The main advantage of powder metallurgy processing route it the possibility to produce near-net-shape compacts and to minimize the finish machining and material loss. The main problem in particulate consolidation process is to suppress porosity, to remove oxide layers, and to retain the microstructure of powder materials. Spark plasma sintering (SPS) combines concurrent uniaxial pressure and direct heating by a pulsed DC current. Sintering occurs at relatively low temperatures for a short time and does not influence significantly the microstructure in the interior of original particulates. Gas atomized Al7075 powder was sintered by the method of SPS. The influence of sintering parameters on the microstructure of compacts was studied by light and scanning electron microscopy. The phase composition was studied using X-ray diffraction. The mechanical behaviour was tested by bending tests. The efficiency of SPS in producing compacts with low porosity can be dependent on the distribution of particulate size in original powder material. The gas atomized Al7075 powder was sieved to several charges and then sintered by SPS. The microstructure investigation and bending test were performed on these compact materials.
Introduction and description of current activities of company ŠKODA JS a.s. and possible future development of the market with components for nuclear power plants. Research and development in nuclear reactors 4th generation brings new demands on materials and their connecting. These reactors carry on at high temperatures, where are used as refrigerants molten salts and metals. These materials have at this temperature extreme corrosion properties, therefore is necessary to seek new construction materials and methods for their protection. Another question is the final storage of spent nuclear fuel in a deep geological repository. Here is the material long term exposed to a corrosive environment. The main goal is to propose such material or coating that would ensure the protection of the container with spent nuclear fuel for the order of a hundred thousand years.
Mechanical properties and microstructure of EN AW 6082 were investigated. The aluminium alloy was processed by combining the solution annealing, severe plastic deformation and artificial age hardening, respectively. The initial state of the investigated material was provided in the form of extruded rods with the diameter of 12 mm. For the solution annealing the temperature 530 °C was chosen. The severe plastic deformation was realized by rotary swaging at ambient temperature and the investigated material was rotary swaged from 12 to 10 mm in diameter. The effect of the age hardening temperature and time was studied at temperatures of 120 and 160 °C and times 1 - 12 hours. The impact of processing parameters on mechanical properties was assessed by tensile testing and hardness measurement. Metallographic examination was carried out by light optical microscopy (LOM) and scanning electron microscopy using electron backscatter diffraction (SEM-EBSD).
The influence of Sc and Zr on mechanical properties of twin-roll cast Al-Mg alloy was studied. A significant effect of Sc and Zr on hardening of the material after annealing in a temperature interval between 250 °C and 400 °C was confirmed. Maximal hardness was obtained after 2 hours of annealing at 300 °C due to a precipitation of a fine dispersion of Sc and Zr containing precipitates. An exposure of the annealed material to higher temperatures results in a partial degradation of mechanical properties due to changes of the strengthening effect of precipitates. However, a partially positive role of remaining precipitates hindering recrystallization persists even up to 550 °C.
Magnesium alloys containing about 3 wt. % of Nd and 0.5 wt. % of Zn are considered as promising materials for application in transport and medical industry. Properly treated materials can reach UTS (ultimate tensile strength) higher than 300 MPa. Also the corrosion resistance of these alloys is superior to many other magnesium based materials. Present work is oriented on the preparation of Mg-3Nd-0.5Zn magnesium alloy by classical casting and thermal treatment. Selected materials were subsequently extruded at 400 °C, extrusion ratio equal to 16 and with velocity 0.2 mm/s. The effect of thermal treatment and also strong plastic deformation during extrusion on final structure conditions and mechanical properties is specified. Present results confirmed significant improvement of TYS (tensile yield strength) and UTS after extrusion process as a consequence of combination of fine-grained structure and precipitation strengthening. Also texture strengthening in the direction parallel to the extrusion has been observed.
Iron and other transition metals are the most common impurity in aluminium and its alloys. They concentrate in scrap, contaminate the aluminium alloys during production and thus hinder the process of recycling. Negative effect of transition metals is caused by the low solubility in solid aluminium which leads to the formation of relatively large intermetallic phases with platelets-like or needle-like morphology. These phases are fragile and deteriorate the mechanical properties. Powder metallurgy, especially methods involving rapid quenching and mechanical alloying, could be a possible way how to process the aluminium scrap with a relatively high content of transition metals. In this work methods of powder metallurgy were used to prepare aluminium alloys with high content of iron. The microstructure and phase composition of compact samples as well as mechanical properties were studied.
The new Al15Ti5Co35Ni25Fe20 high entropy alloy was obtained by the powder metallurgy from the elemental powders (-325 mesh). The obtained alloy should be characterized by the dual BCC + FCC phase microstructure according to the valence electron concentration calculations (VEC=7.9). The main aim of the research was to determine the optimal conditions for sintering and heat treatment of Al15Ti5Co35Ni25Fe20 high entropy alloy. The alloy was sintered for 40 minutes at 600°C for the preliminary consolidation of the powders and initial diffusion of the material. Then samples were annealed at various temperatures: 700, 800, 900, 1000, 1100°C for 1 hour. Samples after annealing were characterized by the light microscope, XRD and SEM. For the chosen temperature the annealing time was elongated to 2, 3, 5, 10 and 20 hours. The porosity and the chemical homogeneity were determined. ACKNOWLEDGEMENTS: Research supported by Ministry of Science and Higher Education Republic of Poland (project No. 15.11.110.428).
Titanium based alloys have been widely used in many applications, ranging from aerospace engineering to biomedical technology. However, high temperature grain size stability and mechanical properties are still needed to be further improved to widen the possible applications of titanium based alloys. One of the approaches available for improving the strength of titanium alloys is the refinement of the grain size. According the Hall–Petch relationship, decrease in grain size increases yield strength. However, as the grain size decreases metals, in general, will have higher tendency for grain growth at elevated temperatures. The purpose of this work is to produce high strength ternary titanium alloys with the addition of Nb and Sn by mechanical alloying and investigate the grain size stability and mechanical properties as a function of solute addition and annealing temperature. This research was supported by Necmettin Erbakan University - BAP under grant number 151219009.
Nowadays, Ni-based superalloys are widely used in many industries, especially for the production of gas turbine engine, due to their superior mechanical properties at high temperature. Therefore, Ni-based superalloys are frequently used in applications which are under harsh environment. However, after using in long term condition, microstructural transformation of Ni-based superalloy occurs, resulting in decreasing mechanical properties. Gamma prime precipitates and other detrimental phases are formed and agglomerated. The present research aims to study the microstructural transformation of Ni-based superalloy, MGA 1400, after heat treatment. The heat treatment conditions consist of solutioning and aging processes. The solutioning and aging temperatures were varied from 1125 to 1175°C for 4 h and from 800 to 885°C for 25 h holding times, respectively. The result showed that gamma prime precipitation size and area fraction increase by increasing aging temperature. In contrast, increasing solutioning temperature resulted in decreasing size and area fraction of gamma prime precipitates.