Papers by Author: Gigel Neagu

Abstract: The paper is a synthesis of essential data regarding the wetting conditions in aluminium – silicon carbide mixtures. Non wetting conditions between the reinforcing element and the matrix turns difficult the incorporation of particles in the aluminium melt. The wettability depends on several elements, like the presence of the oxide layer at the melt surface, temperature, pressure or shape of the complementary material. To improve wetting conditions, several measures are necessary: alloying of the melt with surface active elements, overheating of the melt; coating of the particles with a metallic thin layer. Also, by using existing data reported in the field, some parameters were calculated and interpreted.

Abstract: The mechanical and physical properties of metallic composites with aluminium matrix and alumina particles as complementary material have made them a good candidate for automotive, aerospace and many other applications. Some calculus regarding main aspect of wetting conditions between aluminium and alumina are made by using special literature information. Also, some improvement techniques of wetting conditions are described.

Abstract: Abstract. The paper presents some theoretical and experimental data regarding the directional solidification, revealing the main factors (especially those which are related to the heat transfer process) which have influence on the crystals size and morphology. The crystalline structure of alloys is determined by three important factors: chemical composition, thermal conditions, and characteristics of germination and growth from liquid of solid nuclei. The solidification structure can be influenced by acting on the mould properties or directly on the cast material, both of these actions being based upon the change of temperature distribution in the alloy-mould system. Experimental data demonstrated the major influence of the thermal regime on the crystallization-solidification process, on the transcrystallization zone and they pointed out the limits to direct the crystals formation (size and shape) by changing the cooling regime.

Abstract: The paper presents some aspects concerning the use of infrared thermography (IRT) in the evaluation of composite pipes integrity. Composite pipelines made up of glass fibres reinforced epoxy resins are increasingly used, especially in oil and gas industry, for their good mechanical properties, combined with reduced weight and excellent behaviour under hostile environment conditions. Taking into account that high reliability is required for such pipe networks, it is mandatory to choose reliable non-destructive inspection (NDI) methods to achieve efficient structural health monitoring. The main advantages of the IRT inspection are: non-contact and non-dangerous examination. In order to characterize the integrity of composites pipes, first of all the researches were interested in obtaining a set of reference images and then to examine the samples before and after the impact stress test. The conclusions point out the schemes and the optimal parameters of evaluation as well as the application limits of thermographic inspection

Abstract: The paper presents the principal aspects regarding the obtaining of the mixture aluminium - silicon carbide particles. It is discussed about the wetting conditions and the critical acceleration necessary for the incorporation of particles into the melt. The high values obtained for this parameter involve applying some methods to improve the wettability: the covering of the complementary material with a thin layer of Ni, the alloying of the aluminium melt, the overheating of the metallic bath and the heat treatment of the silicon carbide particles. Also, the mechanical stirring conditions necessary to realize the mixture are presented. The settling process of the silicon carbide particles in the melt as a function of particles size, shape and volumetric concentration is also analysed. The presence of complementary material leads to the growth of the mixture viscosity. Therefore, the liquid alloy was investigated like a continuous medium in connection with the apparent viscosity. The main aspects regarding the solidification of metallic composites processed by casting method based upon theoretical concepts, general knowledge about casting of composites and experimental data are discussed. Finally, the specific defects caused by an insufficiently controlled solidification process and prevention measures are shown.