Activation Energy Measurement of Oxygen Ordering in a Nb-Ti Alloy by Anelastic Relaxation (original) (raw)
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Anelastic relaxation processes due oxygen in Nb–3.1 at.% Ti alloys
Materials Science and Engineering A, 2004
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.
Stress-induced ordering due heavy interstitial atoms in Nb–0.3wt.% Ti alloys
Materials Science and Engineering: A, 2005
The mechanical properties of metals with bcc 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.
Effect of impurities on mechanical relaxation in niobium
Materials Research, 2003
Measurements of internal friction as a function of temperature were performed in samples of Nb containing different amounts of substitutional (Zr) and interstitial (O, N) solutes. These data were resolved using the method of successive subtraction, into a series of constituent Debye peaks corresponding to different interactions. For each relaxation process we obtained the height (Q-1 max) and temperature (T p) of the peak, the activation energy (E) and the relaxation time (t 0). The height, shape and temperature of the peaks depend on the concentration of interstitial and substitutional elements. With the addition of substitutional solute one can observed interactions between the two types of solutes (substitutional and interstitial), showing that the random distribution of the interstitial atoms was affected by presence of substitutional atoms. The peaks observed were associated with matrixinterstitial (Nb-O, Nb-N) and substitutional-interstitial (Zr-O) interaction processes.
Influence of Interstitial Elements on Internal Friction Measurements in Nb and Nb-Zr Alloys
Le Journal de Physique IV, 1996
Internal friction and frequency measurements as a function of temperature have been carried out in Nb and Nb-Zr policrystalline samples, using a torsion pendulum in the temperature range between 300K and 700K, the heating rate was lWmin and the pressure was kept better than 5 x 1 0~~ mbar. Metals with bcc lattice containing solute atoms dissolved interstitially often show anelastic behaviour due to a process know as stress-induced ordering, responsible for the appearance of Snoek peaks. In the Nb sample it has been identified two constituent peaks corresponding to the interstitial-matrix interactions (Nb-0 and Nb-N), but for the Nb-Zr samples with interstitial solute concentrations very close to those measured for the unalloyed Nb, it was not observed any mechanical relaxation peaks due to the presence of oxygen and nitrogen in solid solution .
Effect of interstitial impurities on internal friction measurements in niobium
Materials Science and Engineering: A, 2004
Measurements of internal friction as a function of temperature were carried out in samples of niobium containing different amounts of interstitial solutes (oxygen and nitrogen) and one sample of niobium containing initially only nitrogen as interstitial solute. The experimental spectra of internal friction as a function of temperature were obtained with a torsion pendulum of the inverted Kê-type and resolved, using the method of successive subtraction, into a series of constituent Debye peaks corresponding to different interactions. For each relaxation process it was possible to obtain the height (Q −1 max ) and temperature (T p ) of the peak, the activation energy (E) and the relaxation time (t 0 ). The height, shape and temperature of these peaks depend on the concentration of interstitial elements. The observed peaks were associated with matrix-interstitial (Nb-O, Nb-N) and interstitial-interstitial (O-N) interaction processes.
Materials Research, 2006
Mechanical spectroscopy measurements have been extensively used in the last decades to obtain information about many aspects of the behavior of solutes in metallic materials. Metals of body-centered cubic lattice that contain heavy interstitial elements (oxygen, nitrogen and carbon) in solid solution, present anelastic relaxation peaks when submitted to cyclic tensions, due to process know stress-induced ordering. Internal friction and frequency as a function of temperature were performed between 300 K and 650 K in a polycrystalline sample of Nb, for three distinct conditions, using a torsion pendulum inverted Kê-type operating in a frequency oscillation between 1Hz and 10 Hz range, with a heating rate of 1 K/min and pressure lower than 2 x 10-5 mbar. The experimental spectra obtained for each condition of the sample, were decomposed by the successive subtraction method in elementary Debye peaks. The following metal-interstitial interactions were identified: Nb-O and Nb-N for all conditions of the sample. From the anelastic relaxation parameters obtained (relaxation strength, peak temperature, activation energy and relaxation time) and lattice parameter (obtained from x ray diffraction), the determination of the oxygen and nitrogen interstitial diffusion coefficient in Nb was possible, for each condition of the sample.
Stress Induced Ordering Due to Interstitial Elements in Nb and Ta by Frequency Analysis
Le Journal de Physique IV, 1996
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.
Non-Linear Effects in the Snoek Relaxation of Nb-O
Le Journal de Physique IV, 1996
Internal friction peaks measured as a function of temperature or frequency have been associated to non-linear processes only after studying how the amplitude of the applied stress affects the relaxation process. Here it is demonstrated that the partial derivative of the internal bidion with respect to the frequency at constant temperature is a useful tool to determine that non-linear effects are involved. This analysis applied to actual data of the Snoek relaxation in Nb-0, reveals that at high interstitial contents non-linear effects appear.
Mechanical multiple relaxation spectra in NbZeO alloys
Acta Metallurgica et Materialia, 1990
Mechanical multiple relaxation data has been obtained by internal friction and frequency measurements in the temperature range of 300-600 K for Nb-Zr~9 single crystal alloys, using a torsion pendulum of the inverted K6-type operating at a frequency of oscillation of about 3.5 Hz. The experimental relaxation spectra were resolved into four constituent peaks of Debye type corresponding to the matrix-interstitial interactions, Nb49, Nb4)-O, N~ and to the substitutional-interstitial interaction, Zr~). These results and the estimated relaxation rate parameters of the processes point to the existence of more than one matrix-interstitial interaction in these alloys.