Solid State Phenomena Vol. 216

Abstract: This work describes the fabrication and test of a high temperature (+200°C) capable high frequency transformer. It was manufactured using Low Temperature Co-fired Ceramic (LTCC) technology, which allowed the complex multilayer structure of ceramic and metal windings to be formed. However, the selected LTCC composition is a free sintering ceramic and there is an interaction between the metal conductor and the ceramic substrate during lamination and firing that can lead to significant deformation, presenting a significant engineering challenge. Here the fabrication process for the LTCC is described (screen printing, collation, lamination and firing) for a number of iterations of the transformer design, each of which was analysed for deformation and subjected to electrical tests. In addition a silicone adhesive for assembling the LTCC with the transformer was analysed for high-temperature performance. A test vehicle was assembled and it was subjected to 1000 hours at 210°C. Shear tests were performed at intervals to quantify the loss in bond strength over time. After a good solution for manufacture was found, a batch of transformers was produced, characterized and tested to demonstrate a high reproducibility and manufacturing yield.

Abstract: The paper presents the processing technology that could be used in order to obtain a new design of a stem component for a hip prosthesis type lattice beam. This new design was made based on the analysis of the currently successful stems used in clinical practice and on different biomechanical and biomaterials criteria. Metallic biomaterials used for manufacturing different components for hip prosthesis are usually austenitic stainless steel type 316L, Co-Cr alloy and titanium based alloy. In our study, considering the specific design of the stem, stainless steel type 316L with the nominal compositions (%weight): C <0.03, Cr 17, Ni 14.5, Mo 2.7, Mn <2.0, Si <1.0, P <0.025, S <0.010, Fe balance is used. Different mechanical processing techniques were used in order to obtain the experimental prototype. According to the well-known limitation of the stainless steel type 316L as biomaterial for long term implants, we propose for the new stem component to use a TiN coating obtained using magnetron sputtering technique. The cytotoxicity studies were performed using a CCl 81 (VERO) stabilized cellular line, in order to analyse the biocompatibility properties. The samples were examined for the development of the cellular culture, in order to compare the results obtained using direct contact method. From the point of view of these tests, it was not observed an essential modification of cells and the cellular morphology is not affected by the presence of the TiN coated metallic samples. In the conclusion, the new geometry proposed for a stem component of cemented hip prosthesis could be made using different mechanical processing techniques and appears to be a potential solution in order to solve the problems related to the stability of the total hip prosthesis, with improved biocompatibility properties due to the TiN coatings.

Abstract: A sum of mixed nickel-manganese ferrites, Ni_xMn_1-xFe₂O₄ (x=0, 0.3, 0.5, 0.7) were synthesized by classical ceramic route starting from stoichiometric mixtures of commercially MnO₂, NiO and Fe₂O₃. The polycrystalline ferrites obtained by ceramic route were subjected to the mechanical milling procedure in order to reduce the particles size and to refine de crystallites size. A planetary high energy ball mill Fritch Pulverisette 4 was used and the milling time was up to 120 minutes. The ceramic and as-milled ferrites samples were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and laser particles size analysis (LPSA). After 15 minutes of milling the mean crystallites size for each one of the nickel-manganese ferrites is in nanometric range. After 120 minutes of mechanical milling for all ferrites types the mean crystallites size is at 6-8 nm, depending on Ni/Mn ratio. According to the SEM and LPSA investigations the milled ferrites powders consists in nanometric particles alongside of the micrometric ones. The micrometric particles are formed by multiple nanocrystallites.

