Effect of biocidal additives on the mesostructure of epoxy–siloxane bioactive coatings

We investigate the structure formation of sol–gel synthesized epoxy–siloxane compositions with a ratio of the main precursors of R _{TEOS/EPONEX 1510} = 27/27 wt %, modified with biocidal additives of detonation nanodiamonds (c _DND = 0.13, 0.27, and 0.58 wt %), titanium dioxide (\(^cTi{O_2}\) = 0.1, 0.3, and 0.5 wt %), and Photosens (c _Ph = 0.04, 0.1, and 0.27 wt %), by small-angle X-ray scattering. Based on small-angle X-ray scattering (SAXS) data, it is revealed that the synthesized epoxy–siloxane xerogels are systems with a twolevel fractal structure, in the formation of which the siloxane component plays the dominant role. It is found that the introduction of small additions of detonation synthesis, titanium dioxide, or Photosens (less than 1 wt %) into the epoxy–siloxane compositions affects both the fractal dimension D _S of the surface and the size d _c1 of primary particles, and the fractal dimension D _M and sizes d _c2 of mass fractal clusters formed from them.     

Surface characteristics of Zinc–TiO2 coatings prepared via micro-arc oxidation

Titanium (Ti) and its alloys are widely used as metallic biomaterials for fabrication of dental and orthopedic implants due to their favorable biocompatibility and corrosion resistance in a body environment. However, the thin oxide layer (TiO₂) on Ti substrate formed naturally in air or in many aqueous environments is bioinert and surrounded by fibrous tissues without producing any chemical or biological bond to bone when implanted. In the present work, Zinc-incorporated porous TiO₂ coatings (Zn–TiO₂) were prepared on Ti substrate by micro-arc oxidation (MAO) technique in the zinc gluconate-containing electrolyte. The surface morphology, cross-sectional morphology, composition, and phase of the coatings were analyzed using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffractometry, respectively. Surface topography and roughness of the coatings were investigated by atomic force microscopy operated in tapping mode. The results showed that Zn was successfully incorporated into the porous TiO₂ coatings, which did not alter apparently its surface topography and phase composition. In conclusion, the formation of porous Zn–TiO₂ coatings endow Ti with potential bioactivity and antibacterial activity, and we believe that the porous Zn–TiO₂ coatings on Ti by MAO technique might be promising candidates for orthopedic and dental implants     

Effect of cerium doping on corrosion resistance of amorphous silica–titanium sol–gel coating

The aim of this study was to investigate the effects of ceria doping on corrosion resistance of amorphous silica–titania coating. The microstructural and phase properties of titania–silica and titania–silica–Ceria composite films were investigated by SEM, EDAX and XRD. Potentiodynamic polarization and EIS spectroscopy have been used to study the corrosion behavior of composite coating in 3.5% NaCl solution. Results showed that by cerium doping into silica–titania coating as an inhibitor, the corrosion resistance of the film increased. In addition this study revealed that cerium doping enhanced pitting resistance of the coating.     

Effect of helium ion irradiation on the structure and electrical resistivity of nanocrystalline Cr–N and V–N coatings

The structural stability and electrical resistivity of nanocrystalline Cr–N and V–N coatings prepared by ion beam-assisted deposition were studied. The results showed that under helium ion irradiation up to doses of 1.0^.10¹⁷ ion/cm² the fine-crystalline objects successively increase their resistance without apparent structural changes. The subsequent dose increase leads to gas-vacancy void formation and chromium nitride structure destruction. The presence of the initial closed porosity in vanadium nitride favors its structural stability at investigated maximum damage doses.     

Electrofabrication of multilayer Fe–Ni alloy coatings for better corrosion protection

Electrofabrication of multilayer Fe–Ni alloy coatings were accomplished successfully on mild steel and their corrosion behaviors were studied. Multilayer comprised of alternatively formed ‘nano-size’ layers of Fe–Ni alloy of different composition have been produced from a single bath having Fe²⁺and Ni²⁺ ions using modulated (i.e. periodic pulse control) current density (cd). The deposition conditions were optimized for both composition and thickness of individual layers for best performance of the coatings against corrosion. The deposits were analyzed using scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), Hardness Tester, electrochemical AC and DC methods respectively. The multi layered deposits showed better corrosion resistances compared to the monolayer Fe–Ni (CR = 3.77 mm year^?1) coating deposited using DC from the same bath; the maximum corrosion resistance being shown by the coating having 300 layers, deposited at cyclic cathodic current densities of 2.0 and 4.0 A dm^?2 (CR = 0.03 mm year^?1). Drastic improvement in the corrosion performance of multilayer coatings were explained in the light of changed kinetics of mass transfer at cathode and increased surface area due to modulation and layering.     

