Papers by Author: Delia Patroi

Abstract: Directional solidification techniques have been applied to produce Ni based intermetallic alloys with preferentially oriented columnar crystals extended along the complete length and parallel to the solidification direction. Enhanced ductility is expected from such alloys. In this paper we present the research results concerning the application of this technique to some complex Ni3Al- Fe-B alloys obtained from compacted mixtures of elemental powders. The corresponding master alloys have been obtained in a vacuum induction furnace by the known Exo-Melt process [1]. The directional solidification of these alloys was subsequently performed on cylindrical samples, at two solidification rates, 30 and 15 mm/h. The influence of the rate and composition used on the dimensional variations, densities, microstructure, constituent phases and lattice parameters, as well as on the surface chemical composition have been documented and are presented in the paper.

Abstract: The paper presents some considerations concerning the obtaining and characterisation of some new electrical contact pieces of Ag-SnO2-MeO type, where the MeO is an additive chose from the series of metallic oxides WO3, Bi2O3 and CuO. These have a SnO2 content of 9.5 wt. %, a MeO content of 0.5 wt. %, the balance being Ag. The electrical contact materials were manufactured by powder metallurgy techniques using a new type of powder mixtures obtained from SnO2 and MeO powders which were wet mixed, simultaneously with “in situ” Ag synthesis. These present a very uniform and fine dispersion, which in turn leads to improved functional characteristics of the final electrical contact pieces in comparison to the dry mechanical powders mixtures. The new products were designed for low voltage power engineering switching devices working in air at In = 40, 125 and 200 A.

Abstract: Research results focussed on the combined influence of iron and boron, in proportions of 0.5 and up to 10 wt.% respectively, in complex alloyed Ni3Al synthesised by Self Propagating High Temperature Synthesis (SHS) in the thermo-explosion mode at two ignition temperatures, 950 and 1150 oC, are presented. By XRD and Mössbauer spectroscopy it was established that for 950 oC ignition temperature, the evolved heat is not high enough for the added Fe to be fully incorporated into the synthesised Ni3Al phase, a temperature of 1150 oC being required. For this temperature, the density of the synthesised alloys, their capacity to be cold deformed by re-pressing, hardness and bending strength variations as a function of B and Fe contents, proved their cumulative effects of the ductility and mechanical properties of complex alloyed Ni3Al enhancing.