Coarse-grained State Research Articles

Особенности упрочнения структурированного интенсивной пластической деформацией сплава Al-Cu-Zr

The effect of small additions of copper on the microstructure and physic-mechanical properties of an ultrafine-grained Al-1.47Cu-0.34Zr (wt%) alloy structured by high pressure torsion after preliminary annealing at 375 °C for 140 h has been studied. As a result of processing, high values of strength characteristics (conditional yield strength 430 MPa, ultimate tensile strength 574 MPa) with an acceptable level of electrical conductivity (46.1% IACS) and ductility (elongation to fracture ~ 5%) have been achieved. On the basis of the microstructural parameters determined by X-ray diffraction analysis and transmission electron microscopy, hardening mechanisms responsible for such high strength have been analyzed. It was shown that Cu plays the key role in strengthening. The addition of copper significantly contributes to grain refinement and, consequently, to grain-boundary hardening. Alloying with copper leads to significant additional hardening (~ 130 MPa) in the ultrafine-grained alloy, which is not typical for coarse-grained state. Segregation of Cu at grain boundaries and the formation of Cu nanoclusters are the most probable reasons for this hardening.

Coarse-grained and ultrafine-grained titanium high-temperature creep

The publication describes the study of durability in tensile creep of VT1-0 commercial titanium in its two states-coarse-grained and ultrafine-grained. It is shown that the best temperature for log-term testing is 350°C. At this temperature, the ultrafine-grained titanium structure remains stable both during free annealing and durability testing. The obtained data enable retrieving the difference in fracture initiation energies for titanium in its coarse-grained and ultrafine-grained states.

Calculation of hardening contributions of the TiNi alloy undergoing martensitic transformations in a free state

The paper reports on the studies of the effect of thermal cycling on the microstructure of the Ti - 50.8 at. % Ni alloy in coarse-grained and ultrafine-grained states, mechanical properties, and calculation of contributions to hardening in the studied states. The comparison of the calculated and experimental values of the yield stress in the TiNi alloy was carried out.

Contribution of structural parameters to the strength and electrical conductivity of Cu-0.5%Cr alloy subjected to ECAP and cold rolling

The effect of cold rolling with a reduction rate of 95% at room temperature and subsequent aging on the evolution of the microstructure, strength properties and electrical conductivity of the Cu-0.5Cr alloy (wt.%), which is widely used in the electrical industry in the form of strips and ribbons, has been studied. The cold rolling and aging of the alloy was carried out in coarse-grained and ultrafine-grained states after equal-channel angular pressing. The regularities found were used to assess the contribution of various structural parameters to the level of strength properties as well as the electrical conductivity of the alloy in the obtained states.

A Framework of Nonequilibrium Statistical Mechanics. II. Coarse-Graining

Abstract For a given thermodynamic system, and a given choice of coarse-grained state variables, the knowledge of a force-flux constitutive law is the basis for any nonequilibrium modeling. In the first paper of this series we established how, by a generalization of the classical fluctuation-dissipation theorem (FDT), the structure of a constitutive law is directly related to the distribution of the fluctuations of the state variables. When these fluctuations can be expressed in terms of diffusion processes, one may use Green–Kubo-type coarse-graining schemes to find the constitutive laws. In this paper we propose a coarse-graining method that is valid when the fluctuations are described by means of general Markov processes, which include diffusions as a special case. We prove the success of the method by numerically computing the constitutive law for a simple chemical reaction A ⇄ B A\rightleftarrows B . Furthermore, we show that, for such a system, one cannot find a consistent constitutive law by any Green–Kubo-like scheme.

Coarse-graining holographic states: A semiclassical flow in general spacetimes

Motivated by the understanding of holography as realized in tensor networks, we develop a bulk procedure that can be interpreted as generating a sequence of coarse-grained holographic states. The coarse-graining procedure involves identifying degrees of freedom entangled at short distances and disentangling them. This is manifested in the bulk by a flow equation that generates a codimension-1 object, which we refer to as the holographic slice. We generalize the earlier classical construction to include bulk quantum corrections, which naturally involves the generalized entropy as a measure of the number of relevant boundary degrees of freedom. The semiclassical coarse-graining results in a flow that approaches quantum extremal surfaces such as entanglement islands that have appeared in discussions of the black hole information paradox. We also discuss the relation of the present picture to the view that the holographic dictionary works as quantum error correction.

