Mechanical energy losses in single crystalline molybdenum. Its relation with microstructure

G. I. ZELADA-LAMBRI; P. B. BOZZANO; O. A. LAMBRI; C. L. MATTEO; P. A. SORICHETTI; J. A. GARC¨ªA

Rosario, Argentina

Congreso; 10th Inter-American Congress of Electron Microscopy 2009, CIASEM 2009, 1st. Congress of the Argentine Society of Microscopy, SAMIC 2009; 2009

Argentine Society of Microscopy

Molybdenum and its alloys are used in nuclear reactor vessels and other reactor components, detectors in control systems of Tokamak devices and recently they have attracted interest as components for the development of space nuclear reactor power systems [1]. The temperature range around 0.3 Tm (¡Ö 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 and the ductile-brittle transition temperature [1, 2]. At annealing temperatures within the stage V (>900K), the yield stress and the UTS begin to decrease. In this work we have related the results of both mechanical spectroscopy (MS) also referred to as the internal friction method or damping measurements in early literature, and transmission electron microscopy (TEM), obtained in deformed and neutron- and electron-irradiated molybdenum single crystals. Indeed, our aim is focussed in to investigate the interaction processes between dislocations and point defects; from room temperature (RT) up to 30% of the melting temperature (0.3Tm). Samples used in this work 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. Low flux neutron irradiation were performed at RT, at the Siemens SUR 100 nuclear reactor, RA-4, jointly operated by the University of Rosario (UNR) and the Atomic Energy Commission of Argentina (CNEA). The estimated amount of vacancies promoted in the samples during neutron irradiation is about 5ppm, see for further details Ref. [2]. Electron irradiation was performed at the the J. J. Thomson Phys. Lab., Reading University, UK. An estimation of about 30ppm of vacancies were promoted by the electron irradiation. Fig. 1 shows the damping spectra measured in deformed and deformed plus irradiated samples. During the first heating, after the room temperature deformation, the deformed samples showed an increasing background with temperature. Nevertheless, on cooling a well developed internal friction peak was present (see full blue- and empty light blue- circles and green squares). 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 Ref. [2] for details. Deformed and neutron irradiated <110> sample show an increasing background with temperature, but on cooling the internal friction peak appears (red full triangle). In this case, the peak appears at a lower temperature and has a smaller intensity than the one for non-irradiated samples. In contrast, deformed and neutron irradiated <149> samples present similar behaviour to the non-irradiated one (curve not plotted in the Figure) [2]. Nevertheless, electron irradiated samples exhibits a peak which is about twice higher than for neutron irradiated samples (orange empty triangle). ¡Ö 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 and the ductile-brittle transition temperature [1, 2]. At annealing temperatures within the stage V (>900K), the yield stress and the UTS begin to decrease. In this work we have related the results of both mechanical spectroscopy (MS) also referred to as the internal friction method or damping measurements in early literature, and transmission electron microscopy (TEM), obtained in deformed and neutron- and electron-irradiated molybdenum single crystals. Indeed, our aim is focussed in to investigate the interaction processes between dislocations and point defects; from room temperature (RT) up to 30% of the melting temperature (0.3Tm). Samples used in this work 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. Low flux neutron irradiation were performed at RT, at the Siemens SUR 100 nuclear reactor, RA-4, jointly operated by the University of Rosario (UNR) and the Atomic Energy Commission of Argentina (CNEA). The estimated amount of vacancies promoted in the samples during neutron irradiation is about 5ppm, see for further details Ref. [2]. Electron irradiation was performed at the the J. J. Thomson Phys. Lab., Reading University, UK. An estimation of about 30ppm of vacancies were promoted by the electron irradiation. Fig. 1 shows the damping spectra measured in deformed and deformed plus irradiated samples. During the first heating, after the room temperature deformation, the deformed samples showed an increasing background with temperature. Nevertheless, on cooling a well developed internal friction peak was present (see full blue- and empty light blue- circles and green squares). 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 Ref. [2] for details. Deformed and neutron irradiated <110> sample show an increasing background with temperature, but on cooling the internal friction peak appears (red full triangle). In this case, the peak appears at a lower temperature and has a smaller intensity than the one for non-irradiated samples. In contrast, deformed and neutron irradiated <149> samples present similar behaviour to the non-irradiated one (curve not plotted in the Figure) [2]. Nevertheless, electron irradiated samples exhibits a peak which is about twice higher than for neutron irradiated samples (orange empty triangle). first heating, after the room temperature deformation, the deformed samples showed an increasing background with temperature. Nevertheless, on cooling a well developed internal friction peak was present (see full blue- and empty light blue- circles and green squares). 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 Ref. [2] for details. Deformed and neutron irradiated <110> sample show an increasing background with temperature, but on cooling the internal friction peak appears (red full triangle). In this case, the peak appears at a lower temperature and has a smaller intensity than the one for non-irradiated samples. In contrast, deformed and neutron irradiated <149> samples present similar behaviour to the non-irradiated one (curve not plotted in the Figure) [2]. Nevertheless, electron irradiated samples exhibits a peak which is about twice higher than for neutron irradiated samples (orange empty triangle).