A detailed mechanism of degradation behaviour of biodegradable as-ECAPed Zn-0.8Mg-0.2Sr with emphasis on localized corrosion attack.

In this study, advanced techniques such as atom probe tomography, atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy were used to determine the corrosion mechanism of the as-ECAPed Zn-0.8Mg-0.2Sr alloy. The influence of microstructural and surface features on the corrosion mechanism was investigated. Despite its significance, the surface composition before exposure is often neglected by the scientific community. The analyses revealed the formation of thin ZnO, MgO, and MgCO3 layers on the surface of the material before exposure. These layers participated in the formation of corrosion products, leading to the predominant occurrence of hydrozincite. In addition, the layers possessed different resistance to the environment, resulting in localized corrosion attacks. The segregation of Mg on the Zn grain boundaries with lower potential compared with the Zn-matrix was revealed by atom probe tomography and atomic force microscopy. The degradation process was initiated by the activity of micro-galvanic cells, specifically Zn - Mg2Zn11/SrZn13. This process led to the activity of the crevice corrosion mechanism and subsequent attack to a depth of 250 µm. The corrosion rate of the alloy determined by the weight loss method was 0.36 mm·a-1. Based on this detailed study, the degradation mechanism of the Zn-0.8Mg-0.2Sr alloy is proposed.

Effect of Annealing on the Surface Hardness of High-Fluence Nitrogen Ion-Implanted Titanium.

Commercially pure titanium grade II was kinetically nitrided by implanting nitrogen ions with a fluence in the range of (1-9)·1017 cm-2 and ion energy of 90 keV. Post-implantation annealing in the temperature stability range of TiN (up to 600 °C) shows hardness degradation for titanium implanted with high fluences above 6·1017 cm-2, leading to nitrogen oversaturation. Temperature-induced redistribution of interstitially located nitrogen in the oversaturated lattice has been found to be the predominant hardness degradation mechanism. The impact of the annealing temperature on a change in surface hardness related to the applied fluence of implanted nitrogen has been demonstrated.

Changes to Material Phase and Morphology Due to High-Level Molybdenum Doping of ZnO Nanorods: Influence on Luminescence and Defects.

The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods.

Effect of Double-Step and Strain-Assisted Tempering on Properties of Medium-Carbon Steel.

The present work aimed to study the properties of medium-carbon steel during tempering treatment and to present the strength increase of medium-carbon spring steels by strain-assisted tempering (SAT). The effect of double-step tempering and double-step tempering with rotary swaging, also known as SAT, on the mechanical properties and microstructure was investigated. The main goal was to achieve a further enhancement of the strength of medium-carbon steels using SAT treatment. The microstructure consists of tempered martensite with transition carbides in both cases. The yield strength of the DT sample is 1656 MPa, while that of the SAT sample is about 400 MPa higher. On the contrary, plastic properties such as the elongation and reduction in area have lower values after SAT processing, about 3% and 7%, respectively, compared to the DT treatment. Grain boundary strengthening from low-angle grain boundaries can be attributed to the increase in strength. Based on X-ray diffraction analysis, a lower dislocation strengthening contribution was determined for the SAT sample compared to the double-step tempered sample.

Microstructural and Mechanical Characterization of Newly Developed Zn-Mg-CaO Composite.

In this study, the Zn-0.8Mg-0.28CaO wt.% composite was successfully prepared using different conditions of ball milling (rotations and time) followed by a direct extrusion process. These materials were characterized from the point of view of microstructure and compressive properties, and the correlation between those characteristics was found. Microstructures of individual materials possessed differences in grain size, where the grain size decreased with the intensified conditions (milling speed and time). However, the mutual relation between grain size and compressive strength was not linear. This was caused by the effect of other factors, such as texture, intermetallic phases, and pores. Material texture affects the mechanical properties by a different activity ratio between basal and pyramidal slips. The properties of intermetallic particles and pores were determined in material volume using micro-computed tomography (µCT), enhancing the precision of our assumptions compared with commonly applied methods. Based on that, and the analysis after the compressive tests, we were able to determine the influence of aspect ratio, feret diameters, and volume content of intermetallic phases and pores on mechanical behavior. The influence of the aspects on mechanical behavior is described and discussed.

