Evaluation of in vitro and in vivo tests for surface-modified titanium by H<Subscript>2</Subscript>SO<Subscript>4</Subscript> and H<Subscript>2</Subscript>O<Subscript>2</Subscript> treatment

Titanium is widely used as an implant material for artificial teeth. Furthermore, various studies have examined surface treatment with respect to the formation of a fine passive film on the surface of commercial titanium and its alloys and to improve the bioactivity with bone. However, there is insufficient data about the biocompatibility of implant materials in the body. The purpose of this study was to examine whether surface modification affects the precipitation of apatite on titanium metal. Specimens were chemically washed for 2 min in a 1∶1∶1.5 (vol.%) mixture of 48 %HF, 60%HNO₃ and distilled water. The specimens were then chemically treated with a solution containing 97%H₂SO₄ and 30%H₂O₂ at the ratio of 1∶1 (vol.%) at 40°C for 1h, and subsequently heat-treated at 400°C for 1h. All the specimens were immersed in HBSS with pH 7.4 at 36.5°C for 15d, and the surface was examined with TF-XRD, SEM, EDX and XPS. In addition, specimens of commercial pure Ti, with and without surface treatment, were implanted in the abdominal connective tissue of mice for 28 d. Conventional aluminum and stainless steel 316L were also implanted for comparison. An amorphous titania gel layer was formed on the titanium surface after the titanium specimen was treated with a solution of H₂SO₄ and H₂O₂. The average roughness was 2.175 μm after chemical surface treatment. The amorphous titania was subsequently transformed into anatase by heat treatment at 400°C for 1h. The average thickness of the fibrous capsule surrounding the specimens implanted in the connective tissue was 47.1μm in the chemically treated Ti, and 52.2, 168.7 and 101.9μm, respectively, in the untreated commercial pure Ti, aluminum and stainless steel 316L.     

Cyclic Oxidation of P91 by Thermogravimetry and Investigation of Integrity of Scale by “Transient-Mass-Gain” Method

The growth and degradation of the oxide scale on modified 9Cr–1Mo ferritic steel was studied at 1123 K using a thermogravimetric balance by employing the “transient-mass-gain method” in conjunction with the adaptation of a cyclic-oxidation procedure. The total duration of the oxidation was 1000 h. The experiment revealed that the cracking of the scale was initiated when the average thickness was 72 μm. Spallation occurred when the average thickness was 75 μm. The rate of spallation was found to be enhanced as the scale thickens and attained a higher rate after 90 μm. The rate constants for the different stages of oxidation were found to be different. The specimen was examined by SEM, EDS and XRD. The scale morphology revealed outwardly protruded growth, a uniform adherent oxide layer and a spalled region. Four oxide phases were identified; Cr₂O₃, Fe₂O₃, (FeCr)₂O₃ and FeCr₂O₄. The spall contained more (FeCr)₂O₃ whereas the adherent scale was more FeCr₂O₄.     

The effect of nitric acid surface treatment on CaP deposition of Ti6Al4V open-cell foams in SBF solution

The effect of nitric acid surface treatment on CaP deposition of an open-cell Ti6Al4V foam (60% porous and 300-500 ?m in pore size), prepared by means of the space holder method using 94 and 66 μm average particle size powders, was investigated in a simulated body fluid (SBF) solution up to 14 days. Although, nitric acid surface treatment did not change the foam flat surface roughness values significantly, it increased surface area difference greatly by introducing nano scale undulations on the surface. The increased surface area difference was found to be more pronounced in smaller particle size foam samples. A continuous relatively thin CaP coating layer formed after 5 and 14 days of SBF immersion in nitric acid surface treated small and larger average particle size foam specimens, respectively. Whereas, the cells of untreated foam specimen were observed to be filled with CaP precipitates and a continuous CaP layer development was found after 14 days of SBF immersion. These results were also confirmed with the grazing incidence XRD and FTIR analysis of SBF immersed specimens.     

