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This paper represents emission spectrometric analysis of a hollow-cathode glow discharge plasma with helium–oxygen mixed gas for surface treatment of a cobalt-based alloy, together with surface analysis of the resulting oxide layer. A Co–28Cr–6Mo alloy was employed as a specimen. The objective of this work is to obtain plasma information for the operating conditions to be optimized for producing a stoichiometric oxide layer on the alloy surface. Helium atomic lines, atomic and ionic lines of oxygen atom, and band heads of oxygen molecule ion were observed in the emission spectra. These intensities drastically changed depending on a mixing ratio of helium–oxygen mixed gas; particularly, the emission intensity of the molecular bands was largely enhanced in the mixed gas plasma compared to the pure oxygen plasma. This band spectrum is assigned to an electronic transition from the 4 Σ g to 4 Π u states of oxygen molecule ion, whose excitation energies are 18–19 eV from the ground state of oxygen molecule. It is thus suggested that a Penning-type ionization process with metastables of helium atom (1s2s 1 S 0, 20.6 eV and 3 S 1, 19.8 eV) is an excitation mechanism how the number density of the corresponding excited state can be elevated in the helium–oxygen mixed gas plasma. This effect, which more populated the excited oxygen species in the plasma, also exerted influence on the resultant oxide layer, such as the chemical composition and the layer thickness. Surface analysis by X-ray photoelectron spectroscopy indicated that an oxide layer consisting of iron and chromium oxides was formed by this plasma treatment, and that chromium atom was enriched in it. The thickness of the oxide layer varied with a mixing ratio of the plasma gas.

The purpose of this study is to elucidate the formation mechanism of a toxic-element-free oxide layer on a Ti–6Al–4V alloy by using d.c. glow discharge plasma in pure oxygen atmosphere, which has been found in our previous study. The surface treatment was conducted with monitoring emission spectra irradiated from the plasma to identify the excited species, which revealed that three kinds of excited oxygen species were primarily present there. Our investigation has reported that the oxygen plasma enabled toxic elements, such as Al and V, to be largely removed from the outermost surface of the alloy; in this case, this effect would be attributed to preferential sputtering caused by positively-charged plasma species such as O + and O 2 + which were accelerated toward the sample surface by hundreds of volts. To investigate the effect of the plasma condition on characteristics of the resultant surface layer, this study characterized the oxide layers formed on the alloy under three different conditions by using X-ray photoelectron spectroscopy. Whereas a deficit in the toxic elements on the sample surface was observed regardless of the plasma conditions, there was a significant difference in the growth rate of the oxide layers.

We described a newly developed characterization technique that dislocation density could be individually determined for each texture component of plastically deformed metals by combining the line-profile analysis with the texture analysis by using X-ray diffraction. This method was applied to major texture components of cube, copper, and brass evolved in cold-rolled copper sheets. The Warren–Averbach procedure using two diffraction peaks was used for estimating the dislocation density. An increase in the dislocation density with the rolling reduction was evaluated for individual texture components. Although the individual texture components underwent the different slip paths, the dislocation densities in these texture components were almost comparable; however, the non-texture component was shown to have a higher dislocation density than the texture components. The recovery and recrystallization proceeded preferentially in the non-texture component.

This paper describes a plasma-diagnostic method using an enhancement factor on the Boltzmann distribution among emission lines of iron atom in an argon radio-frequency inductively-coupled plasma (ICP). It indicated that Boltzmann plots of the atomic lines having lower excitation energies (3.4 to 4.8 eV) were well fitted on a straight line while those having more than 5.5 eV deviated upwards from a linear relationship. This observation could be explained by the fact that ICP is not in a complete thermodynamic equilibrium between direct excitation to energy levels of iron atom, ionization of iron atom, and radiative decay processes to the ground state. Especially, the recombination of iron ion with captured electron should accompany cascade de-excitations between closely-spaced excited levels just below the ionization limit, the rates of which become slower as a whole; as a result, these high-lying levels might be more populated than the low-lying levels as if a different LTE condition coexists on the high energy side. This overpopulation could be quantitatively estimated using an enhancement factor (EF), which was a ratio of the observed intensity to the expected value extrapolated from the normal distribution on the low energy side. The EFs were generally small (less than 3); therefore, the cascade de-excitation process would slightly contribute to the population of these excited levels. It could be considered from variations of the EF that the overpopulation proceeded to a larger extent at lower radio-frequency forward powers, at higher flow rates of the carrier gas, or at higher observation heights. The reason for this is that the kinetic energy of energetic particles, such as electrons, becomes reduced under all of these plasma conditions, thus enabling the high-lying levels to be more populated by cascade de-excitation processes from iron ion rather than by collisional excitation processes with the energetic particles. A similar Boltzmann analysis using the EF was also carried out in emission lines of nickel atom, which confirmed the conclusion concerning the atomic lines of iron.

