Diffusion of Nitrogen in Ti-13V-11Cr-3Al Alloys

Metals with a bcc crystalline structure such as Ti-13V-11Cr-3Al alloys have their physical properties significantly changed through the addition of interstitial elements such as oxygen and nitrogen. These metals can dissolve substantial amounts of interstitial elements forming solid solutions. Mechanical spectroscopy measurements constitute a powerful tool for studying interactions of these interstitial elements with other elements that make up the alloy. From these measurements, it is possible to obtain information regarding diffusion, interstitial concentration, interaction between interstitials, and other imperfections of the crystalline lattice, In this paper, Ti-13V-11Cr-3Al alloys with several amount of nitrogen, in a solid solution, were studied using mechanical spectroscopy (internal friction) measurements. The results presented complex internal friction spectra which were resolved in a series of constituent Debye peaks corresponding to different interactions and interstitial diffusion coefficients. Pre-exponential factors and activation energies were calculated for nitrogen in theses alloys.

Nitrogen diffusion in the Nb-1.0wt%Zr measured by mechanical spectroscopy

The scientific and technological development in the area of new materials contributed to several applications of niobium and its alloys in nuclear power plants as well as in aerospace, aeronautics, automobile and naval industries. This paper presents the interstitial diffusion coefficients of nitrogen in solid solution in the Nb-1.0wt%Zr alloy using internal friction measurements obtained by mechanical spectroscopy, which uses a torsion pendulum operating at an oscillation frequency between 1.0 Hz and 10.0 Hz. The temperature range varies from 300K to 700K, at a heating rate of 1 K/min and vacuum better than 2 x 10(-6) Torr. The results showed an increase of the interstitial diffusion coefficient of nitrogen that was correlated with configurational considerations for the octahedral interstitials.

Oxygen diffusion in Ti-10Mo alloys measured by mechanical spectroscopy

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Oxygen Diffusion in an Nb-Ta Alloy Measured by Mechanical Spectroscopy

When metals that present bcc crystalline structure receive the addition of interstitial atoms as oxygen, nitrogen, hydrogen and carbon, they undergo significant changes in their physical properties because they are able to dissolve great amounts of those interstitial elements, and thus form solid solutions. Niobium and most of its alloys possess a bcc crystalline structure and, because Brazil is the largest world exporter of this metal, it is fundamental to understand the interaction mechanisms between interstitial elements and niobium or its alloys. In this study, mechanical spectroscopy (internal friction) measurements were performed on Nb-8.9wt%Ta alloys containing oxygen in solid solution. The experimental results presented complex internal friction spectra. With the addition of substitutional solute, interactions between the two types of solutes (substitutional and interstitial) were observed, considering that the random distribution of the interstitial atoms was affected by the presence of substitutional atoms. Interstitial diffusion coefficients, pre-exponential factors and activation energies were calculated for oxygen in this alloy.

Anelastic Relaxation Measurements in Nb-46wt%Ti Alloys with Interstitial Solutes in Solid Solution

Anelastic relaxation measurements were performed in a Nb-46wt%Ti alloy, in the temperature range of 300 to 700 K, using a torsion pendulum operating at an oscillating frequency near 2.0 Hz. The samples were measured in different conditions: cold worked, annealed in ultra-high vacuum and doped with several quantities of nitrogen. The relaxation spectra obtained were resolved into their component peaks, corresponding to the different kinds of interaction of the interstitial solutes with the metallic matrix. The relaxation parameters of each process were calculated using Debye's elementary peaks.

Nitrogen diffusion in the Nb-2.0wt%Ti measured by mechanical spectroscopy

Metals that present bcc crystalline structure, when receiving addition of interstitial atoms as oxygen, nitrogen, hydrogen and carbon, undergo significant changes in their physical properties, being able to dissolve great amounts of those interstitial elements, thus forming solid solutions. Niobium and most of its alloys possess bcc crystalline structure and, as Brazil is the largest world exporter of this metal, it is fundamental to understand the interaction mechanisms between interstitial elements and niobium or its alloys. In this paper, mechanical spectroscopy (internal friction) measurements were performed in Nb-2.0wt%Ti alloys containing nitrogen in solid solution. The experimental results presented complex internal friction spectra and with the addition of substitutional solute, it was observed interactions between the two types of solutes (substitutional and interstitial), considering that the random distribution of the interstitial atoms was affected by the presence of substitutional atoms. Interstitial diffusion coefficients, pre-exponential factors and activation energies were calculated for nitrogen in the Nb-2.0wt%Ti alloys.

Prediction of Soil Properties from the Concepts of Energy Transfer in Dynamic Penetration Tests

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Stress induced ordering due to interstitial elements in Nb and Ta by frequency analysis

It is well known that the interstitial elements present in solid solution in metals interact with the matrix by a relaxation process known as stress induced ordering. Traditionally this relaxation process is observed in the internal friction measurements. It is a common practice that researchers present the results of the frequency together with internal friction without giving any analysis. In this work we apply an expression which relates the variation of frequency with temperature and analyse the experimental results cited in the literature of the relaxation process due to the stress induced ordering of oxygen and nitrogen present in niobium and tantalum.

