[Show abstract][Hide abstract] ABSTRACT: The interactions of prime interstitial and alloying elements in hexagonal Ti were investigated using a density functional theory calculations. The binding energies of oxygen with all substitution elements whose solubility limit in α-Ti is greater than 3 at% were calculated. The investigations performed reveal no attraction between Zn, Zr, Ag and O, and strong O–Sc and O–Sn binding. It was found that the O–X clustering mechanism is based on a direct and long-range O–X interaction, both controlled by valence structure and electronegativity of substitational elements. The single crystal and isotropic elastic constants together with Pugh's plasticity criterion were calculated for Ti with multiple point defects to evaluate their impact on mechanical properties. The results obtained reveal that a low concentration of O improves ductility in Ti + Sc solid solutions and increases the brittleness of Ti + Sn alloys. The diverse effect on ductility is due to different chemical bond types in the vicinity of O. The results show that the interstitial-substitational elements clustering effect may be used to optimize mechanical properties of α-Ti alloys.
[Show abstract][Hide abstract] ABSTRACT: Electrospun polymeric submicron and nanofibers can be used as tissue engineering scaffolds in regenerative medicine. In physiological conditions fibers are subjected to stresses and strains from the surrounding biological environment. Such stresses can cause permanent deformation or even failure to their structure. Therefore, there is a growing necessity to characterize their mechanical properties, especially at the nanoscale.
[Show abstract][Hide abstract] ABSTRACT: The Portevin–Le Chatelier effect manifests itself as an unstable plastic flow which occurs during tensile tests of some dilute materials in a certain range of temperatures and strain rates. This phenomenon is also exceptionally intense in nickel based superalloys used in the aerospace industry. The aim of this research was to investigate the Portevin–Le Chatelier effect in Inconel 718 solution strengthened superalloy. The tested material was subjected to tensile tests carried out within the temperature range 250–600 °C with three different strain rates 2×10−3 s−1, 10−2 s−1 and 5×10−2 s−1. The strain curves were analyzed in terms of intensity and statistical behavior. A quantitative method to describe the phenomenon was used in the study. The results indicate the presence of clear trends with temperature and strain rates. Additional optical observations were carried out to assess the changes of the microstructure.
Materials Science and Engineering A 12/2014; 619:158–164. · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study concerns imaging of the structure of materials using AFM tapping (TM) and phase imaging (PI) mode, using probes modified with Focused Ion Beam (FIB). Three kinds of modifications were applied–thinning of the cantilever, sharpening of the tip and combination of these two modifications. Probes shaped in that way were used for AFM investigations with Bruker AFM Nanoscope 8. As a testing material, titanium roughness standard supplied by Bruker was used. The results show that performed modifications influence the oscillation of the probes. In particular thinning of the cantilever enables one to acquire higher self-resonant frequencies, which can be advantageous for improving the quality of imaging in PI mode. It was found that sharpening the tip improves imaging resolution in tapping mode, which is consistent with existing knowledge, but lowered the quality of high frequency topography images. In this paper the Finite Element Method (FEM) was used to explain the results obtained experimentally.
[Show abstract][Hide abstract] ABSTRACT: The aim of this research was to investigate the influence of a geometrical notch on the Portevin–Le Chatelier effect. This phenomenon manifests itself as the serrated stress–strain curve obtained for certain materials when they undergo plastic deformation during tensile tests. The Portevin–Le Chatelier effect can often be observed in aluminum alloys especially those with an addition of magnesium. The material examined in the present experiments was a model Al–3Mg alloy. Samples were prepared with notches cut in the specimens with different depths and shapes. The results clearly indicate that the notch has a significant influence on the Portevin–Le Chatelier effect. With increasing notch depth, the stress amplitude of the serrations increases together with their frequency and the course of the serrations changes.
