کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1584628 | 1514906 | 2006 | 4 صفحه PDF | دانلود رایگان |
The high-temperature damping background (HTDB) in various intermetallic compounds, such as γ-TiAl based alloys, NiAl single crystals and quasicrystalline d-Ni–Al–Co exhibits viscoelastic behavior which can be observed as damping, increasing exponentially with temperature. The activation enthalpy H was determined from measurements of the HTDB at various frequencies. In γ-TiAl based alloys with various chemical composition the activation enthalpies are in the range of H = 4.2–4.3 eV for Ti–46 at.%Al–9 at.%Nb, and H = 3.8–3.9 eV for Ti–46.5 at.%Al–4 at.% (Cr, Nb, Ta, B). For a Ni49.5Al50.5 single crystal an activation enthalpy of H = 3.3 eV was determined. The H-values in TiAl and NiAl agree well with activation enthalpies from creep and self-diffusion experiments. Therefore, the HTDB in TiAl and NiAl is assigned to diffusion-assisted climb of dislocations. Decagonal Al–Ni–Co quasicrystals show different behavior. The HTDB is only observed in polycrystalline material, but not in a single crystal. The activation enthalpies, H = 2.4–3 eV, agree with values obtained by tracer diffusion experiments. This indicates that the HTDB in decagonal Al–Ni–Co quasicrystals is due to an intragrain diffusion process which is equivalent to Nabarro–Herring creep.
Journal: Materials Science and Engineering: A - Volume 442, Issues 1–2, 20 December 2006, Pages 138–141