1,720,991 research outputs found
Early instability phenomena of IN792 DS superalloy
No full textMicrostructure stability of the directionally solidified Ni base IN792 superalloy has been investigated by Mechanical Spectroscopy (MS), i.e. internal friction (IF) and dynamic modulus measurements. Repeated IF test runs from room temperature to 1173 K have been carried out on the same samples and a Q-1 maximum has been always observed above 700 K. Its position does not depend on the resonance frequency. After each run the values of modulus and Q-1 at room temperature change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in disordered matrix which modifies dislocation density and average distance of pinning points. The results are supported by X-ray diffraction (XRD) and transmission electron microscopy (TEM) observations
Mechanical properties of several newly produced RAFM steels with Tungsten content in the range of 2 wt%
Full text linkThe contribution of ENEA together with Rina-CSM to the Eurofusion programme “WPMAT-Advanced Seels” deals with the development of innovative RAFM steels able to withstand the critical temperatures typical of the different operational environments foreseen for the blanket of the first DEMO reactor. The optimization of the chemical composition and the Thermo Mechanical Treatment for these materials should be done according to the blanket operating temperatures that are related to two possible working conditions: the WCLL-BB (Water Cooled Lead Lithium Breeding Blanket) or the H(D)CLL-BB (Helium (Dual) Cooled Lead Lithium Breeding Blanket). On the one hand the “water-cooling” option implies a minimum irradiation temperature for the blanket material in the range of 280–350 °C. On the other hand, the “helium-cooled” and the “dual-coolant” solutions imply an operating temperature for the blanket material in the range of 650 °C. Therefore in the first case the target is the improvement of the toughness of the martensitic alloys; whilst concerning the second scenario the target is the development of more creep resistant martensitic steels, suitable to tolerate such a high operating temperature. In both the cases the Tungsten content plays a key role, both in terms of solid solution hardening and influence on the DBTT. Two alloys aimed at fulfilling the specifications for the two DEMO operating conditions, both with increased Tungsten content respect to Eurofer, have been produced and characterized. The mechanical properties of these two alloys are hereby reported and discussed
Achievement of Ultrafine Grain structure by means of recrystallization treatments
No full textThe design of the WCBB (Water Cooled Breeding Blanket) of the first DEMO reactor foresees a minimum irradiation temperature in the range of 280–300 °C. It is well known that the RAFM (Reduced Activation Ferritic Martensitic) steels suffer a marked DBTT (Ductile to Brittle Transition Temperature) increase under irradiation. This DBTT shift depends both on the DPA (Displacement per Atom) damage and on the Helium production. While the former kind of embrittlement goes to saturation for DPA higher than 20 the latter does not saturate with the dose and results therefore the less manageable issue. Several experimental evidences concerning ODS (Oxide Dispersion Strengthened Steels) RAFM (Reduced Activation Ferritic Martensitic) steels showed that it is possible to improve the resistance to irradiation damage by intra-granular precipitation of Y-Ti oxides and by simultaneously decreasing the grain size. In any case, the multiplication of the grain boundaries is expected to increase the dilution of He on grain surface, delaying the formation of He bubbles on grain boundaries and, therefore, the susceptibility to the He embrittlement. Hereafter we show that it is possible to reduce the grain size by an order of magnitude at the tempering stage, by combining cold working and tempering stages, acting on the tempered martensite. The microstructural observations have been carried out by means of both Scanning and Transmission Electron Microscopy (SEM and TEM). Also the positive effect of grain size reduction on the toughness of the material will be taken into account; the DBTT curves resulting from impact tests on KLST specimens show a peculiar nature, characterized by a smoother transition to the brittle regime, compared to the usual abrupt transitions achieved with the “standard” normalization & tempering treatments on RAFM steels. The outcomes of the microstructural observations, as well as the mechanical characterization (tensile, hardness and impact tests) will be discussed in this paper
Single crystal PWA 1483 superalloy: Dislocation rearrangement and damping phenomena
No full textThe structural stability of the single-crystal PWA 1483 superalloy has been investigated by internal friction (IF) and dynamic modulus measurements from room temperature to 1073 K. The examined samples were in the solubilized state. The vibrating reed technique with electrostatic excitation and frequency modulation detection of flexural vibrations has been employed. Frequency was similar to 350 Hz. IF spectra recorded in successive test runs on the same samples show a Q(-1) maximum (M1) above 623 K, whose intensity and position change from one run to another: in correspondence with M1 the modulus undergoes a slow decrease followed by a sudden increase. Sometimes another maximum (M2) has been observed at lower temperature (similar to 523 K). After each run the values of the modulus and of Q(-1) change indicating that a progressive irreversible transformation occurs. Damping phenomena have been attributed to the rearrangement of dislocation structures in the disordered matrix. This rearrangement modifies the density and the average distance of pinning points. This explanation is supported by transmission electron microscopy (TEM) observations. (C) 2009 Elsevier B.V. All rights reserved
Developing the Additive Manufacturing Chain of AlSi7Mg with Laser Powder Bed Fusion and Tailored Heat Treatments for Railway Spare Parts