[Show abstract][Hide abstract] ABSTRACT: Corrosion behavior of a metallic biomaterial is an important characteristic because the biocompatibility of a biomedical grade metallic implant is primarily related to corrosion behavior. The aim of this research was to study the effect of Equal Channel Angular Pressing (ECAP) process on corrosion behavior of the AISI 316L type austenitic stainless steel. ECAP was conducted on an AISI 316L stainless steel up to eight passes. Scanning transmission electron microscopy (STEM) technique was utilized to study the microstructure of the as-received material and the samples subjected to ECAP. Electrochemical corrosion polarization and electrochemical impedance spectroscopy tests were performed in Ringer solution in order to determine and compare the corrosion behavior of initial coarse-grained and ECAP-ed specimens as an indication of biocompatibility. The results showed that an ultrafine-grained/ nanocrystalline 316L stainless steel with a mean grain size of about 78 nm was obtained after performing the eight passes of ECAP. The corrosion resistance of 316L stainless steel was improved considerably by increasing of the number of ECAP passes. After performing the eight passes of ECAP process, the corrosion rate of 316L stainless steel measured to be 0.42 μA.cm2 which is significantly lower than that of initial coarse-grained material (3.12 μA.cm2).
[Show abstract][Hide abstract] ABSTRACT: Precipitation strengthening of an ultrafine-grained Al-Mg-Si alloy has been studied using samples obtained by hydrostatic extrusion. It has been demonstrated that the microstructure after hydrostatic extrusion consists of two types of grains: (1) nano-sized free of dislocations and surrounded with high angle grain boundaries and (2) micron-sized with dislocation substructure. After ageing at 160 °C, small needle-like precipitates appear in grain interiors of both nano- and micron-sized grains, bringing about a significant strength improvement. However, the precipitates are smaller than those in their coarse grained counterparts. As a consequence, they constitute weaker barriers for dislocations and induce a lower strengthening effect. In addition, one may observe intensive precipitation at nano-grains boundaries, which further reduces the strengthening effect. It was also shown that peak ageing and overageing take place for much shorter time than in the case of coarse grained samples and are caused by the grain growth rather than a change in the precipitation state.
Materials Science and Engineering A 07/2014; 609:80–87. · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper the effect of production method and heat treatment of magnesium alloys to their corrosion resistance is presented. The study was carried out on the AZ91D alloy obtained by permanent mould casting, pressure die casting and pressure die casting with the subsequent heat treatment. Studies of the microstructure were carried out using a light microscope. The corrosion resistance was examined using the Potentiodynamic Test. The surface observations after corrosion tests were carried out using the Scanning Electron Microscope (SEM). It was stated that the best corrosion resistance is typical for AZ91D alloy produced by pressure die casting method with heat treatment. The alloy after permanent mould casting has got the worst corrosive properties.
[Show abstract][Hide abstract] ABSTRACT: Bone tissue has a composite nature given by a highly complex and well-harmonized structure of organic and inorganic components on the microscale, macroscale and nanoscale. Thus, biodegradable composite scaffolds made of poly (ε-caprolactone) urethane (PCL_PUR) porous matrix and calcium carbonate (CaCO3) were developed and studied for bone tissue engineering. The aim of this work was to examine the structure of new polyurethane/calcite composites. Micro-computer tomography (μ-CT) and image analysis enabled 3D visualization and quantification of the porosity, wall thickness and internal pore size distribution. The fabricated porous polyurethane composites exhibited porosity >70% with a pore size not exceeding 450 μm and wall thickness about of 50 μm in size. The mechanical properties of the foams were evaluated using Dynamic Mechanical Analysis (DMA). In-vitro bioactivity tests in simulated body fluid (SBF) were carried out and the marker of bioactivity, e.g. formation of surface bone-like apatite layers upon immersion in SBF, was investigated. Our results indicated that PUR/calcite scaffolds were more activity then PUR scaffolds and possessed the function to enhance cell proliferation and differentiation, and might be used as bone tissue engineering materials.
Journal of Bioprocessing and Biotechniques. 04/2014; 4(3).
[Show abstract][Hide abstract] ABSTRACT: The precipitation phenomena in 7475 nanograined aluminium alloy was analysed by means of microhardness measurements, small angle X-ray scattering and electron microscopy. The nanograined samples were obtained by the hydrostatic extrusion of solution annealed and water quenched samples. It has been established that low temperature ageing causes precipitation processes to occur. However, the precipitation phenomena in nanograined materials proceed differently to those in micrograined materials. Moreover, the particle strengthening is limited by enhanced grain boundary precipitation which does not contribute to an increase in strength (when dislocation slip is the dominant deformation mechanism) and by the smaller size of precipitates.
