Nanocrystalline materials studied by powder diffraction line profile analysis

X-ray powder diffraction is a powerful tool for characterising the microstructure of crystalline materials in terms of size and strain. It is widely applied for nanocrystalline materials, especially since other methods, in particular electron microscopy is, on the one hand tedious and time consuming, on the other hand, due to the often metastable states of nanomaterials it might change their microstructures. It is attempted to overview the applications of microstructure characterization by powder diffraction on nanocrystalline metals, alloys, ceramics and carbon base materials. Whenever opportunity is given, the data provided by the X-ray method are compared and discussed together with results of electron microscopy. Since the topic is vast we do not try to cover the entire field

Indentation creep behavior of a Zr-based bulk metallic glass

The deformation behavior of a Zr(44)Ti(11)Cu(10)Ni(10)Be(25) bulk metallic glass (LM-1B) was studied in the supercooled liquid region by indentation creep test. Before indentation the glass transition and the crystallization temperatures were determined by calorimeter as 625 and 725 K, respectively. The phases formed during crystallization were identified by X-ray diffraction. The indentation creep experiments were carried out at different temperatures and loads. It was found that the creep can be regarded as Newtonian flow at strain rates between 5 x 10(-5) and 5 x 10(-4) s(-1). The values of the viscosity and the activation energy of deformation were determined in the temperature range of 667-687 K

Indentation creep study on a Zr-based bulk metallic glass containing nano-quasicrystals

The effect of crystallization on the creep behavior of a Zr-based bulk metallic glass (BMG) with the composition of Zr(44)Ti(11)Cu(10)Ni(10)B(25) (at.%) was studied by indentation technique. The crystallization process was studied by isothermal annealing in a differential scanning calorimeter at three different temperatures above the glass transition temperature (677, 682 and 687 K). Two exothermic peaks are detected, the first one corresponds to the formation of a quasicrystalline phase. Indentation creep tests were carried out isothermally at the same three temperatures for studying the correlation between the amount of quasicrystalline phase and the creep behavior. A simple relationship between the viscosity and the crystalline phase fraction was found and the activation energy was found to decrease with the progress of crystallization

Effect of nano-quasicrystals on viscosity of a Zr-based bulk metallic glass

The effect of formation of nano-quasicrystals on the creep behavior of a Zr44Ti11Cu10Ni10Be25 bulk metallic glass was studied by the indentation technique above the glass transition temperature. The apparent viscosity of the supercooled liquid–quasicrystal composite increases with increasing volume fraction of the quasicrystalline phase following a simple relationship derived previously for dilute suspensions. The formation of quasicrystalline particles is accompanied by the decrease of activation energy of creep. This was related to the increase of the Be/Ti ratio in the supercooled liquid phase

X-ray diffraction study on the microstructure of an Al-Mg-Sc-Zr alloy deformed by high-pressure torsion

The microstructure and thermal stability of plastically deformed Al-5.9Mg-0.3Sc-0.18Zr alloy have been investigated. Severe plastic deformation has been performed by high-pressure torsion (HPT) straining at room temperature. The microstructure as a function of the number of rotations is studied by X-ray diffraction peak profile analysis. It is concluded that the HPT technique results in a nanostructure with about 40 nm crystallite size. The crystallite size first decreases with the number of rotations, however, after five turns it reaches saturation. The dislocation density increases with turns and the character of the dislocations becomes more edge type. The thermal stability of the nanostructure is studied by differential scanning calorimetry. The stored energy increases with the number of rotations and the maximum of the exothermal peak was shifted to higher temperatures. Increasing the temperature of the heat treatment, the dislocation density decreases faster than the increase of the mean crystallite size