Fonte (métallurgie) | EPFL Graph Search

thumb|Lampe à gaz en fonte à Vienne. La fonte, en métallurgie, est un alliage de fer et de carbone dont la teneur en carbone est supérieure à 2 %. Le carbone, qui est en sursaturation dans les fontes, peut précipiter sous forme de graphite ou de cémentite Fe3C. Les fontes se distinguent des autres alliages de fer par leur excellente coulabilité. Plusieurs classifications des fontes existent, mais la plus utilisée, basée sur le faciès de rupture d'un témoin, définit deux catégories : les fontes blanches, à cassure blanche, constituées de fer et de cémentite et les fontes grises, à cassure grise, constituées de fer et de graphite. Caractéristiques Les fontes sont toutes des alliages. Elles se distinguent des autres alliages par leur excellente coulabilité (ce terme regroupe l'inertie thermique et la fluidité de l'alliage en fusion, elle est mesurée de façon normalisée par une éprouvette en colimaçon de section triangulaire). La fonte a une

Study and Characterization of Magnetic Materials for Beam Intensity Monitors at CERN

Silvia Aguilera Murciano

The number of particles in the beams used at CERN is measured by a family of devices called the Beam Current Transformers (BCTs). One of such devices is the DC Current Transformer (DCCT) measuring the total number of particles in an accelerator. The DCCT is built around a magnetic core made of a soft magnetic material. Currently, the DCCT cores are purchased from one of a few industrial partners. This situation might result in some signiï¬cant issues with development of the DCCTs. Firstly, the choice of the core can be made only among the already developed and manufactured cores. Secondly, the industrial partners do not normally guarantee long-term availability of their products which could manifest itself as future maintenance problems. Thirdly, the cores available on the market have not been developed with CERNâs intended application in mind and, hence, might be non-optimal for the DCCTs. These three factors, among others, led to a decision to investigate a possibility of in-house core manufacturing. BCT cores are made up of a soft magnetic material in ribbon-form between 20 and 30 microns thick, wound into a toroidal shape. They are amorphous or nanocrystalline cobalt and iron-based alloys that show high permeabilities and low coercivities. Several commercial alloys in their amorphous as-cast state were purchased after identifying the key parameters of the materials for the application, contacting suppliers and studying the available materials to ï¬nd the most suitable ones. This choice was made by confronting the as-cast properties of the alloys with the needs of the instruments which would house the magnetic cores. The materials were then characterised to determine how to thermally treat them in order to obtain a range of diï¬erent ï¬nal magnetic properties. This study also resulted in establishing the best candidates to fabricate the sample cores. After this, three alloys were selected (iron-based alloy Finemet FT-3 from Metglas and two-cobalt based materials, 6025 G40 from Vacuumschmelze and 2705 M from Metglas) based on their as-cast properties. The cores and ribbons of the selected materials were then annealed at diï¬erent temperatures and durations to study the eï¬ect of the treatment in both. Three treatments were done on the selected samples, below the Curie temperature, between the Curie and the crystallisation temperature and above the crystallisation temperature. Measurements of the samples were taken after the thermal treatment and compared to the results of the as-cast materials to see the eï¬ects of the annealing. This gave a range of diï¬erent ï¬nal materials with various permeability vs frequency behaviours, BH-curves and Barkhausen Noise. These new materials, in addition to the untreated as-cast ones, provide a good range of samples to choose from for applications with diï¬erent needs. Based on the results presented in this thesis, one can suggest that the best material to build DCCT cores would be the iron-based nanocrystallised Metglas Finemet FT-3 material. It shows a high permeability up to 10 kHz, low coercivity and a rounded BH-curve. Regarding FBCTs, the cores need a very ï¬at BH-curve with high permeability and minimum coercivity. From all the materials presented, Vacuumschmelzeâs cobalt-based Vitrovac 6025 G40 is the one that would be the most suitable. It has the lowest coercivity. However, the perfect material would need magnetic thermal annealing to create a high magnetic material anisotropy for a flat curve.

