摘要:

SUMMARYThe paper briefly reviews the advantages of high voltage electron microscopy applied to low temperature radiation damage studies. Such studies may be performed inside the microscope provided a high resolution specimen cooling stage is available. The main features of a new type of cooling stage used in the experiments relevant to this paper are outlined. The applicability of the stage for post‐irradiation annealing experiments is emphasized.During electron irradiation to high doses at 8°K the formation of defect clusters was observed in nickel and copper. This is accompanied by pronounced changes in the diffraction pattern. Post‐irradiation annealing of samples irradiated at 8°K produces defect clusters which can be identified as dislocation

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03766.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe influence of dislocation behaviour on void formation in the high voltage electron microscope (HVEM) has been predicted theoretically and confirmed by experiment. The probability of void nucleation has been computed as a function of the radial distance from a dislocation line in a finite cylinder of material. The observation of strings of voids associated with dislocation lines supports the predictions of the model. Void formation in the HVEM is closely related to the detailed microstructural changes that occur immediately upon electron irradiation, and a good correlation is obtained between the initial interstitial loop density and subsequent swelling by electrons. A minimum foil thickness is necessary for void growth in the HVEM, otherwise the surfaces dominate and the dislocation density always remains low.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03767.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYStripe domains in (001) nickel occur in a variety of structures due to the large number of easy directions present. We have given below a tentative analysis of two of these structures, not previously studied by Lorentz microscopy. In particular it has been shown that, as used hitherto, the technique has not been a reliable method of observing stripe domains since some structures may be invisible until the specimen is tilted.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03768.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYA variable height holder has been constructed for the EM7 which allows the specimen to be displaced along the optic axis of the microscope. In this way a thin foil can be subjected to a large range of vertical magnetic field associated with the objective lens. So far the device has been used for the observation of magnetizing processes in thin single crystals of cobalt with thec‐axis normal to the foil. As the field on the specimen is increased by lowering it further into the lens, the usual plate domain structure is progressively converted to arrays of bubble domains. On reducing the field from saturation, bubble domains are seen to renucleat

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03769.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYA range of internal defects has been observed by high voltage microscopy in carbon fibres prepared from polyacrylonitrile (PAN). In type I fibres, large elongated cavities up to ∼ 3 μm in diameter are found, often associated with particulate inclusions and occur with a frequency of ∼ 2/mm of fibre. In ion thinned type I fibres where smaller defects are visible, a higher density of defects (approx. 1000/mm of fibre, mean size 86 nm) has been observed both in sections from the centre of the fibre and close to the surface. These smaller defects are also visible in type II fibres (heat treated to ∼ 1500°C) and in this case ∼ 70% of the defects are observed to contain small particulate inclusions.A high density of small voids (mean size 20 nm) is observed in type II fibres particularly in the vicinity of larger defects. These voids appear slightly diffuse in type II fibre and disappear during the graphitization heat treatment. They are also not seen in oxidized fibre, but in fibre heat treated to 500°C they are clearly visible, indicating that they are formed during the temperature range 220–500°C where considerable gas evolution occurs.The effect of these defects on fibre strength is discussed and the observed defect size related to expected crack lengths on the basis of a Griffith

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03770.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYSpecimens of the alloy Nimonic 80A have been pre‐strained 11% in tension at room temperature and then heated to 750°C for various times either with or without the application of stress. Examination by means of a high voltage electron microscope revealed large numbers of spherical submicron diameter cavities. The cavities all lay on grain boundaries but were inhomogeneously distributed; a grain boundary usually contained either many cavities or none at all. It is concluded that the cavitation is a direct result of decohesion at the grain boundaries during the pre‐straining and not due to any creep pro

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03771.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe development of environmental cells for transmission electron microscopy is briefly reviewed. The advantages of increased penetrating power and large available space for specimen stages associated with high voltage microscopes are demonstrated. The effect of specimen‐electron beam interactions are considered and the applications of the high voltage microscope toin situstudies of chemical reactions and biological material in the wet state are discusse

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03772.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThin foils of pure molybdenum single crystals with selected surface orientations and tensile axes were tested on a double‐tilt straining stage using a microscope operating at 800 keV. Studies were made of the propagation of screw and edge dislocations, slip geometry, dislocation multiplication and formation of dislocation tangles. Special attention was paid to the influence of the surface on dislocation motion and the comparison of observed effects with those of bulk materia

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03773.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYWhen fitted with a heating stage and suitable equipment for continuous image recording, the high voltage electron microscope is a powerful tool for the direct observation of recrystallization and precipitation in thin metal foils. However, the behaviour of thin specimens is sometimes not even qualitatively typical of bulk material. For example, true precipitation from supersaturated solid solution can only be observed if vacancies play no significant part in the process as in iron‐nitrogen alloys. In this case, the formation of the intermediate precipitates, α“—Fe8N, and the equilibrium phase, γ—Fe4N, is qualitatively and in some respects quantitatively typical of bulk material even in very thin foils. However, extensive electron displacement damage should be avoided because it seriously retards precipitate growth.It is shown elsewhere (Roberts&Lehtinen, 1972) that true bulk recrystallization is only possible in thick areas of an electron microscope specimen. This is confirmed for several metals in the present work. The critical specimen thickness for bulk behaviour is generally between 3–800 nm depending the degree of cold work etc.; this concurs with earlier heating‐stage experiments at 100 kV in which true recrystallization was

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03774.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SUMMARYHydration of alite and tricalcium silicate has been investigated in the NPL environmental cell. In the presence of free water in the cell the hydration reactions occur at a very rapid rate when subjected to electron bombardment and the resulting hydrates cannot be regarded as being typical of the bulk reaction.Specimens have also been hydrated in a controlled environment external to the cell and subsequently examined in the cell with a humid atmosphere. In addition, the same specimen areas were examined in high vacuum and it was found that there were no obvious changes in the morphology of the hydrates.Fungi spores have been examined at atmospheric pressure in the cell and the microstructure of the spore attachments has been studied. The results also indicate that the surface morphology previously determined from replicas is essentially correct.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1973.tb03775.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY