Preliminary Deformation Research Articles

Influence of the deformation type and medium on the mechanodynamic penetration of nitrogen molecules into surface layers of armco iron

The extraction of nitrogen molecules from deformed samples of armco iron with different initial structures (annealed and subjected to equal-channel angular pressing) and different deformation prehistories (deformation in liquid nitrogen at 77 K, rolling in air at room temperature, and their combination) has been studied. It has been shown that the preliminary deformation in liquid nitrogen increases its concentration in the surface layer of the material and shifts the principal peak of its release toward low temperatures during heating. The results are associated with the existence of different types of nitrogen traps in annealed and nanostructured armco iron and with their changes during subsequent deformation.

Influence of the blank’s properties on the hybrid drawing of long profiles

Hybrid drawing is considered: specifically, preliminary deformation with the formation of longitudinal chip-separation channels and subsequent cutting. Optimal tool characteristics are established for each stage in drawing ductile materials and regular materials.

Influence of reactive stresses on thermodynamics and kinetics of martensitic transitions in single crystals of the shape memory Cu-Al-Ni alloy

The heat of the β′1-β1-martensitic transition in single crystals of the alloy Cu-13.5 wt % Al-4.0 wt % Ni was studied under conditions of a constrained shape memory deformation and emergence of reactive stresses. The experiments were performed with samples bended in the form of a clamp. The sample was put into a continuous stainless steel ring, and this construction was placed in the capsule of a differential calorimeter. It was found that, with an increase in the magnitude of preliminary bend deformation, the maximum in the heat release (or heat absorption) curves decreases noticeably and its position shifts to higher temperatures. It was revealed that the latent heat of the transition decreases by a factor of 2 and 3 during heating and cooling, respectively. It was assumed that the observed effects are related to the influence of reactive stresses on the parameters of martensitic transitions. A quantitative analysis of the data obtained was performed in terms of the theory of diffuse martensitic transitions taking into account both the thermodynamic and kinetic factors.

Preliminary deformation experiment of ringwoodite at 20 GPa and 1 700 K using a D-DIA apparatus

A deformation experiment of ringwoodite with a strain of 9% was achieved at 20 GPa and 1 700 K and at a strain rate of 3×10−5 s−1 using a deformation-DIA (D-DIA) apparatus and a multi-anvil 6-6 (MA 6-6) assembly. The crystallographic orientations of the deformed sample were successfully analyzed by the electron backscatter diffraction (EBSD) method, although any notable lattice-preferred orientation (LPO) was not observed presumably due to the insufficient strain in the present experiment. In this study, the deformation experiment on ringwoodite succeeded at P-T conditions consistent with the lower part of the mantle transition zone and at a controlled strain rate for the first time. The present study extended the pressure range of deformation experiments in the D-DIA apparatus from 16 GPa in our earlier study to 20 GPa at 1 700 K. The successful extension of the pressure range demonstrates potential importance of the D-DIA apparatus in studying rheological properties of minerals under the P-T conditions of the whole mantle transition zone.

Application of ENVISAT ScanSAR interferometry to long-range fault creep: a case study of the Xianshuihe fault in the eastern Tibetan margin area

The Xianshuihe fault of Sichuan province, southwest China, is a highly active strike-slip fault approximately 350 km long. Previous studies have described left-lateral slip of up to 10–17 mm/year on the Xianshuihe fault during recent decades, as indicated by geological criteria and GPS observations. Satellite InSAR observations provide an alternative effective technique used to measure the crustal deformation on the active fault. In this article, we present ScanSAR interferometry applied to ENVISAT WSM ASAR data to produce a deformation map of about 400 × 400 km over the Xianshuihe fault zone and the Garzê-Yushu fault zone. The preliminary stacked deformation results of six WS–WS interferograms indicated a northeast–southwest deformation trend nearly perpendicular to the two fault zones and demonstrated the potential to monitor such wide-ranging deformation using ENVISAT WSS data.

Analysis of acceleration response of metal rubber isolator under random vibration

Based on the theoretical study of the dry friction isolation system under the random vibration, a formula for the description of the acceleration response of metal rubber (MR) isolation system under random vibration was derived. An experimental research for the MR isolator subject to random vibration excitation was carried out, and the effects of the relative density, the preliminary deformation, and the acceleration level of excitation on the root mean square of acceleration response for the isolation system were analyzed and depicted in curves. The theoretical root mean square of acceleration response was compared with the experimental ones, and the range for the practical use was determined.

Functional properties of bimetal composite of “stainless steel–TiNi alloy” produced by explosion welding

The functional properties of “TiNi–stainless steel” bimetal composite produced by explosion welding were studied. The influence of the ratio of the TiNi layer thickness to the total thickness of the sample as well as the influence of preliminary deformation on the recoverable strain and a temperature of shape memory effect were studied. It was found that the best combination of strain variation observed in repeated thermal cycles was demonstrated by the bimetal sample in which the thickness of the TiNi layer was 64% of the thickness of the sample. The preliminary deformation resulted in an increase in stress stored in the sample and led to an increase in recoverable strain.