Full text linkThe use of metal additive manufacturing technologies in railways sector can provide increased flexibility in terms of spare part logistics. Combined with lightweight metals such as Al-alloys, the product performance can also be enhanced in terms of weight reduction, vibration and noise control. The railway sector is more likely to exploit large and bulky parts produced by laser powder bed fusion (LPBF), which should have appropriate mechanical properties. Therefore, the whole production chain should be analyzed considering the heat treatment steps suited for a distributed and resource efficient manufacturing scheme. Accordingly, this work analyzes the additive manufacturing of AlSi7Mg alloy by LPBF and its consecutive heat treatment steps. In particular, the impact of LPBF process productivity, heat treatment type and atmosphere composition were considered to analyze the most appropriate route for the needs of the railways applications. The results show that with an appropriate direct aging treatment in air, mechanical characteristics of the alloy could be improved, despite that the high layer thickness used in LPBF could increase process productivity. The absence of a quenching step was found to be favorable for large parts, while the absence of an inert gas such as Ar in the heat treatment did not generate any reduction in the mechanical properties
Development of innovative materials and thermal treatments for DEMO water cooled blanket
No full textOne of the options currently taken into account for the realization of the first DEMO reactor is the “water-cooled lanket”. This option implies an irradiation temperature for the blanket material in the range of 280–350 °C. Therefore, in light of the under irradiation behaviour of EUROFER, namely of the DBTT shift toward high temperature due to the low irradiation temperature embrittlement, the target of the hereby reported activities is the development of much tougher alloys, to try to tolerate the embrittlement due to the low irradiation temperature. We report in this paper the work done to optimize the toughness of Eurofer 97, increasing the normalizing temperature and maintaining a small grain size using multiple normalizing treatments. We report also the mechanical behaviour of two 9Cr1WTa type alloys, produced and tested with the same aim to find alloys more resistant to embrittlement at low irradiation temperature
Development of innovative materials and thermal treatments for DEMO water cooled blanket
Full text linkOne of the options currently taken into account for the realization of the first DEMO reactor is the "water-cooled lanket". This option implies an irradiation temperature for the blanket material in the range of 280- 350 degrees C. Therefore, in light of the under irradiation behaviour of EUROFER, namely of the DBTT shift toward high temperature due to the low irradiation temperature embrittlement, the target of the hereby reported activities is the development of much tougher alloys, to try to tolerate the embrittlement due to the low irradiation temperature. We report in this paper the work done to optimize the toughness of Eurofer 97, increasing the normalizing temperature and maintaining a small grain size using multiple normalizing treatments. We report also the mechanical behaviour of two 9Cr1WTa type alloys, produced and tested with the same aim to find alloys more resistant to embrittlement at low irradiation temperature
Design of an Innovative Oxide Dispersion Strengthened Al Alloy for Selective Laser Melting to Produce Lighter Components for the Railway Sector
Full text linkThe railway industry can take advantage of additive manufacturing (AM) processes from several perspectives such as the production of spare parts on-demand or the use of lightweight structures for vibration and noise control. One of the key issues regarding the limitations of using these technologies is the scarcity of processable material types. Selective laser melting (SLM) is a metal AM process with industrial maturity where material development can open new prospects for the railway industry. In order to respond to such requirements, this study proposes a framework to study a new material from concept to the processability and finally to the preliminary mechanical characterization of alloy for SLM. The new material is an alloy based on AlSi7Mg reinforced by alumina nano-dispersoids. The powder feedstock was produced through VIGA (Vacuum Inert Gas Atomization) technology, while the mechanical alloying of the nano-dispersoids has been carried out through the ball-milling process. The obtained oxide dispersion strengthened (ODS) powder has been used to produce samples by SLM. These samples have been characterized in terms of density, chemistry, and hardness. The obtained results showed that samples, produced by SLM were characterized by >1% porosity. Compared to the reference Al alloy, an increase up to 20% in microhardness was achieved for ODS samples made by the SLM process. The results show promise especially in terms of mechanical properties, even if additional work is needed concerning both the powder production and the AM process
Development of processing strategies for multigraded selective laser melting of Ti6Al4V and IN718
Full text linkIn energy generation applications, Ti- and Ni-alloys are widely used for their complementary features, where Ti-alloys provide lightweight structures while Ni-alloys are adaptable to high temperature use. The combination of these alloys into a single component through additive manufacturing is highly desirable. This work explores the multi-material selective laser melting (SLM) of a Ti6Al4V-IN718 material system to produce multigraded specimens. An in-house developed multi-material SLM platform with double hopper and a mixing chamber was employed. A work frame based on studying process feasibility through premixed blends and assessing the processability of multigraded components is presented. Material characteristics, in terms of chemistry, microhardness and microstructure are investigated and supported by thermodynamic calculations. Defect-free grading was achieved until 20 wt% inclusion of IN718 in Ti6Al4V. The results were interpreted to reveal the processability limits of the metallurgically incompatible alloys as well as the defect formation mechanisms
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