Manufacture and properties of cold spray deposited large thickness Cu coating material for sputtering target

In this study, the manufacture of a large thickness Cu coating layer as sputtering target material via a cold spray coating process was undertaken. The microstructure and properties of the Cu layer as the sputtering target material (before and after the annealing heat treatment) were evaluated, compared, and analyzed. To evaluate the purity, density, grain size and uniformity, microstructure, and properties of the Cu-coated layer as a sputtering target, X-ray diffraction, ICP analysis, SEM, EBSD, porosity analysis, and Vickers hardness tests were performed. The result of the observation of the layer’s purity and microstructure showed that a purity level (99.47%) similar to that of the early powder 2N5 was maintained and that the manufacture of a cold spray deposited, ∼20 mm thick Cu coating material for the sputtering target was performed successfully. As a result of the EBSD mapping, the average grain size near the interface and around the center measured 1.48 μm and 1.49 μm; the grains were small and non-uniform compared with the 1.91 μm size near the surface. Note, however, that the recrystallization and grain growth (caused by annealing) increased the grain size to 1.82 μm (near the interface), 1.83 μm (near the center), and 1.87 μm (near the surface) and improved the level of uniformity. Moreover, through post heat treatment, the overall porosity declined (0.44 % porosity/400 °C/h heat treatment), and the grain texture became uniform. The possibility of controlling the microstructure as a large thickness sputtering target by conducting an annealing heat treatment was also confirmed. Nonetheless, the differences in the porosity and hardness associated with the coating thickness changes were partially maintained. Based on the aforementioned findings, this study suggests that by using cold spray deposition, Cu coating layers with large thicknesses can be applied as a sputtering target.     

Dense Si3N4 coatings with high friction coefficient deposited by high-velocity pulsed plasma spraying

A novel electromagnetically accelerated plasma spraying technique was applied to mixtures of αSi₃N₄, and alumina, yttria, and silica additives to deposit thin coatings (50–100 μm) onto mirror-polished stainless steel surfaces. The dense coatings consisted of crystalline αSi₃N₄ with minor amounts of β'SiAlON, traces of βSi₃N₄ and Y₃Al₅O₁₂ as well as a quinary Si−Al−N−O−Y glass. The adhesion strengths depended on the powder particle size showing values of>77 MPa for coarse powders (median grain size 25 μm) and>67 MPa for fine powders (median grain size 8 μm). The average indentation hardnesses were 450 HV_0.025 (coarse powder) and 620 HV_0.025 (fine powder); the sliding wear resistances were comparable to those of sintered Si₃N₄ used as counterbody in a pin-on-disc friction test. The friction coefficient showed surprisingly large values (1.0–1.1 in water and 1.3–1.4 in air), suggesting application of such coatings as tribological high-friction surfaces.     

Duplex stainless steel fracture surface analysis using x-ray fractography

The fatigue fracture surface of a duplex stainless steel was analyzed using x- ray fractography. A lower than average austenite content was observed at the fracture surface due to the transformation of austenite into deformation- induced martensite. The influence of fatigue cycling on the transformation was confined to a depth of about 30 μm below the fracture surface. X- ray analyses of both the ferrite- martensite and the austenite phases indicated residual stresses (σ_r) increasing with depth from the fracture surface and reaching a maximum some tens of microns below the fracture surface. The lower σ_r observed at the fracture surface has been attributed to the stress relaxation effects caused by the new fracture surfaces created in the crack growth process. The observed decrease in full width at half maximum (FWHM) in the ferrite- martensite phase was presumed to be due to the dynamic recovery effect that was likely to occur within the material close to the crack tip as a consequence of fatigue cycling.     