Poly(4-Styrenesulfonic Acid-co-maleic Anhydride)-Coated NaGdF4:Yb,Tb,Nd Nanoparticles with Luminescence and Magnetic Properties for Imaging of Pancreatic Islets and ß-Cells.

Novel Yb,Tb,Nd-doped GdF3 and NaGdF4 nanoparticles were synthesized by a coprecipitation method in ethylene glycol (EG) in the presence of the poly(4-styrenesulfonic acid-co-maleic anhydride) stabilizer. The particle size and morphology, crystal structure, and phase change were controlled by adjusting the PSSMA concentration and source of fluoride anions in the reaction. Doping of Yb3+, Tb3+, and Nd3+ ions in the NaGdF4 host nanoparticles induced luminescence under ultraviolet and near-infrared excitation and high relaxivity in magnetic resonance (MR) imaging (MRI). In vitro toxicity of the nanoparticles and their cellular uptake efficiency were determined in model rat pancreatic ß-cells (INS-1E). As the NaGdF4:Yb,Tb,Nd@PSSMA-EG nanoparticles were non-toxic and possessed good luminescence and magnetic properties, they were applicable for in vitro optical and MRI of isolated pancreatic islets in phantoms. The superior contrast was achieved for in vivo T2*-weighted MR images of the islets transplanted under the kidney capsule to mice in preclinical trials.

Anisotropic Strain in Rare-Earth Substituted Ceria Thin Films Probed by Polarized Raman Spectroscopy and First-Principles Calculations.

Lattice strain in oxygen ion conductors can be used to tune their functional properties for applications in fuel cells, sensors, or catalysis. However, experimental measurements of thin film strain in both in- and out-of-plane directions can be experimentally challenging. We propose a method for measuring strain in rare-earth doped ceria thin films by polarized Raman spectroscopy. We study epitaxial CeO2 films substituted by La, Gd, and Yb grown on MgO substrates with BaZrO3 and SrTiO3 interlayers, where different levels of strain are generated by annealing at distinct temperatures. The films show in-plane compression and out-of-plane expansion, resulting in a lowering from the bulk cubic to tetragonal lattice symmetry. This leads to the splitting of the F2g Raman mode in the cubic phase to B2g and Eg modes in the tetragonal lattice. The symmetry and frequency of these modes are determined by polarized Raman in the backscattering and right-angle scattering geometries as well as by first-principal calculations. The frequency splitting of the two modes is proportional to the strain measured by X-ray diffraction and its magnitude agrees with first-principles calculations. The results offer a fast, nondestructive, and precise method for measuring both in- and out-of-plane strain in ceria and can be readily applied to other ionic conductors.

Influence of surface pre-treatment with mechanical polishing, chemical, electrochemical and ion sputter etching on the surface properties, corrosion resistance and MG-63 cell colonization of commercially pure titanium.

The impact of four pre-treatment techniques on the surface morphology and chemistry, residual stress, mechanical properties, corrosion resistance in a physiological saline solution and cell colonization of commercially pure titanium is examined in detail. Mechanical polishing, electrochemical etching, chemical etching in Kroll's reagent, and ion sputter etching with argon ions were applied. Surface morphologies reflect the nature of surface layer removal. Significant roughening of the surface and a characteristic microtopology become apparent as a result of the sensitivity of chemical and ion sputter etching to the grain orientation. The hardness in the near surface region was controlled by the amount of residual stress. Etching of the stressed surface layer led to a reduction in residual stress and surface hardness. A compact passivation layer composed of TiO, TiO2 and Ti2O3 native oxides imparted high corrosion resistance to the surface after mechanical polishing, chemical and electrochemical etching. The ion sputter etched surface showed substantially reduced corrosion resistance, where the corrosion process was controlled by electron transfer. The specific topology affected the adhesion of the cell to the surface rather than the cell area coverage. The cell area coverage increased with the corrosion stability of the surface.

Extrusion of the biodegradable ZnMg0.8Ca0.2 alloy - The influence of extrusion parameters on microstructure and mechanical characteristics.

