We report on the synthesis of Fluorine (F) doped -ZnWO₄ photocatalysts and the influence of F-doping on their structure, morphology, optical and photocatalytic properties. A two-step process was used to produce F-doped ZnWO₄ photocatalysts. The quality of synthesized materials was characterized using different analytical methods, such as X-ray diffraction analysis, field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectra (FTIR), as well as photoluminescence (PL) measurement. It was found that the photocatalyst morphology and band gap energy strongly depend on the F-doping concentration. The band gap energy of the photocatalysts decreased when increasing F-doping concentration, and reached a lowest value at a concentration of 4 mol%, and then increased thereafter. At 4 mol% of F-doping, nanowires were formed with approximately 1 μm in length and 50 nm in diameter. On the contrary, others F-doped ZnWO₄ samples were obtained in the shape of nanorods or a mixture of nanorods and granular particles. Moreover, it was demonstrated that F-doped ZnWO₄ enhanced photocatalytic activity by a factor of three, as compared to that of un-doped ZnWO₄. This enhancement can be explained by the nanowire shape of synthesized F-doped ZnWO₄, its narrow band gap energy and the small recombination rate of photogenerated electron-hole pairs, which was indirectly proved by PL spectra.

This paper describes the design of a low-cost α+β type Ti-4V-0.6O alloy and the investigation of its microstructure and mechanical properties, with a focus on heat treatability. The β transus (T_β) of the alloy was found to be 1195 K, as determined from the relationship between the heat treatment temperature and the volume fraction of the equiaxed α phase (f_α). The formation of α′ martensite exhibiting an acicular morphology was observed after heat treatments between 1073 and 1273 K. The O content in the equiaxed α and β phases increased with increasing heat treatment temperature while the V content increased with decreasing heat treatment temperature. The alloy demonstrated a higher tensile strength and lower total elongation when heat-treated between 1073 and 1173 K as compared to the as-forged material, because of the formation of α′ martensite. The reduced total elongation was caused by the increase in the hardness difference between the equiaxed α and β (α′ martensite) grains. The tensile strength and total elongation of the Ti-4V-0.6O alloy were comparable to those of the Ti-6Al-4V alloy, which marks the material as a low-cost α+β type Ti alloy candidate.

Stress corrosion cracking (SCC) and corrosion resistance of Mg–6 mass%Al–1 mass%Zn–2 mass%Ca (AZX612) extruded alloy were investigated by slow strain rate tensile tests (SSRT) in 0.01 M NaCl solution and immersion tests in 5 mass% NaCl solution, and compared with those of Mg–6 mass%Al–1 mass%Zn (AZ61) extruded alloy. In the SSRT in the salt solution, as-received AZX612 exhibited lower elongation and higher SCC susceptibility than those of as-received AZ61, indicating that calcium addition in Mg–Al alloy deteriorated SCC resistance. On the other hand, after solution treatment, improvement of elongation and SCC susceptibility occurred in both the alloys. Observation of surface profiles for AZX612 and AZ61 after the SSRT in salt solution revealed that corrosion pits on surface likely initiated SCC in both the alloys. The results of immersion tests showed the same tendency with those of SSRT in salt solution. It is suggested that SCC resistance of AZX612 and AZ61 was likely related to the microstructural change accompanied with calcium addition and solution treatment such as the change in distributions of Al₂Ca phase and Al-rich phase.

This Paper was Originally Published in Japanese in J. JILM 66 (2016) 266–272.

Defect imaging by a scanning laser source technique has been theoretically and experimentally investigated for a notch and a wall thinning in a plate. This study discusses the applicability of the imaging technique to bonding regions and delaminations in a thin plate. The variations of flexural wave energy generated at a laser source close to a plate edge, a junction of two thin plates, a bonded region, and a delamination are discussed using the Kirchhoff–Love plate theory and a semi-analytical finite element method. The numerical analyses reveal that the flexural wave energy generated in the vicinity of the reflection objects are significantly different in such a source type as normal loading and dipole loading modeled for elastic wave generations due to ablation and thermo-elastic effects, respectively. In particular, the numerical analyses reveal that the dipole loading is more effective to the imaging because the generation energy significantly varies at the boundaries between bonded and separated regions. Moreover, the images of a plate with a bonded region are obtained using an experimental system in which the thermo-elastic effect is dominant for generating elastic waves, and they exhibit similar tendencies with calculated results.

