changes caused by annealing has been observed.     

Deformation and contraction of Poincaré group representations

The irreducible representations of the Poincaré group with p ≠ 0 and discrete spin are analytically deformed to representations of the Galilei group. Via decomposition, reducible representations are also deformed. Consequences for physical interpretation of taking the limit c → ∞ are discussed.     

Method of choosing the adaptive level of discrete wavelet decomposition to eliminate zero component

An improved method is proposed to optimize the discrete wavelet decomposition, which can be used to decompose a deformed fringe by easily applying “ridge” information of continuous wavelet transform. With this method the zero component of a deformed fringe pattern can be extracted and eliminated automatically instead of using traditional repetitious tentative experiments. Computer simulations and experiments are carried out to verify our analysis by comparing the results from the correct level selection with that from the adjacent level selection.     

The annealing of weakly deformed polycrystalline nickel foils in an electron microscope

A study is made of the polygonization of weakly deformed polycrystalline nickel of 99·85% purity during annealing in an electron microscope. It was found that, in contrast to strongly deformed nickel, subgrains are not formed here but the dislocations disappear completely.It was found by simultaneously annealing equally deformed samples of different thickness that the rise in recrystallization temperature in material 0·05 mm thick compared with samples 0·5 mm thick is 200C, in foil-shaped material even around 500C. Analogous conditions were found in material deformed to 97·5% as well.     

Microstructural Evolution and Its Effect on Mechanical Properties of Isotactic Polypropylene by Shear Plastic Deformation at Elevated Temperatures

Isotactic polypropylene (iPP) was plastically shear deformed by equal channel angular extrusion (ECAE) at extrusion temperatures varied from 45 to 125°C (25 mm/min). The evolutions of morphology and crystal orientation were studied by reflected optical microscopy (ROM), scanning electron microscopy (SEM), and X-ray diffraction. It was found that the original spherulites were deformed into nearly ellipsoids with their long axis tilted at an angle away from the flow direction. Azimuthal scanning results revealed that two preferred crystal orientations were formed after ECAE. The crystal plasticity was activated by increasing the extrusion temperature, followed by fast rotation of crystallites toward the shear direction. The thermal mechanical analysis (TMA) indicated that low extrusion temperature was favorable to fix the molecular orientation. The iPP samples processed at the investigated temperatures displayed a significant increase in the impact strength, especially for those extruded at 45°C and 65°C. The tensile results revealed a greater elongation at break in the samples deformed at low temperatures (45°C and 65°C) but not in those deformed at high temperatures (85°C or above).     

Isochronal annealing studies of deformed FeSi alloys using positron annihilation spectroscopy

A series of FeSi samples were deformed to a thickness reduction of 16%. They were isochronally annealed for one hour at different temperatures and characterized by the Doppler broadening of the annihilation radiation (DBAR) measured at room temperature. Optical microscopy (OM) is used to investigate the microstructure of the deformed samples before and after annealing. The S parameter data show a decrease with the increase of the annealing temperature. At 973 K a significant decrease sets in. The microstructures of the alloys, investigated by OM, show that recrystallization is completed at 1173 K.     

Dislocation climb and low-temperature plasticity of an Al–Pd–Mn quasicrystal

Dislocations and phason faults have been studied by transmission electron microscopy in an Al-Pd-Mn sample deformed at 300°C under a high pressure. All dislocation movements have occurred by climb, in contrast with the usual interpretations of dislocation motion in quasicrystals. Several modes of dissociation and decomposition of dislocations have been observed, allowing for estimations of phason fault and antiphase-boundary energies. Work softening is tentatively explained in terms of a varying chemical stress.     

Stress corrosion cracking of alloy C-22 and Ti Gr-12 using double-cantilever-beam technique

Susceptibility to stress corrosion cracking (SCC) of two candidate alloys for the inner container of the multi-barrier nuclear waste package was evaluated by using wedge-loaded precracked double-cantilever-beam (DCB) specimens in deaerated acidic brine (pH≈2.70) at 90°C. Materials tested included Alloy C-22 and Ti Grade-12. Duplicate samples of each material were loaded at different initial stress intensity factor (K_I) values ranging between 22 and 43 MPa√m. Both metallography and the compliance methods were used to determine the final crack length. The final stress intensity for SCC (K_f) was computed from the measured final wedge load and the average crack length. The results indicate that, in general, the final crack lengths measured by metallography and compliance agreed well with one another, thus, providing very similar K_f values. The alloy C-22 showed higher susceptibility to SCC than Ti Grade-12 in terms of the average crack growth. Fractographic evaluation by scanning electron microscopy (SEM) of broken DCB specimens revealed three distinct regions showing the characteristics of fatigue precrack, SCC, and fast fracture.     

