Measurement of oxygen atom diffusion in Nb and Ta by anelastic spectroscopy

Abstract

Impurity interstitial atoms present in metals with BCC structure can diffuse in the metallic matrix by jumps to energetically equivalent crystallographic sites. Anelastic spectroscopy (internal friction) is based on the measurement of mechanical loss or internal friction as a function of temperature. Due to its selective and nondestructive nature, anelastic spectroscopy is well suited for the study of diffusion of interstitial elements in metals. Internal friction measurements were made using the torsion pendulum technique with oscillation frequency of a few Hz, temperature interval from 300 to 700 K, heating rate of about 1 K/min, and vacuum better than 10 -5 mbar. The polycrystalline Nb and Ta samples used were supplied by Aldrich Inc. The results obtained showed thermally activated relaxation structures due to stress-induced ordering of oxygen atoms around the Nb (or Ta) atoms of the metallic matrix. The results were interpreted by three methods and led to activation enthalpy values for the diffusion of oxygen in Nb and Ta of 1.15 eV and 1.10 eV, respectively.

A Perspective of the Design and Development of Metallic Ultra-High Temperature Materials: Refractory Metal Intermetallic Composites, Refractory Complex Concentrated Alloys and Refractory High Entropy Alloys

“…Interstitial contamination is key for the design, processing and properties of metallic UHTMs with/without the addition of reactive elements like Hf, Ti or Zr, owing to the sensitivity of RMs to interstitial contamination [8] and the effect that such contamination has on phase equilibria, e.g., [19,[124][125][126][127][128][129][130][131][132] and stability of microstructures [133]. The interstitial contamination (a) links with properties, e.g., , (b) with diffusivities, e.g., [155][156][157][158][159][160], (c) with solutes that slow down diffusivity of oxygen, e.g., references [43,[161][162][163] and the Figure 17 in [19], and (d) with elastic properties of intermetallics contaminated with oxygen, e.g., [164][165][166]. Interstitial contamination affects the hardness and Young's modulus of the bcc Nb ss solution and Nb 5 Si 3 [20,167,168].…”