Solid State Phenomena Vol. 227

Abstract: The oxides in the case of theirs properties are important materials for industrial application especially, in aircraft industry for application as thermal barrier coatings. Thermal properties of zirconium oxide stabilized by yttria are better than other ceramic materials. This powder could be stabilized in room temperature by addition of rare earth elements. In this article the thermal analyses of yttria stabilized zirconia (YSZ) oxide are presented as a baseline for future measurements of thermal properties of YSZ powder with addition of rare earth elements. The thermal expansion, specific heat, thermal diffusivity and thermal conductivity of commercially available Matco 6700 powder offered by Sulzer Metco company were analyzed by thermal methods.

Abstract: Characterization of microstructure of pack cemented silicide coatings based on MoSi₂ phase was described in this article as well as a short term oxidation resistance of these types of coatings at temperature 1200oC. Silicide coatings were deposited on top surface of Mo and Mo alloys of TZM type by diffusional process of siliconizing in activated powders. Morphology of coatings was characterized by evaluation of chemical and phase’s composition of deposited coatings by EDS and XRD methods respectively. In the case of Mo sheet after diffusion process of siliconizing single layer of MoSi₂ type was obtained, but in the case of TZM alloy, in the same conditions of process, double layered coating was generated. Thick outer layer was build form MoSi₂ phase, but very thin internal layer consist Mo₅Si₃ phase. The thicknesses of coatings were ca. 45μm, and were uniform. Morphology of coatings was free from inclusion and contaminations in their cores. The isolated cracks were observed, but their volume was very small. The oxidation test was performed at temperature 1200oC. The specimens were tested at 25, 500 and 100 hours of test. After each period of test characterization of coatings top surface was made. Total destruction of specimens was observed in range between 50 and 100 h of test.

Abstract: Nonstoichiometry and chemical diffusion in Co₃O₄ oxide have been studied as a function of temperature (973-1173 K) and oxygen pressure (30-10⁵ Pa), using thermogravimetric techniques. It has been found that at very low oxygen pressures, close to the dissociation pressure of the oxide, interstitial cations and quasi-free electrons are the predominant point defects, while at high pressures cation vacancies and electron holes predominate. This behaviour is reflected in complex dependence of the deviation from stoichiometry, y, in the Co_3±yO₄ oxide on oxygen pressure. At low pressures, namely, deviation from stoichiometry decreases with increasing oxygen pressure, reaching virtually constant value in intermediate pressures and increases at highest pressure range. Finally, these data as well as the results of kinetic rate measurements of Co_3±yO₄ formation have been utilized in calculating the chemical diffusion coefficient as a function of temperature.

Abstract: Gears, due to their complex shape, carried load and required accuracy are ones of most complex aircraft engine parts. Single tooth damage usually breaks the power transmission and causes failure of the entire gear system. Adequate sustainability and guarantees of transmission is therefore a condition for secure operation of whole device. Particularly high requirements for reliability are put to transmissions used in the aerospace industry. Due to the loads which are transmitted through the gears, the materials used by the manufacturer must have not only high strength but also show the abrasion resistance of the surface layer and the ductility of the core. Thermo-chemical treatment of industrial gears is a fundamental process, which gives them adequate mechanical properties regarding loads they carry and the surface conditions of work. The most promising method in the discussed field is vacuum carburizing, which by its specification of work significantly reduce the emission of CO₂ and the duration of the process, without reducing the quality of the final product. The main aim of the paper is to present criteria for selection of carburizing parameters (mainly temperature increase) as a part of thermo-chemical treatment process performed using vacuum methods. Proper (higher to compare with conventional methods) carburizing process temperature is crucial in programming of carbon diffusion process meaning in process time and final carburized layer characteristics as carbon profile and homogeneity of the carburized layer.

