E. F. Dudarev

On the nature of anomalously high plasticity of high-strength titanium nickelide alloys with shape-memory effects: I. Initial structure and mechanical properties

This work presents the results of studies of the Ti49.4Ni50.6 alloy of enhanced purity with shapememory effects in an ordinary coarse-grained state with an average grain size of 20–30 μm or in a submicrocrystalline state with an average grain size of 0.2–0.3 μm. In this alloy the initial structure, phase composition, martensitic transformations, mechanical properties, and character of fracture have been investigated in a wide temperature range. It has been shown that upon cooling and mechanical tests at room temperature, the alloy exhibits highly reversible thermoelastic martensitic transformations. It has been established that the alloy exhibits high values of the strength and plastic properties and strain-hardening coefficients.

On the nature of anomalously high plasticity of high-strength titanium nickelide alloys with shape-memory effects: II. Mechanisms of plastic deformation upon isothermal loading

Mechanisms of plastic deformation have been studied in detail in the process of isothermal loading at room temperature in a high-purity shape-memory alloy of composition Ti49.4Ni50.6. The alloy was studied in two initial states: usual coarse-grained (with an average grain size of 20–30 μm) and submicrocrystalline (with an average grain size of 0.2–0.3 μm). It has been shown that during tensile tests there occurs a mechanically induced martensitic transformation in the alloy at stresses corresponding to stages I, II, and III in the tensile curve and then elastic and plastic deformation of B19′ martensite is observed at stages IV, V, and VI, respectively. Optical metallography in situ and electron microscopy have been used to study microstructural features and mechanisms of plastic deformation of the alloy up to its failure.

True grain-boundary slipping in coarse- and ultrafine-grained titanium

The temperature dependence of internal grain-boundary friction in coarse- and ultrafine-grained titanium is investigated. It is demonstrated that true grain-boundary slipping causes internal grain-boundary friction in ultrafine-grained titanium, as in coarse-grained metals. It is established that when going from the coarse-grained structure with perfect grain boundaries to ultrafine-grained structure with imperfect grain boundaries, the temperatures of the beginning and intense development of true grain-boundary slipping decrease together with the activation energy of this process. The diffusion mechanism of true grain-boundary slipping is justified for both structural states.

Structure and mechanical and electrochemical properties of ultrafine-grained Ti

A study is conducted into the microstructure and physico-mechanical properties of ultrafine-grained titanium produced by severe plastic deformation using the method of equichannel angular pressing. The effects of thermal and mechanical treatment on these characteristics are investigated. The possibility of forming mechanical properties in titanium that compare well with those of highly doped titanium alloys is shown.

Microplastic deformation of polycrystalline and submicrocrystalline titanium during static and cyclic loading

A study is made of the laws governing the accumulation of microplastic strain during the static and cyclic loading of polycrystalline and submicrocrystalline titanium. It is shown that a change from the polycrystalline structure to the submicrocrystalline structure does not change the character of development of microplastic strain for either type of loading, but it does increase fatigue strength and fatigue limit. A correlation between the fatigue strength based on 106 cycles and the macroscopic elastic limit was found to exist for both types of loading.

Microplastic deformation and yield strength of polycrystals

ConclusionsThus, the theory considered above permits a unified description of the behavior of pure metals and certain classes of alloys in the transition stage from elastic to homogeneous macroplastic deformation. Tt accurately reflects the law of accumulation of plastic deformation up to the physical yield point and the form of the extension curve above the yield point. Its predictions as to the dependence on grain size of the macroscopic elastic limit, upper and lower creep limits, value of the “tooth,” and extent of the creep area correspond to experimental data.

The Effect of Equal-Channel Angular Pressing on Structure-Phase Changes and Superplastic Properties of Al-Mg-Li Alloy

The effect of equal-channel angular pressing (ECAP) on the structure-phase state and superplasticity development was investigated using the 1421 Al-Mg-Li alloy. The physical reasons for the displacement of the temperature range of superplasticity to lower temperatures after ECAP by comparison with the initial state are considered. Possible reasons are discussed for the decrease in the activation energy of true grain boundary sliding in the alloy produced using ECAP by comparison with the initial condition.

The Effect of Severe Plastic Deformation on the Structure and Mechanical Properties of Al–Mg–Li Alloys

The structural-phase state and mechanical properties of commercial aluminum alloys produced by severe plastic deformation are studied and compared to the initial polycrystalline state. This kind of treatment is found to give rise to the formation of a homogeneous ultrafine-grained structure with second-phase particles occurring predominantly along grain boundaries. With this structure, the strain-temperature and strain-rate intervals wherein the superplastic properties of the alloys under study are observed are shifted to lower temperatures and higher rates.

Role of point defects in martensitic transformations

The effect of point-defect complexes on martensitic phase transformations in a bcc system with low elastic moduli is studied by means of computer simulation. The interaction of strain fields generated by defects in shown to facilitate realization of a martensitic transition from the bcc to fcc or ω-like structure depending on the defect symmetry.

Spall destruction of coarse-grained and ultrafine-grained titanium on exposure to nanosecond heavy-current electron beam

This paper presents results of experimental and theoretical research of spall destruction of volume coarse-grained and ultrafine-grained titanium when using it as a generator of shock wave of nanosecond relativistic heavy-current electron beam. Computer modeling of effect of an intensive electron beam on the condensed target has been carried out taking into account destruction, phase transitions, dependence of strength characteristics of materials on internal energy. This is considered within elastic, ideally plastic Prandtl-Reiss model. The results of calculations are compared with experimental data.