Effect of electropulsing treatment on microstructure and tensile fracture behavior of aged Mg–9Al–1Zn alloy strip

The effect of electropulsing treatment (EPT) on the microstructure, mechanical properties, and tensile fracture behavior of aged Mg–9Al–1Zn alloy strip at room temperature was investigated. The results indicated that EPT accelerated the spheroidizing and dissolution of β phase tremendously in the aged Mg–9Al–1Zn alloy strip. The EPT-induced microstructural change resulted in remarkably increasing elongation to failure, remained tensile strength unchanged. A mechanism for rapid spheroidizing and dissolution process of β phase during EPT was proposed based on the reduction of nucleation thermodynamic barrier and enhancement of atomic diffusion. Fracture analysis showed that with increase in frequency of EPT transgranular dimple fracture becomes predominant instead of the quasicleavage fracture.     

Effect of thermo-mechanical process on structure and high temperature shape memory properties of Ti–15Ta–15Zr alloy

The effect of thermo-mechanical treatment on microstructure evolution, martensite transformation, and shape memory behavior of Ti–15Ta–15Zr high temperature shape memory alloy were investigated. Different martensite morphologies were found with different annealing temperatures. The Ti–15Ta–15Zr alloy exhibits almost perfect shape memory recovery strain of 6% after annealing at 973 K for 0.5 h.     

Effect of cooling speed on structure and properties of rapidly solidified Pb–25wt.% Sn alloy

The effect of cooling speed on structure, hardness, mechanical and electrical transport properties of rapidly solidified Pb–25wt.% Sn alloy have been investigated. A single roller melt spinning technique with linear speeds 15.7 and 31.7 m/s, was used for the preparation of specimens. The results showed that a lower cooling speed increased the precipitation of Sn in a Pb-matrix phase as compared with the higher cooling speed. This decomposition behavior decreased the electrical resistivity and increased the internal friction, thermal diffusivity and Vickers microhardness of the lower cooling speed as compared with those of the higher cooling speed.     

Thermal oxidation and structure of polylactide–polyethylene blends

The thermal oxidation of polylactide–low-density polyethylene mixtures with additives of oxidized polyethylene as an analogue of recyclable materials is studied. It is found that the polylactide is oxidized more slowly than polyethylene, whereas the introduction of up to 30 wt % of oxidized polyethylene accelerates the thermal oxidation of the mixtures, with the physical and mechanical properties of the resultant materials remaining suitable for practical use. It is established that the presence of oxidized polyethylene has virtually no effect on the melting point of polylactide and polyethylene, somewhat increasing, however, the degree of crystallinity of the components of the blend.     

Synergistic effect of ultrasonic cavitation erosion and corrosion of WC–CoCr and FeCrSiBMn coatings prepared by HVOF spraying

The high-velocity oxygen-fuel (HVOF) spraying process was used to fabricate conventional WC–10Co–4Cr coatings and FeCrSiBMn amorphous/nanocrystalline coatings. The synergistic effect of cavitation erosion and corrosion of both coatings was investigated. The results showed that the WC–10Co–4Cr coating had better cavitation erosion–corrosion resistance than the FeCrSiBMn coating in 3.5 wt.% NaCl solution. After eroded for 30 h, the volume loss rate of the WC–10Co–4Cr coating was about 2/5 that of the FeCrSiBMn coating. In the total cumulative volume loss rate under cavitation erosion–corrosion condition, the pure cavitation erosion played a key role for both coatings, and the total contribution of pure corrosion and erosion-induced corrosion of the WC–10Co–4Cr coating was larger than that of the FeCrSiBMn coating. Mechanical effect was the main factor for cavitation erosion–corrosion behavior of both coatings.     

