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1.
Martensitic thermoelastic transformations are considered under nonequilibrium conditions, where a system nonmonotonically
tends toward a stationary process. The specific features of a phase transformation are experimentally studied on molecular
models under these nonequilibrium conditions. A resonance mode of the phase transformation, which can increase the process
rate by an order of magnitude without increasing the heat source temperature, is found. The dissipative processes that occur
under the monotonic and resonance conditions of martensitic thermoelastic transformations are estimated. The resonance mode
is shown to be accompanied by negative entropy production and to demonstrate the self-organization of the system. These results
can be used to design materials and techniques for the processing of low-potential heat sources. 相似文献
2.
V. M. Arzhavitin 《Technical Physics》2007,52(6):721-726
An analytic expression is obtained for the time dependence Q ?1(t) of internal friction associated with plasticity of a phase transformation. Time dependences Q ?1(t) of internal friction of the Pb-62Sn and Pb-1.9Sn alloys (wt.%) alloys were studied in the regime of continuous excitation of resonant flexural vibrations. The measurements of the Q ?1(t) dependences for 1 h at room temperature and a fixed strain amplitude ε0 ≈ 7 and 19 min) for the Pb-62Sn alloy. For the Pb-1.9Sn alloy under the same conditions, an exponential decrease followed by an internal friction peak (at t m ≈ 7 min) is observed. It is shown numerically that the above singularities of internal friction are formed by processes of intermittent phase decomposition of Pb-Sn alloys in the cyclic stress field produced by an external load. Experimental data on Q ?1(t) are used for reconstructing the kinetic curves describing the decomposition (conversion) ratio as a function of time and for calculating the corresponding values of parameters K and n of the Avrami kinetic equation for the Pb-62Sn alloy. 相似文献
3.
In this study, the internal friction (IF) of a CuAlBe alloy during reverse martensitic transformation (MT) was investigated under isothermal and non-isothermal conditions. It was found that the IF decreases regularly with the aging time in the temperature range of phase transformation. It is thought that this phenomenon is caused by the defect movement. The defects diffuse to the interfaces between martensite and austenite and pin there gradually, thus leading to the IF decrease. 相似文献
4.
A. A. Klopotov E. S. Marchenko A. N. Matunin E. V. Kozlov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(8):1033-1036
Analysis of our original results and the data in the literature on the behavior of structural parameters of the austenitic and martensitic phases near phase transitions in alloys of the TiNi-TiMe (Me = Au, Pd, Pt, Rh, Cu, Co, Fe, Rh) system has been performed. It is established that the Bain strain and dilatation changes depend on the martensitic transformation “channel.” 相似文献
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6.
Geometric structures and atomic positions were studied with plane wave pseudo-potential method based on density functional theory for cubic, tetragonal, and monoclinic phases of TiRh alloy. Their phonon dispersion curves were obtained with frozen phonon method at harmonic approximation using density-functional perturbation theory. Our calculations revealed that both B2 and L10 phases are thermodynamically unstable. Jahn-Teller effect triggers the occurrence of Bain transformation from cubic to tetragonal phase, and then soft-mode phonon further leads to the transition from tetragonal to monoclinic phase on cooling. The monoclinic phase was predicted to be P2/m space group through atomic vibrational movement along [001] direction of virtual frequency modes of L10 phase. The temperature from B2 to L10 and then to P2/m were predicted to be about T=1100.53 K and T=324.48 K through free energy calculations with the electronic plus vibrational energy of formation, respectively, which is in good agreement with experimental observations. 相似文献
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8.
Acoustic emission during thermoelastic martensitic transformations in titanium nickelide is investigated. Phase transitions
are initiated by loading the specimen to 200 MPa under isothermal conditions. It is found out that deformation buildup and
acoustic emission in the loading-unloading cycles are observed in the first cycle only, during further cycles the acoustic
emission is comparable to the background, while the deformation buildup and recovery are not associated with martensitic transformations.
It is shown that recovery of the deformation built up during loading occurs due to heating to 600 °C, with the major part
of accumulated deformation undergoing recovery already at 250 °C and recovery of its minor part observed at 400 °C. This behavior
of acoustic emission and accumulation and recovery of deformation provide evidence of martensitic phase stabilization during
cycling of martensitic transformations under conditions of thermo-mechanical cycling.
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Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 89–94, February, 2008. 相似文献
9.
It is shown that residual austenite hardens unevenly during martensitic transformation. The austenite forming at the sites of martensite plates has a higher hardness level than the residual austenite; this austenite plays a vital part in the hardening of alloys by the phase hardening method. 相似文献
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11.
Angheluta L Jettestuen E Mathiesen J Renard F Jamtveit B 《Physical review letters》2008,100(9):096105
The application of stress to multiphase solid-liquid systems often results in morphological instabilities. Here we propose a solid-solid phase transformation model for roughening instability in the interface between two porous materials with different porosities under normal compression stresses. This instability is triggered by a finite jump in the free energy density across the interface, and it leads to the formation of fingerlike structures aligned with the principal direction of compaction. The model is proposed as an explanation for the roughening of stylolites-irregular interfaces associated with the compaction of sedimentary rocks that fluctuate about a plane perpendicular to the principal direction of compaction. 相似文献
12.