Oxidation of nitride layers formed on Ti-6Al-4V alloys by gas nitriding

Ti-6Al-4V alloys were nitrided through gas nitriding at 950 °C for 3 h in deoxygenated, atmospheric nitrogen gas. During nitriding, nitrogen reacted and diffused into the alloys to form Ti₂N and a meager amount of TiN in a Ti-N compound layer with a thickness of 20 μm to 25 μm. An α-Ti(N) diffusion layer with a thickness of 40 μm to 80 μm formed below this layer. A small amount of Al was dissolved at the top of the Ti-N compound layer because of the strong interaction of nitrogen with Ti and Al. Nitriding resulted in the dissolution of interstitial nitrogen and the formation of nitrides. Oxidation of the nitrided Ti-6Al-4V alloys initially resulted in the formation of a Ti-N-O layer, which later oxidized to TiO₂. Above 800 °C, the nitrided alloys oxidized rapidly, accompanied by microcracking of the TiO₂ surface layer.     

Coating of Ni powders through micronozzle in a nano particle deposition system

Nano particle deposition system (NPDS) is a novel method to deposit ceramic and metal powders at room temperature. Nickel powders with a size of 3 μm in diameter were sprayed through the fabricated micro nozzle, varying stand-off distance (SoD), which is a gap between the end of the nozzle and the substrate. Injection time for Ni powders was set to 1 min and the flow rate of air-powder was kept to 10 l/min. When SoD was 300 μm, the average deposition thickness was measured to be 2.49 μm, whereas the average deposition thickness was 300 nm for SoD being 500 μm. Therefore, Ni powder deposition at a SoD of 300 μm was successful compared to a SoD of 500 μm with minimal deposition. Moreover, electrical resistance of the deposited film was measured to study its characteristics. Resistivity of the film deposited at a SOD of 300 μm was substantially lower than that of the film deposited at a SoD of 500 μm, confirming the successful deposition at a SoD of 300 μm. Finally, heated treatment of the deposited Ni powders to 150 °C improved the electrical conductivity significantly by lowering its resistivity to 4.4 × 10⁻⁷ Ωm.     

Printing gold nanoparticles with an electrohydrodynamic direct-write device

A dispersion containing 15nm gold particles in ethanol was subjected to electrohydrodynamic atomization, producing droplets with an average size of ≈26μm as measured by laser diffraction. An electrohydrodynamic direct-write device was used to deposit the dispersion onto silicon wafers with the intention of printing gold tracks. Immediately after deposition ethanol evaporated, leaving the gold particles organised in a ≈75μm wide central region surrounded by two regions, each ≈50μm wide, at the edge of which two further gold tracks, each ≈7μm existed.     

The influence of magnetic and dielectric loss on the noise absorption of iron particles-rubber composites attached to a microstrip line

Magnetic and dielectric loss are systematically controlled by using iron flake powders with various initial sizes (7 μm and 70 μm) as the absorbent fillers in the rubber matrix, and their noise absorbing characteristics have been investigated as a function of frequency and sheet thickness. Flake iron particles were prepared by the mechanical forging of spherical powders using an attrition mill. Composite sheets (thickness=0.2 mm-1.0 mm) were prepared with a mixture of iron particles and silicone rubber. Attaching the composite sheets to a microstrip line of 50 Ω, a network analyzer was used to measure the reflection and transmission parameters (S₁₁ and S₂₁, respectively). A nearly constant value of S₁₁ (about −10 dB) was observed, irrespective of particle size. However, S₂₁ is strongly dependent upon initial particle size. For the composites of 7 μm particles (with high magnetic loss), S₂₁ is reduced below −20 dB in the frequency range of 1 GHz to 10 GHz, and the corresponding bandwidth of noise absorption is not so greatly diminished by reducing the sheet thickness as low as 0.2 mm. For the composites of 70 μm particles (with high dielectric loss), however, the bandwidth is greatly reduced with a decrease in sheet thickness. It is concluded that the attenuation of conduction noise through the microstrip line is primarily controlled by the magnetic loss of the iron particles due to strong magnetic field around the microstrip line.     