The atmospheric corrosion resistance of Al and Si bearing steels welded by MIG (Metal Inert Gas welding) or MAG (Metal Active Gas welding) was evaluated by the wet and dry corrosion test. It was found that welded Al-Si steels experienced much less corrosion than carbon steel (SM). In SEM-EDS analysis, the rust of welded Al-Si steel had the enrichment of Al and Si in inner rust, which made the protective rust. The distribution of corrosion pits was measured with a laser microscope and estimated by Gumbel analysis. A higher corrosion depth was observed near the weld metal of Al-Si steel in the case of large amount of heat input during welding. From Transmission Electron Microscopy (TEM), the layer structure of α and γ phase was observed near the weld metal of Al-Si steel. Increased corrosion sensitivity was present only at the beginning of the test time. At later times in the test, the welded Al-Si steel displayed high corrosion resistance as a result of the forming of the protective rust containing Al and Si in inner rust.

Etching of commercial pure titanium (CP-Ti) covered with metal oxide scale transferred to the surface from roller mills like those used for steel refining was investigated based on potentiodynamic polarization measurements and quantitative analysis of metal dissolved in HF or HF–HNO₃. CP-Ti prepared by an industrial titanium supplier, titanium plate with scale (S-Ti), and annealed and pickled titanium (AP-Ti) were examined. The titanium substrate under the scale layer immediately dissolved in HF solution of concentration 1.0 mol·L⁻¹. The etching behavior was examined in detail by electrochemical analysis in dilute HF. At HF concentrations less than 0.1 mol·L⁻¹, the oxidized layer of S-Ti remained. X-ray photoelectron spectroscopy was used to identify the major components of the S-Ti surface, such as copper and iron impurities. In HF–HNO₃ solution, the scale was removed slowly, even at high HF concentrations. The amounts of dissolved titanium indicated that calcium on the titanium metal surface increased the etching rate, and the minimum apparent activation energies, ΔE_a, of the etching reactions were observed at a concentration of 0.0316 mol·L⁻¹ HF aq. for S-Ti and AP-Ti because of the trade-off between the HF activity and ionic dissociation. Etching of CP-Ti began with dissolution of the passive layer of titanium; corrosion of S-Ti was the result of destruction of the titanium oxide layer by F⁻ and dissolution of the pure titanium substrate. The etching behavior of S-Ti at high HF concentrations suggested that scale peeling by substrate etching is a promising method for efficient scale removal. The HNO₃ concentration had little effect on the anodic polarization curves of CP-Ti. This is attributed to the presence of a stable oxide layer on the titanium metal. We investigated the details of the S-Ti etching mechanism in HF–HNO₃ for efficient scale removal.

This study examines the effects of chromium (Cr), molybdenum (Mo) and niobium (Nb) alloying on the corrosion properties of low alloy steel for water ballast tank using electrochemical tests for 15 days in artificial seawater and surface analyses. The EIS and LPR tests revealed the outstanding corrosion resistance Cr+Mo+Nb bearing steel. An SEM analysis after 15 days immersion in the artificial seawater indicated that, among the tested specimens, the Cr+Mo+Nb bearing steel formed the smoothest rust layer with the least cracks. An EPMA analysis for the cross section of the rust layer confirmed that the Nb elements of the Cr, Cr+Nb, and Cr+Mo+Nb bearing steels were enriched at the rust layer; however, the Mo element was enriched only at the rust layer of the Cr+Mo+Nb bearing steel, and not at that of the Cr+Mo bearing steel. This finding is because the small grain size of the Cr+Mo+Nb bearing steel results in the formation of more active sites, where a dissolution and precipitation of the alloying elements occurs. For this reason, the Cr, Mo, and Nb elements are concentrated at the rust layer of the Cr+Mo+Nb bearing steel, thereby improving the corrosion resistance of low alloy steel.

To predict hot tearing in direct chill (DC) casting and shape casting of aluminum alloys using thermal stress analysis, cooling rate dependence of viscoplastic properties in a partially solidified state is indispensable. Based on viscoplastic properties determined from experiments, this study develops a method to predict the temperature dependence of viscoplastic properties at an arbitrary cooling rate through the Clyne–Kurz microsegregation model. For validation of the developed method, tensile tests were performed on Al–5 mass%Mg alloy in a partially solidified state at three cooling rates. Results show good agreement between the predicted values and experimentally obtained values, which demonstrates that the developed method is effective for predicting the cooling rate dependence of viscoplastic properties.

This Paper was Originally Published in Japanese in J. JILM 67 (2017) 214–221.

