Direct observation of deformation process until formation of fracture on extreme small samples of composite in SEM is interesting from practical and interpretation aspects. In the present work the effects of composite composition, volume fractions of secondary phases as well as the matrix grain sizes (micro and nano size) on deformation and failure processes of Al and Cu-based composites were evaluated. Experimental materials were prepared by the different powder metallurgy methods. Interpretation of results was based on the quantification of the physical parameters of material phases depending on the preparation methods and on the analysis of deformation processes using the ‘in-situ tensile test in SEM’. The mechanism of deformation and fracture for each composite system was estimated and models of fracture were proposed.

The method of "in-situ tensile testing in SEM" is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thanks to which the initiation and development of plastic deformation and fracture can be reliably described. The deformation and fracture mechanisms of Glidcop AL-60 grade with 1.1 wt.% of Al2O3 phase (1.62 vol.% of Al2O3) were analyzed before and after ECAP (Equal Channel Angular Pressing) using technique of the "in-situ tensile testing in SEM". Before ECAP it was showed that the deformation process caused increasing of pores and formation of cracks. Decohesion of small Al2O3 particles and clusters occurred and the final fracture path was influenced by coalescence of originated cracks. The principal crack propagated towards the sample exterior surface. After ECAP initial cracks were formed in the middle of the specimen first of all in triple junctions of nanograins and together with decohesion of Al2O3 particles and clusters at small strains led to the failure. Based on the experimental observations a model of damage and/or fracture mechanisms has been proposed.

Characteristic feature of the most of Selenomonas ruminantium cryptic plasmids is the presence of short, conserved sequences encompassing the gene for replication protein creating a potential rep gene cassette. PCR-based experiment was designed to analyse the genetic organization of putative plasmid rep modules and to assess S. ruminantium plasmid biodiversity. Analysed PCR amplicons contained single open reading frames encoding for putative replication proteins. While most of the derived protein sequences were often found to be conserved among putative plasmid molecules, at noncoding regions, genetic variability was observed to various extents. Complete nucleotide sequence of a plasmid was determined that contained probably a new rep gene only distantly related to known selenomonas Rep proteins but at noncoding regions shared high homology with already known plasmids. Our results document considerable structural instability and sequence variability of analysed rep gene cassettes and suggest a modular structure of S. ruminantium plasmids potentially accessible for rep gene module exchanges.

Deformation of magnesium alloy AZ61-F with 1 wt.% of Al2O3 was analysed by "in-situ tensile test in SEM" and a model of fracture mechanism was suggested. Microstructure of the experimental materials is heterogeneous with grain size of 50 mu m. It has been shown that during tensile deformation the failure of Mg17Al12 particles appeared and at the same time decohesion of the matrix-Al2O3 particles occurred as a result of different physical properties. The increase of stress caused the cracks propagation into the specimen and simultaneously the large damaged Mg17Al12 particles contributed to the fracture process. Fracture surface had transcrystalline ductile character.

The method of “in situ tensile testing in SEM” is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, thank to which the initiation and development of plastic deformation and fracture can be reliably described. The deformation and fracture mechanisms of Cu–Al2O3 nanomaterials with 5 vol.% of Al2O3 phase has been analyzed using technique of the “in situ tensile testing in SEM.” It has been shown that the deformation process causes break-up of large Al2O3 particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations, a model of damage and/or fracture mechanisms has been proposed.

The complete nucleotide sequence of pSRD192 plasmid from Selenomonas ruminantium 19D has been obtained and analyzed. The plasmid, 2334bp in length, was shown to replicate by rolling circle replication mechanism. By PCR method variability of pSRD192-like plasmids was investigated and another variant of pSRD192-like plasmid; the pSRM22 plasmid 2338bp in length; was detected and characterized. Both pSRD192 and pSRM22 plasmids share an identical rep gene and origins of replication to that of another S. ruminantium pONE429 plasmid. Other than that there are additional regions of sequence similarity between the three plasmids, interspersed with divergent regions. The sequence comparisons suggest structural instability of pSRD192-like rolling circle replication plasmids.