STUDY OF THE EFFECT OF PRELIMINARY PLASTIC DEFORMATION IN THE PROCESS OF DISSOLUTION DURING TEMPERING OF LOW-CARBON AND BORON-CONTAINING ALLOYS

In the paper the influence of preliminary deformation on disintegration of martensite in boron-containing and carbonic alloy is explored. It is shown that at the small degree of deformation (7 per cent) both in low-carbonic and boron-containing alloys the process of martensite disintegration takes place less intensively. The increase of degree of preliminary deformation in a boron-containing alloy is instrumental in more even distribution of boron-cementite particles appearing as a result of martensite disintegration.

Strain hardening and plasticity of low-carbon steels with a heterophase structure: I. Strain hardening characteristics of steels during uniaxial tension

The strain hardening characteristics of low-carbon 10kp, 05G2S2, and 05G2R steels with a heterophase structure (ferritic-martensitic, ferritic-bainitic, ferritic-pearlitic) formed upon quenching from the intercritical temperature range and upon normalization are studied during uniaxial tension. The dislocation structures of these steels are examined by electron microscopy and internal friction, and the results obtained are used to explain the factors that cause the high strain-hardening rate of steels with a two-phase ferritic-martensitic structure. Stress-strain diagrams are constructed for steel samples that have various heterophase structures and are subjected to a small preliminary deformation (up to 10%); these diagrams can be used to compare the strain-hardening characteristics of the steels.

Effect of equal-channel multiangular pressing and heat treatment on the properties of an Nb-Ti-based superconductor

Effect of preliminary deformation induced by equal-channel multiangular pressing (ECMAP) in combination with hydroextrusion, drawing, and heat treatment on the structure and physicomechanical properties of a superconductor wire based on Nb-60 at % Ti alloy is studied. The optimal regime of ECMAP deformation is established.

On the strength of a body at temperatures close to its melting point

On the example of frozen soils and ice existing at temperatures close to the melting point, the existence of two mechanisms (types) of destruction related to the phase transitions of water is shown. The first mechanism that operates near the melting point is plastic destruction, it gradually converts an ice body into a liquid-like state. The second mechanism operating far from the melting point is brittle destruction, disintegration into parts, with a slight preliminary deformation. For both types of destruction equations of long-term strength and of the behavior of deformation in time have been obtained.

On the possibility of the self-blocking of dislocations in various materials

Experiments on heating without stress after a preliminary plastic deformation of bcc metals (armco Fe, Mo) have been carried out. The temperatures of deformation and heating were varied in wide limits. No transformations of dislocations from a curvilinear into a rectilinear blocked form were observed; i.e., no self-blocking of dislocations has been found in these bcc metals, in contrast to the previously investigated intermetallic compounds of the Ni3Al and TiAl type. A comparison of the behavior of dislocations in the bcc metals with that of single dislocations in TiAl has been performed. Using a previously suggested model, times that characterize the formation of kinks and their moving apart from one another have been introduced. It is shown that the change in the relationships between these times controls the changes in the shape of dislocations both during plastic deformation and upon heating in the absence of an external load. An analysis of the totality of experimental data obtained leads to a conclusion that it is the multivalley nature of the potential relief that plays the determining role in blocking and self-blocking of dislocations. Since the potential relief in bcc metals is single-valley, neither self-blocking of dislocations nor anomalous behavior of the yield stress has been observed. The problem of what equilibrium structures of the single-dislocation core in TiAl correspond to shallow and deep valleys and, also, what is the barrier that must be overcome for the passage between them, has also been considered.

Propagation of longitudinal and transverse waves in a multimodulus elastic medium

A problem of propagation of longitudinal and transverse waves in a multimodulus elastic isotropic medium is considered. In the model used, the medium is described by a potential depending on three invariants of strains, which allows the influence of preliminary deformation of the medium on the longitudinal and transverse velocities to be taken into account.

Effect of plastic deformations on the dependence of the remanence of steels on elastic tensile stresses

Maximum values of the remanence and the positions of the maxima, which correspond to the average value of body stresses (internal stresses of the first kind), have been found based on the measurements of the dependence of the remanent magnetization of ferromagnetic steels on the elastic tensile stresses. The internal stresses were varied over wide limits with the aid of different amounts of a preliminary plastic tensile deformation. The results obtained make it possible to use magnetic methods of measurements to determine residual stresses and control their changes during exploitation, which offers new possibilities for nondestructive testing of the stress-strain state of articles and constructions.

