Loading...
3 results
Search Results
Now showing 1 - 3 of 3
- Simulation, Structural, Thermal and Mechanical Properties of the FeTiTaVW High Entropy AlloyPublication . Martins, Ricardo; Gonçalves, António Pereira; Correia, J.B.; Galatanu, Andrei; Alves, E.; Tejado, Elena; Pastor, Jose Ygnacio; Dias, MartaABSTRACT: Developing new materials to be applied in extreme environments is an opportunity and a challenge for the future. High entropy alloys are new materials that seem promising approaches to work in nuclear fusion reactors. In this work, FeTaTiVW high entropy alloys were developed and characterized with Molecular Dynamic and Hybrid Molecular Dynamic Monte Carlo simulations. The simulation results show that phase separation originates a lower potential energy per atom and a high level of segregation compared to those of a uniform solid solution. Moreover, the experimental diffractogram of the milled powder shows the formation of a body-centred cubic-type structure and the presence of TiO2. In addition, the microstructure of the consolidated material evidenced three phases: W-rich, Ti-rich, and a phase with all the elements. This phase separation observed in the microstructure agrees with the Hybrid Molecular Dynamic Monte Carlo simulation. Moreover, the consolidated material's thermal conductivity and specific heat are almost constant from 25 degrees C to 1000 degrees C, and linear expansion increases with increasing temperature. On the other hand, specific heat and thermal expansion values are in between CuCrZr and W values (materials chosen for the reactor walls). The FeTaTiVW high entropy alloy evidences a ductile behaviour at 1000 degrees C. Therefore, the promising thermal properties of this system can be attributed to the multiple phases and systems with different compositions of the same elements, which is exciting for future developments.
- New WC-Cu thermal barriers for fusion applications: high temperature mechanical behaviourPublication . Tejado, Elena; Dias, Marta; Correia, J.B.; Palacios, T.; Carvalho, Patricia Almeida; Alves, E.; Pastor, Jose YgnacioABSTRACT: The combination of tungsten carbide and copper as a thermal barrier could effectively reduce the thermal mismatch between tungsten and copper alloy, which are proposed as base armour and heat sink, respectively, in the divertor of future fusion reactors. Furthermore, since the optimum operating temperature windows for these divertor materials do not overlap, a compatible thermal barrier interlayer between them is required to guarantee a smooth thermal transition, which in addition may mitigate radiation damage. The aim of this work is to study the thermo-mechanical properties of WC-Cu cermets fabricated by hot pressing. Focus is placed on the temperature effect and composition dependence, as the volume fraction of copper varies from 25 to 50 and 75 vol%. To explore this behaviour, fracture experiments are performed within a temperature range from room temperature to 800 degrees C under vacuum. In addition, elastic modulus and thermal expansion coefficient are estimated from these tests. Results reveal a strong dependence of the performance on temperature and on the volume fraction of copper and, surprisingly, a slight percent of Cu (25 vol%) can effectively reduce the large difference in thermal expansion between tungsten and copper alloy, which is a critical point for in service applications. The thermal performance of these materials, together with their mechanical properties could indeed reduce the heat transfer from the PFM to the underlying element while supporting the high thermal stresses of the joint. Thus, the presence of these cermets could allow the reactor to operate above the ductile to brittle transition temperature of tungsten, without compromising the underlying materials.
- WC-Cu thermal barriers for fusion applicationsPublication . Dias, Marta; Guerreiro, F.; Tejado, Elena; Correia, J.B.; Mardolcar, U. V.; Coelho, M.; Palacios, T.; Pastor, Jose Ygnacio; Carvalho, Patricia Almeida; Alves, E.ABSTRACT: WC-Cu cermets have been devised for thermal barriers between the plasma facing tungsten tiles and the copperbased heat sink in the first wall of nuclear fusion reactors. Composite materials with 50 and 75 v/v% WC have been prepared by hot pressing at 1333 and 1423 K with pressures of 37 and 47 MPa, respectively. Microstructural changes have been investigated by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and X-ray diffraction. The materials consolidated have also been evaluated in terms of Archimedes' density, thermal diffusivity, Vickers hardness and elastic modulus. Implantation was carried out at room temperature with Ar+ at 100 keV ion beam with a fluence of 4 · 1020 at/m2. The materials consisted of homogeneous dispersions of WC particles in a Cu matrix and presented densifications of about 90%. Incipient swelling in copper-rich regions have been observed on the implanted surfaces, however no significant changes have been detected by X-ray diffraction. Higher WC content in the cermet materials increased hardness and the elastic modulus. The cermets' thermal diffusivity was significantly lower than that of pure copper or tungsten, as desirable for a thermal barrier.