An X-ray absorption spectroscopy investigation of the local atomic structure in Cu–Ni–Si alloy after severe plastic deformation and ageing

The local atomic structure of Cu–Ni–Si alloy after severe plastic deformation (SPD) processing and the decomposition of supersaturated solid solution upon annealing were investigated by means of X-ray absorption spectroscopy. The coordination number and interatomic distances were obtained by analyzing experimental extend X-ray absorption fine structure data collected at the Ni K-edge. Results indicate that the environment of Ni atoms in Cu–Ni–Si alloy is strongly influenced by the deformation process. Moreover, ageing at 973 K affects strongly the atomic structure around the Ni atoms in Cu–Ni–Si deformed by equal channel angular pressing and high pressure torsion. This influence is discussed in terms of changes and decomposition features of the Cu–Ni–Si solid solution.     

Stereometric metallography in the-interpretation of polar figures for compressed iron

Srereometric metallography [1–4] provides a quantitative means of solving many problems in metallography and is applied here to the determinations of the distribution of the texture over the cross-section of a compressed specimen.     

The thermal stability of and nature of damage in Ti alloys subject to high-strain-rate deformation

Samples of Ti–6?wt%?Al–4?wt%?V and Timet 550 (Ti–4?wt%?Al–4?wt%?Mo–2?wt%?Sn–0.5?wt%?Si?wt%), which have been deformed at a strain rate of 5?s^?1, were annealed after thinning so that the visibility of dislocations in transmission electron microscopy could be compared before and after annealing. It has been found that imaging with g?=?0002 produces clear images of dislocations before and after annealing, but that imaging with other diffracting vectors gives reasonable dislocation images only after annealing to at least 700°C. The sharpness of Kikuchi lines in diffraction patterns obtained from fully annealed samples, deformed at 10^?1 and 5?s^?1, has been examined. The lines are sharp for all planes in the fully annealed samples, but become more diffuse in samples deformed at 10^?1?s^?1. However, in samples deformed at 5?s^?1 the Kikuchi lines from (0002) planes are sharp but the lines from all other planes are diffuse. These observations are interpreted in terms of the presence of a high density of defects, which do not distort the elastically strong (0002) planes as significantly as they distort all other planes. These observations are discussed with respect to the recent claim that a particular Ti alloy deforms by a mechanism that does not involve dislocations.     

Thermal transport in heavily deformed and γ -irradiated LiF at temperatures near 1 k

The thermal conductivity κ of heavily deformed LiF crystals has been measured at temperatures T ? 0.5 K following exposure of the samples to γ irradiation. The results are in agreement with recent measurements of ballistic phonon propagation in similar samples at an equivalent temperature of ≈ 4 K. A fraction of the phonons have a mean free path of order 1 cm in the heavily deformed crystal, and γ-irradiation increases the fraction having a long mean free path. The measurements support a dynamic (as opposed to static) model of phonon-dislocation interaction.     

Metallographic study of precipitation in steel N36Kh11

Metallographic observations of the decomposition of the steel N36Kh11 after deformation and quenching have been made. It was found that in the aging of quenched material carbides could be seen metallographically only at the grain boundaries. In deformed material extensive carbide formation occurred not only at the grain boundaries but also within the body of the grains, particularly at the slip lines. It is shown that recrystallization takes place in the region of carbide formation in deformed material. Microhardness measurements are given which agree well with the metallographic observations.     

Universal R operator with deformed conformal symmetry

We study the general solution of the Yang–Baxter equation with deformed sl(2) symmetry. The universal R operator acting on tensor products of arbitrary representations is obtained in spectral decomposition and in integral forms. The results for eigenvalues, eigenfunctions and integral kernel appear as deformations of the ones in the rational case. They provide a basis for the construction of integrable quantum systems generalizing the XXZ spin models to the case of arbitrary not necessarily finite-dimensional representations on the sites.     

