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High- and low-cycle-fatigue properties of additively manufactured Inconel 625
Full text linkIn the last years, additive manufacturing has become a widespread technology which enables lightweight-design based on topological optimization. Therefore, generation of lattice structures with complex geometries and small thicknesses is allowed. However, a complete metallurgical and mechanical characterization of these materials is crucial for their effective adoption as alternative to conventionally manufactured alloys. Industrial applications require good corrosion resistance and mechanical strength to provide sufficient reliability and structural integrity. Particularly, fatigue behavior becomes a crucial factor since presence of poor surface finishing can decrease fatigue limits significantly. In this work, both the low-cycle-fatigue and high-cycle-fatigue behaviors of Inconel 625, manufactured by Selective Laser Melting, were investigated. Fatigue samples were designed to characterize small parts and tested in the as-built condition since reticular structures are usually adopted without any finishing operation. Microstructural features were studied by light-optical microscopy and scanning-electron microscopy. Finally, fatigue failures were deeply investigated considering fracture mechanics principles with the Kitagawa-Takahashi diagram
Selective Laser-Melted Alloy 625: Optimization of Stress-Relieving and Aging Treatments
Full text linkAdditive manufacturing is an innovative solution to produce components characterized by complex geometries. The use of such parts requires a deep knowledge of their behavior under different service conditions, especially from mechanical and corrosion resistance points of view. One of the most well-known and employed materials produced by selective laser melting is nickel alloy 625. It is already commonly used in its conventional form, but the additive manufacturing technology, despite its higher production costs and lower productivity, is becoming competitive because of its excellent mechanical strength. It is in fact significantly higher compared to the conventionally manufactured alloy whose properties are often limited by the difficulty in retaining a fine grain size during plastic deformation and heat treatment. Even though the as-built performance is already quite good, further strength improvement can be attained upon tailored single- and double-aging treatments that are optimized starting from the experimental results obtained in the conventional alloy and also considering the influence on corrosion resistance. In addition, considering that the stress-relieving treatment recommended for the conventional forged alloy at 870 °C is not suitable for the selective laser-melted material because of the more rapid precipitation response, this temperature is optimized to improve both the tensile deformability and the corrosion behavior
Influence of single- and double-aging treatments on the mechanical and corrosion resistance of Alloy 625
No full textNickel–chromium–molybdenum Alloy 625 exhibits an excellent combination of mechanical
properties and corrosion resistance. However, the high-temperature plastic deformation process and the heat treatment represent critical aspects for the loss in mechanical strength by grain coarsening. This detrimental behavior is worsened by the absence of phase transformation temperatures. However, the chemical composition permits slow precipitation-hardening response upon single aging. Therefore, when the soft- or solution-annealed condition is associated with insufficient mechanical properties, this potentiality can be exploited to improve the mechanical strength. Since the gamma double prime precipitation can be accelerated by double-aging treatment, different time–temperature combinations of double aging at 732 °C and 621 °C are investigated. The simultaneous precipitation of intergranular carbides can dramatically affect the corrosion resistance. Such an undesired phenomenon occurs very quickly at 732 °C, but it is obtained only after very long exposure times at 621 °C. For this reason, a performance chart is developed to compare all the tested conditions. In particular, single aging at 621 °C for 72 h and 130 h are associated with an acceptable combination of mechanical and corrosion properties. Double aging permits a conspicuous acceleration of the aging response. For instance, with double aging at 732 °C 3 h and 621 °C 72 h, it is possible to obtain the same mechanical properties of single aging at 621 °C for 260 h. Such acceleration is accompanied by a more critical corrosion behavior, especially because of the primary step. However, even after its optimization, none of the tested conditions were acceptable
Optimization of the mechanical and corrosion resistance of Alloy 625 through aging treatments
Full text linkIn the as-annealed condition, the nickel-based Alloy 625 has excellent mechanical and corrosion properties compared to those of common stainless steels. This peculiarity enables its exploitation in several industrial fields at cryogenic and high temperatures and in the presence of severely corrosive atmospheres. However, in this alloy, when high-temperature plastic deformation processes and heat treatments are not carefully optimized, the occurrence of excessive grain coarsening can irremediably deteriorate the mechanical strength, possibly leading to incompatibility with the standard requirements. Therefore, this research work investigated the possibility of adopting single- and double-aging treatments aimed at improving such strength loss. Their optimization involved identifying the best compromise between the hardening effect and the loss in corrosion resistance induced by the simultaneous formation of intergranular chromium-rich carbides during aging. The investigation of the aging treatments was performed using hardness, tensile and intergranular corrosion tests considering different time–temperature combinations in a range from 621 °C to 732 °C. Double aging resulted in a considerable acceleration in the hardening response compared to single aging. However, even after its optimization in terms of both temperature and time, the intergranular corrosion resistance remained a critical aspect. Among all the tested conditions, only single aging at 621 °C for 72 h was acceptable in terms of both mechanical and corrosion properties. The influence of longer exposures will be investigated in a future study
High and low cycle fatigue properties of selective laser melted AISI 316L and AlSi10Mg
Full text linkIn the last years, additive manufacturing has widely adopted to enable lightweight design based on the topological optimization. In fact, this technology allows generation of lattice structures with complex geometries and small thicknesses. In this work, both the low-cycle-fatigue and high-cycle-fatigue behaviors of selective laser melted AISI 316L and AlSi10Mg were investigated. Fatigue samples were designed to characterize small parts and tested in the as-built condition since reticular structures are usually adopted without any finishing operation. Microstructural features were studied by light-optical microscopy and scanning-electron microscopy. Finally, fatigue failures were studied considering the fracture mechanics principles with the Kitagawa-Takahashi diagram. The analysis of fracture surfaces revealed that crack nucleation mainly occurs close to the surface because of both poor surface quality and presence of near-surface defects. As expected, because of the face-centered cubic lattice, the final rupture of all the investigated alloys was characterized by micro-dimples confirming the presence of a ductile behavior
The spinodal decomposition of ferrite in 2507 biphasic stainless steels: embrittlement and possible toughness recovery
Full text linkBiphasic stainless steels provide an excellent combination of mechanical and corrosion properties. The occurrence of ferrite spinodal decomposition during processing and heat treatment can induce a dramatic drop in impact energy. In this paper, a forged rod of 480 mm diameter made of 2507 biphasic stainless steel was studied. The spinodal decomposition phenomenon upon aging at 475 degrees C (748 K) was investigated by macro- and micro-hardness tests on the constituent phases and by Charpy impact tests. Then, the influence of the microstructural constituents and their morphology on the crack path was studied by optical microscopy, noting possible correlations with the impact energy. Successively, the fracture surfaces of selected specimens were analyzed by a scanning electron microscope (SEM). Finally, reversion heat treatments at 550 degrees C (823 K) and 600 degrees C (873 K) were investigated to evaluate the possibility of recovering the detrimental effects of the alpha' embrittlement. According to the literature, this procedure works well with some biphasic steels, but these steels are characterized by a chromium content lower than that of 2507 grade steel. Regarding the 2507 grade steel studied in this work, complete reversion was obtained by solution-annealing treatment, while reversion heat treatments at both 600 degrees C (873 K) and 550 degrees C (823 K) allowed only a partial recovery
Bioactive compounds in legumes: Implications for sustainable nutrition and health in the elderly population
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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