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Diffuse elastic scattering of electrons by single nanometer-sized defects in ion irradiated Au has been measured quantitatively. Results are given for two dislocation loops and compared with published calculations to establish the loop geometry and interstitial or vacancy nature. Defect images using only diffuse scatttering are achieved with high sensitivity and good resolution by a hollow-cone dark-field method.

We present results of a weak-beam transmission electron microscopy study of “matrix damage” in two nearly-pure irons (designated alloys 1A and 2A) produced by neutron irradiation to a fluence of 0.06 dpa at 280°C. The matrix damage in both materials was found to consist of small (2-6 nm) dislocation loops. About 80 % have Burgers vectors b = a, and the remainder have b = a/2. The loops in alloy 1A have a mean image size dmean = 2.8± 0.1 nm and a mean maximum image size dmax = 4.2± 0.3 nm, while those in 2A have d mean = 3.4± 0.1 nm and d max = 4.5± 0.3 nm. The number densities are about 8.5 × 1021 m−3 in alloy 1A, and 6.6 × 1021 m−3 in 2A. It can be shown that the loops can account for the observed irradiation hardening. At least some loops are stable under thermal annealing to temperatures of at least 430°C. This and other indirect evidence suggests that their nature is interstitial.

The stability of Cu precipitates in an Fe-1.3wt%Cu alloy under 300 keV Fe+ion irradiation has been investigated using transmission electron microscopy and high-resolution electron microscopy. The irradiations were carried out between room temperature and 550°C at displacement rates of 103 to 10−2 dpa(s)−1 to fluences of up to 30 dpa. Copper precipitates were found to keep their shape but decrease in size under all irradiation conditions. The results are discussed within the framework of a competitive process between irradiation induced ballistic destruction of precipitates by cascades and irradiation-enhanced precipitation.

The influence of the irradiation temperature Tirr on the development of disordered zones produced at displacement cascades in Ni3A1 by heavy-ion irradiation with 50 keV Ta+ and 300 keV Ni+ ions has been investigated. The normalised number density (yield) of disordered zones for 300 keV Ni+ irradiation showed a sharp fall between Tirr= 373 K and 573 K. For 50 keV Ni+ irradiation there was a similar fall between 573 K and 673 K. The mean diameters of the disordered zones produced by 300 keV Ni+ ions decreased by about 2 nm between room temperature and 573 K, and there was a tendency for larger zones to become more regular in shape. For 50 keV Ta+ ions, a similar trend was observed between 573 K and 873 K. An annealing experiment confirmed that disordered zones produced at lower temperatures were stable up to a temperature of about 673 K, showing that these trends cannot be due to thermal annealing of disordered zones. The experimental results are consistent with an increased tendency for reordering at the peripheries of disordered zones, due to the increased lifetimes of thermal spikes at higher irradiation temperatures.

A low-temperature in situ ion-irradiation and annealing experiment has been performed by TEM in copper. Most defect clusters which persisted through an anneal to 120 K showed no size changes within the resolution (0.5 nm) of a new weak-beam sizing technique. Of 55 defects measured under a range of weakly diffracting conditions, 7 showed measurable size decreases while 3 showed size increases. We argue that these clusters are likely to be of vacancy and interstitial nature, respectively. Also on annealing to 120 K a fraction of about 25% of the clusters formed by irradiation with 600 kV Cu+ ions at 20 K disappeared, while a similar number of clusters appeared in different locations.

Stereo transmission electron microscopy has been used to characterise the distribution in depth of disordered zones and associated dislocation loops in the ordered alloys Ni3Al and Cu3Au after heavy ion irradiation, most extensively for Ni3Al irradiated with 50 keV Ta+ ions at a temperature of 573 K. The Cu3Au specimen was irradiated with 50 keV Ni+ ions at an incident angle of 45° at a temperature of 373 K. In Ni3Al the defect yield, i.e. the probability for a disordered zone to contain a loop was found to be strongly dependent on the depth of the zone in the foil, varying from about 0.7 for near-surface zones to about 0.2 in the bulk. The sizes and shapes of disordered zones were only weakly dependent on depth, except for a small population of zones very near the surface which were strongly elongated parallel to the incident ion beam. In Cu3Au the surface had a smaller but still significant effect on the defect yield. The dependence of the tranverse disordered zone diameter d on ion energy E for Ta+ irradiation of NiA was found to follow a relationship d = k1, E1/α with k, = 2.4 ± 0.4 and α = 3.3 ± 0.4. A similar relationship with the same value of α is valid for a wide variety of incident ion/target combinations found in the literature.

