BELAMRI CHerif University of Batna

Influence of the Thermo-mechanical Treatments on the Relaxation Phenomena Observed on a single Crastal Alloy (Cu – At.11% Al) in Internal Friction at high Temperature

Co-authors BELHAS Saida, RIVIERE André

The aim of this study is to highlight the thermo-mechanical treatments influence on internal friction behavior at high temperature of a copper single crystal alloy Cu-Al (11% at.). To do this; tests are performed, using the Isothermal Mechanical Spectroscopy technique (IMS), at different stabilized levels of temperatures, on two initial states of a specimen: quenched and cold worked at 1% by torsion after quenched. In the two cases: the specimen have been progressively heated to approximately 1160 K and then cooled down to room temperature. During heating the annealing temperature (TANN.) is equal to the temperature of measurement (TMEAS.) and during cooling after annealing TMEAS. is lower than TANN. The results obtained, on the two initial states, show globally the same behavior. They reveal the existence of three (3) independent relaxation peaks we call respectively: PZ, PMT and PHT. During heating the three peaks exist whereas during cooling after annealing remain only two (2) peaks: PZ and PHT. The Pz peak was identified to a Zener relaxation peak. Its origin being due to the reorientation, under constraint, of the pairs of aluminium atoms. The existence of the other peaks PMT and PHT appear to be associated with thermo-mechanical treatments. Indeed; PMT appears at average temperature and PHT at high temperature during heating but after cooling only PHT persists It is clear that the strain hardening is responsible for the up growth of PMT and is therefore linked to fresh dislocations introduced by cold working. The Arrhenius plots confirm this sensitivity to the annealing. Thus; these curves present two distinct slopes during heating and only one slope during slow cooling. This behavior can be explained by an evolution of the dislocations microstructure. During heating this microstructure evolving continuously and becomes stable only after a high temperature annealing. Otherwise, these results are compatible with the predictions of Darynskyi's model.