Effect of lead on microstructure and some physical properties of Sn–Zn–Cd alloy

The effect of lead on the structure, electrical resistivity, internal friction, elastic modulus and thermal properties of Sn₈₁Zn₉Cd₁₀ ternary alloys have been investigated using different experimental techniques with their analysis. In addition, properties of this alloy were compared with other Sn–Zn or Sn–Zn–Cd alloys and commercial solder alloys. It has a higher electrical resistivity, internal friction and lower elastic modulus when compared with Sn–Zn or Sn–Zn alloys with other additions such as Cd, Bi or In. The Sn₆₁Zn₉Cd₁₀Pb₂₀ alloy has a lower melting point, electrical resistivity and internal friction when compared with the commercial Pb–Sn solder alloy, but it has a similar elastic modulus.     

Effect of growth rate and Mg content on dendrite tip characteristics of Al–Cu–Mg ternary alloys

An experimental analysis is presented to correlate the secondary dendrite arm spacing λ ₂ and dendrite tip radius R with growth rate V and Mg content C _0-Mg of Al–Cu–Mg ternary alloys. Under constant temperature gradient G (4.84±0.13 K mm⁻¹), a series of directional solidification experiments were performed at five different growth rates V (16.7–83.3 μm/s) and five different Mg contents C _0-Mg in Al–5 wt.% Cu–(0.5–5) wt.% Mg alloys. Solid–liquid interface was investigated from the longitudinal sections of the quenched samples, and λ ₂ and R were measured on the dendrite tips. The dependencies of λ ₂ and R on V and C _0-Mg were determined. The experimental results showed that the values of λ ₂ and R decrease as V and C _0-Mg increase at a constant G. The present exponent values related to V are found to be slightly lower than the values of the theoretical models and previous experimental works; however, C _0-Mg exponent values are found to be much lower than the theoretical models and previous experimental works. The ratio of the secondary dendrite arm spacing to the dendrite tip radius is 2.09±0.15, in good agreement with the scaling law. At a constant C _0-Mg, the values of VR ² were found to slightly increase with the ascending V. However, as C _0-Mg increases, the values of VR ² decrease.     

Atmosphere corrosion behavior of plasma sprayed and laser remelted coatings on copper

Nickel and chromium coatings were produced using plasma spraying and laser remelting on the copper sheet. The corrosion test was carried out in an acidic atmosphere, and the corrosive behaviors of both coatings and original copper samples were investigated by using an impedance comparison method. Experimental results show that nickel and chromium coatings display better corrosion resistance properties relative to the original pure copper sample. The corrosion rate of chromium coating is less than that of nickel coating, and corrosion resistances of laser remelted nickel and chromium samples are better than those of plasma sprayed samples. The corrosion deposit film of copper is loose compared with nickel and chromium.     

Preparation of metal–ceramic composites by sonochemical synthesis of metallic nano-particles and in-situ decoration on ceramic powders

Copper and nickel nanoparticles were synthesized using reducing agents in the presence of direct high energy ultra-sonication. The metallic nanoparticles were decorated on various ceramic substrates (e.g. α-Al₂O₃, and TiO₂) leading to metal reinforced ceramics with up to 45% metallic content. Different parameters, such as the amount of precursor material or the substrate, as well as the intensity of ultrasound were examined, in order to evaluate the percentage of final metallic decoration on the composite materials. All products were characterized by means of Inductively Coupled Plasma Spectroscopy in order to investigate the loading with metallic particles. X-ray Diffraction and Scanning Electron Microscopy were also used for further sample characterization. Selected samples were examined using Transmission Electron Microscopy, while finally, some of the powders synthesized, were densified by means of Spark Plasma Sintering, followed by a SEM/EDX examination and an estimation of their porosity.     

