Analysis of the Corrosion Behavior of the TiNi Alloy in the Coarse-Grained State

In this work was investigate the corrosion behavior of the TiNi alloy in a coarse-grained state in inorganic field with different concentration and holding time. An increase in the concentration of the solution leads to a significant acceleration of corrosion processes in the Ti49.1Ni50.9 alloy with a high Ni content, including until the samples are completely dissolved. It was revealed that solutions of 1 M sulfuric and hydrochloric acids after a month's exposure did not change in color and no precipitations were found, while solutions of 5 M hydrochloric and sulfuric acids acquired a violet and then green color, which is due to the predominant release of titanium ions (+4) and nickel (+2).

Strength and Fracture Mechanism of an Ultrafine-Grained Austenitic Steel for Medical Applications

In this paper, we study the corrosion-resistant austenitic steel Fe-0.02C-18Cr-8Ni for medical applications. The microstructure and mechanical properties (tensile mechanical properties, torsional strength, impact toughness, and static and cyclic crack resistance) under different types of loading of the steel are investigated. The results are compared for the two states of the steel: the initial (coarse-grained) state and the ultrafine-grained state produced by severe plastic deformation processing via equal-channel angular pressing. It is demonstrated that the ultrafine-grained steel 0.08C-18Cr-9Ni has essentially better properties and is very promising for the manufacture of medical products for various applications that experience various static and cyclic loads during operation.

Comparison of the corrosion behavior of the TiNi alloy in the coarse-grained and ultrafine-grained state

This article studies the corrosion behavior of the TiNi alloy in the coarse-grained and ultrafine-grained states. The study of the influence of the initial microstructure on the corrosion behavior of the TiNi alloy was carried out by the gravimetric method in the NaCl and H2SO4 solution for a month. Studies was shown that as a result of the action of a corrosive medium from a sample in a coarse-grained state, it undergoes greater destruction, pitting corrosion was observed, at the same time, in an ultrafine-grained sample only traces of corrosion products are observed on the surface of the samples. Investigations with an inverted light microscope in a dark field made it possible to observe corrosion products and determine their volume fraction. Evaluation of the corrosion rate showed that in the coarse-grained state it is 126 times higher than the corrosion rate in the ultrafine-grained state. Analysis of X-ray phase analysis showed that in the coarse-grained state after corrosion tests, a significant proportion of the TiNiH1.4 phase is observed, while in the ultrafine-grained state all phases correspond only to the TiNi phases. The TiNi alloy contains an Ti2Ni phase enriched Ti both in the coarse-grained state and in the ultrafine-grained state. Moreover, in a coarse-grained state, its share is 2 times higher.

The Metastable Mpemba Effect Corresponds to a Non-monotonic Temperature Dependence of Extractable Work

The Mpemba effect refers to systems whose thermal relaxation time is a non-monotonic function of the initial temperature. Thus, a system that is initially hot cools to a bath temperature more quickly than the same system, initially warm. In the special case where the system dynamics can be described by a double-well potential with metastable and stable states, dynamics occurs in two stages: a fast relaxation to local equilibrium followed by a slow equilibration of populations in each coarse-grained state. We have recently observed the Mpemba effect experimentally in such a setting, for a colloidal particle immersed in water. Here, we show that this metastable Mpemba effect arises from a non-monotonic temperature dependence of the maximum amount of work that can be extracted from the local-equilibrium state at the end of Stage 1.

The Investigation of Microstructure and Mechanical Behavior and the Fractographic Analysis of the Ti49.1Ni50.9 Alloy in States with Different Activation Deformation Volumes

In this article, the microstructure and mechanical behavior of the Ti49.1Ni50.9 alloy with a high content of nickel in a coarse-grained state, obtained by quenching, ultrafine-grained (obtained through the equal-channel angular pressing (ECAP) method) and nanocrystalline (high pressure torsion (HPT) + annealing), were investigated using mechanical tensile tests at different temperatures. Mechanical tests at different strain rates for determining the parameter of strain rate sensitivity m were carried out. Analysis of m showed that with an increase in the test temperature, an increase in this parameter was observed for all studied states. In addition, this parameter was higher in the ultrafine-grained state than in the coarse-grained state. The activation deformation volume in the ultrafine-grained state was 2–3 times greater than in the coarse-grained state at similar tensile temperatures. Fractographic analysis of samples after mechanical tests was carried out. An increase in the test temperature led to a change in the nature of fracture from quasi-brittle–brittle (with small pits) at room temperature to ductile (with clear dimples) at elevated temperatures. Microstructural studies were carried out after the tensile tests at different temperatures, showing that at elevated test temperatures, the matrix was depleted in nickel with the formation of martensite twins.

Stochastic Theory of Coarse-Grained Deterministic Systems: Martingales and Markov Approximations

Many works have been devoted to show that Thermodynamics and Statistical Physics can be rigorously deduced from an exact underlying classical Hamiltonian dynamics, and to resolve the related paradoxes. In particular, the concept of equilibrium state and the derivation of Master Equations should result from purely Hamiltonian considerations. In this chapter, we reexamine this problem, following the point of view developed by Kolmogorov more than 60 years ago, in great part known from the work published by Arnold and Avez in 1967. Our setting is a discrete time dynamical system, namely the successive iterations of a measure-preserving mapping on a measure space, generalizing Hamiltonian dynamics in phase space. Using the notion of Kolmogorov entropy and martingale theory, we prove that a coarse-grained description both in space and in time leads to an approximate Master Equation satisfied by the probability distribution of partial histories of the coarse-grained state.

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.

Влияние структурного состояния и оксидного покрытия на механостабильность титана ВТ1-0 при его циклическом нагружении

It was found that the fatigue properties of submicrocrystalline titanium are significantly higher than those for its coarse-grained state. The application of the oxide coating leads to a slight increase in these properties for titanium with a submicrocrystalline and coarse-grained structure. Some features of fatigue fracture of submicrocrystalline and coarse-grained titanium are analyzed.

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

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\rightleftarrows B. Furthermore, we show that, for such a system, one cannot find a consistent constitutive law by any Green–Kubo-like scheme.