Potecasu, O; Potecasu, F; Drugescu, E; Alexandru, P
The paper presents some materials hardened through dispersion with oxide-films, obtained through deformation from superficially oxidized lead powder. The materials hardened through dispersion with hard phases obtained through plastic deformation are advanced materials with mufti-usage in different fields. Fields like aviation, chemical industry, metallurgical industry, car industry, the industry that produces electrical energy mainly because of some specific functional properties (of usage) like: good creep behaviour, high resistance to corrosion, high resistance to weariness, stability at high temperatures, stability at corrosion through electrical spark etc on the one hand, and on the other because of a better mechanical resistance. The powder required for research was obtained in laboratory on an air jet spraying installation and as the powder particles resulted after the impact of the lead melting with the air jet, they are covered with a fine layer of oxides. In order to maintain the same thickness of the oxide layer that "covers" each particle, the parameters of elaborating the powder such as: the overcharging degree of melting, the spraying air pressure, the shape and size of the jets (air jet, the liquid metal jet, the common jet) were kept constant. The powder oxidation degree ranged indirectly by choosing granulometric fractions with the average diameter of the particles smaller and smaller, as it is known that the specific powder surface from the volume unit is rising if the powder is finer. The dispersion of the fine oxide films in metallic matrix was obtained as a result of extrusion with high degrees of deformation of the compressed compounds of superficially oxidized powder. This is because the particles that form the compressed compound have to pass through the matrix calibration zone, and therefore, it suffers a profound deformation. As an effect of this deformation, the films of fragile oxide that cover the particles of lead powder, are "smashed" and are carried away guided by the material that flows through the bottom die along the length of the extruded semi-product. As reference samples, samples of cast lead were deformed under the same conditions (thus unhardened with oxide films) and of Pb-Sb alloy (hardened by alloying with 8% Sb). The films of dispersed oxide in the extruded lead, determine the hardening of the metallic matrix, as they have a role of "barrier" against dislocations thus reducing their mobility. This leads to increased mechanical resistance, to a considerable increase of creep resistance, while maintaining a good electrical conductivity and having a good behaviour to the corrosion in acidic environment.