Vol 38, No 4 (2016)

A composite material consisting of particles of master phase and binder has been considered. Particles of active phase, whose components chemically interact with components of master phase particles forming a new phase, has been introduced into the material. The thermodynamic functions describing the processes of the dissolution of master and active phases in binder phase, chemical interaction of the phases components, and formation of a new phase have been defined and the prerequisites to occurring these processes are discussed.

AlN–SiC–Y₃Al₅O₁₂ composite materials with a high absorption of microwave frequency (27–65 dB/cm) produced by pressureless sintering of mixtures consisting of AlN(2H), Y₂O₃, and SiC (6H) in 46, 4, 50 wt %, respectively, have been studied. The SiC components of the mixtures were used in sizes of 1, 5, and 50 μm. It has been shown that the resistivity of the developed materials depends essentially on the materials structures: sizes of SiC inclusions, distances between them, and state of the interfaces. It has been found that the increase of the SiC inclusions sizes in the material structure from 3 to 7 μm results in the decrease of the resistivity from 10⁴ to 90 Ω·m, and at the decrease of the SiC inclusions sizes from 3 to 0.5 μm there forms a SiC uninterrupted skeleton, which also decreases the resistivity to 210 Ω·m. Thus, composite materials that contain 50 wt % SiC (inclusions sizes of 3 μm) are the most efficient in producing absorbers of microwave radiation. Interlayers of yttrium aluminum garnet, which are located at the SiC grains boundaries, prevent the forming of AlN(2H)–SiC(6H) solid solutions and thus, make it possible to keep high dielectric characteristics of a composite material based on aluminum nitride and afford a high absorption of a microwave radiation.

The effects of N₂ partial pressure in the unbalanced magnetron sputtering process on the microstructure, hardness, and thermal stability of the CrZrSiN nanocomposite coating were investigated. A typical nanocomposite structure, composed of a crystalline phase and an amorphous phase was obtained and the distribution of these phases changed with increasing N₂ partial pressure. The N_1s spectra revealed the presence of two-peak characteristic of nitrogen in the CrZrN and SiN_x phases, and the ratio of the peak’s SiN_x to CrZrN intensity increased with increasing N₂ partial pressure, indicating an increase in the amorphous phase in the nanocomposite microstructure. As N₂ partial pressure increased, the CrZrSiN coating hardness decreased from 38 to 30 GPa due to the increasing amount of the SiN_x amorphous phase. After the thermal stability test, the hardness values of the CrZrSiN coatings were maintained at approximately 30 GPa up to 800°C, but the hardness decreased rapidly to 18 GPa after annealing at 900°C. This drastic change of hardness over 900C was due to the formation of a Cr₂O₃ phase in the CrZrSiN coating.

The authors put forward a procedure of determination of strain tensor components through the analysis of distribution of intensity of back-scattered electrons in Kikuchi patterns. The strain state has been studied in local areas of a synthetic diamond crystal produced by the temperature gradient method in the Fe–Al–C system through growing onto a diamond single crystal synthesized in the Ni–Mn–C system. Characteristic surfaces of the strain tensors and strain ellipsoids have been plotted; special features of strain distribution in the crystal have been analyzed. Diagonal tensor components have been determined from the changes of distributions of intensity of individual bands, the other components have been found from the displacements of axes of zones relative to their positions in the standard Kikuchi pattern.