Effect of in vacuo surface pre-treatment on the growth kinetics and chemical constitution of ultra-thin oxide films on Al–Mg alloy substrates

The effect of in vacuo substrate surface pre-treatment on the growth kinetics and chemical constitution of ultra-thin (<3 nm) oxide films grown on bare Al–1.1 at.% Mg alloy surfaces was studied by a combined experimental approach of real-time in situ spectroscopic ellipsometry (RISE) and angle-resolved X-ray photoelectron spectroscopy (AR-XPS). One alloy surface pre-treatment prior to oxidation consisted of the removal of the native oxide and other contaminants on the alloy surface by sputter-cleaning under UHV conditions. A second surface pre-treatment involved exposing such sputter-cleaned surfaces to a short in vacuo annealing step at 460 K. Next, ultra-thin (<3 nm) oxide films were grown on these two pre-treated alloy surfaces by exposure to O₂(g) within the temperature range of T = 300–485 K (at pO₂ = 1 × 10^?4 Pa). It was found that, as long as the chemical segregation of Mg from the alloy’s interior to the alloy/oxide interface is kinetically hindered, the oxide-film growth kinetics, the developing oxide-film constitution, as well as the local chemical states of the Al and Mg cations in the oxide layer depend strongly on the alloy surface pre-treatment. At T ? 450 K, the thermally-activated interfacial segregation of Mg becomes pronounced and, only then, the developing oxide-film constitution is approximately independent of the surface pre-treatment.     

Effect of irradiation and pre-ageing temperature on the mechanical properties of Al–Si alloy

Al–1wt.%Si alloy samples in the solid solution state were irradiated with doses of gamma rays up to 1.75 MGy for 2 h in the temperature range from 423 to 553 K. Induced variations in structure, mechanical and electrical properties were traced by suitable techniques. Observed changes in the measured parameters, internal friction Q ^?1, thermal diffusivity D _th, dynamic elastic modulus Y and resistivity, ρ, were explained in terms of the role and mode of interaction of lattice defects in irradiated and thermally treated samples. Composition inhomogeneity and variations in mass distribution in the matrix were also considered. The structure identification of the samples was carried out by using conventional X-ray diffraction techniques and transmission electron microscopy micrographs.     

The structure of a long-period stacking phase in an Mg–Al–Y alloy studied by electron microscopy

A new phase with a 10H-type long-period stacking (LPS) structure was found in an Mg₇₅Al₁₀Y₁₅ alloy annealed at 823?K. The LPS structure in the Mg₇₅Al₁₀Y₁₅ alloy annealed at 823?K for 2?h has an ordered arrangement of L1₂-type structural Al₆Y₈ clusters on the two-dimensional plane parallel to the c-plane of hexagonal Mg lattice and a disordered arrangement along the c-axis, whereas a perfectly ordered structure along the c-axis, which has a period with two times of that of the 10H-type LPS structure, was established by annealing at 823?K for 24?h. The structural model of the ordered LPS phase is proposed by high-resolution images taken with a Cs-corrected scanning transmission electron microscope and also electron diffraction patterns.     

Effect of irradiation on microstructure and hardening of Cr–Fe–Ni–Mn high-entropy alloy and its strengthened version

ABSTRACT

A single-phase fcc high-entropy alloy (HEA) of 20%Cr–40%Fe–20%Mn–20%Ni composition and its strength with yttrium and zirconium oxides version was irradiated with 1.4?MeV Ar ions at room temperature and mid-range doses from 0.1 to 10 displacements per atom (dpa). Transmission electron microscopy (TEM), scanning transmission electron microscopy with energy dispersive X-ray spectrometry (STEM/EDS) and X-ray diffraction (XRD) were used to characterise the radiation defects and microstructural changes. Nanoindentation was used to measure the ion irradiation effect on hardening. In order to understand the irradiation effects in HEAs and to demonstrate their potential advantages, a comparison was performed with hardening behaviour of 316 austenitic stainless steel irradiated under an identical condition. It was shown that hardness increases with irradiation dose for all the materials studied, but this increase is lower in high-entropy alloys than in stainless steel.     

Preparation of biomedical Ag incorporated hydroxyapatite/titania coatings on Ti6Al4V alloy by plasma electrolytic oxidation

Nano-Ag incorporated hydroxyapatite/titania(HA/TiO2) coatings were deposited on Ti6Al4V substrates by the plasma electrolytic oxidation process. Compared with the substrate, the deposited coatings display attractive mechanical and biomedical properties. First, the coatings have stronger wear resistance and corrosion resistance. Second, they show a strong antibacterial ability. The mean vitality of the P. gingivalis on the coating surfaces is reduced to about 21%.Third, the coatings have good biocompatibility. The mean viability of the fibroblast cells on the coating surface is increased to about 130%. With these attractive properties, Ag incorporated HA/TiO2 coatings may be useful in the biomedical field.