The purpose of this study is to investigate a nondestructive method for predicting the fatigue limit of spheroidal graphite cast iron using high resolution X-ray CT. Axial load fatigue test specimens were cut out from a large spheroidal graphite cast iron equivalent to FCD 350, and graphite and defects in the material were detected using high resolution X-ray CT for all specimens. Fatigue limit was estimated from the graphite and defect sizes using the fatigue limit estimation formula based on the four-parameter method.
Axial load fatigue test was performed in accordance with JIS (Japanese Industrial Standards). Repetition frequency was 17 Hz, stress ratio was R = −1, and number of cycles during the test was 1.0 × 107. The specimen used was JIS type 1 of 8.00 mm in diameter. Fracture origins were observed in all fatigue fracture surfaces using a scanning electron microscope (SEM) in order to compare the results between the defects observed by X-ray CT and the fracture origins observed in the fatigue test.
The fatigue limit estimated by the defect with the largest volume detected by X-ray CT was 5% lower than the experimental fatigue limit of 125 MPa, which is considered safe estimation. However, in the fatigue test, the fracture origin was not necessarily the defect with the largest volume. Therefore, the fatigue limit was estimated by the average defect size when the cumulative distribution function of ten defects with the largest volume of each test piece was F = 50%. The result was 11% larger than the experimental fatigue limit, which is considered a dangerous estimation. These results indicate that estimation of fatigue limit using a nondestructive method is feasible.
This Paper was Originally Published in Japanese in J. JFS 91 (2019) 264–269.
The oxidation behavior of CuNi, CuFeNi, CrCu0.3FeNi, and Al0.4CrCuFeNi2 Co-free Cu-containing concentrated solid solution alloys was investigated in steam conditions under 500, 600, and 700°C for 25 h. All the alloys have a face-centered cubic structure. The kinetic curves of oxidation were measured, and the microstructure and elemental distribution of oxide scales were analyzed. The oxidation of all the Cu-containing alloys indicated parabolic behavior, and those appeared to have better corrosion resistance than normal 316 SS. The parabolic rate constant increased with increasing temperature. The oxidation resistance of CuNi and CuFeNi were relatively poor due to the formation of unprotective NiO and Fe3O4 oxide scales, which were thicker than that of CrCu0.3FeNi and Al0.4CrCuFeNi2 at all testing temperatures. Cross-sectional electron probe microanalysis (EPMA) and X-ray diffraction (XRD) results revealed that, by the addition of Cr and Al, CrCu0.3FeNi and Al0.4CrCuFeNi2 had the enhanced oxidation resistance, which is probably due to the formation of Cr2O3 and Al2O3 inner oxide layer.
Fig. 2 Oxidation kinetics of the Cu-containing alloys and 316 SS at 700°C in Ar–20% H2O.
The necessity of arsenic (As) removal from metallurgical wastewaters is increasing. Despite its wide recognition as a natural oxidant, the utility of Mn oxide for scorodite production is mostly unknown. In acidic solutions containing both As(III) and Fe2+, simultaneous oxidation of the two progressed by MnO2 and the resultant As(V) and Fe3+ triggered the formation of crystalline scorodite (FeAsO4·2H2O). At 0.5% or 0.25% MnO2, 98% or 91% As was immobilized by day 8. The resultant scorodite was sufficiently stable according to the TCLP test, compared to the regulatory level in US and Chile (5 mg/L): 0.11 ± 0.01 mg/L at 0.5% MnO2, 0.78 ± 0.05 mg/L at 0.25% MnO2. For the oxidation of As(III) and Fe2+, 54% (at 0.5% MnO2) or 14% (at 0.25% MnO2) of initially added MnO2 remained undissolved and the rest dissolved in the post As(III) treatment solution. For the Mn recycling purpose, the combination of Mn2+-oxidizing bacteria and biogenic birnessite (as homogeneous seed crystal) was used to recover up to 99% of dissolved Mn2+ as biogenic birnessite ((Na, Ca)0.5(MnIV, MnIII)2O4·1.5H2O), which can be utilized for the oxidation treatment of more dilute As(III) solutions at neutral pH. Although further optimization is necessary, the overall finding in this study indicated that Mn oxide could be utilized as a recyclable oxidant source for different As(III) treatment systems.
