Solid State Phenomena Vol. 216

Abstract: Amorphous alloys based on titaniumzirconium seem to be perfect candidates as metallic biomaterials. However, the most successful results are based on alloying elements such as nickel, which is responsible for allergic effects to a considerable percent of human population. Therefore the elimination of nickel and addition of other alloying elements with amorphization effect, such as gallium and/or hafnium, have been considered for this paper. Starting from already classic Ti-Zr-Cu-Ni-Si-Sn composition, samples with additions of gallium and hafnium at the expense of nickel have been fabricated by mean of ultra-rapid cooling, using copper mold suction casting. The structures of the as-cast rods have been investigated using X-rays diffraction and electron microscopy.

Abstract: The influence of molybdenum and aluminum on the corrosion resistance of the Ti and other Ti-based biomedical implant alloys under simulated physiological conditions is presented. Ti and its alloys Ti-10Mo and Ti-10Mo-10Al were studied. The electrochemical impedance spectroscopy technique was used and the experimental results were compared with those obtained by potentiostatic and potentiodynamic techniques. All the measurements were made in Ringer ́s solution at different pH and at different potentials as E_corr, -650, -500, 0, +200 and +400 mV vs SCE. It was evident that Mo improved passivity and limited the active corrosion of the β-phase of Ti while Al enrichment of the α-phase was found to be detrimental to the passivity and corrosion resistance of Ti. In most experimental conditions, the passive film is formed by TiO₂, Ti₂O₃ and TiO. When pH is very low, thermodynamically stable state of Ti is titanium anion Ti³⁺.

Abstract: The structural characteristics of ductile irons were studied using different rare earth elements (REE) in Mg-FeSi treatment alloys (0.005 - 0.025%REE_res), in un-inoculated and Ca-bearing FeSi in the mould inoculated irons. In relatively high purity base iron, in terms of anti-nodularising trace elements, (Thielman factor K = 0.7-0.8), increasing REE content after Mg-treatment aggravated the carbides tendency and decreased the nodular graphite compactness, in both un-inoculated and inoculated irons. Graphite parameters improve for lower REE content, and, in both cases, for inoculated irons. A low content of REE_res (0.005 to 0.01%) for K < 0.8 is practical and sufficient in a Ca-bearing FeSi alloys inoculated iron to control carbides sensitivity and to sustain acceptable nodular graphite morphology formation.

Abstract: The aim of this paper is quantitative characterization of a MnZn ferrite with Bi₂O₃ increasing addition using the Image-Pro Plus software from Media Cybernetics. The sample matrix is a ferrite with the following chemical composition: Mn_0.54Zn_0.37Fe_2.06O₄. We applied the conventional ceramic technology in order to obtain the samples. Thus, the raw materials, i.e. αFe₂O₃, Mn₃O₄, and ZnO, in a molar ratio 53:28:19 were mixed in suitable proportions in a steel ball-mill using demineralized water. The mixture was burn off at 800 °C for 1 hour, in air. The pre-sintered powder was milled in steel ball-mill with increasing addition of Bi₂O₃ (0.00, 0.01, 0.03, 0.05, 0.07, 0.10, 0.30, 0.50 wt %). For quick references, the sample without bismuth ions was denoted and the samples with increasing concentrations were numbered from 1, 7.

Abstract: Composite powder of Fe/Fe₂O₃ type was synthesized by mechanical milling using commercially Fe and Fe₂O₃ powders in mass ratio of 35/65. The milling process leads to the powder homogenization, powder activation and formation of some Fe/Fe₂O₃ composite particles. The Fe/Fe₂O₃ composite powder obtained by mechanical milling and the un-milled Fe/Fe₂O₃ mixture were subjected to the reactive sintering procedure in argon atmosphere at 1100 °C for 6 hours. The sintering procedure promotes the reaction of the Fe with the Fe₂O₃ and the result is a sintered composite compact of Fe/Fe₃O₄/FeO type. The microstructure of the Fe/Fe₃O₄/FeO sintered composite compacts presents iron clusters in an oxide matrix. A more homogeneous iron clusters size and distribution in oxide matrix is observed in the case of the sintered compact obtained from mechano-activated powder. The X-ray diffraction (XRD), laser particles size analysis (LPSA), optical (OM) and scanning electron (SEM) microscopies techniques were used for the investigations.

Abstract: Ni based amorphous alloys with Si and B, which can also, contains Fe and Cr, prepared by rapid solidification, have low melting temperatures. This fact increases their susceptibility to be joined by welding and brazing. The glass forming ability (GFA) is conditioned also by the crystallization delay, due to certain chemical composition of the alloys. The thermal stability of these alloys was revealed by DTA analysis and structural characteristics were investigated by XRD. Applying an annealing at temperatures between 420°C and 540°C, with 30 minutes maintaining time, allowed the investigation of phase occurred during the crystallization and the estimation of the crystalline grains dimensions.

Abstract: The implant surface morphology and microstructure significantly affect cells and tissue quantity formed at the interface. Therefore, the biocompatibility of an implant is just one of many parameters that influence tissue response to metallic implants. In order to understand the importance of the surface morphology and microscopic structures, we must retain first the main problem that limit the application and operation of metal implants - the lack of implant viable anchoring within the tissue. On this basis, experimental studies were carried out on implants having different microstructures and macrostructures that have been used in order to achieve a better long-term anchoring and stability of the implant support.

Abstract: Development of Fe-based bulk metallic glasses (BMG) with good mechanical and soft magnetic properties has become a major objective in the materials science field. Bulk metallic glasses present an interesting combination of properties. They exhibit very high strength (both in tension and compression), large elastic elongation limit, high hardness, excellent corrosion resistance, and good soft magnetic properties. These properties makes them suitable for many applications like high resistant control cables, pressure vessels, micro-components, pressure sensors, microgears for motors, magnetic cores for power supplies and hard fibers in composite materials. Multi-component Fe₆₀Co₁₄Ga₂P₁₀B₅Si₃Al₃C₃ bulk metallic glass was synthesized in rod form with a diameter of 1 mm by copper mould casting technique using raw industrial materials. The obtained alloy was analyzed by X-ray diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) techniques, in order to determine the phase constituent, the thermal stability and the fracture surfaces of as-cast samples. The mechanical behaviour was investigated by microhardness and compression tests. The values recorded for hardness and fracture strength includes this alloy in the category of high resistant materials.

Abstract: The main objectiv of this experimental reserch is a comparative analysis of sulphur and oxygen effects on the cooling curves parameters at different iron melt modifying potential (residual Mg content). For the experiment, three irons with different modifying potential (0.0014, 0.0213 and 0.033 wt % residual Mg content respectively) were developed. After Ca-Ba inoculation, the three irons were additional treated by stoichiometric equivalent additions of sulphur or oxygen as FeS₂ and Fe₂O₃ respectively. Both FeS₂ and Fe₂O₃ sources were placed on the bottom of standard Quik-Cup moulds,usualy used for iron melt thermal analysis. The effect of sulphur and oxygen on the standard and nonconventional cooling curves parameters were evaluated to a more deep understanding of the cast iron solidification mechanism. The cooling curves parameters are strongly influenced both by the initial residual Mg level of iron melt and afterwords sulphur/oxygen additions. A very complex and sometimes confused variation of the cooling curves parameters was recorded because of different actions of the three factors (iron melt modifying potential, sulphur and oxygen). As a previous paper highlighted, sulphur addition has a strong graphite decompactizing effect while oxygen addition has mostly an inoculant effect.