The effect of fluoride treatment on titanium treated with anodic spark oxidation

This study examined the effect of fluoride on the surface characteristics of an anodized titanium implant. Commercial pure titanium plate 20mm×10mm×2mm in size, and discs 1.5 mm thick and 1.5 mm in diameter, were used. The prepared samples were polished with #200 to #1, 000 SiC papers and were then washed sequentially with distilled water, alcohol and acetone. Anodic oxidation was performed using a regulated DC power supply in an electrolyte containing a mixture of 0.015 M DL-α-glycerophosphate disodium salt hydrate (DL-α-GP) and 0.2 M calcium acetate hydrate (CA) with an electric current density of 30mA/cm² and voltage ranging from 0 to 290 V. The specimens were divided into four groups and a fluoride treatment was carried out. Group 1 was thermally treated in a 0.05 M TiF₃ solution at 90°C, Group 2 was electrochemically treated at 150 V in a 0.05 M TiF₃ solution, Group 3 was electrochemically treated at 150 V in a 0.05 M NaF solution, and Group 4 was electrochemically treated at 150 V in a 0.05 M HF solution. A porous oxide layer containing pores 1–4 μm in size was observed on the surface treated with anodic oxidation. The diameter of the pores was higher in the protrusion areas than in the sunken areas. A significant amount of fluoride ions was released in the initial period, with small amounts being released continuously thereafter. The viability of MC3T3 cells was high when the fluoride ion concentration was 10 ppm, but decreased with further increases in the fluoride concentration. A six-week immersion test in simulated body fluid (SBF) showed dense HA crystals in the group immersed in 0.05 M TiF₃ at 90°C, which indicated good biocompatibility.     

Effect of pore size on the high temperature oxidation of Ni-Fe-Cr-Al porous metal

This study investigated the effect of the pore size of Ni-22.4%Fe-22%Cr-6%Al porous metal on its hightemperature oxidation. Two types of open porous metals with pore sizes of 800 μm and 580 μm were used. A 24-hour isothermal oxidation test was conducted at three different temperatures of 900 °C, 1000 °C, and 1100 °C under a 79% N₂ + 21% O₂ atmosphere. The results of the BET analysis revealed that the specific surface area increased as the pore size decreased from 800 μm to 580 μm. The high-temperature oxidation results showed that porous metals exhibited far lower levels of oxidation resistance compared with bulk metals, and that the oxidation resistance of porous metals decreased with a decreasing pore size. According to the microstructural observations of the oxide layers, the 900 °C and 1000 °C oxidation layer contained Ni, Cr, and Al oxides mainly on the strut. The 800 μm porous metal strut exhibited similar oxidation behavior at 1100 °C to that found at lower temperatures. In contrast, the 580 μm porous metal strut was found to consist of Ni and Fe oxides in the upper layer and Ni, Cr, and Al oxides in the lower layer, representing a low oxidation resistance. For powders affixed to the strut inside the porous metal, a different oxide-forming behavior from that of the strut was observed. In addition, the Ni-Fe-Cr-Al porous metal high-temperature oxidation microscopic mechanism is also discussed.     

The retentiveness of ceramic microfiltration membranes with respect to ferric iron ions

The retentiveness of microfiltration membranes based on crystalline silicon dioxide with an average pore size of 3 μm with respect to ferric iron ions Fe(III) is studied. A correlation between the state of Fe(III) in water solutions and the degree of retention, as well as the membrane surface origin and structural properties, is found. A comparative assessment of the retentiveness of the microfiltration ceramic and ultrafiltration polyamide membranes—with an average pore size of 7.8 nm—with respect to Fe(III) ions is made.     

Effect of SiC particle size on flexural strength of porous self-bonded SiC ceramics

Porous self-bonded silicon carbide (SBSC) ceramics were fabricated from SiC powders with various particle sizes (0.7 μm, 25 μm, 50 μm, 65 μm), plus Si, C and boron (as a sintering additive). The effects of submicron (0.7 μm) SiC particle incorporation into the SBSC and the SiC particle size (25 μm, 50 μm, 65 μm) on the flexural strength and porosity of the ceramics were investigated as a function of sintering temperature. Incorporating 0.7 μm SiC particles into the ceramic material containing 25 μm SiC particles increased the flexural strength by 3 times, from 11.7 MPa up to 35.5 MPa after sintering at 1800 °C. Simultaneously, the porosity was reduced by ∼5 %. Furthermore, the flexural strength of ceramic with 25 μm SiC particles was superior to that with 65 μm SiC particles. Generally, the flexural strength of the SBSC increased as, both, a function of submicron SiC particle incorporation along with relatively small micron-sized particles (25 μm) in the microstructure of the ceramic plus increased sintering temperature.     

