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The basic properties of the intermetallic compound LaNi4AI intended for storing hydrogen were investigated in [i]. When nickel in the intermetallic compound LaNis is partially replaced by aluminum, the equilibrium pressure of hydrogen in the system LaNi4AI-H 2 becomes much lower without a substantial reduction of the capacity; this compound can therefore be used in flooding systems with exactly stipulated pressure level at ordinary temperatures. Since the intermetallic compound and its hydride are highly active substances, even a low level of impurity concentration affects activity in regard to hydrogen and the speed of the reaction of hydrogenation. The most active deactivator of intermetallic hydrogen accumulators is oxygen which can be obtained from the surrounding air. The aim of the present work is therefore to study how the storing of powder in air affects the state of the surface of its particles, and consequently the change of operational characteristics, in particular the level of equilibrium pressure of the system LaNi4AI-H2, the hydrogen capacity, and the speed of the processes of sorption and desorption. An ingot of the material which according to chemical analysis had the composition Lal.0sNi~.9~Al0.s3 (0.006% oxygen content) was crushed and separated into three fractions: -40 Dm, 40-80 Dm, and 80-100 Dm. In half the freshly crushed powders we immediately investigated the sorptive properties, the other half of each batch of powders was held in air in a dry medium for 6-7 months, and then their hydrogen-sorption properties were investigated in an analogous way with the use of a Sieverts-type standard installation. The hydrogen pressure in the reaction space was measured with a mercury manometer and with a manometer valve LT-4. The batches of investigated material weighed at least i0 g, the accuracy of measurement of the hydrogen content was !0.013 cm 3. The temperature of the reaction vessel was measured with a Pt-Pt/Rh thermocouple and maintained constant with the aid of an electronic potentiometer ~PD-52. X-ray phase analysis was carried out on a diffractometer DRON-3M in Cu radiation. The change of morphology and composition of the surface of the particles was investigated by methods of scanning electron microscopy and Auger microanalysis. Although the weight of the powdered LaNi4AI powders during storage in air remained constant (accuracy of measurement !0.004 g), their sorptive properties underwent noticeable changes. The position of the isothermal lines of the disposition of the hydrides LaNi4AIH x for powders with different degree of fineness, freshly crushed or kept in air, is being compared in Fig. i. It shows the starting points of the isothermal lines of desorption ascertained on maximally saturated materials. The hydrogen capacity of freshly obtained powders is almost the same (curves 1-3), the hydrogen capacity of materials kept in air differs greatly: fairly fine powders lose the ability of becoming fully saturated with hydrogen (curve 4), the hydrogen capacity of coarse powders greatly increases (curve 6), and of powders with particle size 40-80 ~m it remains almost unchanged. Thus the air has an unequal effect on the sorptive properties of powders with different fineness. The

Alloying nickel with chrome, aluminum, and boron, as well as the variation of the spraying conditions makes it possible to control purposefully the composition, structure, and properties of the detonation coatings. In alloying nickel with aluminum and chrome, the strength properties of the coatings are fully utilized at thicknesses not greater than 0.25 mm. The adhesion strength of these coatings to the titanium substrates is 35–150 MPa, to steel substrates 20–120 MPa, in the thickness range 0.1–0.3 mm. The ductility properties of the coating are utilized only to 40–60% in comparison with the dense material of the same composition. The ductility of the coatings is reduced most markedly by additions of aluminum and boron, whereas the addition of chrome causes the smallest reduction.

The technological conditions of obtaining powder materials exert a decisive influence on the course of the processes of concrescence, and consequently on the properties of the obtained specimens. If cooling and oxidation in the transfer of compacts from the furnace to the forging die are reduced to a minimum, then the optimal medium for sintering and hot repressing is a reducing medium, e.g., sharply dried hydrogen or DA. The accompanying removal of admixtures from the surfaces of open pores facilitates the processes of concrescence.

The quality of concrescence is a factor determining the properties of powder material. High-quality concrescence of particles is promoted by shear strains, both at the stage of SCP and of HF. The highest indicates K1C are encountered in sintered and hotforged materials from reduced powder PZh2M3 with ramified shape of the particles.

6. V. G. Zil'berberg, A. I. Strogonov, et al., "Application of gas-thermal coatings at superhigh speeds," Poroshk. Metall., No. I, 28-31 (1989). V. M. Kaptsevich, V. K. Sheleg, A. N. Sorokina et al., "Comparison of the results of measurements of porosity by different methods," Poroshk. Metall., No. 2, 48-52 (1989). Yu. A. Guslienko, R. M. Medyukh, T: N. Tikhonovich, et al., "Structsre, and wear resistance of composite molybdenum base galvanoplasma coatings," Poroshk. Metall., No. i, 31-34 (1989).