High-Temperature Mechanical Relaxations in Metals and Metallic Alloys |
| Journal |
Solid State Phenomena (Volume 115) |
| Volume |
Mechanical Spectroscopy III |
| Edited by |
B.M. Darinskii and L.B. Magalas |
| Pages |
87-98 |
| DOI |
10.4028/www.scientific.net/SSP.115.87 |
| Online since |
August, 2006 |
| Authors |
Andre Rivière
|
| Keywords |
Dislocation, High Temperature, Internal Friction, Mechanical Spectroscopy, Polycrystal, Precipitate, Single Crystal |
| Abstract |
In spite of numerous works, the relaxation phenomena observed at high temperature
(between room temperature and the melting temperature TM) are still under discussion. Because
relaxation peaks were observed in single crystals, it is generally considered that the basis of the
relaxation mechanism is linked to the dislocation network. The main difficulty for high temperature
damping measurements is the great sensitivity of internal friction with several experimental
parameters: the heating/cooling rate, maximal applied strain amplitude, sample purity, thermomechanical
history of the sample, microstructure, etc. This sensitivity can explain the large scatter
in experimental results published by various authors. Moreover, internal friction (IF) measurements
performed during continuous heating or cooling and using an apparatus working at a quasi-static
frequency, do not allow to completely describe the relaxation phenomena. On the contrary,
isothermal mechanical spectroscopy (measurements of internal friction in a large frequency,
temperature and maximal strain amplitude ranges) improves the experiments or evidences new
relaxation effects. This is illustrated in this paper for various examples: slightly cold worked single
crystals, polycrystals after a large cold work and recrystallization, non thermally activated peaks
observed in metallic alloys, and relaxation peaks at very high temperature (above 0.9 TM). |
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