Volumen II - SAM

Fifteen single crystals have been used in this work. They were prepared from zone refined single-crystal rods
of molybdenum in A.E.R.E., Harwell, UK. The residual resistivity of the samples was about 8000, tungsten
being the main residual impurity. Samples with the and crystallographic tensile axis have
been selected to favour deformation by multiple and single slip; respectively.
SANS studies were performed at the D11 instrument in the Institut Laue Langevin, France. Data collected on
the two-dimensional detector were handled employing GRASP V. 3.4 software [5].
The size and shape of the samples and the experimental details used in the MS, ER, DTA, TEM and SANS
measurements, can be consulted in references [2, 5 - 7].
Low flux neutron irradiation were performed at RT, at the Siemens SUR 100 nuclear reactor, RA-4, of the
UNR - CNEA. Details about neutron irradiation processes are given in refs. [2, 5]. The irradiation dose was
less than 1x10 -5 dpa (displacement per atom). In addition, we have made an estimation of the full cascade of
displacements promoted by the neutron irradiation employing SRIM 2006.02 [2] (formerly called TRIM)
software and then, an estimation of the amount of vacancies promoted in the samples during 10 hours
irradiation could be done, that is around 5x10 14 , leading to a vacancy concentration of about 5ppm, value
which is large enough to be detected for both MS and ER measurements [2].
Table 1. Status of the used samples. (*) irradiated again after the MS measurements.
Sample Orientation Elongation (%) Torsion (%) Irradiation time (hs)
a / sheet 110 3 1 0
b / sheet 110 3 1 10 and 10 re-irradiated (*)
c / sheet 110 3 1 20
d / sheet 149 5 1 0
e / sheet 149 5 1 20 and 10 re-irradiated (*)
f / rod 110 3 1 10
g / rod 149 3 1 10
3. RESULTS AND DISCUSSION
Figure 1 shows the damping (internal friction) spectra measured as a function of temperature in a deformed
sample (a) detailed in Table 1, by means of empty symbols and blue colour. During the first heating, after the
RT deformation, the sample showed an increasing background with temperature. Nevertheless, on cooling a
well developed damping peak was present (peak marked A in Fig. 1). The peak height and temperature are
very reproducible for samples of the same type, but they are strongly dependent both on the orientation and
on the plastic deformation degree. See Refs. [2, 6, 7] for more details.
The behaviour of the peak on consecutive warm-ups has been previously reported [2, 6, 7]. The peak moves
to a slightly higher temperature and increases in intensity on consecutive heating to 973K, but then stabilised
at a peak temperature of around 800K, (see peak B in Fig. 1). When the maximum annealing temperature,
during the thermal cycles (heating run plus its cooling run), is increased to 1250K, the peak temperature
changes to around 1000K (peak C in Fig. 1). Further runs to 1250K decrease the intensity of the peak and it
disappears if the sample keeps vibrating for long time at 1250K. When the maximum temperature of the
thermal cycles was increased in smaller steps, the shifting in the peak temperature varied progressively as the
temperature in the test increased [6, 7].
Samples (b) and (c), which were prepared from the same rod of sample (a) and under the same
thermomechanical conditions, were deformed and then 10 and 20 hours irradiated respectively, see Table 1.
Results for sample (b) are also plotted in Figure 1 by means of full symbols and green colour. In the first
heating, sample (b) shows an increasing background with temperature but on cooling the damping peak
appears (peak marked D). In this case the peak appears at lower temperature and has smaller intensity than
the one for non-irradiated samples. Annealing up to 973K, produce a slight increase both in the peak
temperature and peak height. Successive thermal cycles up to 1073K stabilise the peak at around 800K (peak
marked E). The temperature of the relaxation is very similar to the non-irradiated samples but less intense.
Further increase in the temperature of annealing up to 1250K leads to a strong shift in the peak temperature
and to a decrease in the peak height, in a similar mode than for the non-irradiated sample (peak F in Fig. 1).
The damping behaviour for sample (c) after 20 hours irradiation can be seen in Figure 1, plotted by means of
crosses and red colour. Spectrum marked G corresponds to the stabilised peak after thermal cycles to 1073K.
H curve is obtained after annealing up to 1250K. The behaviour of the peak as a function of the different
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