Preparation of dispersion strengthened materials consists of heterogenization of structure. The different methods of how to incorporate the secondary phase particles to the matrix are known. The most optimal one is mechanical alloying during which the matrix particles are fractured and re-welded during the milling process in the attritor and incorporated to the matrix. Following heat treatment, the result is that the dispersion strengthened phase is homogeneously distributed in 3D. The deformation and fracture mechanisms of Al-Al4C3 nanomaterials with 4 vol.% of Al4C3 phase have been analyzed using the technique of the “in-situ tensile testing in SEM”. It has been shown that the deformation process causes the break-up of large Al4C3 particles and decohesion of smaller ones. The final fracture path is also influenced by boundaries of nanograins, through which the principal crack propagates towards the sample’s exterior surface. Based on the experimental observations, a model of the fracture mechanisms of Al-Al4C3 nanosystem has been proposed.

The deformation and fracture mechanisms of Al-Al4C3 nanomaterials with 4 vol% of Al4C3 phase has been analysed using the technique in situ tensile testing in SEM. It has been shown that the deformation process causes break-up of large Al 4C3 particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations, a model of damage and fracture mechanisms has been proposed.

The deformation and fracture mechanisms of Al-Al4C3 nanomnaterials with 4 vol.% of Al4C3 phase have been analysed using technique of the "in-situ tensile testing in SEM". It has been shown that the deformation process causes break-up of large Al4C3 particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations a model of damage and/or fracture mechanisms has been proposed.

The deformation and fracture mechanisms of Al-Al4C3 nanomaterials with 4 vol% of Al4C3 phase has been analysed using the technique " in situ tensile testing in SEM". It has been shown that the deformation process causes break-up of large Al 4C3 particles and decohesion of smaller ones. The final fracture path is influenced also by boundaries of nanograins, through which the principal crack propagates towards the sample exterior surface. Based on the experimental observations, a model of damage and fracture mechanisms has been proposed.

The method of "in-situ tensile testing in SEM" is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, and so the initiation and development of plastic deformation and fracture can be reliably described. With increasing tensile load, local cracks are formed by rupture of large particles and decohesion of smaller particles. Further increase of load leads to the crack growth by coalescence of cavities in the direction from the surface into the specimen centre. Depending on the particle volume fraction, the cracks can be parallel or perpendicular to the load direction. The final rupture takes place in rows of variable density, depending on the volume fractions of carbide (Al4C3) and oxide (Al2O3) particles. The aim of the present study is to evaluate the influence of volume fraction of Al4C3 particles (8 and 12 vol.%) on the fracture mechanism.

In this work layers of colloidal nanoparticles obtained by thermolysis of Co2(CO8) were deposited on substrate surface by drying a drop in air eventually combined with the application of a magnetic field, or by spin coating. The formation of arrays of particles on Si substrates covered by Si3N4 layer was studied by high-resolution scanning electron microscopy and particle arrays on carbon coated copper grids by transmission electron microscopy. The crystalline structure of Co particles and its temperature evolution were analyzed by X-ray diffraction in situ in He gas and ex situ in UHV up to 700 °C. Two-dimensional (2-D) arrays of particles were formed by different types of preparation. The most regular ordering was obtained with the application of magnetic field perpendicular to the substrate surface, where 2-D hexagonal ordered arrays with length and width both between 200 and 500 nm were observed. In external magnetic field also three-dimensional arrays of nanoparticles–columns were formed. In the as-deposited state the nanoparticles show a poorly developed fcc crystalline structure. Most significant structural changes appear in the temperature range 400–450 °C where a well-developed fcc Co phase forms.