Compatibility between agents as a tool for coarse-grained descriptions of quantum systems

Shedding a new light in the coarse-graining scenario, in this contribution we came up with different necessary and sufficient conditions for the existence of a well-defined coarse-grained state. For doing so, we had to break apart with the usual quantum channels perspective and assume a more decision-theoretical posture. Broadly speaking, we reinterpret the coarse-graining problem in the language of quantum state pooling, and by making an extensive use of the conditional quantum states toolkit, we have been able to derive more tangible conditions for the emergence of a compatible effective coarse-grained state.

Information Closure Theory of Consciousness.

Information processing in neural systems can be described and analyzed at multiple spatiotemporal scales. Generally, information at lower levels is more fine-grained but can be coarse-grained at higher levels. However, only information processed at specific scales of coarse-graining appears to be available for conscious awareness. We do not have direct experience of information available at the scale of individual neurons, which is noisy and highly stochastic. Neither do we have experience of more macro-scale interactions, such as interpersonal communications. Neurophysiological evidence suggests that conscious experiences co-vary with information encoded in coarse-grained neural states such as the firing pattern of a population of neurons. In this article, we introduce a new informational theory of consciousness: Information Closure Theory of Consciousness (ICT). We hypothesize that conscious processes are processes which form non-trivial informational closure (NTIC) with respect to the environment at certain coarse-grained scales. This hypothesis implies that conscious experience is confined due to informational closure from conscious processing to other coarse-grained scales. Information Closure Theory of Consciousness (ICT) proposes new quantitative definitions of both conscious content and conscious level. With the parsimonious definitions and a hypothesize, ICT provides explanations and predictions of various phenomena associated with consciousness. The implications of ICT naturally reconcile issues in many existing theories of consciousness and provides explanations for many of our intuitions about consciousness. Most importantly, ICT demonstrates that information can be the common language between consciousness and physical reality.

Altered Global Brain Signal during Physiologic, Pharmacologic, and Pathologic States of Unconsciousness in Humans and Rats.

Consciousness is supported by integrated brain activity across widespread functionally segregated networks. The functional magnetic resonance imaging-derived global brain signal is a candidate marker for a conscious state, and thus the authors hypothesized that unconsciousness would be accompanied by a loss of global temporal coordination, with specific patterns of decoupling between local regions and global activity differentiating among various unconscious states. Functional magnetic resonance imaging global signals were studied in physiologic, pharmacologic, and pathologic states of unconsciousness in human natural sleep (n = 9), propofol anesthesia (humans, n = 14; male rats, n = 12), and neuropathological patients (n = 21). The global signal amplitude as well as the correlation between global signal and signals of local voxels were quantified. The former reflects the net strength of global temporal coordination, and the latter yields global signal topography. A profound reduction of global signal amplitude was seen consistently across the various unconscious states: wakefulness (median [1st, 3rd quartile], 0.46 [0.21, 0.50]) versus non-rapid eye movement stage 3 of sleep (0.30 [0.24, 0.32]; P = 0.035), wakefulness (0.36 [0.31, 0.42]) versus general anesthesia (0.25 [0.21, 0.28]; P = 0.001), healthy controls (0.30 [0.27, 0.37]) versus unresponsive wakefulness syndrome (0.22 [0.15, 0.24]; P < 0.001), and low dose (0.07 [0.06, 0.08]) versus high dose of propofol (0.04 [0.03, 0.05]; P = 0.028) in rats. Furthermore, non-rapid eye movement stage 3 of sleep was characterized by a decoupling of sensory and attention networks from the global network. General anesthesia and unresponsive wakefulness syndrome were characterized by a dissociation of the majority of functional networks from the global network. This decoupling, however, was dominated by distinct neuroanatomic foci (e.g., precuneus and anterior cingulate cortices). The global temporal coordination of various modules across the brain may distinguish the coarse-grained state of consciousness versus unconsciousness, while the relationship between the global and local signals may define the particular qualities of a particular unconscious state.

