Papers by Keyword: Dislocation Model

Abstract: A theoretical analysis of low-temperature plastic deformation processes and acoustic relaxation in the high-entropy alloy Al_0.5CoCrCuFeNi has been conducted. Within the framework of proposed dislocation model it was established the key types of dislocation defects in the alloy's lattice structure; types of barriers that hinder the movement of dislocation lines (strings); and mechanisms of thermally activated movement of various dislocation line elements through these barriers at room and low temperatures. Using this model, quantitative estimates have been derived for significant dislocation characteristics and their interaction with barriers, such as the distance between local obstacles in the slip plane ∼ 4 nm, the Peierls stress for dislocations in an easy slip system 4 · 10⁶ Pa, and more. Additionally, an estimated speed of sound 3.4 · 10³ m/s based on the proposed model aligns well with the direct experimental data. The empirical estimates for the energy per unit length of a dislocation ∼ 10^-8 J/m and the linear mass density ∼ 10^-15 kg/m are consistent with modern continuum dislocation theory. A detailed examination of the structure of the alloy Al_0.5CoCrCuFeNi was carried out using X-ray diffraction and Energy Dispersive Spectroscopy techniques. Numerical estimates of the dislocation density ∼ 5 · 10¹⁵m^-2 were obtained through Williamson-Hall analysis of X-ray diffraction patterns. It was found to correlate with the estimates overall length of dislocation segments per unit volume which effectively interacts with elastic vibrations of the sample ∼ 4 · 10¹³m^-2, as determined from acoustic relaxation measurements.

Abstract: Study on tensile fracture behavior of TiAl alloy by means of the macro fracture theory and micro dislocation block theory. A quantitative analysis method of micro crack nucleation and crack mechanism for TiAl alloy is performed with the help of the dislocation distribution model, and is based on the strain energy density theory and criterion, a crack criterion of TiAl alloy instability is established. The experimental results confirmed that the dislocation model and S criterion on tensile fracture behavior of TiAl alloys are effective.

Abstract: Au₆₀Ag₃₀Cu₁₀ (in at%) gold alloy exhibits a mechanical loss spectrum composed of a Zener peak due to Cu atoms in the solid solution and of a second relaxation peak at higher temperature or lower frequency. It is shown that this second peak is related to the presence of grain boundaries as it is absent in the spectrum of a single crystal. This mechanical loss peak, which is stable and reproducible in heating and cooling cycles, is thermally activated with an activation enthalpy of 2.35 eV and an apparent limit relaxation time of 9.6·10^-17s. As it is hard to imagine that a whole grain should slip at once along a touching grain, the relaxation peak is interpreted by a dislocation model, which may account not only for the activation parameters but also for the stress amplitude dependency of the peak.