Volumen II - SAM

Hvf, and migration energy, Hvm, and that into the dislocations line the diffusion process is of the pipe
diffusion type, the activation energy, Hd, is related to Hsd through: Hd = a Hsd, where a takes values
between 0.6 and 0.8, depending on the type of dislocation core [3]. In Molybdenum the reported values for
Hvm and Hvf are among 1.35 eV ≤ Hvm ≤ 1.60 eV and 3.0 eV ≤ Hvf ≤ 3.2 eV [2, 6], respectively;
leading thereof to Hd between 2.61 eV and 2.88 eV taking a=0.6, due to the complex structure of the
nucleus of dislocations in bcc metals [2]. This value is in reasonable agreement with the activation energy
measured for the HTP relaxation. Consequently, the HTP can be related to the formation and diffusion of
vacancies assisted by dislocation movement. In this case vacancies can be produced and diffuse at the core
by the moving dislocations or by the movement of jogs. The movements of dislocation at these high
temperatures are the ones which generate vacancy type defects producing the mechanical energy losses that
can be detected in MS.
4. CONCLUSIONS
The physical mechanism controlling the dislocation dynamics in single crystalline deformed and irradiated
molybdenum has been determined in the temperature range 300K - 1273K. The mobility of dislocations after
plastic deformation and/or irradiation is controlled by the agglomerates of defects which reduce their
mobility. The starting of the mobility of vacancies out of thermodynamic equilibrium at temperatures within
the stage III of recovery was found. At around 550 K, the agglomerates of vacancies achieve the largest size.
After annealing at temperatures higher than 973K, both the defects agglomerates dissolve and the
concentration of vacancies out of thermodynamic equilibrium decreases markedly and then the dislocations
start their movement. At temperatures around 800K, which correspond those of the LTP, the dislocations
move by the dragging of jogs assisted by vacancy diffusion. At higher temperatures at about 1000K, which
correspond to temperatures where the HTP appears, the movement of dislocations is controlled by the
formation and diffusion of vacancies assisted by the dislocation movement.
ACKNOWLEDGEMENTS
We acknowledge to Profs. J. N. Lomer, J. H. Evans and J. F. Ziegler for the interest on this work and for
stimulating discussions, Prof. J. N. Lomer is also acknowledge for the single crystal samples. The ILL, D11
Instrument, is acknowledge for the allocated neutron beamtime (Exp. Num.: 1-01-38)Thanks also to B. A.
Pentke and G. M. Zbihlei for the assistance during the TEM observations. This work was partially supported
by the Collaboration Agreement UPV-EHU / UNR Res. CS.788/88 - 1792/2003, UPV224.310-14553/02 and
Res. 3469/2007, the CONICET-PIP No. 5665 and 2098 and the PID-UNR ING 115 y 227.
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