Volumen II - SAM

Congreso SAM/CONAMET 2009 Buenos Aires, 19 al 23 de Octubre de 2009
DISLOCATION DYNAMICS IN MOLYBDENUM IN THE TEMPERATURE RANGE
AROUND 0.3 OF THE MELTING TEMPERATURE
G. I. Zelada-Lambri (1) , O. A. Lambri (1) , P. B. Bozzano (2) , G. J. Cuello (3) ,
J. A. García (4) , and C. A. Celauro (5)
(1) Instituto de Física Rosario - CONICET, Facultad de Ciencias Exactas, Ingeniería y Agrimensura (FCEIA),
Universidad Nacional de Rosario (UNR), Lab. de Materiales, Avda. Pellegrini 250, (2000) Rosario, Argentina.
(2) Lab. de Microscopía Electrónica. Unidad de Actividad Materiales, Centro Atómico Constituyentes, Comisión
Nacional de Energía Atómica (CNEA), Avda. Gral. Paz 1499, (1650) San Martín, Argentina.
(3) Institut Laue Langevin, 6, rue Jules Horowitz, BP 156, 38042 Grenoble, France.
(4) Depto. de Física Aplicada II, Facultad de Ciencias y Tecnología, Universidad del País Vasco,
Apdo. 644, 48080 Bilbao, País Vasco, Spain.
(5) Reactor Nuclear RA-4, FCEIA, UNR, Riobamba y Berruti, (2000) Rosario, Argentina.
E-mail (O. A. Lambri): olambri@fceia.unr.edu.ar
ABSTRACT
The dislocations dynamics in deformed and neutron irradiated single crystalline molybdenum has been
studied by means of mechanical spectroscopy in the temperature range between room temperature and
1273K. The behavior of the arrangements of defects agglomerates and dislocations has been determined, as
a function of temperature, using transmission electron microscopy and small angle neutron scattering.
Furthermore, electrical resistivity and differential thermal analysis were also used in order to obtain
thermodynamic information about the state of the microstructure in the studied temperature range. The
analysis of the damping spectra, from mechanical spectroscopy measurements, gave rise to find two different
interaction processes between dislocations and points defects, depending of their temperature of
appearance. In fact, the physical mechanism which controls the damping peak at around 800K and thereof
the movement of dislocations at these temperatures, was related with the dragging of jogs by the dislocation
under movement assisted by vacancy diffusion. However, at higher temperatures of about 1000K, where the
high temperature peak appears, the dislocations dynamics was more consistent with the formation and
diffusion of vacancies assisted by the dislocation movement.
Keywords: Molybdenum, vacancies, dislocation dynamics, radiation damage, recovery stages
1. INTRODUCTION
Nuclear materials are exposed to external stresses and at the same time to irradiation, because of that, it is of
great importance to understand the mechanisms of interaction between the defects produced, in order to
predict the long time behavior of these materials [1].
The temperature range at around 0.3 Tm (≈ 865K), usually related to the stage V of recovery, is particularly
interesting in molybdenum due to the strong influence on the mechanical properties both in the pure metal,
as in technological molybdenum based alloys. In fact, neutron irradiation in molybdenum at temperatures
below 1000K followed by annealing at temperatures higher than 473K, lead to the increase in the yield
stress, the ultimate tensile strength (UTS) and the ductile-brittle transition temperature (DBTT). At annealing
temperatures within the stage V (> 900K), the yield stress and the UTS begin to decrease [2 - 4].
Our aim is to investigate the interaction processes between dislocations and point defects from room
temperature (RT) up to near one third of the melting temperature (0.3Tm), in deformed and neutron
irradiated molybdenum single crystals by means of mechanical spectroscopy (MS, referred to as the internal
friction method or damping measurements in early literature). Furthermore, the behavior of the arrangements
of defects agglomerates and dislocations has been determined, as a function of temperature, using
transmission electron microscopy (TEM) and small angle neutron scattering (SANS). In addition, electrical
resistivity (ER) and differential thermal analysis (DTA) studies are also used in order to obtain
thermodynamic information about the state of the microstructure in the studied temperature range.
2. EXPERIMENTAL
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