The Zn-based alloys, alloyed with the elements of the 2nd group of the periodic table, are considered as potential biodegradable materials suitable for the fabrication of small orthopaedic implants or cardiovascular stents. Unfortunately, the as-cast Zn-based alloys do not fulfil the requirements for mechanical properties for such applications. Extrusion is a thermomechanical process which is very powerful for breaking the cast microstructure and enhancing mechanical characteristics of metallic materials. In this study, we focused on the influence of extrusion parameters, such as temperature and extrusion ratio, on microstructural and mechanical characteristics of a ZnMg0.8Ca0.2 (wt.%) alloy. The extrusion led to a significant grain refinement and the formation of a crystallographic texture. Extrusion temperature played a more significant role in the mean grain size compared to the extrusion ratio (ER). At lower extrusion temperatures, the texture was less intensive and the subsequent mechanical anisotropy was weaker. Constants for the prediction of the grain size based on the Zener-Hollomon parameter were obtained. Prediction of mechanical properties using the Hall-Petch relationship appeared to be difficult because of the dependence of the texture on the extrusion temperature. Extrusion at the temperatures of 200 °C (ER = 25:1) and 150 °C (ER = 11:1) led to mechanical performance fulfilling the requirements for implantology.

Structure and Properties of High­Strength Ti Grade 4 Prepared by Severe Plastic Deformation and Subsequent Heat Treatment.

Severe plastic deformation represented by three passes in Conform SPD and subsequent rotary swaging was applied on Ti grade 4. This process caused extreme strengthening of material, accompanied by reduction of ductility. Mechanical properties of such material were then tuned by a suitable heat treatment. Measurements of in situ electrical resistance, in situ XRD and hardness indicated the appropriate temperature to be 450 °C for the heat treatment required to obtain desired mechanical properties. The optimal duration of annealing was stated to be 3 h. As was verified by neutron diffraction, SEM and TEM microstructure observation, the material underwent recrystallization during this heat treatment. That was documented by changes of the grain shape and evaluation of crystallite size, as well as of the reduction of internal stresses. In annealed state, the yield stress and ultimate tensile stress decreased form 1205 to 871 MPa and 1224 to 950 MPa, respectively, while the ductility increased from 7.8% to 25.1%. This study also shows that mechanical properties of Ti grade 4 processed by continual industrially applicable process (Conform SPD) are comparable with those obtained by ECAP.

Laser-synthesized nanocrystalline, ferroelectric, bioactive BaTiO3/Pt/FS for bone implants.

The goal of our study is to design BaTiO3 ferroelectric layers that will cover metal implants and provide improved osseointegration. We synthesized ferroelectric BaTiO3 layers on Pt/fused silica substrates, and we studied their physical and bio-properties. BaTiO3 and Pt layers were prepared using KrF excimer laser ablation at substrate temperature Ts in the range from 200°C to 750°C in vacuum or under oxygen pressure of 10 Pa, 15 Pa, and 20 Pa. The BaTiO3/Pt and Pt layers adhered well to the substrates. BaTiO3 films of crystallite size 60-140 nm were fabricated. Ferroelectric loops were measured and ferroelectricity was also confirmed using Raman scattering measurements. Results of atomic force microscopy topology and the X-ray diffraction structure of the BaTiO3/Pt/fused silica multilayers are presented. The adhesion, viability, growth, and osteogenic differentiation of human osteoblast-like Saos-2 cells were also studied. On days 1, 3, and 7 after seeding, the lowest cell numbers were found on non-ferroelectric BaTiO3, while the values on ferroelectric BaTiO3, on non-annealed and annealed Pt interlayers, and on the control tissue culture polystyrene dishes and microscopic glass slides were similar, and were usually significantly higher than on non-ferroelectric BaTiO3. A similar trend was observed for the intensity of the fluorescence of alkaline phosphatase, a medium-term marker of osteogenic differentiation, and of osteocalcin, a late marker of osteogenic differentiation. At the same time, the cell viability, tested on day 1 after seeding, was very high on all tested samples, reaching 93-99%. Ferroelectric BaTiO3 films deposited on metallic bone implants through a Pt interlayer can therefore markedly improve the osseointegration of these implants in comparison with non-ferroelectric BaTiO3 films.

Gas-sensing behaviour of ZnO/diamond nanostructures.