Fig. 4 XRD patterns and SEM images before (a, a′) and after (b–d, b′–d′) the scorodite precipitation reaction at different MnO2 doses: 0.15% (b, b′), 0.25% (c, c′), 0.5% (d, d′). XRD peaks: M (ε-MnO2; Akhtenskite, PDF No. 01-089-5171), S (scorodite; JCPDS 37-0468).
A novel Cu-powder contained solderable epoxy-solder composite (Cu-SESC) was introduced, and its interconnection mechanism was proposed as a means to improve the interconnection properties of the SESC joints. To identify the possibility and strengthening effect for the SESC joints by added Cu powder, two types of wetting tests using planar and line type metallization formed test boards, and a microhardness evaluation were performed. The Cu-SESC showed appropriate wetting and spreading properties. The Cu powders in the wetted low melting-point alloy (LMA) exhibited a uniform dispersion state, and a Cu–Sn intermetallic compound created on the surface of the Cu powders. The SESC that had Cu powders showed a superior microhardness value to that of the SESC without Cu powders because of the strengthening effect from the added Cu powder. Additionally, the selective conduction joint establishment properties obtained through the flowage, integration, and selective wetting behaviors of the fused LMA were not interrupted by the incorporated Cu powders.
Fig. 5 Selective wetting morphology of fused fillers in Cu-SESCs. (a) Initial condition and that after reflow process and (b) cross-sectional inspection result.
One significant issue associated with in situ stress measurements is that the uncertainty of the results cannot be determined. In this study, we propose a novel analytical procedure for the anelastic strain recovery (ASR) method, an in situ stress measurement method, enabling us to conduct uncertainty quantification based on Bayesian statistical modeling (BSM). The new procedure consists of the following steps: i) measuring the ASR of a rock core with strain gauges, ii) applying a probability model based on BSM to the measured ASR data and simulating the probability densities of the elements of an in situ stress tensor and other parameters; and iii) regarding the probability densities as the results of in situ stress measurements with uncertainty. This paper presents the results obtained by applying the proposed procedure to simulated ASR data. The results show that the uncertainties of some parameters are reduced by giving the elastic moduli. Notably, the rates of uncertainty decrease vary for each parameter. To reveal the cause of these differences, we introduce the new evaluation tool, Sobol’ indices, which comprise a global sensitivity analytic tool, to facilitate a quantitative discussion.
This Paper was Originally Published in Japanese in J. Soc. Mater. Sci., Jpn. 70 (2021) 573–580.
We developed a hot stamping method for panel parts with a step-shaped wall. The die-set for the developed method divides the punch at a step-shaped wall into an outer punch and an inner punch. The outer punch is placed first. In addition, an opening is added to the blank of the developed method. The developed method makes it possible to change the main forming type from draw forming to cylindrical stretch flange forming in the middle of a forming stroke. The stretch flange forming can prevent a fall in temperature at a hole edge, because the hole edge does not come into contact with the die-set during forming and because the high ductility of high-temperature materials can be used, making it advantageous for hot stamping. If the preceding amount of the outer punch is large with the developed method, the effect of suppressing wrinkles is large but the sheet thickness reduction that can cause cracking rises. If the preceding amount of the outer punch is small, the rate of sheet thickness reduction ratio is greatly restrained, but the wrinkles become larger. By setting an appropriate preceding amount of the outer punch with the developed method, forming without cracks or wrinkles is possible.
This Paper was Originally Published in Japanese in J. JSTP 61 (2020) 75–80. Figure 1 is slightly modified. Table 2 is slightly modified. The caption of Fig. 9 is slightly modified.
Fig. 1 Schematics of the developed hot stamping method and a conventional cold stamping method.
Announcement Concerning Article Retraction The following paper has been withdrawn from the database of Mater. Trans., because a description based on a misinterpretation of the experimental results was found by the authors in advance of publication after acceptance. Mater.Trans. 52(2011) Advance view. Improvement in Fatigue Strength of Biomedical β-Type Ti-Nb-Ta-Zr Alloy while Maintaining Low Young’s Modulus through Optimizing ω-Phase Precipitation