Determination of the oxygen and nitrogen interstitial diffusion coeficient in niobium by mechanical spectroscopy

Odila Florêncio,Thais França Stefanini,Carlos Roberto Grandini,Paulo Sergio Da Silva Jr

doi:10.1590/s1516-14392006000400015

Abstract

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.

Highlights

When a tension wave is applied in a crystalline material, occur the interaction this tension wave with the defects present in solid, causing the energy loss
Other factor that influences the results found is the difference between estimate concentrations in solid solution of oxygen and determined by TC-436 DR equipment, which indicate the formation of precipitated
The anelastic relaxation spectra for Nb samples containing different amounts of interstitial elements were obtained as a function of temperature with a torsion pendulum at oscillation frequency in the hertz bandwidth, for three conditions of Nb sample; 2

Summary

Introduction

When a tension wave is applied in a crystalline material, occur the interaction this tension wave with the defects present in solid, causing the energy loss. Materials containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. Elastic dipoles represent atomic defects the produce an anisotropic local distortion of the crystal lattice. Heavy interstitial atoms, such as O, N, or C, in body centered-cubic (BCC) metals induce elastic dipoles with tetragonal symmetry. The stress-induced ordering of the dipoles is the elementary step of interstitial diffusion One manifestation this anelastic behavior is the internal friction, which was originally described by Snoek[1] in iron (Fe) containing carbon and nitrogen as interstitial solutes. Internal friction and frequency were measured as a function of temperature in an Nb sample containing oxygen and nitrogen in solid solution, for three different conditions: (A) as received sample, (B) annealed and (C) annealed followed by a treatment in a oxygen atmosphere during three hours

Materials and Experimental Procedure

Results and Discussion

Conclusions