Dynamic Strength of Submicrocrystalline and Nanocrystalline Copper Obtained by High-Strain-Rate Deformation

Abstract—The dynamic properties of commercial copper (99.8 wt % purity) with a submicrocrystalline and nanocrystalline structure obtained by high-strain-rate deformation using the dynamic channel-angular pressing (DCAP) method have been studied in this work. The tests were carried out under conditions of shock compression at a pressure of 5.6−6.8 GPa at a strain-rate of (0.9−2.0) × 105 s–1. The analysis of the evolution of the structure and mechanical properties, namely, the dynamic elastic limit, dynamic yield stress, and the spall strength of copper before and after DCAP in different regimes, made it possible to evaluate the influence of the dispersity and imperfection of the crystal structure on its resistance to the high-strain-rate deformation and fracture. It has been shown that the grain refinement from 100 to 0.5−1.0 μm increased the dynamic elastic limit and the dynamic yield stress of copper by six times, but only slightly decreased the spall strength. The further refinement of the structure (up to 0.05−0.40 μm) increases the spall strength of copper by 1.4 times as compared to its value in the initial coarse-grained state.

Microstructural and Mechanical Stability of a Ti-50.8 at.% Ni Shape Memory Alloy Achieved by Thermal Cycling with a Large Number of Cycles

The influence of thermal cycling (TC) with a large number of cycles on the microstructure, the parameters of martensitic transformations (MTs), and the mechanical properties of a Ti-50.8 at.% Ni shape-memory alloy in coarse-grained (CG) and ultrafine-grained (UFG) states was investigated. The effect of microstructural and mechanical stability was found in both coarse-grained and ultrafine-grained states starting from the 100th cycle of martensitic transformations. In addition, an unusual temperature change was observed in martensitic transformations occurring with the formation of an intermediate R phase.

Mechanical properties and fractographic analysis of the Ti49.14Ni50.86 alloy in a coarse-grained state during multiple martensitic transformations

The mechanical behavior of the coarse-grained Ti49.14Ni50.86 alloy after multiple martensitic transformations B2-B19’ was investigated. A fractographic analysis of the samples after mechanical tests was carried out. The fracture pattern of the Ti49.14Ni50.86 alloy in the coarse-grained state has a viscous and heterogeneous character with microdepths on the fracture surface, the average size of which decreases as the number of thermal cycles increases.

Влияние ультрамелкозернистого состояния на теплофизические свойства сплавов Zr - 1 мас. % Nb и Ti - 45 мас. % Nb и процессы диссипации и накопления энергии при деформировании

The results of studying the thermal conductivity and specific heat capacity of Zr-1 wt.% Nb and Ti-45 wt.% Nb in coarse-grained and ultrafine-grained states are presented. The influence of the utrafine-grained state on the thermo physical properties and the processes of dissipation and accumulation energy during deformation of the alloys are estimated. It is shown that formation of the ultrafine-grained state in the Zr-1 wt.% Nb alloy by abc -pressing and subsequent rolling leads to a decrease in its thermal conductivity and specific heat capacity by 10 and 20%, respectively, due to substructural hardening under severe plastic deformation. It is found that thermal conductivity and specific heat capacity of the ultrafine Ti-45 wt.% Nb alloy increase by 7.5 and 5%, respectively, due to dispersion hardening of the ω phase by nanoparticles and formation of a new α phase. It is established that the ultrafine-grained structure has a significant influence on the regularities of the dissipation and accumulation energy during plastic deformation, which in turn depend on their thermo-physical characteristics and on the structural and phase state.

The microstructure and mechanical characteristics of the alloy Ti-50.7 at.%Ni with different deformation processing during multiple martensitic transformations

The influence of thermal cycling in the temperature range of B2-B19’ martensitic transformations on the TiNi alloy structure and properties are studied. Different states are considered, namely the initial coarse-grained (CG) state, the ultrafine-grained (UFG) state after ECAP, the state after ECAP and cold upsetting by 30%. It is shown that, as a result of thermal cycling, microhardness and strength grow in all the three states. According to the data from TEM analysis, the increment of the dislocation density is observed, resulting from thermal cycling.

Wear and friction dependence on grain size

The tribological characteristics of pure metals and ceramics with graphene obtained by electrochemical, deformation and powder metallurgical methods are compared for a coarse-grained and nanocrystalline state. Reducing the grain size to the nanoscale region in the structure helps to reduce wear and friction coefficient compared to conventional analogues. The possibilities of modelling the contact of solids with the atomic structure of the surface are considered.

