Papers by Keyword: Amorphous Material

Abstract: The mechanism of annealing-induced amorphization of metallic glass is investigated in this study via molecular dynamics simulation. Spherical nucleuses of Cu–Ni–Al alloy with a face-centered cubic structure are embedded to simulate nanograins in Cu–Ni–Al amorphous alloy; subsequently, the material is annealed at different temperatures. The results show that the critical radius for nucleation at temperatures above the glass transition temperature (Tg) affected the behavior, grain growth, and annihilation of nanograins in the Cu–Ni–Al amorphous alloy during annealing. When the temperature increased, the critical radius for nucleation increased as well. This causes the small nanograins to annihilate quickly and the large nanograins to develop rapidly. When the annealing temperature is higher than Tg, part of the crystal nuclei, which is smaller than the critical radius, can be eliminated. The crystallinity of the metallic glass decreased, and the minimum crystallinity is attained after a period of annealing simulation. Subsequently, as the residual effective nanograins began developing, the crystallinity of the amorphous metal increased again. Therefore, the annealing duration time is critical to the crystallinity of the amorphous alloy after annealing.

Abstract: Amorphous alloy strips has been widely used in the field of distribution transformers due to its good soft magnetic properties. The resources, energy consumption of the amorphous alloy strips production with the rapid solidification technique and the environmental impacts were calculated based on the life cycle assessment method. The results showed that the largest contribution to the non-renewable resource consumption was ferroboron production process, accounting for 98% of abiotic resource depletion (ADP). And the strip production process had the largest contribution to the global warming potential (GWP), acidification potential (AP), photochemical oxidation potential (POCP), human toxicity potential (HTP),eutrophication potential (EP). Ferroboron production process contributed the biggest environmental impact when producing 1 ton amorphous strip, accounting for 70% of the total environmental impact. Under the new technology for energy-saving and emission-reduction, when the utilization rate of boric acid increased in ferroboron production process, all the environmental impact decreased.

Abstract: This study aims to investigate the microscopic origin of viscosity by simplifying an amorphous system to a mixture of many independent atomic subsystems. The response of the macroscopic system is then taken as an ensemble average of the relaxations of such subsystems. The result shows that with the reduction of temperature, the overall viscosity changes from the harmonic mean of the subsystems, which is dominated by the fast relaxations, to the arithmetic mean governed by the slowest relaxation. The successful application of our model to the amorphous Selenium indicates the model captures the fundamental mechanism of the viscosity variation.

Abstract: The magnetic properties of the (Fe_0.53Nd_0.37Al_0.10)₉₆B₄ bulk amorphous alloys annealed in the temperature range of 293-623K for 30 min with and without an external pulsed magnetic field of 5T were studied. The results reveal that the remanence and coercivity of the samples are obviously improved with a pulsed magnetic field when annealed below the Curie temperature of the alloy. The increment of remanence reaches 25.9% for the sample annealed at 523K with a pulsed magnetic field, because of the enhancement of exchange coupling roles between the soft and hard magnetic phases. It provides a new way to improve the magnetic properties of the bulk amorphous alloys produced by pulsed magnetic annealing at temperatures below the Curie point of the alloys.

Abstract: Molecular dynamics simulation was used for investigating hydrogen migration in Pd-Si alloy at a temperature Т = 300 K. The strong affect of hydrogen dynamics and its defects creation to structure of palladium matrix is stated. The partial radial distribution function calculation for silicon specifies a preferable arrangement of silicon atoms relative to each other in the second coordination sphere. Model calculations have shown that not only silicon atoms can affect hydrogen mobility. Hydrogen itself also can significantly change the diffusion of the other components in the alloy.

Abstract: Recently, a new class of materials - called nanoglasses - with a glassy structure was synthesized. The novel feature of these materials is that the atomic structure in the entire volume of the material as well as the density of the material can be tuned. Nanoglasses are generated by introducing interfaces into metallic glasses on a nanometer scale. Interfaces in these nanoglasses delocalize upon annealing, so that the free volume associated with these interfaces spreads throughout the volume of the glass. This delocalization changes the atomic structure and the density of the glass throughout the volume. In fact, by controlling the spacing between the interfaces introduced into the glass as well as the degree of the delocalization (by modifying the annealing time and/or annealing temperature), the atomic structures as well as the density (and hence all structure/density dependent properties) of nanoglasses may be controlled. A comparable tuning of the atomic structure/density of crystalline materials is not conceivable, because defects in crystals do not delocalize upon annealing.

Abstract: The shape memory effect and the high damping in shape memory alloys are based on the martensitic phase transformation, which takes place essentially without diffusion and any change of order have an influence on its side effects: the memory effect, the superelasticity and the high damping capacity of the martensitic phase. A new method to control the performance of shape memory alloys is presented, which is based on selective modification of specified parts of working components. In this research, ion irradiation has been used to introduce locally disorder into a crystal or even amorphise it. A pre-deformed Ni-Ti, 6μm thin film in its martensitic state has been irradiated with Ni-ions of energy of 5 MeV up to a dose of 1016 ions/cm2. By this treatment, a 2μm thin surface layer has been finally transformed into an amorphous state, in which the martensitic transformation is suppressed. During heating the underlying non-modified layer is contracting and an out-of-plane movement is observed. The amorphous layer is elastically deformed and its energy is used during cooling to bring the film in its original shape. In this way, a reversible movement of the film is created. This new technique not only allows us to design new types of micro-actuators, but also to influence locally the high damping, which can be of great importance for micro-engineering applications.