[en] Dislocation dynamics in Ni₃Al intermetallic single crystals has been studied by mechanical spectroscopy between 300 and 700 K. It has been found that in the anomaly domain of the flow stress, which is characteristic of this material, the mechanical loss of predeformed specimens is strongly dependent on strain amplitude, predeformation level, annealing temperature and time. The results can be interpreted as a combination of two phenomena which simultaneously occur as temperature is increased from 300 K to about 500 K: exhaustion of the mobile dislocation segments (superkinks) and pinning of the screw dislocation segments via cross-slip from the (111) onto the (010) planes

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[en] In the present work, the effect of small doses of neutron irradiation on mechanical behaviour is correlated with changes found in the internal friction spectrum of their alloys after irradiation. As the mechanisms contributing to this spectrum have been previously investigated, these results are applied to evaluate microstructural changes due to neutron irradiation. (Author)

[en] With the aim of determining how some variables of the fabrication process influence on the alloy behaviour after its submission to a rapid neutrons flux, gauges of different chemical compositions were irradiated for subsequent internal friction assays, traction assays and transmission electronic microscopy. (Author)

[en] Magnesium (Mg) and magnesium nickel (Mg-23.5 wt%Ni) reinforced with multiwalled carbon nanotubes (CNTs) were processed by powder metallurgy and then charged with hydrogen by annealing at 620 K under a pressure of 0.4 MPa of hydrogen. Mechanical spectroscopy revealed that such a treatment has no effect in the composites with pure Mg matrix. On the other hand, Mg-23.5 wt%Ni alloys, unreinforced as well as reinforced with CNTs, exhibit a mechanical loss spectrum, which is deeply modified by hydrogen charging. Two relaxation peaks are observed at ∼190 K and ∼330 K (frequency ∼6 kHz), the height of which increases strongly with hydrogen charging. These peaks may be interpreted by atomic relaxation due to hydrogen in the Mg₂Ni phase. Both peaks decrease strongly in height by degassing under vacuum at 750 K. In bulk specimens of Mg-23.5 wt%Ni/CNTs composites a concentration of hydrogen as high as 6.1 wt% (∼86% of specific weight of liquid hydrogen) has been obtained by the mentioned hydrogenation process.