Materials and Technologies

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Authors: Vasile Rus, Gavril Negrea, George Arghir, Nicolae Jumate
Abstract: The experimental researches was made on X3CrNiMo17-13-3 stainless steel samples ion nitrided at different temperatures, duration and work atmospheres. The analysis of superficial layers was made in order to identify the microstructure of the ion nitrided layer using X-ray diffraction, and also the determination of the superficial hardness and hardness gradient. The nitrided samples were subjected to two thermal shock regimes, one in the range of 500-20°C and the other in the range 600-20°C. The crack and crack networks initiation process as a result of thermal fatigue was analyzed quantitatively and qualitatively using optical microscopy. The study of the cracking process highlighted the fact that thermal shock resistance is influenced by the characteristics of the superficial layer and also by the maximum temperature of the thermal stress cycle.
Authors: Radu L. Orban, Mariana Lucaci, Mario Rosso, Marco Actis Grande
Abstract: There are investigated the possibilities to avoid or at least to reduce the Al2O3 scales formation on NiAl powder particles at its plasma spray deposition on steel substrates. The optimum processing parameters and the necessity to surround the plasma jet by an inert gas have been established. In appropriate processing conditions, the obtained coating layer is formed by flattened particles, welded together and to the substrate, proving their melting during spraying. It is dense and adherent, consisting of NiAl with only small Al2O3 inclusions, proving the NiAl stability preserving without decomposition or a notable oxidation, as premises of its desired functionality achievement.
Authors: Andrea Meneghini, Luca Tomesani
Abstract: The influence of the effective metal head height on the HTC (Heat transfer coefficients) in sand casting of A357 aluminum alloy is analyzed here. Different metal heads were used for the same casting process, evaluating the heat transfer at the metal-chill interface. Thermal analysis and inverse modeling techniques were used, based on the temperature measurements at selected locations in the casting and the chill. The experiments were specifically developed for replicating typical sand casting manufacturing conditions. Aluminum was used as the chill material. Evolutions of HTC and heat flow are reported as a function of time, casting temperature, chill temperature and variation in temperature between casting and chill.
Authors: Mariana Lucaci, Radu L. Orban, M. Lazarescu, Stefania Gavriliu, Magdalena Lungu, 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.
Authors: Iulian Riposan, Mihai Chisamera, Stelian Stan, P. Toboc
Abstract: In laboratory experiments Thermal Analysis data were recorded and different solidification parameters were identified to characterize the inoculation effect of the carbon materials (amorphous and crystalline structure) in low sulphur (<0.025 %S) grey cast iron. These parameters are linked to graphite morphology as well as chill formation in carburized cast irons. In low sulphur base iron the difference in inoculation efficiency between crystalline and amorphous carbon materials is limited. Secondary granular carbon materials, previously used as conductive or resistive media in electric graphitizing furnaces were found to be potential carbon raisers with visible inoculation effects in grey irons, especially those from a petroleum coke origin. A controlled presence of a low amount of SiC (2-3%) is effective, including low sulphur grey irons.
Authors: Mohammad M. Haque, Ahsan Ali Khan
Abstract: Aluminium-silicon alloys have low density, high electrical and thermal conductivity and high resistance to corrosion at ambient temperature. However, these alloys usually contain numerous alloying and impurity elements, which consist essentially of a fairly ductile matrix of alpha aluminium solid solution with a variety of non-ductile particles of silicon and various intermetallic compounds. The shape and distribution of these constituents largely control the deformation behaviour of the alloy. The addition of magnesium makes the alloys lighter and harder, but its hardening effect is fully responsive only after proper heat treatment. Therefore, in the present study, microstructures and properties of the alloys have been evaluated on the as-cast and heattreated conditions. Results show that the addition of magnesium to aluminium-silicon eutectic base alloy refines microstructure up to certain level and increases the strength and hardness at the expense of ductility.
Authors: Petru Moldovan, Gabriela Popescu, C.A. Popescu, Ioana Apostolescu, Aurelian Buzaianu
Abstract: The paper’s aim is to present the processing of a new master alloy similar to STROBLOY. This alloy represents a combination of two master alloys, already known in aluminum industry (AlTiB and AlSr). The benefits of this new alloy are the cut of Ti, B and Sr consumption, as well as a grain refining/modification ecological technology for Al-Si and Al-Mg-Si alloys. So, this alloy was obtained from binary AlB8, AlSr10 and AlTi10 master alloys melted in an electric resistance furnace and argon atmosphere. Samples were cast in an iron mould. As STROBLOY, this new quaternary alloy contains fast dissolving SrAl4 particles important in modification stage, and nucleating particles such as TiB2 and (Al, Ti)B2 essential for grain refining of aluminum alloys.
Authors: Dan Porcar, Şerban Domşa, Nicolae Jumate, Iozefina Porcar
Abstract: The paper presents an experimental study regarding two Al-Si alloys concerning the influence of ultrasonic treatment on the hardness and microhardness. AlSi12 ultrasound treated function as time hardness important decreases are observed. AlSi7 ultrasound treated function as time hardness easily increases is observed. The contradiction between two measurements was studied by microhardness of AlSi7 grain and eutectic mass materials. Important microhardness decreasing on eutectic mass materials is observed.
Authors: Mihai Chisamera, Iulian Riposan, Stelian Stan, C.B. Albu, C. Brezeanu, Rod Naro
Abstract: Inoculation comparisons were made between Calcium-bearing FeSi75 and a new complex alloy tablet (CAT) inoculant to compare their effects on late inoculation. Thermal analysis was used to study the solidification behavior and how FeSi75 and the CAT inoculants affect graphite nucleation. Quick-cup addition rates for FeSi75 ranged from 0.1% to 0.3% while the CAT, was added in much smaller amounts, 0.01 to 0.03%. Thermal analysis of the base low sulphur iron (0.02 %S) was characterized by excessive eutectic undercooling. It was found that an addition of 0.03% of the CAT had inoculation efficiency comparable to 0.2% to 0.3% Ca-FeSi75 in reducing the level of undercooling, recalescence and the maximum recalescence rate. A greater negative peak of the first derivative at the end of solidification process, that would minimize micro-shrinkage tendencies, was also obtained.
Authors: Stelian Stan, Iulian Riposan, Mihai Chisamera, Michael Barstow
Abstract: Successful inoculation is not guaranteed and effects may even be deleterious. The main risks are the appearance of types B and D graphite, associated with ferrite and/or carbides due to lack of control of undercooling during eutectic solidification. Alternatively coarse type C graphite in hypo to eutectic grey irons may result from inadequate or excessive inoculation. Sulphur and aluminium content in a molten iron are considered to be the main factors to control the degree of eutectic undercooling, graphite morphology and inoculation efficiency. Thermal conditions, such as superheating, inoculation and pouring temperature play an important role in controlling these effects. Cooling rates due to different mould materials and casting thickness were also considered. In order to resolve individual problems, different inoculant systems have to be considered, such as Sr-FeSi, Ca-FeSi, Ti,Ca-FeSi, Zr,Ca-FeSi, Ba,Ca-FeSi, RE-FeSi (Ca). The present paper made a synthesis of other published papers by the authors, but also added many original un-published results.

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