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Due to their physical and mechanical properties, niobium products are used in the nuclear power industry, chemical industry, electronics, medicine and in the defence industry. Traditional manufacturing technology for these products is characterized by long production cycles and significant material losses during their surface machining. This paper presents the results of a study on the fabrication of niobium products by Spark Plasma Sintering (SPS). Structural and mechanical tests were conducted on the products obtained, as well as a comparative analysis with the properties of products obtained using traditional technology. Based on the analysis of the test results obtained, recommendations were made for the sintering of Nb powders. It was found that the optimum temperature for sintering the powder is 2000 °C as the density of the material obtained is close to the theoretical density. The microstructure obtained is comparable to samples obtained by the traditional method after recrystallization annealing. Samples obtained according to the new technology are characterized by higher mechanical properties Rp0.2 and Rm and the highest hardness.
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This paper presents a comparison of surface morphology obtained after machining Inconel 718 by the conventional insert, by Wiper insert and by using the cutting insert made by Spark Plasma Sintering (SPS). The shape of the special insert was obtained by employing Wire Electrical Discharge Machining (WEDM). The paper focuses on the description of surface topography after turning in dry and wet conditions. The performed investigation included longitudinal turning tests of Inconel 718 performed in a range of variable feeds. Surface topography measurements have been performed with the application of Nanoscan 855. The performed analysis includes a parametric evaluation of the obtained surfaces. With the Wiper insert, the Sa surface roughness parameter was obtained below 0.6 µm in the whole range of used feed rates. The surface roughness parameter Sa measured on the surface after machining by special insert depends on the cutting conditions (wet and dry machining). After, the dry machining parameter Sa, similar to the Wiper insert, was below 0.6 µm in the whole range of used feed rates. Unfortunately, cutting Inconel 718 using special insert with feed rate f = 0.25 mm/rev and cooling generated a surface with Sa parameter over 2 times higher than for the same feed rate without cooling, while this parameter, after turning by conventional insert, increases over 4 times using feed rate f = 0.25 mm/rev compared to feed rate f = 0.05 mm/rev during machining with cooling. This ratio is lower for conventional insert in dry machining because of sticking, which arises at the smallest feed rate according to previous research.
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We present the deposition and characterization of tungsten-tantalum diboride (W,Ta)B2 coatings prepared by the high-power impulse magnetron sputtering technique. We evaluated the influence of pulse duration and substrate bias on the properties of (W,Ta)B2 films. A high hardness of up to 35 GPa measured by nanoindentation was simultaneously obtained with good elastic properties. Changing the pulse duration greatly affected the B/(W+Ta) atomic ratio, which influenced the properties of the coatings. The deposited films are thermally stable at up to 1000 °C in vacuum and are able to withstand oxidation at 500 °C.
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Attempts were made to describe the effect of the sintering temperature and pure iron powder addition on the properties of HSS-based materials produced by the spark plasma sintering method (SPS). After sintering, their density, hardness, flexural strength, and tribological properties were determined. The sintered materials were also subjected to microstructural analysis to determine the phenomena occurring at the particle contact boundaries during sintering. On the basis of analysis of the obtained results, it was found that the mechanical properties and microstructure were mainly influenced by the sintering temperature, which was selected in relation to the previously tested steel M3/2, adjusted upwards due to its chemical composition. The use of the temperature of 1050 °C allows materials to be obtained with a density close to the theoretical density (97%), characterized by a high hardness of about 360 HB. The addition of iron slightly reduces the hardness and also increases the flexural strength to 577 MPa. There was no diffusion of the alloying elements from the steel to the iron due to the short time of exposure to the sintering temperature.
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The paper presents the effect of the holding time, varying between 1 min 15 s and 10 min, on the microstructure evolution and development of selected properties of spark plasma sintered AA7075-based composites reinforced with 3, 5 and 10 wt% sub-micro B4C powder. The sintering temperature and the compaction pressure were 500 °C and 80 MPa, respectively. Composites with a near full density of 96-97% were obtained. Microstructure studies were performed employing the techniques of light microscopy and scanning electron microscopy, along with an analysis of the chemical composition in micro-areas. Additionally, the phase composition was investigated by means of X-ray diffraction. In addition, hardness and flexural strength tests were performed. It was found that the holding time did not significantly influence the microstructures of the examined materials nor the hardness or flexural strength. The sintered composites had a fine-grained microstructure with a strengthening phase located at the grain boundaries. As a result of the spark plasma sintering process, fine precipitates of intermetallic phases were also observed in the aluminum grains, suggesting partial supersaturation, which occurred during fast cooling.
