Papers by Author: Mircea Nicoară

Abstract: Experimental research in both medical sciences and material science rely in many situations on a reduced quantity of available data, due to limited number of patients or high costs of samples. Some statistical data manipulation methods are discussed regarding their applicability, information content, value and limits. A special attention is given to the extreme values eliminated by the GRUBBS test. The necessity of the elimination of the extreme values is demonstrated.

Abstract: A research program has been completed in order to analyze structural changes during heating of amorphous alloys belonging to Fe-Ni-P system. Special attention has been given to thermodynamics and mechanism of crystallization, to determine some aspects of development for crystalline phases. Experimental material used to determine characteristics of crystallization consisted in long ribbons, 30 thick and 18 mm wide, fabricated by mean of “Planar Flow casting” as amorphous Fe₄₂Ni₃₈P₁₆B₄ alloy. Differential Thermal Analysis (DTA) and X-rays diffraction have been used to determine crystallization temperature of this alloy. Curves of differential thermal analysis for heating rates ranging between 1°C/minute and 20 °C/minute have been used to determine activation energy of crystallization.

Abstract: Fabrication of aluminum matrix composites reinforced with ceramic particles via powder metallurgy techniques present considerable advantages, especially large flexibility of reinforcement volume content. However since metal particles are considerably larger than ceramic reinforcement, ceramic clustering become more and more frequent as the reinforcement proportion increases, and high ratio plastic deformations are mandatory. An experimental program has been developed to determine particle redistribution of ceramic reinforcement by mean of large-ratio extrusion of aluminum composites, containing up to 20% vol. of reinforcement. Evaluation of particle redistribution by extrusion has been determined using a computer-based technique of image analysis for resulting optical micrographies.The image processing has included particle detection, particle measurement and classification.

Abstract: Nickel–titanium- group 5A metal (V, Nb, Ta, Zr) alloys are known as promising hydrogen-selective membrane materials. They can potentially be used in membrane reactors, which can produce high-purity H₂ and CO₂ streams from coal-derived syngas at elevated temperatures. The master alloys were prepared by arc melting using high purity metals in a Ti-gettered argon atmosphere. The alloys were melted several times in order to improve homogeneity. The ingots were induction-melted under a high-purity argon atmosphere in a quartz tube and graphite crucible injected through a nozzle onto a Cu wheel to produce rapidly solidified amorphous ribbons. Thermal stability of the Ni40Ti40Nb20 and Ni32Ti48Nb20 thin tapes has been examined using DTA analysis.

Abstract: In this work, hollow spherical nickel based superalloy powders obtained by liquid phase atomization were used. The obtained powder was divided into six size particle ranges between 200 µm and 630 µm using a shatter box. Samples from all six ranges were obtained by spreading the powder into the sintering die and consolidating them by sintering at 900°C and 1000°C for 30 minutes in vacuum (10-4 Torr). The metallic foams obtained by sintering hollow particles presents high porosity, and can be used as thermal barriers, catalyst support, shock absorbers or lightweight structural elements.