The surface chemistry and microstructures of titanium alloys (both new and used) and CoCrMo alloys used for hip and knee endoprostheses were determined using SEM (morphology), EBSD (phase analysis), AES and XPS (surface chemistry). Two new and two used endoprostheses were studied. The SEM SE and BE images showed their microstructures, while the EBSD provided the phases of the materials. During the production of the hip and knee endoprostheses, these materials are subject to severe thermomechanical treatments and physicochemical processes that are decisive for CoCrMo alloys. The AES and XPS results showed that thin oxide films on (a) Ti6Al4V are primarily a mixture of TiO2 with a small amount of Al2O3, while the V is depleted, (b) Ti6Al7Nb is primarily a mixture of TiO2 with a small amount of Al2O3 and Nb2O5, and (c) the CoCrMo alloy is primarily a mixture of Cr2O3 with small amounts of Co and Mo oxides. The thin oxide film on the CoCrMo alloy should prevent intergranular corrosion and improve the biocompatibility. The thin oxide films on the Ti alloys prevent further corrosion, improve the biocompat- ibility, and affect the osseointegration.
COBISS.SI-ID: 1331882
Contact type of tribofilms formed under the tribological contact of CrN coated steel samples subjected to lubricated reciprocating sliding contact under different contact conditions was investigated. Contact surface and tribofilms formed were studied by X-ray Photoelectron Spectroscopy (XPS). Sample surfaces were first imaged by Scanning Electron Microscopy (SEM) to determine areas of tribofilm formation as well as areas not affected by tribological contact. In these areas survey and high resolution (HR) XPS measurements were performed to obtain information about surface chemistry and oxidation states of the constituent elements. It was found that differences between different samples, observed by the XPS measurements, may reflect differences in chemistry of tribofilms formed under different contact conditions.
COBISS.SI-ID: 1288874
This work investigates the evolution from superhydrophilic to superhydrophobic surface state on corrosion behaviour of SS316L produced by Nd:YAG nanosecond direct laser texturing (DLT). Results confirm perfect correlation among wettability and corrosion, hence superhydrophobic surface with a contact angle of 168 +/- 3.0° reflects in enhanced passivity, lower anodic dissolution and corrosion current reduction. Characterization of the corrosion attack by 3D microscopy reveals high sensitivity of superhydrophilic surfaces on corrosion propagation direction in regard to the laser beam passage (90°/0°). However, this trend completely diminishes with superhydrophobic development. Further, DLT also completely prohibits intergranular corrosion detected with the non-processed sample.
COBISS.SI-ID: 15482907
Research published in leading journal in this field in North-Holland; Applied Surface Science. The study of the temperature dependence of tin and antimony segregation at grain boundaries of binary Fe–Sb and Fe–Sn polycrystalline alloys using Auger Electron Spectroscopy suggests that during the brittle intergranular fracture mainly the general grain boundaries are opened in the samples annealed at low temperatures which are more segregated than the special ones. On the contrary, the special grain boundaries are opened in the samples annealed at higher temperatures because – as a consequence of the enthalpyentropy compensation effect – they are more enriched by the solute. The limiting temperature between these two states is the so-called compensation temperature. Therefore, the temperature dependence of the grain boundary segregation measured in polycrystals should be described by two sets of the thermodynamic parameters (i.e. segregation enthalpy and entropy): one of them correlating the segregation under the compensation temperature, the other one for the segregation at higher temperatures.
COBISS.SI-ID: 1180330
In this study we determine the optimal parameters for surface modification using the laser surface melting of powder-metallurgy processed, vanadium-rich, cold-work tool steel. A combination of steel pre-heating, laser surface melting and a subsequent heat treatment creates a hardened and morphologically modified surface of the selected high-alloy tool steel. The pre-heating of the steel prior to the laser surface melting ensures a crack- and pore-free modified surface. Using a pre-heating temperature of 350 °C, the extremely fine microstructure, which typically evolves during the laser-melting, became slightly coarser and the volume fraction of retained austenite was reduced. In the laser-melted layer the highest values of microhardness were achieved in the specimens where a subsequent heat treatment at 550 °C was applied. The performed thermodynamic calculations were able to provide a very valuable assessment of the liquidus temperature and, especially, a prediction of the chemical composition as well as the precipitation and dissolution sequence for the carbides.