Transformation processes in deformed Al-30 wt.% Zn alloy containing metastable precipitates

The Al-30wt.%Zn alloy containing metastable α′_R or α′ precipitates was cold rolled to investigate the effect of plastic deformation on transformation processes during the subsequent ageing at 200 °C. Transmission electron microscopy and X-ray diffraction studies proved that the deformation leads to the rapid decomposition of deformed α′_R and α′ precipitates and enhances also the decomposition of α′ precipitates formed from α′_R to α′ transformation. The deformation does not, however, change the growth rate of α′ particles. It leads, therefore, to the decrease of critical sizes of α′ particles for the α′ to β transformation. The increasing degree of deformation enhances the density of nucleation sites for the β formation on α/α′ interfaces and leads to the decrease in sizes of stable β precipitates. The acceleration of transformation processes is associated with the partial relaxation of stresses introduced by the applied deformation.     

CEMS study of strain induced phase transformation in manganese Hadfield steel

A Conversion Electron Mössbauer Spectroscopy, (CEMS), study of phase transformations in a Hadfield steel induced by high rate strains is reported. Hadfield steel samples were impact deformed and the ensuing changes in the magnetic properties at the deformed zone and its surroundings have been studied by CEMS. The CEMS results are compared with wear tests and optical microscopy and show a formation of martensite by impact deformation only at the surface. Martensite is not produced by compression or tensile stresses but appears after wear tests in proportions that depend on the load and velocity conditions of test. The understanding of martensite phase formation and its evolution during deformation processes is also addressed.     

Structure and defects at Y2BaCuO5 interfaces in melt-textured YBa2Cu3Ox superconductors

Y₂BaCuO₅ (211) inclusions are prominent microstructural features found in melt-textured YBa₂Cu₃O_x (123) superconductors. These particles are of interest because the 123/211 interfaces and the interface-associated defects have been proposed to be flux pinning centers. In addition, the 211 particles are believed to be heterogeneous nucleation centers of dislocation which can increase the critical current density of 123. Unfortunately, only limited studies have been performed on these particles to ascertain their roles in flux pinning. In this investigation, 211 particles, the interfacial structure and defects in undeformed and mechanically deformed melt-textured 123 have been studied by transmission electron microscopy. It was found that there appears to be a preferred orientation between large oblong 211 particles and the 123 matrix. In addition, while the 123/211 interfaces in undeformed 123 are sharp and relatively undistorted, the interfaces in deformed 123 samples are much thicker. Also, the distribution of strained regions and dislocations around oblong 211 particles in undeformed 123 is nonuniform; the interfaces of low surface curvature are relatively free of defects while the surfaces of high curvature are abundant in dislocations. In contrast, the 123/211 interfaces in deformed 123 samples contain high density of dislocations regardless of interface curvature.     

Thermodynamic stability of the structure of a deformed Fe-C solid solution

An analysis is made of the thermodynamic stability of the dislocation structure in polycrystalline samples of Fe-C, deformed under conditions of high rates and hydrostatic pressures, based on experimental and theoretical data concerning the internal energy and on diffractometer measurements of the broadening of x-ray lines. The method of deformation calorimetry was used to determine the internal energy in a wide range of deformations. A theoretical model is proposed for estimating the change in internal energy in deformed alloys. An investigation is made of the dependence of the interdislocation interaction parameter on the deformation rate for different stressed state-schemes and large plastic deformations. It is shown that the relative quantity δU/A is correlated in a wide range of deformations with the relative root-mean-square distortions of the crystal lattice of the deformed solid solution. The mechanisms for the accumulation of energy in deformed solid solutions having a body-centered cubic lattice are considered. Don State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 77–83.     

Transformation of Slip Dislocations in Σ3 Grain Boundary

Grain boundary processes during plastic deformation of bicrystals were studied by TEM. Two methods were used. In situ straining in the electron microscope followed by post mortem examination and post mortem observation of specimens previously deformed by in situ synchrotron radiation X-ray topography. Two mechanisms governing slip propagation across a coherent twin boundary in a Fe-Si alloy bicrystal were identified. The first mechanism is a dissociation of a slip dislocation with the Burgers vector lying parallel to the boundary into three equal grain boundary dislocations. The second mechanism is a decomposition of a slip dislocation with Burgers vector inclined to the boundary into a dislocation mobile in the other grain and two screw grain boundary dislocations.