Papers by Author: Dana Salomie

Abstract: The objective of this study is to improve the sintering of W powder through increasing the density of the crystalline structure imperfections. The powder of W was processed by short processes of mechanical milling in a high energy planetary mill. The paper presents the influence of mechanical milling process duration upon the modifications of the structural characteristics of W powder. The fine structure has been studied by using X-ray diffraction.

Abstract: FeTi has one of the highest hydrogen volume storage capacity and its hydride - very favourable absorption/desorption conditions and a high reversibility. However, for applications its low hydrogen mass storage capacity (HMSC) has to be improved. The authors of this paper supposed this would be possible by Al and Ni additions and by a nanocrystalline state. However, FeTi synthesis and alloying with Al and Ni is difficult in a Fe-Ti-Al-Ni system due to the undesired secondary compounds formation. The presented researches proved the possibility of this impediment overcoming and of NiTi-Al-Ni alloy obtaining in a nanocrystalline state, from a mixture of elemental powders of components, by mechano-synthesis carried out in a planetary ball mill, for 24 h, in Ar atmosphere. The obtained alloy proved to have a HMSC of ~3.5 % at 50 0C and 1.5 atm, higher than of FeTi, its dehydrogenation occurring at the same temperature and 1.0 atm.

Abstract: Nb additions to NiTi smart alloys are known to lead to the PTT-hysteresis broadening and transformation temperatures raising – required in numerous applications. As Nb has a high affinity for oxygen, NiTi-Nb alloys processing by powder metallurgy, via SHS, from elemental Ni-Ti-Nb powder mixtures, seems to be more advantageous and cost-effective than by classical one. However, its application encounters difficulties determined by the NiTi higher Gibbs Free Energy of Formation than of Ni3Ti and NiTi2, possible Ni-Nb compounds formation, Nb acting as diluent in SHS. This research proved the possibility to overcome these difficulties and of NiTi-Nb alloys obtaining by SHS using energetically activated powder mixture by controlled Mechanical Alloying. Also, it was proved the possibility to reduce Nb content from the common one of 9 at.% to 5 at.% without a significant effect of transformation temperatures and hysteresis decreasing.

Abstract: The goal of present work was to study the possibility to produce bars from heavy alloys based tungsten through rotary forging. For the experiment there were selected two compositions from the system W-Ni-Fe (90, respectively 93 %W/wt., Ni/Fe ratio = 7/3). From the two compositions there were prepared samples by conventional route of liquid phase sintering, followed by thermal treatment in a neutral atmosphere (N2, Ar) and by rotary forging with different reduction degree.

Abstract: The main objective of this study is to find out a simple method to ensure a good dispersion of Al2O3 in the Cu matrix. The method should avoid the segregation effect due to the high difference of the densities of Cu (8.93 g/cm3) and Al2O3 (3.96 g/cm3). In the process of obtaining of the Cu-Al2O3 composite we have considered starting with a material whose density is closer to the density of Al2O3. We have chosen CuO whose density is about 6 g/cm3 so the composite material was obtained starting with copper oxide and alumina powder. We have studied the influence of Al2O3 content and of the compacting pressure upon material’s compactness and hardness. The dispersion finer is highlighted by the microstructure of the surfaces.