Microstructured single- and double-layered sensor devices based on p-type hydrogen-terminated nanocrystalline diamond (NCD) films and/or n-type ZnO nanorods (NRs) have been obtained via a facile microwave-plasma-enhanced chemical vapour deposition process or a hydrothermal growth procedure. The morphology and crystal structure of the synthesized materials was analysed with scanning electron microscopy, X-ray diffraction measurements and Raman spectroscopy. The gas sensing properties of the sensors based on i) NCD films, ii) ZnO nanorods, and iii) hybrid ZnO NRs/NCD structures were evaluated with respect to oxidizing (i.e., NO2, CO2) and reducing (i.e., NH3) gases at 150 °C. The hybrid ZnO NRs/NCD sensor showed a remarkably enhanced NO2 response compared to the ZnO NRs sensor. Further, inspired by this special hybrid structure, the simulation of interaction between the gas molecules (NO2 and CO2) and hybrid ZnO NRs/NCD sensor was studied using DFT calculations.

PLD prepared bioactive BaTiO3 films on TiNb implants.

BaTiO3 (BTO) layers were deposited by pulsed laser deposition (PLD) on TiNb, Pt/TiNb, Si (100), and fused silica substrates using various deposition conditions. Polycrystalline BTO with sizes of crystallites in the range from 90nm to 160nm was obtained at elevated substrate temperatures of (600°C-700°C). With increasing deposition temperature above 700°C the formation of unwanted rutile phase prevented the growth of perovskite ferroelectric BTO. Concurrently, with decreasing substrate temperature below 500°C, amorphous films were formed. Post-deposition annealing of the amorphous deposits allowed obtaining perovskite BTO. Using a very thin Pt interlayer between the BTO films and TiNb substrate enabled high-temperature growth of preferentially oriented BTO. Raman spectroscopy and electrical characterization indicated polar ferroelectric behaviour of the BTO films.

Structure determination of KLaS2, KPrS2, KEuS2, KGdS2, KLuS2, KYS2, RbYS2, NaLaS2 and crystal-chemical analysis of the group 1 and thallium(I) rare-earth sulfide series.

One of the purposes of this work is to provide a crystallographic review of group 1 and thallium rare-earth ternary sulfides M(+)Ln(3+)S2. We have therefore determined crystal structures of KLaS2, KPrS2, KEuS2, KGdS2, KLuS2, KYS2, RbYS2, which belong to the α-NaFeO2 structural family (R3m), as well as NaLaS2, which is derived from the disordered NaCl structural type (Fm3m). The determined structures were compared with known members of the group 1 as well as thallium(I) rare-earth sulfides by the standard tools of crystal-chemical analysis such as comparison of bond-valences, analysis of interatomic distances and comparison of the unit-cell parameters. The results indicate why the cubic structural type is limited to Li(+) and Na(+) members of the series only. The analysis has also revealed frequent problems in the reported crystal structures, especially in the determination of the K(+) compounds, probably due to severe absorption and different accuracy and sensitivity of various instruments. Intense diffuse scattering has been discovered in NaLaS2, which will be the subject of further investigation. The newly determined as well as already known structures are summarized, together with critical comments about possible errors in the previous structure determinations.

The effect of antiphase boundaries on the elastic properties of Ni-Mn-Ga austenite and premartensite.

The evolution of elastic properties with temperature and magnetic field was studied in two differently heat-treated single crystals of the Ni-Mn-Ga magnetic shape memory alloy using resonant ultrasound spectroscopy. Quenching and slow furnace cooling were used to obtain different densities of antiphase boundaries. We found that the crystals exhibited pronounced differences in the c' elastic coefficient and related shear damping in high-temperature ferromagnetic phases (austenite and premartensite). The difference can be ascribed to the formation of fine magnetic domain patterns and pinning of the magnetic domain walls on antiphase boundaries in the material with a high density of antiphase boundaries due to quenching. The fine domain pattern arising from mutual interactions between antiphase boundaries and ferromagnetic domain walls effectively reduces the magnetocrystalline anisotropy and amplifies the contribution of magnetostriction to the elastic response of the material. As a result, the anomalous elastic softening prior to martensite transformation is significantly enhanced in the quenched sample. Thus, for any comparison of experimental data and theoretical calculations the microstructural changes induced by specific heat treatment must be taken into account.