In this study, we examined the effect of pre-existing dislocation structures in a face-centered cubic γ-phase on strain-induced martensitic transformation (SIMT) to produce a hexagonal close-packed e-phase in a hot-rolled biomedical Co-Cr-Mo alloy. The as-rolled microstructure was characterized by numerous dislocations as well as stacking faults and deformation twins. SIMT occurred just after macroscopic yielding in tensile deformation. Using synchrotron X-ray diffraction line-profile analysis, we successfully captured the nucleation of e-martensite during tensile deformation in terms of structural evolution in the surrounding γ-matrix: many dislocations that were introduced into the γ-matrix during the hot-rolling process were consumed to produce e-martensite, together with strong interactions between dislocations in the γ-matrix. As a result, the SIMT behavior during tensile deformation was accelerated through the consumption of these lattice defects, and the nucleation sites for the SIMT e-phase transformed into intergranular regions upon hot rolling. Consequently, the hot-rolled Co-Cr-Mo alloy simultaneously exhibited an enhanced strain hardening and a high yield strength. The results of this study suggest the possibility of a novel approach for controlling the γ → e SIMT behavior, and ultimately, the performance of the alloy in service by manipulating the initial dislocation structures.

This paper describes an ionization/excitation phenomenon of singly-ionized iron occurring in an Okamoto-cavity microwave induced plasma (MIP) as well as an argon radio-frequency inductively-coupled plasma (ICP), by comparing the Boltzmann distribution among iron ionic lines (Fe II) having a wide range of the excitation energy from 4.76 to 9.01 eV. It indicated in both the plasmas that plots of Fe II lines having lower excitation energies (4.76 to 5.88 eV) were fitted on each linear relationship, implying that their excitations were caused by a dominant thermal process such as collision with energetic electron. However, Fe II lines having higher excitation energies (more than 7.55 eV) had a different behavior from each other. In the ICP, Boltzmann plots of Fe II lines assigned to the higher excited levels also followed the normal Boltzmann relationship among the low-lying excited levels, even including a deviation from it in particular excited levels having an excitation energy of ca. 7.8 eV. This deviation can be attributed to a charge-transfer collision with argon ion, which results in the overpopulation of these excited levels, but the contribution is small. On the other hand, the distribution of the high-lying excited levels was non-thermal in the Okamoto-cavity MIP, which did not follow the normal Boltzmann relationship among the low-lying excited levels. A probable reason for the non-thermal characteristics in the MIP is that a charge-transfer collision with nitrogen molecule ion having many vibrational/rotational levels could work for populating the 3d 6 4p (3d 5 4s4p) excited levels of iron ion broadly over an energy range of 7.6–9.0 eV, while collisional excitation by energetic electron would occur insufficiently to excite these high-energy levels.

We present the application of a plasma-oxidation technique for modifying a the corrosion resistance of a Ti–6Al–4V bio-implant material in a physiological environment. The corrosion resistance of a plasma-oxidized Ti–6Al–4V alloy sample was evaluated by immersing the sample in a lactic acid solution and determining the amounts of eluted elements in the immersion-test solution. The amounts of toxic elements, aluminum and vanadium, eluted from the plasma-oxidized sample were compared with those from the thermally oxidized sample to demonstrate the corrosion resistance of the plasma-oxidized surface to be greatly improved. To elucidate the reasons for this improvement in corrosion resistance, the oxide layers formed on the Ti–6Al–4V alloy were characterized by X-ray photoelectron spectroscopy, which revealed that Al and V oxides were enriched at the outermost surface of the thermally oxidized sample, whereas they were less segregated at the outermost surface of the plasma-oxidized sample. Based on the atomic fractions of elements at the outermost surface of the oxide layers after the immersion test, it was deduced that the elution occurred mainly at the outermost surface of the oxide layer. Therefore, it can be deduced that the characteristic surface composition of the plasma-oxidized sample, with reduced fractions of toxic elements, played an important role in suppressing the elution of toxic elements.

Hydroxyapatite (HAp) and octacalcium phosphate (OCP) coatings deposited on a pure magnesium (Mg) substrate from an aqueous solution containing C10H12N2O8Na2Ca (Ca-EDTA) and KH2PO4 were precisely analyzed using X-ray photoelectron spectroscopy (XPS) and high-resolution X-ray diffractometry (XRD) to clarify their chemical and crystallographic characteristics. The calcium phosphate coatings comprised single-phase HAp or OCP containing small amounts of sodium (Na). The intermediate layer formed underneath the coatings consisted of Mg(OH)2 mixed with calcium phosphate. The atomic ratios of calcium to phosphorus ([Ca]/[P]) in the HAp and OCP coatings were notably smaller than those of stoichiometric compounds. The expansion along the a-axis compared to that of stoichiometric HAp was observed in XRD results. Also, we did not detect Na compounds in the coating. Therefore, it is presumed that Na existed as a substitute of Ca in the OCP and HAp structures.