The method of “in-situ tensile testing in SEM” is suitable for investigations of fracture mechanisms because it enables to observe and document deformation processes directly, by which the initiation and development of plastic deformation and fracture can be reliably described. With increasing tensile load, local cracks are formed by rupture of large particles and decohesion of smaller particles. Further increase of load leads to the crack growth by coalescence of cavities in the direction from the surface to the specimen centre. The cracks can be oriented parallel or perpendicular to the loading direction in depending on the particle volume fraction. The final rupture takes place in variably dense rows, depending on the volume fractions of carbide (Al4C3) and oxide (Al2O3) particles.

The Fe3O4 and CoFe2O4 nanoparticles of radius 3.2 +/- 0.3 and 3.8 +/- 0.3 nm, respectively, were synthesized by the high-temperature solution phase reaction of metal acetylacetonates. Nanoparticles with the spherical shape and well-developed crystalline structure are superparamagnetic at room temperature. The CoFe2O4 showed high coercivity up to 1.7 T at low temperatures and a step-like change of magnetization at 138 K, which might point at the Verwey transition. (C) 2006 Elsevier B.V. All rights reserved.

Ordering of Co nanoparticles (∼11 nm in diameter) into 2-D and 3-D arrays on Si/Si3N4 substrates in external magnetic field and without field is reported. Arrays of particles were studied by TEM, SEM and GISAXS. The GISAXS measurements were performed at the wavelengths 0.155 nm and 0.336 nm and the spectra were simulated using distorted wave Born approximation approach. From results it follows that 2-D ordered monolayers of particles are composed of hexagonal close-packed mosaic blocks. 3-D arrays – rods are formed along magnetic field direction, being parallel or perpendicular to the substrate surface, when the colloid was more concentrated. Distribution of particles in rods was analyzed only by GISAXS and it was described by close packing of hard spheres. Their effective diameter was 14.7 nm.

The purpose of the present investigation was to explore microstructure and mechanical properties of two types of composite materials with different amounts of secondary phase (10% and 15% ZrO2), and their comparison with monolithic MoSi2. Following metallographic analyses the identification of phases and residual pores in microstructure was realised. The main criteria for assessment of mechanical properties were hardness, mechanical strength, and fracture toughness determined by two different methods. The results showed that materials with added ZrO2 particles had better mechanical properties compared to the monolithic one and these properties improved with increase of the ZrO2 content. Comparison of the two methods of fracture toughness measurement indicates better sensitivity and reliability of the IS method which is less influenced by human factor. The results of EDX analysis showed that the microstructures of the toughened materials contain monolithic MOSi2 phase, Mo5Si3 phase and secondary ZrO2 phase.

The composite prepared by mechanical alloying of mine Pt powder obtained by waste recovery from linings of glass furnaces with Y2O3 dispersed particles (0.5 mass %) has shown better mechanical properties at room temperature as well as at higher temperatures in comparison with those of Pt alloys commercially produced. The qualitative factor, which is known to be a function of starting powders parameters, technology of preparation and compacting operations, shows some correlation particularly with size and space distribution of Y2O3 phase in the Pt matrix.

Deformation of the Al-Al4C3 system was analyzed by "in situ tensile test in SEW and a model of fracture mechanism was suggested. It has been shown that during tensile deformation, the first cracks appeared due to decohesion of the matrix- particle interphase as a result of different physical properties of the matrix and the particles. The stress increase caused crack propagation into the specimen and simultaneously the large damaged particles contributed to the fracture process. The path of final fracture was formed preferably in the loading direction in the rows of Al4C3 and Al2O3 particles. The fracture surface was transcrystalline ductile. (C) 2003 Elsevier B.V. All rights reserved.

Ball milled NiAl30 powder studied in this paper is formed by a heterogeneous mixture of particles containing various fractions of components. It appeared that substantial part of powder particles exhibit fine lamellar microstructure resulting from severe deformation, fracture and welding in the ball milling process. Lamellar domains are formed by elemental Ni and Al as well as by ordered β-NiAl. Nanocrystalline Ni2Al3 was observed too. No amorphous phase was observed in the studied microstructure.