Littérature scientifique sur le sujet « Quite-fast sinterin »

The oxidation characteristics of WC-20%TiC-10%Co sintered carbides were studied by oxidizing at 700, 800 and 900 °C for 3 h in air. The samples oxidized fast with large weight gains, displaying quite poor oxidation resistance. The formed oxide scales that consisted primarily of CoWO4, WO3, and TiO2 were porous, and prone to cracking.

Tungsten carbides are quite attractive for their superior properties, e.g., high melting point, high hardness, high thermal and electrical conductivities, and relatively high chemical stability. Tungsten carbides with a binder metal, for example Co or Ni, are mainly used to produce cutting tools, nozzles and molds in the composite form. But these binder materials show inferior chemical characteristics compared to the tungsten carbide phase. There has been enormous interest recently in finding alternative binder phases because of the low corrosion resistance and the high cost of Ni or Co. Al has been reported as an alternative binder for WC and TiC, since Al is less expensive and shows a higher oxidation resistance than Ni or Co. Nanostructured WC-BN-Al composites were rapidly sintered using high-frequency induction heated sintering (HFIHS). The microstructure and mechanical properties (fracture toughness and hardness) were investigated by Vickers hardness tester and FE-SEM. The HFIHS method induced very fast densification, nearly at the level of theoretical density, and successfully prohibited grain growth, resulting in nano-sized grains. The fracture toughness was improved by consolidation facilitated by adding Al to the WC-BN matrix. The 5vol % Al added WC-BN composites showed higher mechanical properties (hardness and fracture toughness than the WC-BN composite.

Zirconia-alumina ceramic foam scaffolds with a nanocrystalline HAP coating were used for the preparation of integrated motile orbital implants. This study demonstrated that open-cell ceramic foams with enhanced strength-to-density ratio are quite suitable as biocompatible materials for the manufacture of orbital implants for post-enucleation syndrome treatment. In-vivo studies demonstrated that the application of a nanocrystallyne (not sintered) HAP coating facilitated the formation of dense fibrous capsule around the implant as well as the fast tissue ingrowth into the implant’s internal space. Orbital implants with the optimized pore size and HAP content were implanted to the animal’s eye cavity with their fixation to the extraocular muscles, and their motility was ensured.

The market is changing very quickly, demanding the companies the capability of producing better and/or more performing products. This changing market leads the companies to be more flexible and agile. In particular, for the tool makers and the stamping companies, they are requested to participate in the design phase of the product and process, as well as to produce prototypes and small series in very short time and with low costs. To answer to these demands in the stamping steps design and consequently in the tool design, several finite elements packages are widely used, allowing the tool designers to foresee the results of their options/decisions without the need to manufacture and test tools, with the inherent excessive cost of money and time. Following this methodology, CAE analysis, the final phase of tool try out, always necessary, will be certainly shorter and less expensive, once they start with a solution quite more worked and, for sure, closer to the final solution. In this industrial context, appeared the great motivation for the development of competences on the rapid manufacturing of stamping tools (active elements: punch, die and blankholder), on the numerical simulation of the process and, on the development of the modular tool concept. In this paper the main results of the development of these areas of research, are presented. In particular, the use of the numerical simulation, using PAM-STAMP 2G software, for the validation of the stamping phases, the realisation of laboratorial stamping tests using tools produced by the several techniques available on Portugal for rapid prototyping. At the same time, it was developed the modular tool concept, i.e., a tool in which by fast and easy change of the active elements, different parts can be formed. The active elements of the tool have been manufactured by several rapid tooling techniques, like DMLS - Direct Metal Laser Sintering, LOM - Laminate Object Manufacturing, HSM – High Speed Milling and also the machining of non-traditional materials such as nylon, ureol and aluminium. Some inserts have been produced by indirect techniques such as reinforced resins (polyurethane, epoxy and urethane) using shells produced by SLstereolithography. Finally some conclusions are drawn.

Good reproduction is key for successful dairy farming. Detection of estrus is the first step in getting a cow pregnant. Inadequate and inaccurate estrus detection is frequently a cause of cows becoming repeat breeders. Sensor technologies are being used to monitor the production and physiological condition of the animals. Increasingly, these innovations are leading to a more efficient performance of dairy cows, in terms of both physiology and profitability. Three types of sensors used in this area; electrochemical sensors, chemoresistive gas sensors chemoresistive sensor. Chemoresistive gas sensors have received impulse great deal of attention because of its many advantages over other sensing technologies. Electrochemical sensors are becoming unpopular as they have a short lifetime, rendering them unacceptable for some applications. Optical sensors show excellent characteristics of sensitivity, selectivity, adequate lifetime, and fast response; however, they have a high cost and large size. A chemoresistive sensor is based on a sensitive material, in bulk or deposited on a suitable support, upon which the molecular recognition process takes place. Classical Taguchi sensors have a sensitive material in the form of sintered porous ceramic body. Planar-type gas sensors are constituted of a sensing thick/thin layer deposited by chemical or physical methods onto a ceramic substrate with interdigited electrodes. Sensing nanomaterials may be quite unstable under thermal conditions due to their high surface energy leading to severe grain growth, which may result in the degradation of the device performances. Under such operations, the mechanical deterioration of electrodes can also lead to performance degradation due to the possible formation of micro-cracks on the electrode structure. Therefore, the development of novel sensors with higher sensitivities is the goal of much recent research efforts. This paper will give an overview of the commercial sensor-based devices that are currently available in market.