Advanced Materials Research Vol. 1128

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: The paper focuses on the mechanical characterization of porous biocomposites based on hydroxyapatite submicronic powders (< 200 nm), respectively micronic powders particle (30-50 μm) as matrix, reinforced by titanium hybrid powders (15 and 20% mass; 100-150 μm) as foaming agent. Another foaming agent used is calcium bicarbonate powder (5 and 10% mass). The mixture homogenization was made in a Frisch-Pulverisette 6 type planetary mill (n=200 rpm), for 30 minutes. The green compacts were processed by unilateral cold compaction at 150 MPa. The two-step sintering technology (TSS) has been applied to the green parts, on the Nabertherm conventional furnace: at 900°C for few minutes (first step) and at 800°C for 450 minutes, respectively 600 minutes (the second step). The mechanical characteristics (compression modulus G [MPa] and ultimate compression strength σ_UTS [MPa]), were studied using the universal mechanical testing machine INSTRON 3382 and compared with the mechanical characterization of the human bone.

Abstract: Thermal conductivity of composites is anisotropic in nature and data about thermal conductivity of resin facilitates to reduce stresses related to shrinkage of composites during cure and mismatch in thermal expansion coefficients. Before conducting experiments to determine thermal conductivity of various composites, knowledge about effect of different parameters influencing thermal conductivity is essential. The increasing use of composites, for various applications, emphasizes its importance/significance in the thermal property analysis of an engineering system. Published literature is rich with investigations of mechanical properties of composites, but fewer publications are focused on thermal properties. Several publications addressing different theoretical approaches for predicting thermal conductivity of composite materials have been noted. Various theoretical approaches are used to yield the thermal conductivity of a composite material so that the heat flow in anisotropic composite material in any direction can be estimated. In this paper few models will be considered and a theoretical study on thermal conductivity uncertainties will be conducted and discussed. The results identified the need and importance of carrying out further investigations on thermal behavior of composites materials.

Abstract: This paper presents a comparative analysis of the foaming process developed in hydroxyapatite (HAp)-based bicomposites as a function of the foaming agent. The matrix of the biocomposite consists of either submicronic or micronic powder particles of HAp. The titanium hydride powder was added as reinforcement’s precursor as well as blowing agent, and in order to increase the biocomposites’ porosity calcium carbonate was added as space holder agent. The powders mixture was homogenized in a planetary ball mill with a single grinding bowl for 1 minute in air. Uniaxial cold compaction at 120-170 MPa was performed in order to obtain cylindrical green parts, which next were heated in argon atmosphere using the two step sintering technique at temperatures of 900 °C for 1 minute and 800°C for 450 - 600 minutes. The porosity of the biocomposite is analysed through calculations and SEM and EDS analysis highlighting the influence of the above mentioned foaming techniques (blowing and space holder).

Abstract: Based on the requirements of achieving lightweight components and mechanical performance, the paper aims to present the structure of technology for use fiber reinforced plastics, especially plastics reinforced with carbon fiber wrap winding space technology and additional tests results for steering column console.

Abstract: The vertical welding is generally considered difficult because of the danger of the flow of the melting bath and the melted slag under the action of gravity. In the case of the MIG/MAG welding process, the technological measurements that are being regarded in the ascending and descending of the vertical welding refer to: the use of transfer modes through short circuit and pulsed current, the use of core wires instead of solid wires, the crossing from the semi-mechanized to automatic or robotical welding, that allows the use of complex radial oscillation systems, that assure a good control of the metal bath. The paper wants to make a comparative technological and economical analysis between the vertical ascendent MAG welding using solid wire or core wire. The advantages that are being presented are for the use of the core wire with a rutilic core for the vertical, ascendent welding from a technological, qualitative and economical point of view in the mechanical corner welding process of a 10 mm thickness steel plates.

Abstract: Welding in pulsed current is specific to welding procedures carried out in MIG / MAG and WIG shielding gases environment, and which is appealling from both technological and process quality points of view because of the advantages this procedure provides, especially controlling the transfer mode and the power introduced into components. Making use of pulsed current in manual welding with coated electrodes is a new challenge to modern inverter based sources with potential technological advantages. In this case the advantage of pulsed current is linked to controlling the molten metal bath, its volume as a result of partial solidification, similar to the manual WIG welding using low frequency pulsed current < 5 Hz. The paper presents some technological issues related to the use of pulsed current in the case of manual welding with coated electrodes by arc oscillograpy. Experimental research aimed at recording the shapes of current pulses for different brands of electrodes and diameters, and for different parameters of welding current, different levels of pulses frequency respectively, and the oscillograms analysis through the variation of welding current and arc voltage in order to explain phenomena occurring in the arc when welding. This will allow also a better understanding of the technological issues in the case of manual welding with coated electrode in pulsed current.

Abstract: The paper presents results of the researches conducted upon the use of the arc-air gouging process with coated electrodes, in comparison with the plasma gouging process, in case of the welded structures. The paper aims at submitting the arc-air gouging technologies with electrodes and the plasma gouging technologies. The research consists in gouging a structural steel, of the quality S275JR and in comparing the surfaces obtained by the enumerated processes. The obtained samples will be analyzed in terms of microstructure, macrostructure, hardness of the thermally influenced area, hardness of the gouged area.The gouging process is based on melting the raw material, with an electric arc achieved between an electrode and the raw material; and on removing the melt material with a compressed-air jet, in the case of the arc-air gouging and plasma gouging. The gouging with coated electrode is different, given that it requires special electrodes, with thick flux cover, in order to generate an electric arc and a strong gas flux. During the gouging process, the raw material will be oxidized; yet, this does not influence the process. The gouging process can be either manual or automated. In this paper, the manual variant will be submitted, in the case of the arc-air gouging technology and the gouging with coated electrodes; in the case of the plasma gouging, both variants will be submitted.

Abstract: The paper presents research made in order to assure additional conditions, compared to those in the general standard, to brazing rods, in order to guarantee safety for the environment and for the brazed joints, against corrosion and embrittlement, in high risk conditions. Environmental safety is ensured by limiting the amount, at 0.25% in depositions, of dangerous residual elements at: Cd<0.1%; Hg<0.1%; Pb<0.1%; Cr<0.1%; As<0.1%. The safety of structures against corrosion is provided by the alloying level of deposits and by neutralizing the coat’s activity. The structure safety towards the embrittlement of brazed joints is ensured by limiting the content of embrittling elements, namely: Sb+Fe+Bi at a maximum of 0.3% and the content of diffusible hydrogen at maximum 5 cm³/100g raw material and by limiting the coat humidity at maximum 10%. The experiments were performed to ensure the set out requirements by following the selection of raw materials on the input criteria of prohibited chemicals, reducing the water content from the elements that make up the coat and by diminishing it’s hygroscopicity by neutralizing it. Prescribing additional conditions has an effect on manufacturing costs, which requires productivity increase at brazing, diminishing work temperature, increasing the moistening capacity of products, reducing the smoke level, effects pursued by the research.