Search

A homogeneous HfNbTaTiZr high-entropy alloy was successfully processed via powder metallurgy route. For the initial powder feedstock material fabrication, the electrode induction-melting gas atomization procedure was used, resulting in a spherical powder morphology and dual bcc phase composition distinguishable within the individual particles. Spark plasma sintering was then used for the powder compaction at sintering temperatures ranging from 800 to 1600 °C. By the characterization of the compact microstructures, lattice defects (microscopic porosity and vacancy-like misfit defects), and mechanical properties (hardness and three-point bending strength), the sintering conditions were optimized to obtain a fully dense, homogeneous, single-phase bcc material. It was found that such properties are achieved when sintering at 80 MPa pressure for 2 min at temperatures above 1200 °C, where the single bcc phase structure exhibited ductile behavior with considerable flexural strength and ductility at ambient temperature. Positron annihilation spectroscopy was used to characterize the evolution of atomic and mesoscale defects during optimization of the sintering process.

Light-weight ferromagnetic Co-Ni-Al:Ti composites were consolidated by spark plasma sintering. Powders of ball-milled Co-Ni-Al and gas atomized α-Ti were mixed together in three different ratios and spark plasma sintered at 950°C, using two sintering times, i.e. dwell times at the maximal temperatures: 1 and 5min. The composites were successfully compacted and new intermetallic phases were formed at the Co-Ni-Al/Ti interfaces. The composites exhibit favourable flexural strength, excellent high-temperature stability, and relatively high saturation magnetization. On the other hand, the newly emerged intermetallic phases are non-ferromagnetic, which slightly deteriorates the magnetic properties. Keywords: Metal–metal composites, Spark plasma sintering, Light metals, Ferromagnetic alloys, Mechanical properties

A series of samples was sintered from nanometric BaTiO 3 powder by spark plasma sintering (SPS). Porosity on ultra-fine size scales, hardly accessible for quantification by conventional techniques, was measured by small angle neutron scattering (SANS). Band gap was estimated from diffuse reflectance measurements. Sintered tablets were polished, sputtered by aluminum to create electrode system and tested in DC and AC electric fields. The results were correlated with the SPS processing parameters and are discussed in connection with other BaTiO 3 samples produced by SPS with or without additional heat treatment. Majority of our SPS fired samples had, even without subsequent thermal treatment, advantageous combination of high permittivity, DC resistivity and low loss factor, seldom reported for SPS technology.

The feasibility of iron-zinc intermetallic-phase preparation by spark-plasma sintering (SPS) was investigated. The samples were prepared with a combination of powder metallurgy, where the powder was prepared in evacuated quartz tubes, and a sintering process using SPS. Since the Fe-Zn intermetallic phases are mostly used for hot-dip galvanized steels, the knowledge of the properties of individual intermetallic phases is vital for a better understanding and even further optimization of galvanization processes. The main aim of the article is to compare the phase composition of the initial powder with the SPS samples using X-ray diffraction. Furthermore, the hardness and microstructure were investigated as well.

The main advantages of powder metallurgy processing route are the possibility to produce near-net-shape compacts and to minimize the finish machining and material loss. The main problem in particle 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 interiors of original powder particles. The efficiency of SPS in producing compacts with low porosity might be dependent on the distribution of particle size in original powder material. The gas atomized Al7075 powder was sieved to several charges and then sintered by SPS. Microstructure of sintered compacts was studied by light and scanning electron microscopy. The phase composition was investigated using X-ray diffraction. The mechanical behaviour was tested by bending tests.