[Show abstract][Hide abstract] ABSTRACT: Equal channel angular pressing (ECAP) CP-Ti Ultrafine-grained materials Corrosion resistance Cell behavior The electrochemical and cellular behavior of commercially pure titanium (CP-Ti) with both ultrafine-grained (UFG) and coarse-grained (CG) microstructure was evaluated in this study. Equal channel angular pressing was used to produce the UFG structure titanium. Polarization and electrochemical impedance tests were carried out in a simulated body fluid (SBF) at 37 °C. Cellular behaviors of samples were assessed using fibroblast cells. Results of the investigations illustrate the improvement of both corrosion and biological behavior of UFG CP-Ti in comparison with the CG counterpart.
Materials Science and Engineering C 03/2014; · 2.74 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nerve tissue engineering (TE) is a rapidly expanding area of research advancing towards the repair and regeneration of non-union peripheral nerve defects caused by injuries. The current challenge for researchers is to develop a biomimetic scaffold that is capable of stimulating the re-growth of the native tissue, thus structurally mimicking the extracellular matrix (ECM), providing chemical guidance cues and mechanical support for re-enervation of the damaged region. Laminin is a glycoprotein naturally occurring in nerves and it plays a significant role towards the migration of nerve cells and axonal outgrowth. In this study, laminin incorporated scaffolds were produced by co-axial electrospinning and blend electrospinning techniques, in order to develop suitable biomaterial constructs for peripheral nerve tissue regeneration. Core–shell and blend nanofibers of laminin incorporated poly(L-lactic acid)-co-poly(ε-caprolactone) (PLCL) with diameters of 316 ± 110 nm and 350 ± 112 nm were respectively, fabricated and the morphology, surface hydrophilicity, chemical and mechanical properties were investigated. The ability of attachment and proliferation of Schwann cells on the electrospun nanofibrous scaffolds was investigated by cell proliferation assay and their phenotype was evaluated by immunocytochemical staining using specific S100 antibody. The cells were found to attach and proliferate on core–shell PLCL–laminin scaffolds, expressing bi- and tri-polar elongations retaining their typical phenotype. Results of 7 days of in vitro culture of Schwann cells, showed 78% increase in cell proliferation on core–shell structured nanofibers compared to blend PLCL–laminin scaffolds, which confirmed the potential application of these constructs as substrates for peripheral nerve regeneration.
European Polymer Journal 01/2014; 50:30–38. · 3.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Fabrication of scaffolds for tissue engineering (TE) applications becomes a very important research topic in present days. The aim of the study was to create and evaluate a hybrid polymeric 3D scaffold consisted of nano and microfibers, which could be used for bone tissue engineering. Hybrid structures were fabricated using rapid prototyping (RP) and electrospinning (ES) methods. Electrospun nanofibrous mats were incorporated between the microfibrous layers produced by RP technology. The nanofibers were made of poly(L-lactid) and polycaprolactone was used to fabricate microfibers. The micro- and nanostructures of the hybrid scaffolds were examined using scanning electron microscopy (SEM). X-ray microtomographical (μCT) analysis and the mechanical testing of the porous hybrid structures were performed using SkyScan 1172 machine, equipped with a material testing stage. The scanning electron microscopy and micro-tomography
analyses showed that obtained scaffolds are hybrid nanofibers/microfibers structures with high porosity and interconnected pores ranging from 10 to 500um. Although, connection between microfibrous layers and electrospun mats remained consistent under compression tests, addition of the nanofibrous mats affected the mechanical properties of the scaffold, particularly its elastic modulus. The results of the biocompatibility tests did not show any cytotoxic effects and no fibroblast after contact with the scaffold showed any damage of the cell body, the cells had proper morphologies and showed good proliferation. Summarizing, using RP technology and electrospinning method it is possible to fabricate biocompatible scaffolds with controllable geometrical parameters and good mechanical properties.
BULLETIN OF THE POLISH ACADEMY OF SCIENCES. 01/2014; 62(3):551-556.
[Show abstract][Hide abstract] ABSTRACT: Fatigue crack growth tests are performed to determine materials service life using standardized geometry of samples and test procedures, which are difficult to fulfill in the case of ultrafine-grained metals, such as obtained by hydro-extrusion. This calls for the use of mini-samples. However, mini-samples require a special approach to displacement measurements.
