[en] Aluminium alloys containing Mg and Si as the major solutes are strengthened by precipitation of the metastable precursors (β'') of the equilibrium β (Mg₂Si) phase. In this study, both static and dynamic ageing of two Al-Mg-Si alloys--the 6061 (Al-1.34% Mg₂Si) and 6069 (Al-2.25% Mg₂Si) alloys--were aged at 170 deg. C and compared to evaluate the potential for improving the mechanical properties. Dynamic ageing was conducted through the procedure of equal channel angular extrusion (ECAE). It is shown that the ageing time scale is reduced from ∼1000 min for conventional static peak-ageing to ∼10 min by using ECAE-aided dynamic ageing. Compared to the significant strengthening effect in static peak-ageing treatment, a notable further increase in ultimate tensile strength (UTS) is achieved by dynamic ageing: over 40 MPa for the 6061 alloy and 100 MPa for the 6069 alloy. Ductility of dynamically aged alloys is found to be comparable to that of the statically peak-aged samples. Microstructures of both statically and dynamically aged alloys were characterised using transmission electron microscopy; dislocation-assisted precipitation was observed to be the primary precipitate nucleation and growth mechanism during dynamic ageing process. It is concluded that dynamic ageing using ECAE is efficient in executing ageing treatment that results in superior mechanical properties of the Al-Mg-Si alloys

[en] The effect of two different barrier materials (sputtered Ta and TaN) and their layering schemes on the microstructure of the sputtered copper seed and electroplated Cu films and interconnects was investigated using electron backscatter diffraction and X-ray diffraction. The films had a predominantly (111) texture and the microstructural change with the change of barrier layer material was minimal. The sidewall constraint effect on the microstructure development in narrow damascene trenches on Ta barrier was also examined by analyzing 0.5 μm deep lines over a range of different line widths (0.2-5.0 μm). The constraint due to the sidewall produces an [011] orientation along the line length. The in-plane texture strengthens with decreasing line width. The crystallographic texture was a function of line width with the intermediate line widths (near 1 μm) having the weakest texture and highest fraction of twin boundaries compared to the other line widths. The effect of alloying on the microstructure and texture was examined in similar damascene lines with a Cu-1% Ag seed layer before electroplating with pure Cu. The Ag addition decreased the average grain size without affecting the texture

[en] The development of annealing twin boundaries in pure nickel was investigated using instantaneous heating in a salt bath and in situ annealing on a heating stage designed for use with electron backscatter diffraction. It was observed that twin grains form to assist in the recrystallization process and that a significantly higher fraction of twin boundaries form when the deformed specimen is heated at a slow rate, regardless of the annealing temperature

[en] In this paper determination of an interface damage function (IDF), from a stereological procedure similar to that presented by Hillard is described. The mathematical and experimental simplicity of the method is utilized in measuring an IDF for polycrystalline copper crept at 0.6T_m under uniaxial tension. Whereas previous work focussed on a five parameter description of the local state of a grain boundary, the domain of the IDF is increased to eight degrees of freedom in the present study to include the complete geometrical description of grain boundary structure. The resulting functions identify certain types of grain boundaries which were preferentially damaged. Most of the damage occurred on interfaces oriented nearly normal to the principal stress axis. Some relatively small angle boundaries demonstrated a surprising propensity to cavitate as did certain special boundaries distinguished by a group multiplicity in misorientation space greater than one. A sequence of two dimensional projections through the eight-dimensional domain of the IDF is shown to identify a number of interface structures which are readily damaged

[en] Intergranular cracking of aluminum alloys occurs by a variety of processes in a host of structural components. Cracks emanate from holes and corners of support structures and heterogeneously spread along grain boundaries. In the present study, cracked specimens were investigated using local orientation measurement techniques. True representation of grain boundaries in spaces of five or eight dimensions was emphasized in characterizing the microstructure. Orientation of the grain boundary plane with respect to the stress axis and with respect to the crystal lattice was found to play an important role in determining GB 'specialness' in addition to misorientation of the crystallite lattices. (author). 23 refs., 6 figs

