Mechanism of SiC crystals growth on {100} and {111} diamond surfaces upon microwave heating

The subject of this work is focused on characterization of the microstructures and orientations of SiC crystals synthesized in diamond–SiC–Si composites using reactive microwave sintering. The SiC crystals grown on the surfaces of diamonds have either shapes of cubes or hexagonal prisms, dependent on crystallographic orientation of diamond. The selection of a specified plane in diamond lattice for the TEM investigations enabled a direct comparison of SiC orientations against two types of diamond facets. On the {111} diamond faces a 200 nm layer of 30–80 nm flat β-SiC grains was found having a semi-coherent interface with diamond at an orientation: (111)[112]SiC║(111)[110]C. On the {100} diamond faces β-SiC forms a 300 nm intermediate layer of 20–80 nm grains and an outer 1.2 µm layer on top of it. Surprisingly, the SiC lattice of the outer layer is aligned with the diamond lattice: (111)[110]SiC║(111)[110]C

Influence of Y2O3 and Fe2Y additions on the formation of nano-scale oxide particles and the mechanical properties of an ODS RAF steel

The main goal of this work was to manufacture an oxide dispersion strengthened (ODS) reduced activation ferritic steel from a pre-alloyed, gas atomised Fe-14Cr-2W-0.2Ti (in wt.%) powder mechanically alloyed with either 0.3%Y2O(3) or 0.5%Fe2Y particles and consolidated by hot isostatic pressing, and to investigate its microstructure, microhardness and Charpy impact properties

Microstructure and mechanical properties of an ODS RAF steel fabricated by hot extrusion or hot isostatic pressing

Ingots of an oxide dispersion strengthened reduced activation ferritic steel with the Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) chemical composition (in wt.%) were synthesized by mechanical alloying of elemental powders with 0.3 wt.% Y2O3 particles in a planetary ball mill, in a hydrogen atmosphere. and compacted by either hot extrusion or hot isostatic pressing. The microstructures of the obtained materials were characterized by means of light microscopy, transmission electron microscopy and chemical analyses. The mechanical properties were evaluated by means of Vickers microhardness measurements and tensile tests. It was found that the microstructure of both materials is composed of ferritic grains having a submicron size and containing nanometric Y-Ti-O oxide particles with a mean size of about 10 nm, uniformly distributed in the matrix. The oxide particles in the hot extruded steel were identified as YTiO3 phase. In larger (>10 nm) oxide particles Cr was found next to Ti, Y and O. The steel produced by hot extrusion exhibits much higher tensile strength and hardness at low to moderate temperatures, as compared to the steel fabricated by hot isostatic pressing, which was mainly attributed to smaller pores but also to more severe work hardening in the case of the hot extruded steel. (C) 2011 Elsevier B.V. All rights reserved

FEM modeling of structure and properties of diamond-SiC-(Al) composites developed for thermal management applications

Thermal management materials frequently have multi-phase composite character with complex architecture of the constituents. As a result, design rules are needed which can be used in selection of the phases and optimizing their volume fractions. The study shows that such are provided by finite element modeling of these composites. This is demonstrated for a diamond-SiC-Si-(Al) composites, which have been optimized in terms of the volume fraction of SiC, contact area between the components and presence of open porosity

Structure of complex oxide nanoparticles in a Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) ODS RAF steel

One of the most crucial steps in the development of oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels is the engineering of their microstructure, which includes control of the type and size of oxide nanoparticles. In this work, the composition and crystal structure of oxide particles grown in the Fe-14Cr-2W-0.3Ti-0.3Y(2)O(3) ODS RAF steel were characterized using advanced spectroscopic and microscopic techniques. The electron energy loss spectroscopic mapping has shown presence of numerous fine Y-Ti-O oxides but also larger Cr-Ti-O and Cr-N particles among those extracted from the bulk samples. In addition, atom probe tomography of the as-compacted ODS RAF samples revealed a uniform spatial distribution of fine oxides containing mainly Y, Ti, and O. The orthorhombic YTiO3, having distorted perovskite structure, was identified in all analyzed oxides using HR-STEM and diffraction pattern analysis. (C) 2013 Elsevier B.V. All rights reserved

Statistical analysis of oxides particles in ODS ferritic steel using advanced electron microscopy

In this work a combination of advanced transmission electron microscopy and spectroscopy techniques enabled a statistically significant analysis of various types of few nanometer size oxides particles in Fe-14Cr-2W-O.3Ti-0.3Y(2)O(3) ferritic steel. These methods include a scanning TEM with EDS and EFTEM coupled with EELS. In addition, principal component analysis was applied to the chemical maps obtained by EFTEM, which drastically improved the signal to noise ratio. Three types of particles were identified in a size range from 2 to 300 nm, namely Cr-Ti-O, Y-O and Y-Ti-O particles, with an average size of 33,16 and 8 nm, respectively. The Cr-Ti-O particles contain Y and Ti enriched zones, which were not observed previously. The EFTEM analysis showed that the titanium addition leads to formation of Y-Ti-O nanoparticles, which constitute 84% of the oxides but also precipitation of larger Cr-Ti-O. The presence of small amount of Y-O particles indicated a not sufficient amount of Ti available for reaction during mechanical alloying or consolidation. (C) 2012 Elsevier B.V. All rights reserved