Stress induced ordering due interstitials in Nb-4.7 at.%Ta

The presence of interstitial elements in metals cause strong changes in their physical, chemical or mechanical properties. These interstitial impurities interact with the metallic matrix atoms by a relaxation process known as stress induced ordering. Relaxation processes give rise to a peak in the internal friction spectrum, known as Snock effect. The presence of substitutional solutes has a strong influence on Snoek effect, particularly if the substitutional solute element is the one, which interacts with the interstitial element. Anelastic spectroscopy measurements provide information of the behavior of these impurities in the metallic matrix. In this paper, polycrystalline samples of Nb-4.7 at.%Ta alloy have been analyzed in the as-received condition. Measurements of anelastic spectroscopy were carried out using an inverted torsion pendulum, operating with frequency of 2.0-30.0 Hz and in a temperature range between 300 and 700 K. It was observed the presence of a relaxation structure that have been attributed to stress induced ordering due to interstitial atoms around atoms of the metallic matrix. The relaxation structure have been decomposed in its constituent peaks, what it allowed to identify the following relaxation processes: Ta-O, Nb-O and Nb-N. (c) 2005 Elsevier B.V. All rights reserved.

Possible structural phase transitions on Bi2Sr2CaCu2Oy measured by anelastic spectroscopy

Anelastic spectroscopy measurements (internal friction) are sensitive tools for the study of defects in solids, in particular the mobility of interstitial oxygen. Samples of Bi2Sr2CaCu2Oy were analyzed after being submitted to two thermal treatments in vacuum, one at 973 K and another at 673 K. Anelastic spectroscopy measurements were performed using a torsion pendulum operating at around 38 Hz and at a temperature range of 88 and 700 K with heating rate of 1 K/min and vacuum better than 10(-5) Torr. Complex relaxation structures reversible with new thermal treatments were observed. These relaxation structures were attributed to O-M structural phase transitions. (c) 2005 Elsevier B.V. All rights reserved.

Interstitial oxygen mobility in superconducting samples of Bi2Sr2CaCu2O8+y

Since high-temperature superconductors were discovered, several studies have been made on their physical properties, attempting to associate them to the origin of superconductivity. Obviously, the oxygen atoms interstitially dissolved in the matrix have an important role in superconductivity, since they move easily in the lattice. In addition, they contribute to hole creation in the CuO2 planes. Anelastic spectroscopy ( internal friction) measurements are sensitive tools for the study of defects in solids, in particular for oxygen mobility. In this paper, Bi2Sr2CaCu2O8+y samples with several different amounts of interstitial oxygen were analysed by means of anelastic spectroscopy measurements. The measurements were performed by using a torsion pendulum operating at a frequency of about 40 Hz. Complex relaxation structures were observed and attributed to the shift of the oxygen interstitial atoms in BiO chains.

Oxygen mobility in SmBa2Cu3O7-delta measured by anelastic spectroscopy

Anelastic spectroscopy has been performed on a sample of superconducting oxide SmBa2Cu3O7-delta (SBCO) using a torsion pendulum operating with frequency around 10 Hz. A thermally activated relaxation peak is observed near 500 K with the activation enthalpy of 1.55 +/- 0.03 eV and the pre-exponential factor of approximately 10(-15) s, which is attributed to the mobility of non-stoichiometric oxygen by jumps in positions O1 and O5 of the lattice. (c) 2006 Elsevier B.V. All rights reserved.

Prediction and spatial variability of soil dynamic properties in sugar cane fields of São Paulo State Brazil

The objective of this work was to model and diagnose the spatial variability of soil load support capacity (SLSC) in sugar cane crop fields, as well as to evaluate the management impact on São Paulo State soil structure. The investigated variables were: pressure preconsolidation (sigma(p)), apparent cohesion () and internal friction angle (). The conclusions from the results were that the models and spatial dependence maps constitute important tools in the prediction and location of the mechanical internal strength of soils cultivated with sugar cane. They will help future soil management decisions so that soil structure sustainability will not be compromised.

Anelastic relaxation processes due oxygen in Nb-3.1 at.% Ti alloys

In the last 50 years several studies have been made to understand the relaxation mechanisms of the heavy interstitial atoms present in transition metals and their alloys. Internal friction measurements have been carried out in a Nb-Ti alloy containing 3.1 at.% of Ti produced by the Materials Department of Chemical Engineering Faculty of Lorena (Brazil), with several quantities of oxygen in solid solution using a torsion pendulum. These measurements have been performed by a torsion pendulum in the temperature range from 300 to 700 K with an oscillation frequency between 0.5 and 10 Hz. The experimental results show complex internal friction spectra that have been resolved, into a series of Debye peaks corresponding to different interactions. For each relaxation process it was possible to obtain the height and temperature of the peak, the activation energy and the relaxation time of the process. (C) 2003 Elsevier B.V. All rights reserved.

Stress-induced ordering due heavy interstitial atoms in Nb-0.3 wt.% Ti alloys

The mechanical properties of metals with bee structure, such as niobium and their alloys, are changed of a significant way by the introduction of heavy interstitial elements. These interstitial elements (oxygen, for example) present in the metallic matrix occupy octahedral sites and constitute an elastic dipole of tetragonal symmetry and might produce anelastic relaxation. Polycrystalline samples of Nb-0.3 wt.% Ti (Nb-Ti) alloy with oxygen in solid solution were analysed. The anelastic spectroscopy measurements had been made in a torsion pendulum, with frequencies in the Hz range, in a temperature range between 300 and 700 K. The results showed thermally activated relaxation structures were identified four relaxation process attributed to stress-induced ordering of single oxygen, nitrogen and carbon atoms around niobium and stress-induced ordering of single oxygen atoms around titanium atoms. (c) 2005 Elsevier B.V. All rights reserved.