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Ti–Ni powder compacts were prepared by mechanical alloying (MA), followed by hot isostatic pressing (HIP). Afterwards, the samples were sintered at different temperatures (950, 1050, 1150 and 1250 °C). Microhardness, density, crystallite size as well as microstrain of the sintered samples were measured and analyzed. Wear characteristics in phosphate-buffered saline (PBS) solution was tested under different applied loads of 2 N, 10 N, and 20 N, respectively. The results indicated that the crystallite size continuously decreases with increasing sintering temperature and reaches the lowest value of 31.3 nm at 1250 °C. The relative density of the sample sintered at 1250 °C is 98.0%. Moreover, the higher sintering temperatures lead to the higher relative density and the increase in hardness and young’s modulus of the sample. At the same time the friction coefficient and wear rate were lower for the samples sintered at 1250 °C. This improvement in friction and wear resistance is attributed to the grain size refinement. Ti–Ni sintered at 1250 °C showed good tribological performance under all test conditions.
The microstructural and functional behavior of TiNi-based wires with a silver content of 0–1.5 at.% was evaluated. The concentration range for Ag doping determined for the TiNi wires with potential for the medical industry was 0–0.2 at.%. Microstructure analysis of TiNi wires with different silver contents at room temperature indicated a multiphase structural state. Various internal structures with tangled grain boundaries were formed by intense plastic deformation. The nanocrystalline structure and phase state of wire with the minimum silver content (0.1 at.% Ag) provide full shape recovery, the greatest reversible strain, and optimal strength and ductility. TiNi ingots with a high Ag content (0.5–1.5 at.%) cracked under minimum load due to excess silver that crystallized along the grain boundaries and broke cohesion bonds between the TiNi grains.
The central commitment of the 2015 World Climate Conference is to limit geothermal heating by massively reducing greenhouse gas emissions by decreasing the use of fossil fuels and promoting environmentally friendly energy. However, since renewable energies have so far not been available as required and are difficult to store, there is a short-term solution in the conversion, storage and reuse of climate-damaging combustion gases. An efficient solution for using CO2 is to convert it into a gas that can be stored and used to generate energy. With the so-called “power-to-gas technology”, a significant reduction in greenhouse gas emissions can be achieved by methanation of CO2 if methane slip is avoided. Methanation is a chemical reaction in which carbon dioxide reacts with hydrogen to methane. This transformation, which normally takes place at 350 ° C to 600 ° C, is also known as the Sabatier reaction. In addition to methane and water, the remaining reactants such as carbon dioxide, hydrogen, oxygen and nitrogen as well as small amounts of impurities from the combustion process, occur as reaction products. Reaction containers and lines are usually made of stainless steel. Due to high ambient temperature and aggressive ambient media, corrosion can also occur with the generally temperature and corrosion-resistant 316L material, influence material properties and lead to material failure. To assess the influence of the CO2 methanation process on 316L, a laboratory-scale methanation reactor was fractioned and examined after use. Corrosion deposits were found in various components of the reactor (gas supply line, gas outlet, reactor segment). Depending on their position within the component, these corrosion layers are structured very differently. Microstructure and element composition of the layers were analyzed using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. While the gas supply shows only moderate corrosion attack, crevice, contact- and pitting corrosion were detected in the corroded area of the gas outlet. Three zones (multilayer structure, particle accumulation and brittle passive film) were identified within the corrosion layers. The multi-layer zone is composed of columnar and granular structures, the particle accumulations consist of cylindrical and spherical particles. The element composition within the corrosion layers suggests contact corrosion caused by the material of the sealing rings.
Die Weltklimakonferenz fordert eine massive Senkung der Treibhausgasemissionen mittels Abkehr von der Nutzung fossiler Brennstoffe hin zur Verwendung umweltverträglich hergestellter Energie. Da erneuerbare Energien aber bisher nicht durchweg bedarfsgerecht zur Verfügung stehen und schlecht speicherbar sind, besteht eine kurzfristige Lösungsmöglichkeit in Umwandlung, Speicherung und Wiederverwendung klimaschädlicher Verbrennungsgase. Eine effiziente Lösung zur Nutzung von CO2 ist dessen Umwandlung in ein speicherbares, zur Energieerzeugung nutzbares Gas. Mit der Methanisierung von CO2 kann eine erhebliche Reduzierung der Treibhausgasemissionen erreicht werden, wenn Methanschlupf vermieden wird. Bei dieser sogenannten Sabatier-Reaktion, die normalerweise bei 350°C bis 600°C stattfindet, reagiert Kohlendioxid mit Wasserstoff zu Methan. Als Reaktionsprodukte treten außer Methan und Wasser die Rest-Reaktanten sowie kleine Mengen an Verunreinigungen aus dem Verbrennungsprozess auf.