The aim of the present study was to demonstrate the possibility of fatigue crack growth rate tests with mini-samples made of Al 5483 and 7475 alloys in as delivered states and subjected to the grain size refinement by hydro-extrusion. The optical Digital Image Correlation, DIC, was used to this end. The results of the measurements were transformed into maps of displacements near to the crack tip registered at the maximum load for pre-selected loading cycles. The displacement fields were subsequently used to determine stress intensity factor values, positions of the crack tip and to develop Paris plots. The results allowed to compare fatigue crack growth rates in standard and ultrafine-grained aluminum alloys.
Mechanics of Materials 12/2013; 67:46–52. · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the reported work, the combination of severe plastic deformation (SPD) and annealing under high hydrostatic pressure was used to enhance the ductility whilst maintaining the high mechanical strength possessed by the nanostructured 316LVM stainless steel. The nanostructure was obtained by a multi-step hydrostatic extrusion process to a total true strain of 1.8. This process produced a microstructure consisting of nanotwins and shear bands. The extruded samples were annealed at 700 and 900 °C for 10 min under atmospheric or hydrostatic pressures of 2 or 6 GPa. The resulting microstructures were examined using TEM and FIB techniques. The microstructural observations and X-ray measurements were used to estimate the crystallite sizes. The mechanical properties were determined by microhardness and tensile tests. It was established that annealing under high pressure improved the ductility of the material whilst retaining its high ultimate tensile strength.
Mechanics of Materials 12/2013; 67:25–32. · 2.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work, the effects of vanadium addition in the range of 0.3-3%
(in weight percent) for an oxide dispersion strengthened reduced
activation ferritic (ODS RAF) steel were investigated. Samples of the
V-modified steel have been prepared using elemental (Fe, Cr, W, Ti) and
Y2O3 powders with the nominal composition of
Fe-14Cr-2W-0.3Ti-0.3Y2O3. Consolidated and heat
treated samples were investigated using Scanning Electron Microscopy and
Scanning Transmission Electron Microscopy equipped with Electron Energy
Loss Spectroscopy detector. Hardness and Charpy impact tests (KLST
specimens) were also performed. The microstructure investigations
revealed numerous particles of the size up to 0.5 μm. They are
primarily Ti-Cr-V oxides located at the grain boundaries and inside the
grains. These particles increase hardness and significantly reduce
fracture resistance of the ODS RAF alloys developed here. However, it
should be noted that the 0.3% V-ODS steel has unexpectedly the lowest
transition temperature of about 282 K and that the 1-3% V-ODS steels, in
spite of the transition temperature about 373 K, exhibit almost two
times higher the lower shelf energy values in comparison with the 0.3%
V-ODS and 0% V-ODS steels.
Journal of Nuclear Materials 11/2013; 442(1-3). · 2.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ab-initio molecular dynamics (MD) study of oxygen ion diffusion in the oxide ion conducting solid electrolyte δ-Bi3YO6 is presented. Vacancy ordering models were tested by structure relaxation and that for < 111 > vacancy pairs was found to have the highest total energy per atom, while those for < 110 >, < 100 > and random vacancy distributions were found to have similar energies. Evidence for polarization of bismuth charge density is seen for < 100 > and < 110 > vacancy pair configurations, consistent with stereochemical activity of the Bi 6s2 lone pair. MD studies of oxygen diffusion were carried out at three temperatures. Vacancy pair alignments during these simulations were predominantly in the < 110 > direction, consistent with previous neutron total scattering results.
Solid State Ionics 09/2013; s 245–246:43–48. · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, the stability of grain size and oxide nanoparticles in the ODS steel upon annealing at high temperature (650–1350 °C) has been evaluated. The ODS Fe–Cr–W–Ti–Y2O3 steel has been manufactured by powder metallurgy, consolidated by hot isostatic pressing and processed by hydrostatic extrusion. Such a processing brings about ultrafine grain structure reinforced with oxide nanoparticles (few nm in diameter) and results in superior mechanical properties. The stability of nano-oxides has been analyzed by small angle X-ray scattering together with transmission electron microscopy. The results obtained revealed excellent thermal stability of ultrafine grained ODS ferritic steel, which was attributed to the resistance of oxides against coarsening.
Journal of Materials Science 07/2013; 48(13):4620-4625. · 2.31 Impact Factor