In the present study, we propose a characterization technique to determine the amount of calcium phosphate (CP) precipitate formed on a titanium (Ti) substrate. The quantitative analysis of the CP precipitate on a metallic substrate is significant for researchers of metallic biomaterials because CP that spontaneously precipitates in a simulated-body fluid gives information on the bioactivity of the metallic biomaterials. We focused on X-ray fluorescence (XRF) analysis and adopted the thin-film fundamental parameter method (thin-film FP method) because it allows direct (non-pretreatment) and rapid quantitative analysis without any reference materials. We show that XRF analysis using the thin-film FP method can be adequately applied to the quantitative analysis of the CP precipitate in the simulated-body fluid immersion test. We also show that the density of the CP-precipitate layer can be estimated by combining the XRF results with images of cross-sectional scanning electron microscopy (SEM). Consequently, XRF analysis combined with the thin-film FP method can provide a convenient means to evaluate the CP precipitate on a Ti substrate, which improves the accuracy and accessibility of the simulated-body fluid immersion test. [doi:10.2320/matertrans.M2013020]

Core-level and valence-band XPS spectra for Fe 3 Si, FeSi, and FeSi 2 were collected from the surfaces of polycrystalline silicides. The clean surfaces were prepared by mechanically fracturing the bulk polycrystalline silicides in a spectrometer under ultra-high vacuum, and then the chemical shifts and spectral shapes characteristic of each iron silicide phase were investigated in detail. The Fe 2p spectra for these samples exhibited positive chemical shifts as compared to those of elemental Fe, and the shifts observed for FeSi 2 were slightly larger than the others. The spectral shapes of the Fe 2p 3/2 spectra had asymmetric shapes, decreasing in magnitude with increasing Si content. The Fe 3s spectra for Fe 3 Si exhibited multiple splitting due to the exchange interaction between the 3s core and the 3d unfilled shell; such splitting was not found in the other silicide phases. In comparing the valence band spectra of these silicides, the spectral intensity at the Fermi edge was found to be notably higher for Fe 3 Si. Similar results were obtained from theoretical consideration of the partial density of state (PDOS) using a first-principle calculation method. These features affect the asymmetric spectral shape of the Fe 2p spectra for Fe 3 Si.

Further strengthening of biomedical Co−Cr−Mo alloys is desired, owing to the demand for improvements to their durability in applications such as artificial hip joints, spinal rods, bone plates, and screws. Here, we present a strategy—multipass “low-strain-per-pass” thermomechanical processing—for achieving high-strength biomedical Co−Cr−Mo alloys with sufficient ductility. The process primarily consists of multipass hot deformation, which involves repeated introduction of relatively small amounts of strain to the alloy at elevated temperatures. The concept was verified by performing hot rolling of a Co−28Cr−6Mo−0.13N (mass%) alloy and its strengthening mechanisms were examined. Strength increased monotonically with hot-rolling reduction, eventually reaching 1400 MPa in 0.2% proof stress, an exceptionally high value. Synchrotron X-ray diffraction (XRD) line-profile analysis revealed a drastic increase in the dislocation density with an increase in hot-rolling reduction and proposed that the significant strengthening was primarily driven by the increased dislocation density, while the contributions of grain refinement were minor. In addition, extra strengthening, which originates from contributions of planar defects (stacking faults/deformation twins), became apparent for greater hot-rolling reductions. The results obtained in this work help in reconsidering the existing strengthening strategy for the alloys, and thus, a novel feasible manufacturing route using conventional hot deformation processing, such as forging, rolling, swaging, and drawing, is realized. Statement of significance The results obtained in this work suggested a novel microstructural design concept/feasible manufacturing route of high-strength Co−Cr−Mo alloys using conventional hot deformation processing. The present strategy focuses on the strengthening due to the introduction of a high density of lattice defects rather than grain refinement using dynamic recrystallization (DRX). The hot-rolled samples obtained by our process exhibited exceptional strength, which is comparable to the highest strength reported for biomedical Co−Cr−Mo alloys. It was also found that the acceptable ductility can be obtained even in such highly distorted Co−Cr−Mo alloys. We described the strengthening mechanisms in detail; this will be helpful for further investigations or industrial realization of the proposed strategy.

The objective of this study was to clarify the longitudinal epidemiology of Chlamydia trachomatis serovars in Japan. A total of 339 endocervical swab specimens obtained from female patients who attended the Department of Obstetrics and Gynecology, Saitama Medical School, were used. Positive specimens of either transport medium of IDEIA Chlamydia (1st group, from 1999 to 2001), or DNA extract of Cobas Amplicor STD-1 Chlamydia trachomatis (2nd group, from 2003 to 2005) were used for serotyping. Typing of C. trachomatis serovars in DNA extracts was performed by polymerase chain reaction-restriction fragment length polymorphism. Ten serovars, A, B, D, E, F, G, H, I, J and K, were identified in the 1st group, and serovar E was most frequently identified (27.6%). In the 2nd group, nine serovars, B, C, D, E, F, G, H, I and K, were identified, and serovar D was most frequently identified (24.7%). Serovars B and Ba were significantly more common around 2000 and the mid-1990s (from 1993 to 1996), respectively. Numbers of serovar I increased significantly during the research period. In addition, serovar I was more frequent in the 2nd group than in the 1st group in women aged 20-29 years. There were no significant differences of serovar distribution between pregnant and non-pregnant women.