COBISS.SI-ID: 13845275
Oxidation state of individual alloying elements (Si, Al) and impurity element (Cu) upon segregation onto the surface of the sample FeSiAl alloys was investigated in an in situ study of segregation behavior in ultra-high vacuum. Chemical state of surface Si, Al and O as well as Cu was evaluated, by measuring the kinetic energy shifts that affect Si KLL, Al KLL, O KLL but also Cu LMM transitions, depending on chemical state of the element. It was found that Al oxidizes with temperature in all samples while Si behaves differently with maximum oxidation occurring around 300 °C, and oxidation not occurring at all in some samples. Segregated Cu stays predominantly in its elemental state which is consistent with relevant literature reports.
COBISS.SI-ID: 13283355
In this paper we focus on the preparation and mechanical properties of the nanosilica-reinforced, epoxy resin Epikote 828LVEL. Epoxy composites containing two sizes of spherical silica nanoparticles, 130 nm and 30 nm, were prepared at a fixed volume fraction (VP = 0.5%). To prevent agglomeration, the silica fillers were initially pre-treated with diglycidyl ether of bisphenol A (BADGE). Due to the low content of silica fillers, their inclusion in the matrix was confirmed by the increased roughness of a fracture surface compared to the smooth surface of the neat epoxy. Raman spectroscopy was employed to obtain additional information about the crack-propagation path. The mechanical properties, characterized by a three-point bending test, revealed a 10- 20% increase in the composite's modulus of elasticity with 30-nm and 130-nm silica-filler inclusions. Elongation at break, on the other hand, decreased for 5-10% in both composites compared to neat epoxy, suggesting brittle fracture behavior in silica/epoxy composites. The fracture toughness results showed a 25-30% improved toughening for both composites compared to the pure epoxy. The composite's resistance to failure in terms of the impact energy was, however, strongly dependent on the size of the silica: we observed a 30% increase for the 130-nm, and a 60% increase for the 30-nm, silica/epoxy composites, compared to the pure epoxy.
COBISS.SI-ID: 5394970
Zn-Al metallized film capacitors in two different production stages were investigated to explain the decrease of capacitors performance with time. Unsealed and sealed capacitors with different aluminium content in metallization layer were investigated. Scanning electron microscopy (SEM) was used to image the surface of the metallization layers, Energy dispersive X-ray spectroscopy (EDS) was used to determine the chemical composition and Auger electron spectroscopy (AES) was used to determine the chemical composition of the top of the metallization layers as well as to estimate the degree of oxidation. It was found that air humidity degraded the metallization layer of unsealed capacitors, especially at lower Al contents. Sealed capacitors were exposed to high electric fields, typical for standard usage. It was found - rather unexpectedly ž that the perfomance was decreased by increasing Al content. A crystallographic explanation was proposed.
COBISS.SI-ID: 953514
The decomposition of commercially available TiH[sub]2 was investigated while performing different thermal treatments. TiH[sub]2 powder, which is widely used as a foaming agent, was heat treated at 450 [compositum]C for various times, from 15 min. to 120 min. Scanning electron microscopy (SEM) images of the surfaces at different magnifications were obtained and interpreted. A Bragg-Brentano X-ray diffractometer was used to measure the X-ray diffraction (XRD) spectra on all five samples. A close examination of the diffraction spectra showed that for an as-received sample and samples undergoing the longest thermal treatment (1 and 2 h) these spectra can be explained as deriving from cubic TiH[sub]1.924, while for the other two samples they can beexplained as deriving from tetragonal TiH[sub]1.924. A constant-unit-cell-volume phase transition between the cubis and tetragonal phase in TiH[sub]{2-y}-type compounds had been described in the literature. The unit-cell parameters obtained from measured spectra confirm that within the measurement uncertainty the unit-cell volume is indeed constant in all five samples. Thermogravimetry (TG) and differential thermal analysis (DTA) measurements were performed on all the samples, showing that the intensity of the dehydrogenation depends on the previous treatment of the TiH[sub]2. After the thermal analysis XRD of the samples was performed again and the material was found to exhibit a Ti-like unit cell, but slightly enlarged due to the unreleased hydrogen.
COBISS.SI-ID: 924074
The evolution of the passive films on 2205 duplex stainless steel (2205 DSS) and AISI 316L stainless steel in artificial saliva, and with the addition of fluoride, was studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic measurements. The extent of the passive range increased for the 2205 DSS compared to the AISI 316L in both solutions. The formation of the passive film was studied by EIS at the opencircuit potential (OCP). The passive layers were studied at the OCP by Xray photoelectron spectroscopy (XPS). The passive films on both materials predominantly contained Cr oxides, whereas the Fe species were markedly depleted.
COBISS.SI-ID: 24275239