Development of plasma nitrocarburizing and post-oxidation technology for the replacement of Cr<Superscript>6+</Superscript> plating for application to vehicle engine shafts

Plasma nitrocarburizing and post-oxidation treatments were performed to improve the wear and corrosion resistance of S45C steel. Plasma nitrocarburizing was conducted for 3 h at 570°C in a nitrogen, hydrogen and methane atmosphere to produce the ε-Fe₂₋₃(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of the ∈-phase with traces of the γ′-Fe₄(N,C) phase. The thickness of the compound layer was approximately 12 μm and the diffusion layer was approximately 300 μm in thickness. Plasma post oxidation was performed on nitrocarburized samples with various oxygen/hydrogen ratios at a constant temperature of 500°C for 1 h. The very thin magnetite (Fe₃O₄) layer 1 μm to 2 μm in thickness on top of the compound layer was obtained by plasma post oxidation. It was also confirmed that further improvement of the corrosion characteristics of the nitrocarburized compound layer was possible with an application of the superficial magnetite layer. Finally, throttle valve shafts of S45C steel were treated under optimum plasma processing conditions. Accelerated life time test results using a throttle body assembled with a shaft treated by plasma nitrocarburising and post oxidation showed that plasma nitrocarburizing and plasma post-oxidation processes could be a viable technology in the very near future in place of Cr⁶ plating.     

Growth behaviors of GaN/Si heteroepitaxy with various terrace widths grown by the LEPS method

Epilayers of GaN were grown on patterned Si (111) substrates of various terrace widths by means of metal organic chemical vapor deposition. The technique of lateral epitaxy on a patterned substrate used the growth of GaN epilayers from the periodic and parallel stripes that form as a result of the substrate etching. Silicon substrates were patterned for various terrace widths of 3 μm, 8 μm, and 18 μm. A low temperature AlN was used as a seed layer for the growth of a 1.5 μm thick GaN epilayer. The as-grown samples were characterized by using double-crystal X-ray diffractometry (DCXRD), photoluminescence and atomic force microscopy (AFM). From the DCXRD spectra, the full width at half maximum (FWHM) of the samples was found to decrease as the terrace width decreased. This behavior indicates that there is an improvement in the crystalline quality of the GaN epilayers as the terrace width decreases. The photoluminescence spectra reveal a decrease in the FWHM and an increase in the peak intensity as the terrace width decreases. This behavior indicates that there is an improvement in the optical quality of the GaN epilayer as the terrace width decreases. The atomic force micrographs reveal a dislocation-free homogeneous surface in the trench region compared to the terrace region with defects such as pits and dislocations. The results clearly show that GaN epilayers grown on a patterned Si substrate with a terrace width 3 μm have a good crystalline quality with minimal threading dislocation and excellent band edge emission.     

Temperature and grain size dependence of superplasticity in a Zn−0.3wt.%Al alloy

The superplastic deformation behavior of quasi-single phase Zn-0.3 wt. %Al was investigated. A series of load relaxation and tensile tests was conducted at various temperatures ranging from RT (20 °C) to 200 °C. The recently proposed internal variable theory of structural superplasticity was applied. The flow curves obtained from load relaxation tests were shown to consist of contributions from interface sliding (IS) and accommodating plastic deformation. In the case of quasi-single phase Zn-0.3 wt.% Al alloy with an average agrain size of 1 μm, the IS behavior could be described as a viscous flow process characterized by a power index of M_g=0.5. A large elongation of about 1400% was obtained at room temperature and the strain rate sensitivity parameter was about 0.4. Although relatively large-grained (10 μm) single phase alloy showed a high value of strain rate sensitivity comparable to that of fine-grained alloy at very low strain rate range, IS was not expected from the analysis based on the internal variable theory of structural superplasticity at room temperature. As the temperature increased above 100 °C, however, the contribution from IS was observed at a very low strain rate range. A high elongation of ∼400% was obtained in a specimen of 10-μm-grain-size at 200 °C under a strain rate of 2×10⁻⁴/sec. Jointly appointed at Center for Advanced Aerospace Materials (CAAM)     

