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- Haack, M, et al.
(författare)
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Investigation on the formation of grain boundary serrations in additively manufactured superalloy Haynes 230
- 2020
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Ingår i: Journal of laser applications. - : American Institute of Physics (AIP). - 1042-346X .- 1938-1387. ; 32:3
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Tidskriftsartikel (refereegranskat)abstract
- Solid-solution and carbide-strengthened superalloys such as Haynes 230 are the materials of choice for the hot-section components of gas turbines, e.g., combustion cans and transition ducts. Under severe thermal conditions, to which those parts are exposed, creep strength is a crucial property of the related materials during their lifetime. Recently, the introduction of serrated grain boundaries in Haynes 230 has been intensively studied [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015); L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)], and nearly a triplication of the time to creep failure at high temperature and low stress conditions has been observed [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. The aim of this paper is to achieve serrated grain boundaries in Haynes 230 through an appropriate thermal process chain including the intrinsic heat treatments of the laser metal deposition (LMD) process, subsequent hot isostatic pressing and suitable heat treatments. The formation of serrations is a relatively new technique for Haynes 230 (i.e., first paper in 2012), and similar alloys and thus serrations have only been introduced in conventionally cast or wrought alloys so far. Optical and scanning electron microscopies are employed in this work to investigate the created microstructures, whose grain and carbide structure is finer compared to the recently studied conventionally processed alloys. Within the LMD samples, serrations were already found on almost all of the observed grain boundaries even in the as-build condition. This result was rather unexpected, as literature reports slow-cooling to be responsible for the formation of serrations, while fast-cooling is prevalent in LMD. Some authors associated the formation of serrations to the precipitation of M23C6-carbides at the grain boundaries during slow cooling conditions [L. Jiang, R. Hu, H. Kou, J. Li, G. Bai, and H. Fu, "The effect of M23C6 carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy,"Mater. Sci. Eng. A 536, 37-44 (2012)]. The lower density of carbides along grain boundaries in the as-build state, however, makes this mechanism seem unlikely. Other authors attributed the emergence of serrations to a phenomenon similar to the faceting mechanism [J. G. Yoon, H. W. Jeong, Y. S. Yoo, and H. U. Hong, "Influence of initial microstructure on creep deformation behaviors and fracture characteristics of Haynes 230 superalloy at 900 °C,"Mater. Charact. 101, 49-57 (2015)]. It can be said that no uniform theory for the emergence of grain boundary serrations exists as of now. The electron backscatter diffraction (EBSD) investigations performed in this work indicated a correlation between serrated grain boundary segments, the {111}-directions of the crystal lattice, and possibly segregations along dendritic subgrain boundaries for a two-dimensional case. Serial sectioning in combination with EBSD analysis confirmed an agreement between the three-dimensional orientation of serrated grain boundary segments and the {111}-direction of adjacent grains. Hence, a mechanism different from the ones described in previous works is proposed for the formation of grain boundary serrations in the additively manufactured Haynes 230 alloy.
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| 2. |
- Campi, Riccardo, et al.
(författare)
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Novel Liquid Biomarkers and Innovative Imaging for Kidney Cancer Diagnosis : What Can Be Implemented in Our Practice Today? A Systematic Review of the Literature
- 2021
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Ingår i: European Urology Oncology. - : Elsevier. - 2588-9311. ; 4:1, s. 22-41
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Forskningsöversikt (refereegranskat)abstract
- CONTEXT: The epidemiological signature of renal cell carcinoma (RCC) during the past decades is explained by overdetection and overtreatment of indolent cancers; furthermore, a non-negligible proportion of patients undergoing surgery for suspected RCC harbour benign renal tumours. As the gold standard for RCC diagnosis remains histopathological analysis of surgical or biopsy specimens, implementation of noninvasive diagnostic strategies to discriminate between benign and malignant renal masses is an urgent unmet need. OBJECTIVE: To systematically review novel liquid biomarkers and imaging modalities for RCC diagnosis. EVIDENCE ACQUISITION: A systematic review of the recent English-language literature was conducted according to the European Association of Urology guidelines and the PRISMA statement recommendations (PROSPERO ID: CRD42020190773) using the MEDLINE, Cochrane Central Register of Controlled Trials, Web of Science, and ClinicalTrials.gov databases. Risk-of-bias assessment was performed according to the QUADAS 2 tool. EVIDENCE SYNTHESIS: Overall, 15 studies (six on biomarkers and nine on imaging) and eight clinical trials were included. None of the biomarkers or imaging modalities has been validated or shown to have a distinct clinical value for RCC. Specific combinations of urinary cell-free and exosomal miRNAs, urinary miR-15a, and specific panels of urinary metabolites assessed by metabolomics appear promising. In addition, machine/deep learning algorithms and radiomics applied to cross-sectional images may have potential to improve RCC diagnosis. Most studies are limited by the retrospective design, size, and lack of external validation. CONCLUSIONS: Liquid biomarkers or imaging modalities are not ready for integration in the clinic and further well-designed studies must validate preliminary findings and explore utility in clinical decision-making. PATIENT SUMMARY: We provide a comprehensive overview of the currently available biomarkers (measured in blood or urine) and novel imaging tests (other than conventional imaging) to discriminate kidney cancer from benign renal masses in a noninvasive fashion. None of the biomarkers or imaging modalities studied was validated or added clinical value; therefore, none of them can be implemented in the clinic. However, these approaches appear to be promising for improving the diagnosis of kidney cancer in the future.
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