Papers by Author: Nicoleta Lupu

Abstract: Titanium has excellent mechanical properties, low density, high chemical stability, good heat transfer properties and a good corrosion resistance. In recent years, a new process technology is emerging by which titanium and titanium alloys can be made by sintering titanium hydride (TiH₂) and its mixture with alloying elements. The feasibility of this manufacturing approach has been fully demonstrated from powder to sintering and from microstructure to mechanical properties. This paper describes a study concerning Powder Metallurgy (PM) technology processing of Ti by conventional PM and non-conventional PM method such as Spark Plasma Sintering (SPS) route. The influence of the technological parameters on the micro-hardness and SEM microstructures during bulk titanium materials processing has been studied. The STATISTICA program has been used to monitor the influence of the technological parameters on the micro-hardness of bulk titanium processed products. The tribological behaviour of the bulk titanium materials on the basis of the coefficient of friction and wear rate is presented, too.

Abstract: Thermal processing of materials in external magnetic field is employed in order to produce a controllable uniaxial anisotropy and to tailor a domain structure in the series of soft magnetic FeCo-and FeNi-based amorphous/nanocrystalline alloys. Examples of our recent work on the utilization of both longitudinal and transverse magnetic field annealing for tuning the shape of hysteresis loops as well as the giant magnetoimpedance (GMI) characteristics are briefly presented. The beneficial effects of a heat treatment under magnetic field are discussed in terms of the improved application-oriented properties of these soft magnetic alloys.

Abstract: The objective of this research is the development of a detailed structural analysis of biocomposites with ceramic matrix of hydroxyapatite (Hap) reinforced by titanium (Ti), elaborated by powder metallurgy technology. Nanometric Hap powders (<200nm) 75% wt and micrometric Ti powders (<150μm) are homogenized in a high energy ball mill Pulverisette 6. Spark plasma sintering (SPS) is the sintering route able to lead to nanostructured sintered samples when nanopowders are used as raw material. The SPS parameters are: the sintering temperature, T=(1000-1100)°C and the maintaining time, t=(10-20) minutes in vacuum. The influence of the sintering parameters on the composites structures is monitored using the optical microscopy (OM), electronic microscopy (SEM) and the X-Ray diffraction (XRD).

Abstract: Nanocomposite NdFeB/αFe magnets were obtained by spark plasma sintering technique using high energy ball-milled Nd-Fe-B melt-spun ribbons mixed in different weight ratios with Fe commercial powders. The remanence of SPS nanocomposite magnets increases with the Fe powders content from 6.1 for 4 wt.% Fe to 6.4 kG for 5 wt.% Fe, while the estimated maximum energy product is also increased from 9.0 to 10.6 MGOe.