EPFL2018

Study and characterization of soft magnetic materials for beam intensity monitors at CERN

Silvia Aguilera Murciano, Heinrich Hofmann

At CERN, the circulating beam current measurement is provided by two types of transformers, the DC Current Transformer (DCCT) and the Fast Beam Current Transformer (FBCT). Each transformer is built based on toroidal cores made from a magnetic material. Depending on the type of measurement to be performed these cores require different magnetic characteristics for parameters such as permeability, coercivity and the shape of the magnetization curve. In order to study the effect of changes in these parameters on the current transformers, several interesting raw materials based on their as-cast properties were selected. The materials have been characterised to determine a suitable annealing processes to tailor their properties. As-cast properties such as the permeability, coercivity and Barkhausen noise have also been measured to enable the study of the effect of thermal treatment in the microstructure of the alloys, and the correlation of this with the change in the magnetic properties. The comparison of the measured properties have narrowed down the best materials for further study.

Iop Publishing Ltd2017

Periodic cellular aluminum structures for space applications

Florian Thibaut Gallien

Mass is one of the crucial parameters for hardware that has to be placed in Earth orbit. Due to its harsh environment, a material with highest specific properties is desired to achieve space missions. The rise and development of new technologies, such as additive manufacturing (AM), opened new opportunities in part-design complexity, periodic cellular structures (PCS) being one of them. The present thesis investigates the potential implementation of PCS in space applications, particularly for structures and micro-meteoroids and orbital debris (MMOD) impact shields. This was achieved in three steps: Four different types of AlSi12 PCS manufactured by selective laser melting (SLM) were tested under quasi-static compression to measure the mechanical properties dependency versus topology and to characterize the failure mode. Properties ranging from 3 to 4 GPa for the compressive modulus, 5 to 12 MPa for the yield stress, 12 to 20 MPa for the plateau stress, and 2 to 8 MJ/cm3 for the absorbed energy were obtained. An unexpected failure mode was observed when compared to classical cellular metals, namely a brittle failure occurring by global shearing. A predictive failure criterion was established based on topology considerations and correlated to most of the reported results in the literature. A preliminary test campaign on tensile specimens was performed to compute numerical models that were fed into a finite element analysis. Good agreement with experimental data was shown, and the importance of microplasticity effects in this class of material was highlighted. An alternative process was developed to produce AlSi1 PCS by investment casting. The process is based on replication of a polymer preform used to build a NaCl mold. It was observed that the quality of the final cast part depends mainly on the grain size of the salt, with an optimum identified for distributions between 125 and 180 um. Optimization of the process allowed to reduce the drying time by a factor 6. Main process parameters include a drying temperature of 80C and infiltration at 660C under 300 mbar. From this process, PCSs having an energy absorption capacity of 15 MJ/m3 with an efficiency of 80% were produced. Hypervelocity impact tests were conducted on cast PCS and stochastic structures. The objective being to hit the structures with a 2mm-diameter aluminum sphere at velocities close to 7 km/s. Influence of the sample topology, the orientation, and the bumper material was assessed. Stochastic structures successfully stopped the projectile in all configurations. The beneficial effect of the bumper was measured reducing the crater depth from 20 mm to 14 mm. This type of structure exhibited a comparable areal density (0.8 g/cm2) to simple Whipple shield design. PCS poorly performed in mitigating the impact as the debris passed through all the structures, independently of the test configuration due to the open-channels present. PCS are good candidates to be used in space hardware, but their design and the manufacturing process need to be carefully chosen depending on the specific application. AM PCS are suitable for structural application with a high compressive modulus and yield stress. Cast PCS would perfectly fit in shock absorbers. A more random design would be preferable for MMOD shielding applications.

EPFL2018

Periodic cellular aluminum structures for space applications

Florian Thibaut Gallien

EPFL2018

Study and Characterization of Magnetic Materials for Beam Intensity Monitors at CERN

Silvia Aguilera Murciano

EPFL2018