Papers by Keyword: Grain Boundary Energy

Abstract: An approach based on statistical analysis is proposed for the processing of data obtained using scanning tunneling microscopy of grain boundaries, which allows a numerical estimation of the relative energy of grain boundaries. The proposed statistical model also gives a possibility to separate groups of grain boundaries depending on their average relative energy and fraction in general distribution. Scanning tunneling microscopy data analyses have been carried out on data obtained by investigating copper and nanostructured copper were analyzed coarse-grain commercially pure copper and on copper nanostructured by the equal-channel angular pressing (ECAP) method. Obtained results were compared with available in literature experimental data for these types of materials, received by other methods. It is established that the grain boundaries in coarse-grain copper have significantly lower relative energy in contrast to the grain boundaries of ECAP-treated copper. Besides, there is, except for boundaries with high relative energy, a fraction of boundaries in the deformed sample with energy corresponding to those in coarse-grain copper.

Abstract: In this paper, the effect of grain boundary energy in AZ31 Mg alloy with multi-order parameters phenomenological phase field model has been discussed during the progress of recrystallization. The average grain size of the recrystallization grain at a certain temperature and a certain restored energy but various grain boundary energies have been studied, and the simulated results show that the larger the grain boundary energy is, the larger the average grain size will be, and the speed of grain growth will increase with the increase of grain boundary energy. Additionally, temperature will also increase the grain growth rate.

Abstract: The phase field models have been built to study the influence of the nonuniform grain boundary energy for abnormal growth of grains in the AZ31 magnesium alloy in the real time and space. The simulated results show that if the grains of a certain orientation with low grain boundary energy in the AZ31 Mg alloy, abnormal grain growth will occur after annealing treatment, and only if the local low grain boundary energy is less than 0.98σ_0, can the certain grains grow abnormally in the microstructure.

Abstract: This article considers the issues related to the correct description of the internal structure of grain boundaries in metals. We offered a mathematical model describing grain boundaries formation as a result of two-sided crystallization by applying molecular dynamics method with third-type boundary conditions for heat extraction (Newton-Richman law). In the construction of the interatomic potential, the embedded atom method (EAM) is used. The work offers an algorithm for generation of initial conditions for two adjacent grains with different crystal lattices orientation and melt between them. To detect defects and defective areas we use a central symmetry parameter. The system energy before and after the crystallization process is estimated.

Abstract: In this study, an atomistic simulation was performed to investigate intrinsic resonance propensity of clamped-clamped copper nanowires with Σ5 (310)/[001] symmetric tilt grain boundary. Grain boundary energy γ_GB for bicrystal structure was calculated based on an iterative approach. The stable atomic configuration was then doubly clamped and excited via flexural oscillation under varied temperatures. From the result, the appearance of grain boundary significantly alters the resonance properties of Cu nanowires. Greater attenuation in kinetic energy can be observed with increased temperature. Quality factors attains Q ~ 1/T^0.7144 and 1/T^0.7249 with temperatures from kinetic energy and centroid root mean square spectrum, respectively, where the former seems more reliable to employ at elevated temperatures.

Abstract: The faceting and migration behavior of low angle <100> grain boundaries in high purity aluminum bicrystals was investigated. In-situ technique based on orientation contrast imaging was applied. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry – the energy of pure tilt low angle <100> boundaries is anisotropic, whereas that of mixed tilt-twist boundaries isotropic with respect to boundary inclination.

Abstract: In solidification experiments of binary eutectic alloys, the eutectic spacing and undercooling are measured as function of the solidification rate. A new theoretical relationship is derived herewith between the Gibbs-Thomson coefficient and the above mentioned values for both lamellar and rod type eutectics. This new equation allows the estimation of the interfacial energy between eutectic solid phases. For the Sn/Pb eutectics the value of about 0.15 N/m is found in this paper using experimental literature data on eutectic solidification experiments. This is consistent with an earlier value obtained by a more complex experimental method of Gündüz and Hunt.

Abstract: The effect of the triple line energy on grain growth was studied by means of computer simulations with a network model. The results showed that the driving force stemming from the triple lines can influence significantly the evolution of grain growth.

Abstract: The thermal groove technique has been used to measure relative grain boundary energies in two 100 ppm Ca-doped yttria samples. The first has a normal grain size distribution and the boundaries have a bilayer of segregated Ca. In the second sample, there is a combination of large grains and small grains. The boundaries around the large grains are known to have an intergranular film. The results show that the relative energies of boundaries in the sample with normal grain growth and the boundaries around small grains far from larger grains in the second sample are similar. Also, boundaries surrounding the largest grains and small grains immediately adjacent to them have the same and significantly lower energies. The results indicate that grain boundaries with an intergranular film have a lower energy than those with bilayer segregation and that the intergranular film extends beyond the periphery of the largest grains, but not throughout the entire sample.

Abstract: Grain boundary properties depend on both composition and structure. To test the relative contributions of composition and structure to the grain boundary energy, we calculated the energy of 388 grain boundaries in four elemental, fcc metals: Ni, Al, Au and Cu. We constructed atomic-scale bicrystals of each boundary and subjected them to a rigorous energy minimization process to determine the lowest energy structure. Typically, several thousand boundary configurations were examined for each boundary in each element.