Papers by Keyword: Metastable

Abstract: The paper is focused on microstructure characterisation of five bulk metastable β-type Ti-based alloys, with improved mechanical properties, composed of non-toxic (bio inert) elements like: Nb, Ta, Cr, Zr, Ag, and In. These types of alloys designed in this study, are expected to have also higher corrosion resistance in biological media and good performance such as lower Young’s modulus of elasticity, greater strength, good workability, also in as cast state. However, high strength as well as low Young’s modulus is required for the implants subjected to cyclic loading under complicated stress conditions. Thus, the major aim is decreasing the Young’s modulus and increasing the tenacity of these alloys.

Abstract: Metastable precipitates govern the mechanical properties of hardenable Al-alloys. A computational precipitation simulation approach is presented that is based on a combination of compiled and assessed thermodynamic and diffusion data with predictive physical models. Predictive precipitation kinetics simulation delivers approximations of thermodynamic properties that would otherwise require time-consuming computational techniques based on density functional theory. Coupling of thermodynamics with thermo-kinetic simulation of hardenable Al-alloys Al-Mg-Si 6016 is presented.

Abstract: Crystal defects in a large diamond crystal synthesized by high pressure and high temperature (HPHT) method were investigated by synchrotron radiation topography. Five bundles of dislocations were observed in the specimen. Two bundles of the dislocations are in the <100> direction and three of the others are extended at <110>. The Burgers vectors of the dislocations are different within the same bundle as the extinction hinted. The dislocations in <100> direction possess higher energy than the dislocations in <110> and {111}, so they are in the metastable state. The <100> dislocations has not been found in natural diamond yet. The reason of that was the great difference of the growth rate of synthetic and natural diamonds.

Abstract: The method of perturbed angular correlation (PAC) was used to determine lattice locations of ¹¹¹In impurity probe atoms present in extreme dilution in the intermetallic compound FeGa₃. In slightly Ga-poor samples, probes were found to strongly prefer one of two inequivalent Ga-sites. In slightly Ga-rich samples at room temperature, 293 K, the PAC spectrum exhibited an unperturbed quadrupole interaction signal that is consistent with indium probes dissolved in small liquid pools of the excess Ga. A myriad of such pools are probably located along grain boundaries in the sample. Cooling from 293 K down to 12 K, the site fraction of indium in liquid decreased, being offset by the increase in a signal attributed to indium solutes in precipitates with other impurities at the sides of the Ga pools. However, these changes were completely reversible upon heating, and no crystallization of the liquid gallium pools was observed down to 12 K. This is attributed to the extraordinarily small volumes for the pools, which, while not measured directly, are orders of magnitude smaller than cubic microns. The measured temperature dependence of the site fraction of indium in the liquid was used to extend the metastable solubility curve for indium in liquid gallium down to a temperature of 150 K, much lower than the eutectic temperature of Ga-In at 288.5 K.

Abstract: In this paper, a theoretical calculation of the miscibility gap taking modified interaction parameter and mismatch strain into account are performed for the Mg_xZn_1-xO ternary compound system using the modified strictly regular solution model. The calculated results shows that the Mg_xZn_1-xO alloys are metastable at the temperatures commonly used for crystal growth and the miscibility gap shifts remarkably into the areas of higher Mg concentration and higher temperature because of the interaction parameter modifiability and strain effect. The strain relaxation is discussed synchronously, with the increasing of the strain relaxation, the MgO segregation boundary expands to a bend band region.

Abstract: Nanoparticles of metastable copper nitride(Cu3N) have been successfully fabricated from Cu mask using Ar ion ‘transcription method’ which is firstly invented by B.-S. Xu, C. Iwamoto and S.-I. Tanaka in 1996 [1]. The structural and morphological changes with irradiation time are studied by transmission electron microscopy (TEM). The thin film-like crystalline Cu3N which is covered with amorphous or polycrystalline cuprite (Cu2O) layer in the as-received Cu mask plays a role of target. Polycrystalline Cu3N nanoparticles nucleate and grow up to the average size of 15nm after 30 sec-irradiation. Coalesence of 50nm-sized grown Cu3N nanoparticles forms polycrystalline thin film after 2min-irradiation and its growth behavior follows Volmer-Weber mode. As irradiation time increases from 30 sec to 15 min, Cu3N nanoparticles are thought to be grown preferentially along the [111] and [100] directions. Cu2O still remain with Cu3N after 15 min.-irradiation.