Reaktionsbehälter und Leitungen bestehen üblicherweise aus Edelstahl. Durch hohe Umgebungs-temperatur und aggressive Umgebungsmedien kann auch bei dem normalerweise temperatur- und korrosionsbeständigen Werkstoff 316L Korrosion auftreten, Materialeigenschaften beeinflussen und zu Materialversagen führen. Zur Bewertung des Einflusses des CO2 Methanisierungs-Prozesses auf 316L wurde ein Methanisierungs-Reaktor im Labormaßstab nach der Nutzung demontiert und untersucht. In verschiedenen Bauteilen des Reaktors (Gaszuleitung, Gasaustritt, Reaktorsegment) wurden Korrosionsbeläge gefunden. Abhängig von ihrer Lage im Bauteil sind diese Korrosionsschichten sehr unterschiedlich aufgebaut. Mikrostruktur und Elementzusammensetzung der Schichten wurden mittels Rasterelektronenmikroskopie kombiniert mit energiedispersiver Röntgenspektroskopie analysiert. Während die Gaszuleitung nur moderaten Korrosionsangriff zeigt konnten im Bereich des Gasaustritts Spalt-, Kontakt- und Lochkorrosion nachgewiesen werden. Innerhalb der Korrosions¬schichten wurden drei Zonen (Mehrschichtenstruktur, Partikelansammlung und brüchiger Passivfilm) identifiziert. Die Mehrschichtzone setzt sich aus kolumnaren und granularen Strukturen zusammen, die Partikelansammlungen bestehen aus zylinderförmigen und kugelförmigen Partikeln. Die Elementzusammensetzung innerhalb der Korrosionsschichten lässt auf Kontaktkorrosion verursacht durch das Material der Dichtringe schließen.
β-type Ti–20Nb–13Zr alloys with low Young’s modulus were prepared at different sintering temperatures (950, 1050, 1150, and 1250 °C). The morphological and structural characteristics of as-prepared samples were investigated by several methods. Wear tests were conducted using a ball-on-plate type oscillating tribometer under different applied loads (2, 10, and 20 N). The morphological characterization indicated that the mean pore and crystallite size continuously decreased with increasing sintering temperature to reach lowest values of 40 nm and 38 nm at 1250 °C, respectively. The relative density of the 1250 °C sintered sample was as high as 98.7%. Moreover, the higher sintering temperature resulted in higher relative density and closed porosity of the sample. Both the friction coefficient and wear rate were lower in the sample sintered at 1250 °C as compared to other samples. This enhancement in tribological properties was attributed to a closed porosity.
Hot isostatically forged TiAl turbine blades made of TNM-B1 are commercially used in aircraft engines, as they offer significantly lower weight than the traditional nickel-based blades while exhibiting similar strength. Like other TiAl alloys, TNM-B1 displays high peak stress followed by a strong softening behavior (i.e. stress reduction) during hot deformation. This softening can be used to accelerate the deformation process by reducing the processing time and in turn the costs for TNM-B1 parts. In order to avoid increased damage during the accelerated process, a pre-heat treatment (HT) for the hot isostatically pressed material (HIP) is required. To simulate the accelerated forming process, hot compression tests were performed with a DIL805A/D/T dilatometer from TA Instruments (New Castle, Delaware, USA) with different strain rates (0.0013, 0.005, 0.01 and 0.05) and temperatures (T=1150, 1175 and 1200°C). Deformation of the heat-treated state revealed lower flow stress (in both, peak stresses and steady state stresses) and fewer voids compared to the HIP state (Fig. 1.a). The compression test data were used to develop material and temperature specific strain rate profiles based on a material model. Subsequently, hot compression tests were performed with different strain rate profiles (starting strain rates 0.0013 and 0.0052) for the HIP and the HT state. The results were evaluated with regard to their microstructure, deformation, and damage behavior. A reduction of the processing time for all tested strain rates profiles by factors 2-3 could be achieved compared to constant strain rates. Furthermore, the results indicated that the deformation with strain rate profiles (compared to constant strain rates) did not significantly change the resulting microstructure or damage tolerance of the HT state.
Hexavalent chromium pollution from industrial waste water is a serious problem as it can cause adverse effects on the environment. Several methods are used to reduce the harmful effects of this pollutant, especially physico-chemical methods, such as adsorption technology. The present study aims to remove Cr (VI) from industrial sources in a fixed-bed column of activated carbon. The experiments were carried out at natural pH and temperature with a flow rate (5, 10, and 20 mL/min) and bed height (3.5 cm). Breakthrough curves for feed concentrations (0.01, 0.03, and 0.05 mol/L) were investigated. The results indicated a marked decrease up to 99%. The value of the flow constant for the Thomas model decreased with the increase in the concentration of the incoming substance, but increased with the increase in the flow rate.