Mechanical behavior at elevated temperatures of the ultrafine-grained titanium alloy VT8M-1 processed by rotary swaging

This paper investigates the mechanical properties at elevated operation temperatures of the Ti alloy VT8M-1(Ti-5.3Al-4.0Mo-1.2Zr-1.3Sn-0.2Si) in the coarse-grained (CG) and ultrafine-grained (UFG) states. The duplex UFG structure was produced by rotary swaging at a temperature of 750 °C. The UFG state was studied in terms of thermal stability during annealing at temperatures 500, 550, 600, 700 °C for a period of 1 hour. It was demonstrated that the recrystallization processes in the UFG structure start after annealing at 550 °C and above. We performed tensile mechanical tests at such temperatures. In a range of 300-450 °C, the ultimate tensile strength of the UFG alloy was stably above that of the CG alloy. Mechanical tests at 500 and 550 °C revealed a more significant decrease in the ultimate tensile strength of the UFG alloy as compared to the CG alloy, conditioned by the intensification of the recovery and recrystallization processes at these temperatures.

Elastic properties of Ti and its alloys nanostrctured due to severe plastic deformation

Studies of elastic properties of titanium and its alloys processed by severe plastic deformation are presented. The evolution of the modulus of elasticity resulting from the transformation from a coarse-grained state to an ultrafine-grained one due to severe plastic deformation (SPD) was investigated. The acoustic composite oscillator technique was used to measure the elastic modulus in a wide strain amplitude range. The microstructure was studied in detail by scanning electron microscopy and electron backscatter diffraction methods. Parameters of nanoscale porosity were measured by small-angle X-ray scattering before and after treatment with a high hydrostatic pressure (1.5 GPa). In addition, densities of titanium and its alloys in various structural states were determined by the precision method of hydrostatic weighing. As experiments showed, noticeable changes in the elastic properties resulting from the change in the grain state can be attributed to several factors, such as dislocations, nanoporosity, high internal stresses, and the structure of the materials before SPD processing.

Evolution of the structure and mechanical properties of the Mg-1%Zn-0.2%Ca alloy during ECAP

Microstructure of the Mg-1%Zn-0.2%Ca magnesium alloy after equal-channel angular pressing (ECAP) has been investigated. It was shown that an increase of the shear strain leads to significant grain refinement, as well as to the improved uniformity of microhardness. As a result of grain refinement by ECAP processing, the microhardness was increased to a value of 45.5, which is 28% higher than the initial state. Tensile tests demonstrated the enhanced ultimate tensile strength of 248.1 MPa, yield stress of 153.2 MPa, ductility of 19.4 % whereas in the initial coarse-grained state these parameters were 124 MPa, 45.3 MPa and 8.7 %, accordingly.

The influence of ultrafine-grained structure on the mechanical properties and biocompatibility of austenitic stainless steels.

In this study, equal-channel angular pressing (ECAP) of austenitic 316L and Cr-Ni-Ti stainless steels was carried out. Effect of ECAP at 400°C on the evolution of the microstructure, mechanical properties, and biocompatibility of these steels was investigated. The biocompatibility of samples with the ultrafine grain structure obtained in the ECAP process did not deteriorate in comparison with an austenitic 316L stainless steel in coarse-grained state. However, this treatment enhances the multipotent mesenchymal stromal/stem cell proliferation by 26% for 316L steel and by 17% for Cr-Ni-Ti stainless steel in comparison with coarse-grained counterparts. At the same time, ECAP contributes to a significant improvement in performance and weight reduction of medical devices, which is especially important for the creation of implanted prostheses for replacement of skeletal defects, due to significant increase in specific strength of steels. The strength properties of austenitic stainless steels were remarkably improved due to the grain refinement and deformation twinning resulted from ECAP at 400°C. After ECAP, the yield strength of 316L and Cr-Ni-Ti stainless steels increased by 4.2 and 2.9 times up to 950 and 900 MPa, and the fatigue limit by 2 and 1.7 times up to 500 and 475 MPa, respectively, comparing to coarse-grained counterparts.

Закономерности формирования стадийности деформационных кривых и микроструктуры в зоне разрушения крупно- и ультрамелкозернистых сплавов титана и циркония

Закономерности формирования стадийности деформационных кривых и микроструктуры в зоне разрушения крупно- и ультрамелкозернистых сплавов титана и циркония