Abstract: Open cell foams from AlSi12 alloy were successfully fabricated by the Sintering and Dissolution Process, using NaCl as space holder (60 %). The size of the aluminum alloy powder is less than 45 μm, while the space holder powder size is 315-500 μm, 630-800 μm and 800-1250 μm respectively. The appropriate quantities of alloy powder and salt were mixed and cold pressed at 250 MPa. The sintering process was done at 500 °C and 545 °C, in vacuum (10^-5 torr) for 10, 20 and 30 minutes respectively. The space holder was eliminated by holding the sintered samples in running hot water (70 °C). After the salt was dissolved, the samples were dried and the mass loss was analyzed. Keywords: Aluminum foam, Powder metallurgy, Sintering and dissolution process

Abstract: Fabrication of aluminum-based composites reinforced by ceramic particles or intermetallic phases has focused considerable attention in recent decades because significant improvement in mechanical properties and thermal stability. This paper has considered in-situ fabrication by mean of reactive sintering of blended and compacted powders containing an aluminum-copper hardenable alloy and titanium dioxide. An experimental program has been dedicated to optimize the sintering parameters in terms of both treatments temperature, between 650 and 800°C, and duration, in the range of 3 to 6 hours. Microstructural analysis based on Scanning Electron Microscopy (SEM) has been used to determine of distribution of elements involved in sintering reactions, such as aluminum, titanium and oxygen.

Abstract: The current study is focused on deposition of different carbide based powders as WC/10Co/4Cr, Cr3C2/25NiCr, CrC/37WC/18M using High Velocity Oxygen Fuel (HVOF) spraying technique onto the surface of low carbon steel substrates. The obtained coatings were characterized by means of X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to study their phases and morphology. Hardness and porosity values of the coatings were also measured. The sliding wear behavior was evaluated using the pin-on-disk method and the corrosion resistance was determined by open cell potential measurements and salt spray tests. Comparative results of the investigated samples showed that the WC/10Co/4Cr coating had the best wear properties and the Cr3C2/25NiCr coating had the best corrosion resistance.

Abstract: The existence of gases in the solid metals (hydrogen and nitrogen) assumes the presence of these gases in metals even before solidification, respectively in the elaboration, secondary treatment and casting phases. Usually, great amounts of gases dissolved in steels can be detected, between 3.5-8ppm for hydrogen and 0.02-0.03% for nitrogen, respectively. There are also cases when the purpose is to alloy with nitrogen, this being the case of austenitic stainless steels where the nitrogen content can reach 0.5% using ferrochromium or ferromanganese alloyed with nitrogen in 3-5.5 %. The main method of removing these gases is bubbling with inert gases and /or treating the steel in a vacuum facility. The paper presents a study regarding increasing the removal efficiency of nitrogen from the liquid steel by changing the bubbling parameters (flow, pressure, duration) but also the basicity of the refining slag. The equations of the regression surface and the identified fields are of a real help for the technologists, allowing quick decisions but they are also important for the quality of the metallic products [.

Abstract: This paper presents the results obtained in what concerns the ranges of technological parameters of the secondary treatment of steel in LF plants to improve its quality by reducing the hydrogen content. The use in the industrial practice of the optimum values for these parameters allows obtaining steels with a low content of gases, especially hydrogen.

Abstract: The non-destructive control of the welded joint in the case of transport pipelines of oil substances raises major problems by the difficulty of identifying the welded joints once the pipeline is imbedded. This paper presents the results of the research that were obtained by using a mobile station for digital radiography which, by GPS systems identifies all welded beads within a gas pipeline. By the technique that is presented in this paper, the process of control is more efficient, by using the modern technique of digital gammagraphy, with the possibility of transmitting real-time data on the field using the informatics system. This study presents the methodology and advantages of using the mobile intelligent testing system ND made by Receptor GR-3 and Controller TOPCON FC 250.

Abstract: Fe-Si alloy with a Si content of 10 wt. % was obtained in nanocrystalline state by mechanical alloying of elemental iron and silicon powders. The mechanical alloying process was carried out in a high energy ball mill (Fritsch, Pulverisette 4) in argon atmosphere. The X-ray diffraction (XRD) studies indicated that after 4 hours of milling the Fe-Si alloy is formed. The mean crystallites size decreases down to 7 nm after 8 hours of milling. The particles morphology investigated by scanning electron microscopy (SEM) showed an evolution during milling process from two different kinds of particles to a one kind of particles with irregular shape. The magnetisation of powders decreases upon increasing the milling time up to 4 hours as a consequence of the Fe-Si alloy formation.