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Zirconium is used as a structural material for use in aggressive environments, including the core of nuclear reactors. The traditional technology of manufacturing the structural elements of zirconium nuclear reactors is characterized by a long technological process and a significant amount of waste in the form of metal shavings. The paper presents the results of an alternative technology, spark plasma sintering, for manufacturing zirconium products. A complex of microstructural and mechanical studies of the obtained samples was carried out according to the ASTMB-351 standard. The sintering of zirconium powder and options for subsequent processing by various methods, including non-standard ones such as radial shear rolling, are justified.
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This paper describes the microstructure and properties of titanium-based composites obtained as a result of a reactive spark plasma sintering of a mixture of titanium and nanostructured (Ti,Mo)C-type carbide in a carbon shell. Composites with different ceramic addition mass percentage (10 and 20 wt %) were produced. Effect of content of elemental carbon covering nc-(Ti,Mo)C reinforcing phase particles on the microstructure, mechanical, tribological, and corrosion properties of the titanium-based composites was investigated. The microstructural evolution, mechanical properties, and tribological behavior of the Ti + (Ti,Mo)C/C composites were evaluated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction analysis (EBSD), X-ray photoelectron spectroscopy (XPS), 3D confocal laser scanning microscopy, nanoindentation, and ball-on-disk wear test. Moreover, corrosion resistance in a 3.5 wt % NaCl solution at RT were also investigated. It was found that the carbon content affected the tested properties. With the increase of carbon content from ca. 3 to 40 wt % in the (Ti,Mo)C/C reinforcing phase, an increase in the Young's modulus, hardness, and fracture toughness of spark plasma sintered composites was observed. The results of abrasive and corrosive resistance tests were presented and compared with experimental data obtained for cp-Ti and Ti-6Al-4V alloy without the reinforcing phase. Moreover, it was found that an increase in the percentage of carbon increased the resistance to abrasive wear and to electrochemical corrosion of composites, measured by the relatively lower values of the friction coefficient and volume of wear and higher values of resistance polarization. This resistance results from the fact that a stable of TiO2 layer doped with MoO3 is formed on the surface of the composites. The results of experimental studies on the composites were compared with those obtained for cp-Ti and Ti-6Al-4V alloy without the reinforcing phase.
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The paper presents the results of research on the tribological properties of spark-plasma-sintered Al-SiC composites. Composites with contents of 50 and 70 wt.% SiC were prepared. The sintering process was carried out using an HP D 25/3 spark plasma sintering furnace under vacuum, at the sintering temperature of 600 °C and compaction pressures of 50 and 80 MPa, respectively. The heating rate was 100 °C/min and the holding time was 10 min. Composites with a density of 91-100% were obtained. The tribological properties of the composites were evaluated based on weight loss and the coefficient of friction using a block-on-ring tribotester. Along with the weight percentage of SiC and compaction pressure, the sliding distance, and load during the tribological test were considered. Both the weight percentage of SiC and compaction pressure affected the tribological behavior of Al-SiC composites. It was found that the wear resistance was higher when a lower compaction pressure and a smaller amount of reinforcing phase (50 wt.%) were used.
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Combining high energy ball milling and spark plasma sintering is one of the most promising technologies in materials science. The mechanical alloying process enables the production of nanostructured composite powders that can be successfully spark plasma sintered in a very short time, while preserving the nanostructure and enhancing the mechanical properties of the composite. Composites with MAX phases are among the most promising materials. In this study, Ti/SiC composite powder was produced by high energy ball milling and then consolidated by spark plasma sintering. During both processes, Ti3SiC2, TiC and Ti5Si3 phases were formed. Scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction study showed that the phase composition of the spark plasma sintered composites consists mainly of Ti3SiC2 and a mixture of TiC and Ti5Si3 phases which have a different indentation size effect. The influence of the sintering temperature on the Ti-SiC composite structure and properties is defined. The effect of the Ti3SiC2 MAX phase grain growth was found at a sintering temperature of 1400-1450 °C. The indentation size effect at the nanoscale for Ti3SiC2, TiC+Ti5Si3 and SiC-Ti phases is analyzed on the basis of the strain gradient plasticity theory and the equation constants were defined.