The interfacial reaction and shear strength of Ti₅₀Ni₅₀ SMA and Inconel 600 alloy infrared brazed with a gold-based filler metal Au-22Ni-8Pd (BAu-6) were investigated. The shear strengths of Ti₅₀Ni₅₀/Au-22Ni-8Pd/Inconel 600 joints brazed for 180 s and 300 s were as high as 387 MPa and 527 MPa, respectively. Cracks initiated and propagated along the interface between Ti(Ni,Au)₃/TiNiAu eutectic and/or TiNi₂Au layer. The joints show high potential for industrial applications.

C/C composite has been recommended for use in molten fluoride salt-cooled reactors as structural containment for the highly corrosive salts in heat exchangers, piping, pumps, etc. Despite their excellent high-temperature mechanical properties and chemical compatibility with molten fluoride salts, the inherently high porosity level of C/C composites is one major challenge to the material for such applications. The numerous inherent and/or high temperature heat treatment-induced macrocracks and microcracks in C/C composites are difficult to seal completely using conventional methods such as CVD or CVI. To overcome the porosity-related molten salt permeation problem, a graphite foil-incorporated PAN fiber, a pitch/phenolic resin matrix-derived C/C composite, was developed in the authors' laboratory. Experimental results showed that the C/C composite with the graphite foil had lower density value, higher porosity value, and lower bending strength value than the C/C composite without the graphite foil. A preliminary result of the hermetic sealing test in a molten mixture of LiF, NaF and KF salts (“Flinak” salt) showed that the graphite foil could effectively seal the underlying C/C composite against permeation from high temperature molten salts. Furthermore, given appropriate process parameters, the graphite foil could remain tightly bonded to the C/C structure during the entire fabrication process and the subsequent bending and hermetic sealing tests.

Due to its good comprehensive mechanical properties and low cost, 45 steel has long been widely used for the manufacture of various components. However, the relatively low corrosion resistance of 45 steel has negative effect on its application and should be further improved. In this work, a Zr₅₀Ti₅Cu₂₇Ni₁₀Al₈ metallic glass (MG) coating was successfully obtained on 45 steel by laser cladding method. The microstructure and the morphology of the MG coating were also examined. Corrosion test indicated that the glass coated 45 steel exhibited much higher corrosion resistance than that of bare 45 steel. This is due to the alloying element Zr and the structurally and chemically homogeneous structure of MG coating.

This study was carried out to analyze the flow and heat transfer characteristics in a furnace, and to evaluate the influence of the two major design factors for improving the flow mixing and heat transfer. The grid system was constructed using ANSYS ICEM (V.17.0), and numerical simulations were conducted using the commercial CFD code (ANSYS Fluent V.17.0). The fan plays an important role in flow mixing and convective heat transfer in the furnace. Accordingly, temperature uniformity was improved with an increase in the fan speed owing to an enhancement of the convective heat transfer. Moreover, when swirl flow was applied to the inlet gas, temperature uniformity was improved in the lower section of the furnace. This is because the swirl flow of the inlet gas improved the flow mixing in the vicinity of the gas inlet where it is not affected by the rotational force of the fan. Controlling the swirl intensity of the inlet gas with lower fan speeds is more energy efficient because flow mixing and temperature uniformity could be improved sufficiently.

The corrosion resistance of sensitized Alloy 82 welds is improved by laser surface melting (LSM) with a continuous CO₂ laser beam. The effects of the LSM treatment on the segregation of impurities in the matrix and the precipitation of carbides at the grain boundaries are systematically explored. The observation results show that the LSM process results in the formation of a rapidly solidified surface layer with a thickness of approximately 160～180 μm. In addition, the corrosion test results show that the LSM treatment improves the resistance of the weld to both intergranular corrosion (IGC) and pitting corrosion. The improved corrosion resistance can be attributed to a higher proportion of low-angle boundaries (2～15°) in the solidified microstructure, the elimination of Cr-carbide precipitates in the matrix, and the suppression of Cr-depletion zones at the grain boundaries. Overall, the results confirm the effectiveness of LSM treatment for the in-situ repair and corrosion resistance restoration of Alloy 82 welds.

The recycling of secondary resources to close material cycle loops should reduce the consumption of natural resources and thus help to reduce the environmental impact. For recycling, it is crucial to consider not only the nickel (Ni) content in the secondary resources, such as Ni plating waste liquids and sludge, but also the impurity levels, particularly the phosphorus (P) concentration. This study characterized the P species in three sludges from Ni electroplating processes using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The Ni and P concentrations in the sludges ranged from 11 to 41% and 2,800 to 24,000 ppm, respectively, depending on the type of sludge. The P K-edge XANES analysis identified phosphates and organic P as the major P species in the sludges, and hypophosphite and phosphite species as minor species. These findings provide detailed knowledge that should help to control P in Ni electroplating sludge.