Institute of Fundamental Technological Research

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.

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

In this work, tantalum-doped tungsten boride ceramic coatings were deposited from a single sputtering target with the radio frequency (RF) and high-power impulse magnetron sputtering (HiPIMS) methods. Two-inch torus targets were synthesised from pure elements with the spark plasma sintering (SPS) method with a stoichiometric composition of W1-xTaxB2.5 (x = 0, 0.08, 0.16, 0.24). Films were deposited with RF and HiPIMS power suppliers at process temperatures from RT to 600 °C. The substrate heating and the energy of the ionised material impacting the substrate increase the surface diffusivity of adatoms and are crucial in the deposition process. The results of SEM and XRD investigations clearly show that the addition of tantalum also changes the microstructure of the deposited films. The coatings without tantalum possess a finer microstructure than those with 24% of tantalum. The structure of films is homogeneous along the film thickness and composed mainly of columns with a (0001) preferred orientation. Deposited coatings are composed mainly of P6/mmm α-WB2 structures. The analysis of nanoindentation results allowed us to determine that ceramic coatings obtained with the HiPIMS method possess hardness above 41 GPa and a ratio of hardness to reduced Young modulus above 0.1. The thickness of HiPIMS-deposited films is relatively small: only around 60% of the RF magnetron sputtered coatings even when the average power input was two times higher. However, it has been shown that the RF coatings require heating the substrate above 400 °C to obtain a crystalline structure, while the HiPIMS method allows for a reduction of the substrate temperature to 300 °C.

RF magnetron sputtering, HiPIMS magnetron sputtering, Superhard ceramic coatings, Transition metal borides, Deposition temperature

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.

The paper presents experimental and numerical characterization of damage evolution for ion-irradiated materials subjected to plastic deformation during nano-indentation. Ion irradiation technique belongs to the methods where creation of radiation-induced defects is controlled with a high accuracy (including both, concentration and depth distribution control), and allows to obtain materials having a wide range of damage level, usually expressed in terms of displacements per atom (dpa) scale. Ion affected layers are usually thin, typically less than 1 micrometer thick. Such a low thickness requires to use nano-indentation technique to measure the mechanical properties of the irradiated layers. The He or Ar ion penetration depth reaches approximately 150 nm, which is sufficient to perform several loading-partial-unloading cycles at increasing forces. Damage evolution is reflected by the force-displacement diagram, that is backed by the stress–strain relation including damage. In this work the following approach is applied: dpa is obtained from physics (irradiation mechanisms), afterwards, the radiation-induced damage is defined in the framework of continuum damage mechanics to solve the problem of further evolution of damage fields under mechanical loads. The nature of radiation-induced damage is close to porosity because of formation of clusters of vacancies. The new mathematical relation between radiation damage (dpa) and porosity parameter is proposed. Deformation process experienced by the ion irradiated materials during the nano-indentation test is then numerically simulated by using extended Gurson–Tvergaard– Needleman (GTN) model, that accounts for the damage effects. The corresponding numerical results are validated by means of the experimental measurements. It turns out, that the GTN model quite successfully reflects closure of voids, and increase of material density during the nano-indentation.

radiation-induced damage, evolution of vacancy clusters, nano-indentation test, ion irradiation, radiation hardening

The study presents a detailed analysis of the impact of the coating type of silicon carbide particles and its share by volume on the microstructure and micromechanical properties of Cu-SiC composites. In order to protect the carbide from decomposition during the manufacturing of the composites, the surface of SiC was modified via a plasma vapour deposition technique with a layer of metals (W, Cr, Ti and Ni). Composites with a variable share of the ceramic phase (10–50 %vol.) were obtained at a temperature of 950 °C using spark plasma sintering. An analysis of the structures of the composites, especially in the metal-ceramic boundary region, was conducted with the use of scanning and transmission electron microscopy. The mechanical properties of the composites in the Cu-interface-SiC system were studied via a nanoindentation technique. The comparison of the results of hardness and Young's modulus studies were completed in relation to the actual structures of the materials, which in turn made it possible to determine the impact of the interfacial structure on the global properties of the composite materials.

copper-silicon carbide composites, nanoindentation, SPS, interface study