[en] The experimental features of the peaking effect (P.E.) are reviewed and the theoretical models of interpretation are analyzed. 31 references, 12 figures

[en] Calculations of electron energy near edge structures (ELNES) are compared with experimental data obtained in a high-resolution transmission electron microscope. This study concerns small precipitates of aluminium nitride in low carbon steels. The ELNES technique allows to clearly establish that these precipitates crystallize in a cubic rather than in a hexagonal crystallographic cell. The influence on simulated spectra of different parameters are investigated: the size of the atomic shell and its relation with the electron inelastic mean free path. We also examine the influence of the core hole and the sensitivity to cell parameters. We particularly examine the Al L₂₃ near edge structure and features relating to the different transition channels (A_1g, E_g and T_2g). Results of a multiple scattering and band structure calculations using ICXANES and WIEN97 codes, respectively, are compared in the region from 0 to 30 eV above the edge onsets. Both calculations are in a rather good agreement

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No abstract available

[en] The results of work in which tungsten wafers (25x4x0.3mm), made by electrolytic polishing and ionic bombardment, were carburised by being surrounded by graphite pellets at 2000₀-2100₀C for several minutes (the amount of carbon so introduced varying from 1 per mille to several atom percent) are reported. The reported observations confirm previous results on the precipitation of the hexagonal phase of Me²C obtained by transmission electron microscopic observation of a variety of metals. The appearance of an incoherent precipitate, surrounded by helical dislocations and the presence of the W²C phase together with its orientation in the matrix are illustrated, consistent with the relations found by Burgers. Successive stages of the precipitation were observed qualitatively in different specimens, all suggesting that the precipitation of the W²C in the tungsten operates in the same way as in other systems of transition metal and carbon. Further work is required to clear up some finer points concerning deviation of axes. (C.J.O.G.)

[en] The characterization of tribofilms has already been studied by various surface analysis tools for many years. The analytical techniques usually performed on this kind of samples are X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and X-ray absorption near-edge structure (XANES). XPS is interesting for chemical environment information. AES has a good spatial resolution (approx. 0.5 μm) permitting AES mapping or making AES linescans. With XANES, the polyphosphate chain length can be characterized in case of ZDDP tribofilm. AES and XPS depth profiles can also be performed in order to follow the composition of the tribofilm with depth. Therefore, coupling XPS, AES and XANES is interesting to clarify the different layer composition of the tribofilm. In this work, AES, XPS, secondary ion mass spectroscopy (SIMS) and transmission electron microscopy (TEM) are carried out on tribofilm made by ZDDP additives. By a SIMS analysis, information on the elemental distribution in the surface near layers can be obtained with high lateral and high depth resolution. The use of a time-of-flight (ToF) analyser allows to obtain information on all elements quasi-simultaneously resulting in a very high sensitivity. Our aim is to investigate the tribofilm in its depth and the interface tribofilm/substrate by using a multi-technique approach on the same ZDDP tribofilm. First, depth profiles (by AES XPS and SIMS) were carried out. Secondly, a transverse section made by focused ion beam (FIB) was evaluated by TEM. All results are discussed in order to give a better understanding of the tribofilm composition

[en] Numerical calculation are made of internal friction due to the thermally activated formation of double-kinks (Seeger-Pare model), by applying the rate theory without making approximations. All the characteristics of the Bordoni relaxation are well explained by this model. In particular, a distribution of internal stresses and dislocation lengths leads to a peak broadening which may be of about 3 to 4. Besides, the model gives important non-linear effects: the stresses (internal or applied) must satisfy the Pare condition, the peak temperature is reduced when the stress increases, the peak is shifted towards high temperatures when the loop length increases and the relaxation strength presents a maximum as a function of stress. (author)

[en] Very high purity magnesium is electron (2 MeV) bombarded at different temperatures between 15 and 350 K. The peaking effect appears between 35 and 250 K, its variations with the strain amplitude of measurements and with the irradiation temperature are determined and discussed. (author)

[en] A precise thermodynamic analysis of the mechanical test results carried out between 800 and 2200⁰C on polycrystalline W/sub 2/C allows us to determine the terms of the constitutive law. Particularly, the stress dependence of the preexponential factor is determined following the analysis of Surek and Co-workers. The preceding results are compared with those obtained by the measurement of carbon diffusion coefficient, electron microscope observations and crystallographic determinations by neutron diffraction. All the results are consistent with the proposed deformation mechanism

[en] Internal friction and modulus of high-purity polycrystal line aluminium has been studied at low temperature ((10/50)K). After annealing at high temperatures, we have observed either an important decrease of internal friction with temperature from 10 to 40 K or a hysteric type of internal-friction peak around (20/25)K, or both phenomena. These manifestations are explained by the unpinning of geometrical kinks from impurity atoms