Abstract: Biodegradable alloys are currently studied as prospective biomaterials for temporary medical implants like stents and fixation devices for fractured bones. Among biodegradable metals, only magnesium, zinc and iron meet general requirements of biocompatibility and relative non-toxicity. In the present paper, Mg-, Zn- and Fe-based biodegradable alloys are compared. Advantages and disadvantages of the three kinds of alloying systems are demonstrated regarding the corrosion behavior, mechanical performance and biocompatibility. From the corrosion behavior point of view, Zn- and Fe-based alloys appear as promising alternatives to Mg-based alloys.

Abstract: The corrosion behaviour of titanium alloys is not well understood – especially the role of the microstructure and plastic strain. In this paper, the influence of the microstructure and plastic strain on the corrosion resistance of TiMo10Zr4 and Ti6Al4V alloys was studied in the Ringer’s solution at 37 °C. Measurements were performed for different pH values and in aerated and de-aerated solutions using potentiodynamic polarization techniques. Results obtained on the two alloys were compared. It was shown that in the absence of plastic strain TiMo10Zr4 shows better corrosion resistance than Ti6Al4V (especially for pH = 8). By contrast, the current density in the passive range measured after 8% plastic strain was greater on TiMo10Zr4 than on Ti6Al4V, indicating that the passive film on TiMo10Zr4 is less protective than that formed on Ti6Al4V.

Abstract: The aim of this paper was investigating the corrosion resistance of Mg₆₇Zn₂₉Ca₄ metallic glass and evaluating the ability of use studied amorphous alloy for medical applications as biodegradable implants. For comparative purposes the corrosion studies of the amorphous Mg₆₇Zn₂₉Ca₄ samples were performed in a few simulated body fluids at 37°C. The immersion tests were performed in Ringer’s solution, PWE (multielectrolyte physiological fluid) and 3%NaCl water solution. The amount of evolved hydrogen[ml/cm²] and a corrosion rate V_corr [g/(day·m²)] of studied Mg₆₇Zn₂₉Ca₄ alloy were compared. Surface morphology of metallic glass after corrosion study was performed using the scanning electron microscopy.In aim determination dissolution rate and amount of evolved hydrogen was simulated the environment of human body fluids during immersion tests. The work presents structure characterization and corrosion properties analysis of Mg₆₇Zn₂₉Ca₄ bulk metallic glasses in the form of plates. Samples structure was analyzed by means of X-ray diffraction. Fractographic study a cross section of the sample in plates form was performed using scanning electron microscopy

Abstract: The pitting potential, E_pit, of the passive layer on the implant alloy can be treated as an accelerated laboratory test to assessment a susceptibility to pitting corrosion of metallic biomaterials in simulated body fluids. This study deals with an evaluation of E_pit of the self-passivated TiO₂ layer formed on the surface of the NiTi implant alloy as a function of the scan rate of polarization. Cyclic potentiodynamic studies were performed in Ringer’s solution at 37°C. It was found out that the more noble value of E_pit in the range of 0.99-2 V was registered at a given polarization scan rate that ranged from 0.16 to 2 mV s^-1, the lower susceptibility of the self-passivated NiTi implant alloy to the initiation of pits was detected.

Abstract: Favorable physical and chemical properties of titanium led to its use in the medical and dental specialties such as: orthodontics, prosthodontics, dental implantology and dental surgery. Estimating the biocompatibility of the material, determine the risks and benefits with its use is a complex process. In dental implantology, the attachment of a dissimilar metal abutment (Ti6Al4V) to an implant (commercially pure Ti) forms a galvanic couple in the mouth; they are placed in physical contact in an electrically conductive mediums – body fluids.

Abstract: The purpose of this paper was to study the corrosion resistance of Co-Cr and Ni-Cr dental alloys in simulated artificial saliva by means of electrochemical techniques. Co and Ni based alloys are widely used in dental skeletal structures and orthopedic implants such as screws, pins and plater. And recently they have been applied for making stents. The advantages of these alloys include low cost of casting, matching thermal expansion coefficient with the ceramics of metal-ceramic restorations, and acceptable mechanical and tribological properties in vivo. The microstructure of investigated alloys were studied by using optical microscopic observation, X-ray diffraction measurements and Scanning Electron Microscope with X-ray microanalyzer. The mechanical properties were characterized by microhardness tests.