V. G. Pushin N. N. Kuranova E. B. Marchenkova E. S. Belosludtseva V. A. Kazantsev N. I. Kourov 《Technical Physics》2013,58(6):878-887
The properties and structure of the martensitic phase of alloys with a near-stoichiometric equiatomic Ni50Mn50 composition, as well as martensitic transformations in them, are investigated in a wide temperature range by measuring the resistivity and thermal expansion coefficient and applying transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. It is found that Ni50Mn50 and Ni49Mn51 alloys experience the B2 → L10 highly reversible thermoelastic martensitic transformation and its related high-temperature deformation of the transformation and shape memory effect. Critical temperatures, volume (ΔV/V = ?1.7%) and linear size effects attributed to the direct and reverse martensitic transformations, and the high-temperature dependences of the martensitic and austenite lattice parameters are determined. It is found that the morphology of tetragonal L10 martensitic represents a hierarchy of thin coherent sheets of submicrocrystallites and nanocrystallites with plane near-{111}L10 habit boundaries, the crystallites being pairwise twinned according to the {111}〈11 $\bar 2$ 〉 L10 ∥ {011}〈-1 $\bar 1$ 〉 B2 twinning shear scheme. 相似文献
13.
The lattice dynamical property of AuCuZn2 has been investigated by means of inelastic neutron scattering technique in connection with its martensitic phase transformation. The temperature dependent soft phonon was observed transformation. The temperature dependent soft phonon was observed around of TA2 phonon branch. We have also found a premartensitic metastable phase, in which new satellite reflections at (H± , K ? , 0) have been observed around fundamental reflections with H + K = 4n. The atomic displacements of the soft phonon mode correspond to the atomic arrangement of the premartensitic phase. 相似文献
14.
S. P. Belyaev V. A. Ermolaev V. A. Likhachev V. M. Kovalev M. N. Korolev 《Russian Physics Journal》1989,32(2):151-154
A Carnot cycle is proposed for a working material undergoing martensitic transformation while operating a finite temperature interval. The size of the interval depends on the thermodynamic characteristics of the transformation. Diagrams are presented to decribe the deformation of titanium under adiabatic and isothermal conditions. The diagrams confirm the possibility of realization of the transformation. A comparison is made with other known cycles. It is shown that transformation hysteresis diminishes the efficiency of the actual cycle.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 91–94, February, 1989. 相似文献
15.
H.G. Schuster 《Solid State Communications》1973,13(9):1361-1363
It is shown on the basis of the Labbé-Friedel model for A3B compounds that the martensitic phase transformation in Nb3Sn can be changed from a first to a second order transition by an external stress. The Hamiltonian operator describing the phase transition in an external stress field has been mapped to a spin Ising model with infinite range interactions showing a second order phase transition. Estimates of the transition temperature and the maximum order parameter are given suggesting new experiments. 相似文献
16.
The NixAl1−x alloys exhibit shape memory effect, for which thermoelastic phase transformations are essential, in the composition range of 60<x<65. The analytical studies are very difficult on the thermoelastic phase transformations because these types of transformations exhibit anharmonic behaviour. In order to overcome this difficulty, it is possible to benefit from the molecular dynamics (MD) calculations based on interatomic interaction potentials. In the present study, the interatomic interactions of Ni62.5Al37.5 alloy have been modelled by means of Lennard-Jones potential energy function. A MD cell of 1024 atoms in B2 super lattice has been chosen and the structural changes were investigated on this system with changing temperature. It has been observed that the model alloy exhibits the thermoelastic phase transformation with thermal cycling. A hysteresis has been determined between forward and backward transformation temperatures. The structural analysis is also done before and after the transformation. 相似文献
17.
R. I. Babicheva Kh. Ya. Mulyukov I. Z. Sharipov I. M. Safarov 《Physics of the Solid State》2012,54(7):1480-1485
The temperature dependence of thermal expansion of the Ti-49.8 at % Ni alloy has been measured after rolling at temperatures of 470, 570, 670, 770, and 870 K. The maximum dilatation jump during the martensitic phase transition has been observed for the samples rolled at 570 and 670 K. A fragmented structure, in which the phase transformations are hampered, is formed during the low-temperature rolling. An increase in the rolling temperature to 770–870 K leads to the return processes and dynamic recrystallization of the material; as a result, the slope of dilatation curves changes and the range of phase transitions narrows. 相似文献
18.
X-ray studies show the effects of elements added to the Nb or of strain on the martensitic phase transformation of Nb3Sn at low temperature. Additives to the Nb suppress the transformation, superimposed strains produced by a surrounding bronze matrix tend to mask the lattice transformation, and calculations show that the detailed line shape must be considered. 相似文献
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20.
The microstructural evolution and the martensitic transformation (bcc–hcp and bcc–fcc) mechanisms during the solidification process of liquid metal Pb were studied by molecular dynamics simulation. Results indicate that, with the decrease of temperature, the system undergoes two phase transitions: from the liquid state into a metastable bcc phase first and then from the bcc phase into a coexisting crystal structure of hcp and fcc phases. Moreover, the complicated martensitic transformation processes are clearly observed by cluster type index method (CTIM) and the tracing method. The two transformation mechanisms are very analogous at the atomic level; the essential difference between them is that, in the bcc–hcp transformation, two adjacent layers shift in opposite directions, whereas in the bcc–fcc transformation, the top layer and bottom layer shift in opposite directions relative to the middle layer. The specific mechanisms for the bcc–hcp and bcc–fcc transformations are confirmed to correspond to the revised Burgers mechanism and Bain mechanism, respectively. 相似文献