Layered core-shell bimetallic silver-gold colloids in the size range of 10-16 nm have been prepared by the seed-growth method. Silver nuclei were covered by gold shells of various thicknesses without any stabilization agent. Interfacial (Ag)Au colloid-2,2′-bipyridine films were prepared from these bimetallic colloids and used for the purpose of analysis of transmission electron microscopy (TEM) images and electron diffraction. Both observed and calculated TEM images were used to characterize the prepared nanoparticles. On the basis of the analysis of TEM images, the calculated TEM image contrast, and results obtained by electron diffraction, energy-dispersive X-ray analysis, and other experiments, the core-shell structure of the prepared (Ag)Au nanoparticles was revealed. Particles were found to consist of a silver core and a gold shell enriched with silver.

Compatibility stresses have been calculated in the model of a bicrystal composed of two semi-infinite crystals. The elastic anisotropy of the component crystals is fully taken into account. Various particular cases chosen for the cubic bicrystals with the (100) and (110) rotation axes commonly used in experiments are discussed in detail. The effects of elastic and plastic deformation have also been.compared. The model provides compatibility stresses as functions of grain boundary geometrical parameters and of the loading axis orientation.

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all at.-%), using hardness measurements, electron microscopy of replicas and thinfoils, atom probe field ion microscopy (APFIM), and thermochemical calculations. Two different families of inter metallic phases (Ti 6 Si 7 Ni16 G phase and 11 Ni3 Ti) have beenfound to contribute to age hardening. The composition and morphology of these precipitates were studied in deformed and undeformed alloys after aging at 420-570°C for various times. In addition, reverted austenite has beenfound in the aged structure. Results obtained using AP F I M are compared with equilibrium thermodynamic calculations and previous AP F I M studies of conventional Cr free low Al and Si maraging steels having higher Mo contents.MSTj1558

Tensile tests were performed in situ in a transmission electron microscope to investigate the twinning mechanism in non-modulated NiÀMnÀGa martensite. The reorientation of the twin variants occurs via twinning dislocations. Their generation and movement were followed; the glide plane and Burgers vector were verified. Individual twinning dislocations were visualized.NiÀMnÀGa is an interesting and widely investigated shape memory alloy showing remarkable properties, such as magnetoresistance, 1 magnetocaloric behavior, 2 thermally induced shape memory effect, 3 superelasticity 4 and, particularly, magnetic-field-induced-strain. 5 In alloys that transform upon cooling into modulated martensites, the martensitic twin structure is coupled with magnetic domains in such a way that the magnetic field can reorient martensitic twin variants, which results in very large strains. 6 The magnetic-fieldinduced-strain (magneto-plasticity) in NiÀMnÀGa is directly related to the reorientation of one martensite variant to another twin variant. 5 The mobility of the twin boundaries plays a decisive role in these processes. A microscopic model of the reversible motion of the twin boundary in the ferromagnetic shape memory alloys was proposed by Müllner et al.,7,8 with their concept being based on the movement of twinning dislocations. 9 Although the magnetoplasticity in NiÀMnÀGa has been described and discussed thoroughly in the literature, detailed investigations of the twin variant reorientation by transmission electron microscopy (TEM) are very rare. 10À12 The in situ TEM straining method used in the present study is highly suitable for this purpose as it enables the direct observation of the stress-induced processes. The experiments were intended to be carried out on modulated as well as nonmodulated martensites. However, they could be successfully performed only on the non-modulated samples. The results were partly published in Refs. 10 and 11. The samples of 5M martensite were too brittle for tensile tests inside the electron microscope, and only preliminary results were obtained for 7M martensite. The non-modulated tetragonal NiÀMnÀGa martensite exhibits superelasticity and shape memory effect while the magnetic-field-induced-strain was reported only 0.17%. 13 Nevertheless, we believe that an understanding of the stress induced twin variant reorientation in the non-modulated martensite will provide insight into the magnetically induced reorientation processes in the modulated martensites as well.The experiments were performed on a Ni 52:4 Mn 27:3 Ga 20:3 alloy, with M s ¼ 398 K, A f ¼ 408 K, T c ¼ 380:2 K. The structure of the alloy at room temperature was tetragonal martensite, a ¼ 0:549 nm, c ¼ 0:661 nm. The samples, 1:67 mm  5:5 mm  0:07 mm, were prepared from a plate with [001] normal in the austenite state, and thinned in the central part in a double jet polisher (30% solution of HNO 3 in methanol, À40 ○ C) to form a hole. The samples were strained in tension at room temperature in a JEM 1200EX microscope equipped wit...

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