[en] Spent fuel elements from the Bohunice A1 reactor were stored in a pond. To limit corrosion of the cladding, they were held within thimbles which contained a corrosion inhibiting solution of potassium chromate (Chrompik). This proved to be not effective enough, fuel pins did fail, releasing significant amounts of radioactive caesium and also, due to hydrogen gas pressurisation, significant amounts of contaminated Chrompik were released into the pond together with approximately 100 TBq of Cs-137. This paper presents the work undertaken to remove this Cs-137 as part of the first phase of decommissioning the pond. The design is based on a skid mounted unit, comprising a shielded mechanical filter unit and a shielded ion exchange (IX) column unit, with interconnecting pipework and valves. The IX column is housed within a lead shielded overpack and connections to it are made by self-sealing quick release couplings. The IX column is of upward flow design and filled with a composite ion exchanger containing Nickel Hexacyanoferrate (II). The IX column packages may be stored within their own shielding once spent. Two operational runs have been completed, removing 25 TBq of Cs137 in each run. With a fresh column, the Decontamination Factor (DF) for Cs-137 uptake was initially over 5000. The DF then fell slowly over the first 1000 bed volumes to 3500, where it remained for most of the run. The run was terminated when calculations indicated that the column packing had absorbed the specified maximum loading of 25 TBq of Cs137. At this point the DF was 1500

[en] This paper explains the background to the projects, and the setting up of the contracts to dismantle two Oscar-I submarines and one Victor-III submarine. As a pre -cursor to the dismantling, Russian documentation covering environmental, safety, operational and technical issues had to be prepared and submitted to the Russian regulatory bodies for approval, including a full Environmental Impact Assessment (EIA) of the projects. In addition to the dismantling projects, funds were also made available for shipyard infrastructure improvement projects necessary to ensure the safe and efficient completion of the projects. The paper describes these aspects as well as the submarines themselves and gives an overview of the dismantling process. It also describes the nature of the wastes produced, including handling and processing together with the safety and environmental issues. Project Management and monitoring contracted to RWE NUKEM by the U.K. Department of Trade and Industry (DTI) is described emphasizing the importance of strong working relationships between British and Russian teams. Finally the paper discusses the 'end products' of the Oscar-I and Victor-III dismantling and how the projects have provided a useful, high-profile platform on which to demonstrate the success of the DTI and their contractors in helping the U.K. meet its commitments under the Global Partnership Initiative. (authors)

[en] Tantalum and tantalum-based thin films have gained precedence as the diffusion barrier for copper interconnects used in the latest generation of integrated circuits (ICs). The paper presents insight and observations on the covariance of texture and grain size of wrought tantalum sputtering targets and their influence on sputtering performance. Previous studies involving deposition trials of tantalum targets of varying metallurgical character had demonstrated that both grain size and textural homogeneity is critical for assuring reliable sputtering performance of tantalum. Subsequently, a model had been proposed to prescribe how localized texture bands and orientation clusters in tantalum are effectively resistant to sputter erosion. In this paper, results of atomic force microscopy (AFM) and orientation imaging microscopy (OIM^TM) analyses on the eroded surface of a tantalum sputtering target are presented. Initial findings support the model's hypothesis regarding the erosion mechanics of crystallites with respect to grain size and discrete orientation. However, additional work is necessary to understand the formation and erosion of facet planes in polycrystalline tantalum sputtering targets. (orig.)

[en] The use of a composite ion-exchanger, containing nickel hexacyanoferrate, to remove radioactive caesium from the water contained in a fuel storage pond is described. Three operational runs have now been completed, removing 80 TBq of ¹³⁷Cs in total. In the first run, the Decontamination Factor (DF) for ¹³⁷Cs uptake was initially over 5000. The DF then fell slowly over the first 1000 bed volumes to 3500, where it remained for most of the run. The run was terminated when calculations indicated that the column packing had absorbed the specified maximum loading of 25 TBq of ¹³⁷Cs. At this point the DF was 1500. (author)

[en] A series of plate-impact spall experiments was conducted to study the spall strength of seven microstructural conditions of aluminum, including three grain sizes of 6061 Al alloy, both ultrapure and commercially pure (1060) polycrystalline aluminum, and single-crystal Al with two different orientations, over the stress range of 4-22 GPa. The pullback velocity, which is a characteristic signature of spall strength, is observed to depend on initial microstructure, impact stress, pulse duration, and loading rate. The pullback velocity generally increases over the stress range of 4-14 GPa and achieves a maximum as the impact stress approaches 22 GPa. The pullback velocity of [100] single-crystal Al is higher than that for both polycrystalline samples and [111] single-crystal samples, indicating that grain orientation strongly affects material response. Experimental results also show that the spall behavior is strongly dependent on sample thickness, while the effect of shock pulse duration was observed to be less significant. Comparison among three 6061 materials indicates that the observed differences depend on initial yield strength. The results also show that initial microstructures and impurities have a diminishing effect on the pullback velocity at stresses near 22 GPa. However, initial properties are observed to have a pronounced effect on the detailed structure of the pullback velocity profile at all stress levels. In particular, an interesting feature, i.e., a sharp slope during pullback followed by a distinct transition to a slower slope, is consistently observed. The occurrence of this change in slope is observed to depend on impact stress, loading rate, and grain size