A. D. Panasyuk

Protective coatings for SiC fibers in contact with nickel alloys

Conclusions1.SiC vigorously reacts with Ni-Cr base alloys and cannot be used in direct contact with them.2.TiN and Al2O3 coatings applied to SiC fibers are compatible with Ni-Cr base alloy matrices and may be utilized for barrier protection in the formulation of composite materials.3.Si3N4 and BNC coatings react with Ni-Cr base alloys and are therefore unsuitable for operation at high temperatures.

Electron-microprobe investigations of interfacial reactions in systems composed of a refractory compound and a liquid metal

Conclusions1.A study was made, by the technique of electron probe microanalysis, of the character of the reaction in the system ZrB2-Ni. It is shown that zirconium diboride has a limited solubility (of the order of 0.6 wt. %) for nickel and that zirconium diboride, too, is soluble in a drop of nickel.2.The effects were investigated of the thickness and composition of the surface oxide film on ZrB2 upon the character of the reaction in the system and the dissolution kinetics of the solid and liquid phase components. It was found that thick oxide films, having a defective structure, accelerate the diffusion of nickel into the boride phase.3.The distribution of nickel in the diffusion zone was examined, and the limits of solubility of the metal in zirconium diboride were determined.

Electron-microprobe investigations of interfacial reactions in systems composed of a refractory compound and a liquid metal: 3. Effects of carbon on the contact reaction in the system ZrC-Ni

Conclusions1.A study was made, by the technique of electron-probe microanalysis, of the character of the reaction in the system ZrC-Ni. It is shown that the solubility of nickel in zirconium carbide amounts to 2.5-2 wt.%.2.The effects were investigated of the addition of carbon (from 0 to 7 wt.%) to nickel upon the dissolution of the latter in zirconium carbide. It was found that carbon inhibits the penetration of nickel into the carbide and reduces the depth of the resultant diffusion zone.3.The phase composition of the metal drop after its reaction with zirconium carbide was determined. It is demonstrated that the reaction leads to the formation of a nickel-base solid solution, a carbide eutectic, and the intermetallic compound ZrNi5.4.A study of the distribution of nickel in zirconium carbide grains established that the variation in nickel concentration between the boundary of a grain and its core obeys a parabolic law.

The effect of the special characteristics of the electronic structure of elements on their surface properties

An explanation of the surface properties of the elements, from the point of view of the electronic structure of their atoms was advanced in [10-14]. The authors of [12], in their evaluation of data on surface tension, used the dependence of cr on the position of the elements in the periodic table. Here, they observed a certain regularity in the laws governing the surface properties of the elements, depending on their atomic number, but did not propose any explanation of the laws obtained. In the present paper an attempt is also made to correlate the data on the surface tension of the elements in the liquid state and to propose an explanation, taking into account the special characteristics of the electronic structure of their atoms. Use has been made of the most reliable data on the surface tension of liquid metals, taken from [13-28] (Table i). Figure I shows the dependence of the surface tension of the elements on their atomic number. Starting from the rules presented with respect to the surface properties (Fig. i), all the elements of the periodic system can be arbitrarily divided into 6 series, of which 2 are small, 3 are large, and one series comprises the lanthanides~ For the small series, comprising the elements of periods I/and III of the periodic system, identical rules for the changes in the surface tension are characteristic: With an increase in the atomic number the surface tension increases, while, from the middle of the periods (B, Si) there is observed a decrease. The 3 large series comprise the elements of the IV, V, and VI periods of the Mendeleev system. For them there is characteristic an almost identical law governing the dependence of the surface tension on the atomic number. With an increase in the atomic number, the surface tension of the elements increases, right up to the elements of the VI group, Cr, Mo, W, which form exceptions to the general rule. Starting with the elements of the VII-VIII groups, the surface tension decreases with an increase in the atomic number, reaching minimum values for the elements standing at the end of the period. Institute of Materials Science, Academy of Sciences of the Ukrainian SSR. Translated from Poroshkov