Heat Treatment Control of Residual Stress and Microstructure of 3D-Printed 316L Stainless Steel

One of the major drawbacks of selective laser melting (SLM) as a form additive manufacturing is that it produces parts with severe residual stress that leads to poor mechanical performance due to the thermal cycling of the printing process. In this project, two different heat treatments (high temperature annealing and low temperature annealing) are applied to 316L stainless steel subsized tensile bars fabricated by SLM process to minimize the amount of residual stress in the samples. Residual stress is indirectly measured by X-ray diffraction (XRD), as well as microscopic analysis, hardness testing, and tensile testing are applied to characterize the samples. Unfortunately, the residual stress could not statistically be determined because of large measurement errors even though error corrections were applied. However, the HRB hardness values are determined to be 91.8 HRB for as-built samples, 80.7 HRB for after high temperature annealed samples, and 95.5 HRB for after low temperature annealed samples. The high temperature heat treatment followed by annealing showed a reduction in hardness values, as expected. The low temperature heat treatment appeared to show an increase in hardness. Optical microscopy and scanning electron microscopy (SEM) showed that small dendritic structures, which are ubiquitously seen throughout as-built samples, are gone in the high temperature annealed samples

Intersections of ultracold atomic polarons and nuclear clusters: How is a chart of nuclides modified in dilute neutron matter?

Neutron star observations, as well as experiments on neutron-rich nuclei, used to motivate one to look at degenerate nuclear matter from its extreme, namely, pure neutron matter. As an important next step, impurities and clusters in dilute neutron matter have attracted special attention. In this paper, we review in-medium properties of these objects on the basis of the physics of polarons, which have been recently realized in ultracold atomic experiments. We discuss how such atomic and nuclear systems are related to each other in terms of polarons. In addition to the interdisciplinary understanding of in-medium nuclear clusters, it is shown that the quasiparticle energy of a single proton in neutron matter is associated with the symmetry energy, implying a novel route toward the nuclear equation of state from the neutron-rich side.Comment: 28 pages, 2 figure

Generation of Seed Magnetic Field around First Stars: the Biermann Battery Effect

We investigate generation processes of magnetic fields around first stars. Since the first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magnetic fields are generated by effects of radiation force as well as the Biermann battery effect. We have calculated the amplitude of magnetic field generated by the effects of radiation force around the first stars in the preceding paper, in which the Biermann battery effects are not taken into account.In this paper, we calculate the generation of magnetic fields by the Biermann battery effect as well as the effects of radiation force, utilizing the radiation hydrodynamics simulations. As a result, we find that the generated magnetic field strengths are ~ 10^{-19}G-10^{-17}G at ~ 100pc-1kpc scale mainly by the Biermann battery, which is an order of magnitude larger than the results of our previous study. We also find that this result is insensitive to various physical parameters including the mass of the source star, distance between the source and the dense clump, unless we take unlikely values of these parameters.Comment: 19 pages, 7 figures, Accepted for publications in Ap

Scintigraphic studies on the etiology of Ampulla Cardiomyopathy

SummaryBackgroundAlthough there are many reports on Ampulla Cardiomyopathy, its etiologic mechanisms are not well known.AimEtiology of Ampulla Cardiomyopathy was investigated by myocardial scintigraphy with various nuclear tracers.Subjects and methodsIn nine patients with Ampulla Cardiomyopathy, myocardial scintigraphy was performed at acute, subacute and chronic phases. Total defect score (TDS) of tallium-201 (Tl) or technetrium-99m sestamibi (MIBI) myocardial perfusion and iodine-123-beta-methyl-p-iodophenyl penta-decanoic acid (BMIPP) scintigraphies was calculated. Cardio-mediastinal ratio (H/M) and washout rate (WR) of early and delayed images of iodine-123-meta-iodobenzylguanidine (MIBG) scintigraphy were also calculated. The patients in whom TDS of myocardial perfusion scintigraphy at acute phase was 0, were classified into group N (n=5) and those with TDS≥1 into group D (n=4).ResultsTDS of BMIPP at acute, subacute and chronic phases was higher in D than in N; 28.8±10.3 vs. 7.2±4.7 (p=0.0039), 15.5±2.1 vs. 1.0±0.8 (p<0.0001) and 2.7±1.2 vs. 0 (p=0.05), respectively. WR of MIBG at acute phase was also higher in D (50.3±5.7% vs. 36.6±10.5%, p=0.05). H/M (dH/M) on the delayed images and WR at chronic phase were not different between the two groups. H/M (eH/M) on the early images was lower in D. Blood noradrenaline (ng/ml) at acute phase was higher in D than in N (1.21±0.55 vs. 0.45±0.33, p<0.05). Left ventricular ejection fraction (LVEF) was decreased in both at acute phase but it was lower in D than in N (48.1±3.7% vs. 69.9±9.7%, p<0.05) at subacute phase.ConclusionThese findings suggest that the etiology of Ampulla Cardiomyopathy is neurologically stunned myocardium induced by coronary microcirculatory disorder.Due to the significant amount of time that was necessary for normalization of wall motion in the D group, myocardial scintigraphy is believed to be also useful in assessment of severity

Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting

The microstructure and tensile properties of β-containing Ti–44Al–4Cr alloy rods additively manufactured by electron beam melting (EBM) process were examined as a function of input energy density determined by the processing parameters. To the best of our knowledge, this is the first report to demonstrate that two types of fine microstructures have been obtained in the β-containing γ-TiAl alloys by varying the energy density during the EBM process. A uniform α2/β/γ mixed structure containing an α2/γ lamellar region and a β/γ dual-phase region is formed at high energy density conditions. On the other hand, a lower energy density leads to the formation of a peculiar layered microstructure perpendicular to the building direction, consisting of a ultrafine α2/γ lamellar grain layer and a α2/β/γ mixed structure layer. The difference in the microstructures originates from the difference in the solidification microstructure and the temperature distribution from the melt pool, which are dependent on the energy density. Furthermore, it was found that the strength of the alloys is closely related to the volume fractions of the β phase and the ultrafine α2/γ lamellar grains which originates from the massive α grains formed by rapid cooling under low energy density conditions. The alloys with high amounts of these peculiar microstructures exhibit high strength comparable to and higher than the conventional β-containing γ-TiAl at room temperature and 1023 K, respectively.Cho K., Kawabata H., Hayashi T., et al. Peculiar microstructural evolution and tensile properties of β-containing γ-TiAl alloys fabricated by electron beam melting. Additive Manufacturing, 46, 102091. https://doi.org/10.1016/j.addma.2021.102091