Dina V. Dudina

Microstructure changes in TiB2-Cu nanocomposite under sintering

Stability and growth of nanoparticulate reinforcements in metal matrix composites during heating are widely studied for dispersion-strengthened alloys, which contain several volume percent of reinforcing phase. When high volume content of nanoparticles distributed within a matrix is concerned results of particles aggregation and growth as well as crystallization mechanisms are not so evident. In this work microstructural evolution under sintering in metal-matrix composite TiB2-Cu with high volume content (up to 57%) of titanium diboride nanoparticles 30-50 nm in size was investigated. The nanocomposite powders were produced through synthetic method combining preliminary mechanical treatment of initial powder mixtures in high-energy ball mill, self-propagating exothermic reaction and subsequent mechanical treatment of the product. We focused on microstructure changes in TiB2-Cu nanocomposite consolidated by Spark-Plasma Sintering and conventional sintering and showed that in the former case fine-grained skeleton of titanium diboride is formed with connectivity between particles well established. In the latter case behavior of nanoparticles is surprising: at low temperatures fiber-like structures are formed while increasing temperature causes appearance of faceted crystals. These unusual results allow us to propose the direct involvement of nanoparticles in the processes of crystallization by moving as a whole in the matrix.

In-situ Synthesis of Cu-TiB 2 Nanocomposite by MA/SPS

Nano-sized was in situ synthesized in copper matrix through self-propagating high temperature synthesis (SHS) with high-energy ball milled Ti-B-Cu elemental mixtures as powder precursors. The size of particles in the product of SHS reaction decreases with time of preliminary mechanical treatment ranging from 1 in untreated mixture to 0.1 in mixtures milled for 3 min. Subsequent mechanical treatment of the product of SHS reaction allowed the particles to be reduced down to 30-50 nm. Microstructural change of -Cu nanocomposite during spark plasma sintering (SPS) was also investigated. Under simultaneous action of pressure, temperature and electric current, titanium diboride nanoparticles distributed in copper matrix move, agglomerate and form a interpenetrating phase composite with a fine-grained skeleton.

Surface modification of synthetic diamond with tungsten

In the present study, tungsten-containing coatings on diamond particles were obtained by chemical vapor deposition using tungsten carbonyl as a precursor. It was found that tungsten reacts with diamond, which results in the formation of tungsten carbide WC crystallizing along certain crystallographic directions of the diamond crystal. Morphological studies of the coated diamonds have shown that the {111} facets of diamond are more reactive than the {100} facets.

Structural and mechanical characterization of detonation coatings formed by reaction products of titanium with components of the spraying atmosphere

Structural characterization of detonation deposits formed by reaction products of titanium with the components of the spraying atmosphere showed that ceramic-based coatings of unique microstructures—consisting of alternating layers of different compositions—can be formed. For the first time, mechanical characteristics of the coatings formed by reaction-accompanied detonation spraying of titanium were evaluated. It was found that high-yield transformation of titanium into oxides and nitrides during spraying can result in the formation of coatings with high fracture resistance and interface fracture toughness. The hardness of the coatings measured along the cross-section of the specimens was higher than that on the surface of the coatings, which indicated mechanical anisotropy of the deposited material. In terms of mechanical properties, coatings formed by the reaction products appear to be more attractive than those specially treated to preserve metallic titanium.

SPARK PLASMA SINTERING OF Cu-TiB 2 NANOCOMPOSITE

The microstructural evolution during sintering of a Cu-TiB 2 composite having a high volume content (up to 57%) of titanium diboride nanoparticles was investigated. The nanocomposite powders were produced by a synthetic method combining the mechanical treatment in a high-energy ball mill and a self-propagating exothermic reaction. The fine-grained skeleton of titanium diboride is formed with connectivity between particles well established during spark plasma sintering of Cu-TiB 2 nanocomposite. This interpenetrating phase composite of the Cu-TiB 2 system was produced under simultaneous action of pressure, temperature, and electrical current. Titanium diboride nanoparticles distributed in copper matrix agglomerate and form a fine-grained skeleton.