Instytut Podstawowych Problemów Techniki

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This study investigates the effect of Nb concentration on the mechanical properties, superelasticity, as well as deformation behavior of metastable β-phase Ti–Nb alloys produced via powder metallurgy. The alloys were fabricated through mechanical alloying, followed by consolidation using hot pressing. The resulting microstructure comprises fine β-phase grains with TiC carbide precipitates at the grain boundaries. The study reveals non-linear variations in the values of yield strength for the manufactured materials, which were attributed to the occurrence of various deformation mechanisms activated during the loading. It was found that the mechanisms change with the increasing concentration of Nb in the manner: stress-induced martensitic transformation, twinning, slip. However, all these mechanisms were activated at a reduced concentration of Nb compared to the materials obtained by casting technology previously reported in the literature. This is most probably associated with the elevated oxygen content, which affects the stability of the parent β-phase. The study revealed that superelasticity in Ti–Nb-based alloys prepared using powder metallurgy may be achieved by reducing the content of β-stabilizing elements compared to alloys obtained by conventional technologies. In this study, the Ti–14Nb (at. pct) alloy exhibited the best superelasticity, whereas conventionally fabricated Ti–Nb alloys displayed superelasticity at an Nb concentration of approximately 26 at. pct. The developed material exhibited a non-conventional, one-stage yielding behavior, resulting in a superelastic response at significantly higher stresses compared to conventionally fabricated Ti–Nb alloys.

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Oxide Dispersion Strengthened (ODS) ferritic steels are promising materials for the nuclear power sector. This paper presents the results of a study on the sintering process using the Spark Plasma Sintering (SPS) technique, focusing on ODS ferritic steel powders with different contents (0.3 and 0.6 vol.%) of Y2O3. The novelty lies in the analysis of the effect of pre-annealing treatment on powders previously prepared by mechanical alloying on the microstructure, mechanical, and thermal properties of the sinters. Using the SPS method, it was possible to obtain well-densified sinters with a relative density above 98%. Pre-annealing the powders resulted in an increase in the relative density of the sinters and a slight increase in their thermal conductivity. The use of low electron energies during SEM analysis allowed for a fairly good visualization of the reinforcing oxides uniformly dispersed in the matrix. Analysis of the Mössbauer spectroscopy results revealed that pre-annealing induces local atomic rearrangements within the solid solution. In addition, there was an additional spectral component, indicating the formation of a Cr-based paramagnetic phase. The ODS material with a higher Y2O3 content showed increased Vickers hardness values, as well as increased Young’s modulus and nanohardness, as determined by nanoindentation tests.

Słowa kluczowe:

spark plasma sintering, ODS ferritic steel, mechanical alloying, Mössbauer spectroscopy, nanoindentation

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The paper presents the effect of He+ ion irradiation of selected polymeric materials: poly(tetrafloroethylene), poly(vinyl chloride), ethylene-propylene-diene monomer rubber, nitrile-butadiene rubber, styrene-butadiene rubber, and natural rubber, on their chemical composition, physical structure, and surface topography. The modification was studied by scanning electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, and differential scanning calorimetry. Irradiation with a high-energy ion beam leads to the release of significant amounts of hydrogen from the surface layer, resulting in an increase in cross-linking that manifests itself by shrinkage of the surface layer, which in turn causes significant stresses leading to the formation of a crack pattern on the polymer surface. The development of microroughness is combined with oxidation. Shallow range of the ions makes the modified layer “anchored” in the substrate via bulk macromolecules, assuring its good durability and adhesion to elasto-plastic substrates. Changes in the surface layer were manifested by the modification of functional properties of the polymers. The hardness of the layer subjected to the ion irradiation process increases even up to 10 times. After modification with the ion beam, a significant decrease in frictional forces was also observed, even up to 5–6 times. The microscopic analysis of wear traces confirmed that the wear resistance also significantly increased. However, ion bombardment of polymeric materials caused a reduction in their mechanical strength (despite the range limited to the surface layer of the order of micrometers) and electrical resistance, which has a negative impact on the possibility of using the materials in some applications.

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The performance of the present-day scanning electron microscopy (SEM) extends far beyond delivering electronic images of the surface topography. Oxide dispersion strengthened (ODS) steel is on of the most promising materials for the future nuclear fusion reactor because of its good radiation resistance, and higher operation temperature up to 750°C. The microstructure of ODS should not exceed tens of nm, therefore there is a strong need in a fast and reliable technique for their characterization. In this work, the results of low-kV SEM characterization of nanoprecipitates formed in the ODS matrix are presented. Application of highly sensitive photo-diode BSE detector in SEM imaging allowed for the registration of single nm-sized precipitates in the vicinity of the ODS alloys. The composition of the precipitates has been confirmed by TEM-EDS.

Słowa kluczowe:

ODS steels, scanning electron microscopy, spark plasma sintering

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