We have carried out systematic experiments to explore the range of applicability of the two direct methods which are available for the determination of the nature of small clusters. Experiments in heavy-ion irradiated silver and copper, including direct comparisons with the results of Black-White contrast analysis (B-W), forced us to the conclusion that use of the 21/2D technique for the analysis of faulted loops is effectively impossible because of reciprocal-lattice spike and other effects. We used B-W analysis to investigate the nature of the clusters produced by room-temperature heavy-ion irradiation of copper. In-situ irradiations were performed in the Argonne HVEM-Tandem Facility using 40keV and 80keV Kr+ ions. Nearly all of the analysable first-layer loops were found to be vacancy in nature. Some deeper clusters were also certainly vacancy. There is no unequivocal evidence for interstitial loops under these conditions. The near impossibility of establishing that interstitial loops are not present is shown by the fact that a large fraction of loops - over 50% - could not be analysed either because they did not display clear B-W contrast under any condition or sufficiently consistent B-W contrast under several different operating conditions.

Crack/particle interactions in Al2O3/SiC and Al2O3/TiN nanocomposites have been observed by TEM on samples containing cracks produced by Vickers indentations. No significant crack deflection by intragranular SiC particles or microcracking around nanoparticles was found. Intergranular cracks were observed to be deflected into the matrix grains by SiC particles on grain boundaries inclined to the direction of crack propagation. TiN particles were not effective in this way. These features are briefly discussed within the framework of the interfacial fracture energies. These were calculated from interfacial energies, which were determined by the measurement of grain boundary-interface dihedral angles.

Tensile fatigue behavior of a hot-isostatically-pressed (HIPed) silicon nitride was investigated over ranges of constant stresses, constant stress rates, and cyclic loading at 1150-1370°C. At 1150°C, static and dynamic fatigue failures were governed by a slow crack growth mechanism. Creep rupture was the dominant failure mechanism in static fatigue at 1260 and 1370°C. A transition of failure mechanism from slow crack growth to creep rupture appeared at stress rates ≤10−2MPa/s for dynamic fatigue at 1260 and 1370°C. At 1 150-1370°C, cyclic loading appeared to be less damaging than static loading as cyclic fatigue specimens displayed greater failure times than static fatigue specimens under the same maximum stresses.

The crack-propagation behavior and fracture toughness at room temperature of extruded and heat-treated NiAl and FeAl were examined by testing chevron-notched, three-point flexural specimens at constant crosshead speeds. In Ni-50 at. % Al, sudden load drops occurred repeatedly, indicating run-arrest crack propagation. The fracture resistance was not found to depend on the crosshead speed. Iron additions of up to 1 at. % and boron additions of 0.01 at. % did generally not improve the fracture toughness. By contrast, crack propagation in Fe-40 at. % Al occurred in a stable manner. In agreement with the environmental sensitivity of this intermetallic alloy, fracture resistance did depend on the crack-propagation velocity, indicative of the kinetic nature of this process. While the crack-growth resistance of iron aluminides was reduced by changing the aluminum content from 40 to 45 at. %, it was increased significantly by small additions of boron.

Fluorite-related structures of mixed uranium oxides (Uy,M1-y)O2−x, where M = Ce, Sc, Y, have been studied using High Resolution Electron Microscopy (HREM). Ordered domains have, been observed directly in crystallites of urania-ceria solid solution. Preliminary investigations of urania-yttria also show evidence for the presence of ordered domains. A possible model for the structure of these regions is suggested.

Polycrystalline magnesium aluminate spinel (MgAl2O4) and Al23O27 N5 (ALON) were irradiated with 4 MeV Ar+ ions to doses from 0.5 to 6 displacements per atom (dpa) at a temperature of 1070K and subsequently examined using transmission electron microscopy. Faulted dislocation loops were found in both materials, although their habit planes ({110} and {111} respectively) and Burgers vectors (a/4 and a/6 ) differ. Cavities were found in spinel but not in ALON. Both materials exhibited a similar, low, degree of radiation damage and we conclude that polycrystalline ALON is a good potential reactor window material.