Kinetics of Early Decomposition Stages in Diluted bcc Fe–Сu–Ni–Al Alloy: MC+MD Simulation

Physics of the Solid State - A combined approach including the Monte Carlo and molecular-dynamics simulation, decomposition kinetics and segregation formation in the multicomponent low-alloy...     

Interaction of dislocations with nanoprecipitates of the metastable phase and dispersion strengthening of the Fe-Cu alloy

The interaction of dislocations with copper-enriched precipitates in the matrix of body-centered cubic iron has been investigated by the molecular dynamics method. It has been shown that dislocations stimulate the development of a phase instability of body-centered cubic copper precipitates in a specific range of their sizes. This process is accompanied by the pinning of dislocations by precipitates and makes a significant contribution to strengthening. The results obtained provide an adequate explanation for the observed dependence of the strengthening in the Fe-Cu system on the precipitate size.     

Magnetism and local distortions near carbon impurity in gamma-iron

Local perturbations of the crystal and magnetic structure of gamma-iron near carbon interstitial impurity is investigated by ab initio electronic structure calculations. It is shown that the carbon impurity creates locally a region of ferromagnetic ordering with substantial tetragonal distortions. Exchange integrals and solution enthalpy are calculated, the latter being in very good agreement with experimental data. The effect of the local distortions on the carbon-carbon interactions in gamma-iron is discussed.     

Microscopic description of the kinetics of a martensitic transition in real crystals: bcc-hcp transition in Zr

The kinetics of the bcc-hcp transition in Zr in the presence of dislocations is investigated by numerical simulation methods. It is shown that the transition occurs in a nondiffusional (at a velocity of the order of the speed of sound) in two stages: relatively long development of instability of long-wavelength acoustic phonons and a fast stage of instability of short-wavelength phonons. The elastic stresses near a dislocation make it possible for these instabilities to develop at much lower temperatures than in an ideal crystal. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 6, 376–380 (25 September 1999)     

Size effect during two-particle agglomeration: Results of molecular dynamics simulation

The microscopic mechanisms controlling the atomic rearrangements during agglomeration of Ni particles 3 to 7 nm in size at temperatures T = 0.6–0.95 T _m have been studied by the molecular dynamics method. Pentagonally twinned crystals were obtained as a result of coalescence for the disorientations corresponding to special Σ11 and Σ27 large-angle boundaries.     

Photoluminescent nematic liquid crystalline elastomer actuators

Nematic liquid crystalline elastomer (LCE) actuators possessing both photoluminescent (PL) and stimuli-responsive functions were fabricated and studied. PL-dyes (1-pyrenemethyl acrylate and 4-bromo-2,6-bis-(1?-methyl-benzimidazolyl) pyridine loaded with Eu(III) ion) were synthesised and characterised, and then the dyes were mixed with an acrylate side-on liquid crystalline monomer, a cross-linker and a photo-initiator. Through magnetic field alignment, well-defined LCE micropillar PL actuators were fabricated from the mixed samples by a method combining soft lithography and photo-polymerisation/photo-cross-linking. Microscopic observations indicated that the LCE micropillars showed reversible thermomechanical deformation at the nematic-to-isotropic transition temperature. During the reversible contraction and extension process, the LCE actuator containing 1-pyrenemethyl moieties showed stable photoluminescence, while for the LCE actuator doped with 4-bromo-2,6-bis-(1-methyl-benzimidazolyl)pyridine/Eu(III) complex, the PL emission was quenched at about 100°C, which was before the pillars contraction occurring at a higher temperature. When cooled down to room temperature, the contracted LCE micropillars recovered their original shape and the initial PL emission state. The micron-sized LCE actuators can be used for thermomechanical devices and machines with different PL functions at the same time.     

Composition of cementite in the dependence on the temperature. In situ neutron diffraction study and Ab initio calculations

The structure state of carbon eutectoid steel has been studied by the in situ neutron diffraction method in the temperature range from room temperature to 800°C. It has been shown that an increase in the temperature is accompanied by a decrease in the concentration of carbon in cementite, whereas its weight fraction and the parameters of the orthorhombic lattice change slightly. The ab initio calculations of the nonstoichiometric carbides Fe₃C _x (0 < x < 1) indicate that the structure of cementite remains stable upon the appearance of vacancies in the carbon sublattice with a relatively low formation energy. Thus, cementite should be considered as an interstitial phase Fe₃C _x with a wide homogeneity range.     

Comparison of interactions between beta-hairpin decapeptides and SDS/DPC micelles from experimental and simulation data

Background  

We applied a combined experimental and computational approach to ascertain how peptides interact with host and microbial membrane surrogates, in order to validate simulation methodology we hope will enable the development of insights applicable to the design of novel antimicrobial peptides. We studied the interactions of two truncated versions of the potent, but cytotoxic, antimicrobial octadecapeptide protegrin-1, PC-72 [LCYCRRRFCVC] and PC-73 [CYCRRRFCVC].     

Decomposition kinetics in Fe–Cu dilute alloys. Monte Carlo simulation using concentration-dependent interactions

A generalization of the statistical (Monte Carlo) simulation technique for determining the structure of alloys is proposed. It takes into account the dependence of effective interactions between the atoms of a dissolved chemical element on their local concentration. Using the ab initio parametrization of the model, the decomposition of the bcc Fe–Cu alloy accompanied by the formation of Cu nanoprecipitates is studied. It is shown that the concentration dependence of effective interactions significantly affects the decomposition kinetics by displacing its onset to longer times in agreement with the experiment.