Effect of plastic working on hydrogen permeability in an FeAl-based alloy

The electrochemical hydrogen permeation tests were applied to determine permeability and the effective diffusivity of hydrogen in a plastically deformed FeAl-based alloy. The experimental results reveal that both the hydrogen permeation rate and effective diffusion coefficient are reduced with the increase in plastic working degree. Structural defects induced by preliminary deformation are the main retardation factor for hydrogen transport in iron aluminides.

Degradation of a low-carbon steel in long operation in an oil-hydraulic unit

We present an atypical example of corrosion fracture of a low-strength high-plasticity steel from an internal surface formed by a hole in a choke of an oil-hydraulic unit, operated for 35 years. The conclusion that, in terms of the effect on the mechanical behavior of the metal operated for a long time, oil can be considered to be an aggressive medium is made. Its influence is enhanced by the preliminary plastic deformation of subsurface layers of the metal using force drilling of the hole in the choke. We detected fractographically the subcritical growth of a crack from the internal surface of the choke with multiple secondary cracking, which is interpreted as a manifestation of the mechanism of hydrogen embrittlement of the metal degraded during long operation.

Effect of the temperature and way of preliminary torsion in the austenitic state on the shape memory effect in TiNi alloy

The effect of temperature and direction of preliminary torsion in the austenitic state on the degree of strain recovery upon heating of a TiNi alloy has been investigated. It is shown that an increase in the preliminary deformation temperature from 500 to 700 K leads to an increase in the degree of shape recovery upon heating of the material studied. In particular, a 20% strain at a temperature of 500 K decreases the recovery coefficient by 20%, whereas the same preliminary strain at 700 K deteriorates the shape recovery by only 4%. It is established that, applying preliminary torsion in the austenitic and martensitic states in opposite directions, one can obtain an increase in the shape memory strain with an increase in the preliminary plastic strain. Thus, at some plastic strains (λpl > 10%), the strain recovered upon heating may even exceed the strain set in the martensitic state.

THE STUDY OF THE INFLUENCE OF PRIOR COLD PLASTIC DEFORMATION ON THE DIFFUSION OF CARBON AND BORON IN THE BORON-CONTAINING ALLOYS ON THE IRON BASE

In the article the influence of preliminary cold deformation on the process of diffusion of carbon and boron in the boron-containing alloy on the basis of iron was explored. The preliminary cold plastic deformation of boroncontaining alloy decreases boron and carbon diffusion mobility under surface saturation.

Some features of the formation and destruction of dislocation barriers in intermetallic compounds: V. Single-valley and multivalley potential relief for dislocations

A sufficiently general problem of thermoactivated transitions of dislocations between valleys of the potential relief (single-valley and multivalley) has been considered. The possibility of straightening of dislocations along a preferred direction in the absence of an external stress has been investigated. The controlling factor of this process is a thermoactivated transition (flip) of a dislocation from a shallow valley into a deeper valley of the potential relief. The flip process involves the formation of a double kink and its subsequent reorientation resulting in the formation of an asymmetric kink. The driving force of the flip process has been calculated and shown to be determined by the difference in the depths of the valleys. It has been shown that in the absence of an external stress the flip process is allowed under specific conditions, whereas the escape from a deep valley is hindered with a result that self-blocking of dislocations becomes possible. An analysis of experiments on heating of intermetallic compounds without stress after a preliminary deformation have been analyzed (see parts II-IV of this work), and owing to the experiments, self-blocking of dislocations has been found. The observation or nonobservation of self-blocking in different materials is a tool that enables the character of the potential relief of dislocations to be restored; the self-blocking is possible only in the presence of two types of valleys of different depth. Moreover, the two-valley character of the relief is a prerequisite for the development of an anomalous behavior of the yield strength upon dynamic loading.

Some features of the formation and destruction of dislocation barriers in intermetallic compounds: IV. Thermoactivated straightening of dislocations along a preferred direction in TiAl

As a result of experiments which include plastic deformation and subsequent heating without stress, self-blocking of dislocations in TiAl has been revealed. The transformations of glissile dislocations into dislocation barriers has been observed both for superdislocations with Burgers vectors <101] and 1/2<112] and for single dislocations. The preliminary deformation was performed at room temperature; the heating without stress, at temperatures both below and above the peak temperature T max in the temperature dependence of the yield stress σy(T). With a proper choice of the temperature of heating and its duration, it proved to be possible to fix the initial stages of the straightening of single dislocations along a preferred direction parallel to their Burgers vector and the subsequent formation of long blocked dislocations. As a result of TEM analysis, it has been shown that the barriers were formed during heating without stress but they were not destroyed. It has been revealed that the barriers with a total Burgers vector <101] in TiAl, in contrast to Ni3Al, remain indestructible even when the experiments included a repeated deformation.