Characterization of irradiated simulated DUPIC fuel

A simulated DUPIC (Direct Use of Spent PWR Fuel in CANDU Reactors) fuel was irradiated at HANARO research reactor of KAERI in 1999. Post-irradiation examinations, such as measurements of γ-scanning, profilometry, density, hardness, microstructure, and fission product distribution were performed on the irradiated simulated DUPIC fuel. In γ-scanning, the intensity along the axial direction was sharply decreased at the areas between the pellets. There was no significant change in the profilometry of SEU-1.47%, but variation was detected in SEU-2.19%+F.P by 67 μm, and the peaks precisely coincided with the ridges of the pellets. The marked difference between SEU-1.47% and SEU-2.19%+F.P pellets after irradiation was the configuration of cracks arised in the pellets. Some large equiaxed grains of 11.1 μm were observed at the center of the SEU-2.19%+F.P pellet, while the grain size near the surface of the pellet was remained almost the same as the original grain size of 5.58 μm. The hardness had no tendency toward change to the direction, but average hardness was increased as much as 10% compared with a fresh simulated DUPIC fuel. This article is based on a presentation made in the “Symposium on Nuclear Materials and Fuel 2000”, held at the Korea Atomic Energy Research Institute (KAERI), Taejon, Korea, August 24–25 under the auspices of the Ministry of Science and Technology (MOST).     

On the nature of anomalously high plasticity of high-strength titanium nickelide alloys with shape-memory effects: II. Mechanisms of plastic deformation upon isothermal loading

Mechanisms of plastic deformation have been studied in detail in the process of isothermal loading at room temperature in a high-purity shape-memory alloy of composition Ti_49.4Ni_50.6. The alloy was studied in two initial states: usual coarse-grained (with an average grain size of 20–30 μm) and submicrocrystalline (with an average grain size of 0.2–0.3 μm). It has been shown that during tensile tests there occurs a mechanically induced martensitic transformation in the alloy at stresses corresponding to stages I, II, and III in the tensile curve and then elastic and plastic deformation of B19′ martensite is observed at stages IV, V, and VI, respectively. Optical metallography in situ and electron microscopy have been used to study microstructural features and mechanisms of plastic deformation of the alloy up to its failure. Original Russian Text ? E.F. Dudarev, R.Z. Valiev, Yu.R. Kolobov, A.I. Lotkov, V.G. Pushin, G.P. Bakach, D.V. Gunderov, A.P. Dyupin, N.N. Kuranova, 2009, published in Fizika Metallov i Metallovedenie, 2009, Vol. 107, No. 3, pp. 316–330.     

Influence of processing parameters on the phase composition of ZrN-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> synthesized from zircon

The optimum parameters were determined for synthesizing ZrN-Si₃N₄ composite powder from zircon by carbothermal reduction-nitridation (CTRN) process. The samples were prepared by mixing the carbon black of an average particle size less than 30 μm and the zircon of 40 μm with C/ZrSiO₄ mass ratios of 0.2, 0.3, 0.4, and 0.5. The prepared samples were subjected to the CTRN process at temperatures of 1673, 1723, 1753, and 1773 K for 6, 9, and 12 h. The CTRN process was conducted in an atmosphere-controlled tubular furnace in a nitrogen gas flow of 1.0 L/min. All the products were examined by X-ray powder diffraction to determine the transformation. The results showed that the proper transformation of ZrN-Si₃N₄ occurred at 1773 K for 12 h with a C/ZrSiO₄ mass ratio of 0.4.