Microstructure and Solute Segregation around the Melt-Pool Boundary of Orientation-Controlled 316L Austenitic Stainless Steel Produced by Laser Powder Bed Fusion

For this article, we studied the microstructure and solute segregation seen around the melt pool boundary of orientation-controlled 316L austenitic stainless steel produced by laser powder bed fusion, using transmission electron microscopy and energy-dispersive x-ray spectroscopy. We found that the solidification cellular microstructures could be visualized with the aid of solute segregation (Cr and Mo) during solidification. Mn–Si–O inclusions (10–15 nm in diameter) were distributed along the lamellar boundaries, as well as in the dislocation cell walls. It is believed that the grain growth of the inclusions can be effectively suppressed by rapid quenching during the laser powder-bed fusion process. A thin region without cellular microstructures was observed at the melt-pool boundary. The cellular spacing widened near the bottom of the melt-pool boundary, owing to the decrease in the cooling rate. Atomic-structure analysis at the lamellar boundary by high-resolution transmission electron microscopy revealed a local interfacial structure, which is complementary to the results of electron back-scatter diffraction.Sato K., Takagi S., Ichikawa S., et al. Microstructure and Solute Segregation around the Melt-Pool Boundary of Orientation-Controlled 316L Austenitic Stainless Steel Produced by Laser Powder Bed Fusion. Materials 16, 218 (2023); https://doi.org/10.3390/ma16010218

Local valence analysis of 316L austenitic stainless steel produced by laser powder bed fusion

Sato K., Takagi S., Ichikawa S., et al. Local valence analysis of 316L austenitic stainless steel produced by laser powder bed fusion. Materials Letters 372, 136978 (2024); https://doi.org/10.1016/j.matlet.2024.136978.Ultra-rapid cooling of laser powder bed fusion (LPBF) generates a cellular solidification microstructure with submicron-sized periodicity accompanied by non-negligible segregation. In 316L austenitic stainless steel, an important corrosion-resistant alloy, the effect of segregation, particularly variations in Cr concentration, on the corrosion resistance of the LPBF product is unknown. Local valence analysis of the LPBF-produced 316L by electron energy-loss spectroscopy revealed no obvious changes in the energy-loss near-edge structures of Cr and Fe measured within the solidification cellular microstructure, at the cell boundary, or at the melt-pool boundary. This result indicates that solidification segregation in the LPBF-produced 316L is unlikely to affect the corrosion resistance of the material

Preparation of Polyrotaxane Fibers. Part II: Tensile Properties of Polyrotaxane Fibers Treated with Two Cross-linking Reagents

Polyrotaxane fibers prepared with wet spinning of polyrotaxane consisting of poly(ethylene glycol) and cyclodextrins were cross-linked with two different cross-linking reagents, i.e., divinyl sulfone (DVS) and ethylene glycol diglycidyl ether (EGDE), to improve the tensile properties of the fibers. By cross-linking with DVS, the values for the tenacity at break and the initial modulus were increased with cross-linking time, while the elongation at break was improved only moderately. On the other hand, drastic improvements in elongation at break were observed after EGDE cross-linking, up to 645% of its original length, although the tenacity at break and the initial modulus showed only slight improvements. After cross-linking, only minor changes in the degree of crystallinity of the fibers were observed by wide-angle X-ray scattering measurements.ArticleTEXTILE RESEARCH JOURNAL. 80(12):1131-1137 (2010)journal articl

Evolution of long-period stacking order (LPSO) in Mg₉₇Zn₁Gd₂ cast alloys viewed by HAADF-STEM multi-scale electron tomography

This is an Accepted Manuscript an article published by Taylor & Francis in Philosophical Magazine on 23 July 2018, available at https://doi.org/10.1080/14786435.2018.1468940.We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg₉₇Zn₁Gd₂ cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to ~10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0 0 0 1)ᴍ plane is notable compared to the out-of-plane growth in the [0 0 0 1]ᴍ direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)₃Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time–Temperature–Transformation diagram for precipitation in Mg₉₇Zn₁Gd₂ alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram

Three-dimensional shapes and distributions of long-period stacking ordered structures in Mg₉₇Zn₁Gd₂ cast alloys characterized by electron tomography

Three-dimensional (3D) configurations of 14H long-period stacking ordered (LPSO) structures formed in Mg97Zn1Gd2 cast alloys at intermediate stages of the formation process have been studied by single tilt-axis electron tomography using high-angle annular dark-field scanning transmission electron microscopy. Lateral morphology of the 14H LPSO is clearly visualized by reconstructing 3D volumes. An existence of "dent-shaped" area was found in a 3D reconstructed volume for the first time. The edge of LPSO shows a characteristic triangular shape with an angle of 60°, which indicates that the growth front is parallel to {112¯0}Mg. It is suggested that in-plane irregular or characteristic shapes are related to the lateral growth mechanism of LPSO. Electron tomography has proven to be an indispensable tool to characterize in-plane structural information of LPSO formed in α-Mg matrix

Three-dimensional imaging of a long-period stacking ordered phase in Mg₉₇Zn₁Gd₂ using high-voltage electron microscopy

Spatial configurations and lateral morphology of the 14H long-period stacking ordered (LPSO) phase have been studied by single tilt-axis electron tomography using high-voltage scanning transmission electron microscopy (STEM) operated at 1 MV. A "Quonset hut-like" lateral shape of the LPSO was found in a tomogram of a specimen as thick as 1.7 μ m. The reconstructed volume reveals spatial distribution of residual particulate precipitates of (Mg, Zn)3Gd phase 20-30 nm in diameters. The precipitates act as a source of solute elements for the formation and growth processes of 14H LPSO. 1 MV-STEM realizes enough resolution for imaging the morphology of LPSO as well as high electron transmittance (∼4.1 μ m) without any obvious electron irradiation damages on microstructures

Percutaneous coronary intervention for a healed erosion with excimer laser coronary angioplasty and drug-coated balloon angioplasty: a case report

BackgroundHealed plaque, characterized by distinct layers of organizing thrombus and collagen, is the hallmark of tissue self-repair. However, the efficacy of excimer laser coronary angioplasty (ELCA) followed by drug-coated balloon (DCB) angioplasty in patients with healed plaques is not fully understood.Case summaryA 42-year-old woman with a history of anxiety disorder was admitted to our institution with worsening chest pain and subsequently diagnosed with anterior non-ST-elevation myocardial infarction. Coronary angiography revealed severe stenosis in the proximal left anterior descending artery (LAD) despite Thrombolysis in Myocardial Infarction (TIMI) grade 3. Optical coherence tomography (OCT) showed healed plaques with partial macrophage accumulation and no fresh thrombus. Plaque disruption and thin-cap fibrous atheroma were not identified in the culprit lesions. Intravascular ultrasound (IVUS) confirmed high-intensity marginal irregular masses at the culprit site, suggesting that the thrombus was formed by plaque erosion rather than lipid plaque or necrotic tissue. With lesion modification using ELCA prior to DCB angioplasty, OCT examination of the LAD after ELCA showed a significant reduction in plaque burden and preserved lumen size. Post-percutaneous coronary intervention angiography revealed no stenosis with TIMI grade 3. A follow-up coronary computed tomography scan showed no angiographic restenosis, and the patient remained symptom-free.ConclusionsHere we describe a case in which OCT and IVUS evaluation suggested organizing thrombus due to erosion healing, and a favorable outcome was achieved with the combination of ELCA and DCB. The combination use of ELCA and DCB might be a potential strategy for acute coronary syndrome patients with organizing thrombus