Research Interests:
In the framework of the Horizon 2020 project C3HARME, an experimental campaign has been carried out to characterize a new class of Ultra-High-Temperature Ceramic Matrix Composites for near-zero ablation Aerospace Thermal Protection... more
In the framework of the Horizon 2020 project C3HARME, an experimental campaign has been carried out to characterize a new class of Ultra-High-Temperature Ceramic Matrix Composites for near-zero ablation Aerospace Thermal Protection Systems. Small sized specimens, with ZrB2-based matrix and different carbon fiber architectures, were exposed to a supersonic flow of simulated air generated by an arc-jet wind tunnel, achieving specific total enthalpies up to 20 MJ/kg, in an aero-thermo-chemical environment representative of atmospheric re-entry. Ablation rates were estimated by means of mass and thickness measurements before and after testing, demonstrating a good performance of the analyzed samples, although with some mechanical resistance issues. Surface temperatures were monitored by means of infrared pyrometers and a thermo-camera, and during most of the tests a spontaneous temperature jump was observed, with temperatures that reached values over 2800 K at the steady state. Computational Fluid Dynamics simulations allowed for the rebuilding of the thermo-fluid-dynamic and chemical flow field. Moreover, it was possible to propose a correlation of the temperature jump with an increased catalytic activity and a dramatic reduction of the thermal conductivity of the oxide layers forming on the exposed part of the sample, which anyway had a key role in preserving the unoxidized bulk materials at reasonable temperatures.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Abstract The effect of chromium diboride addition on the densification process and oxidation behavior of two ZrB2-MoSi2 and ZrB2-SiC baseline systems was studied. CrB2 was beneficial in lowering the sintering temperature owing to the... more
Abstract The effect of chromium diboride addition on the densification process and oxidation behavior of two ZrB2-MoSi2 and ZrB2-SiC baseline systems was studied. CrB2 was beneficial in lowering the sintering temperature owing to the tendency of its oxide to react with MoSi2 and SiC forming low-melting phases that helped the powder consolidation. Oxidation at 1500 °C induced the formation of further boron oxide as first consequence. In one case, when CrB2 was combined with MoSi2, an improved oxidation resistance was observed due to the stabilization of Cr-borides in the subscales saturated with B2O3. In the other case, when it was combined with SiC, the excessive low viscosity of the borosilicate glass facilitated the consumption of a thicker portion of materials as compared to the ZrB2-SiC reference.
Research Interests:
Research Interests:
The materials currently used in aerospace and aviation, such as C/C and C/SiC composites, possess excellent mechanical properties but are limited to a maximum operational temperature of 1600°C (C/SiC) and poorly oxidizing environments... more
The materials currently used in aerospace and aviation, such as C/C and C/SiC composites, possess excellent mechanical properties but are limited to a maximum operational temperature of 1600°C (C/SiC) and poorly oxidizing environments (C/C). For more demanding applications, new materials able to withstand extreme temperatures without recession are required. In the framework of the C3harme project, a new class of materials labelled UHTCMCs, consisting of a UHTC matrix reinforced with carbon fibers, has been developed and characterized in order to overcome these challenges. Different fiber reinforcements and sintering parameters have been investigated from the microstructural point of view. The composites were fabricated via slurry infiltration of fiber, using a powder mixture of ZrB2 and SiC; the green pellets were then sintered via hot pressing. Extensive microstructural analysis was carried out on the sintered samples, showing how the sintering parameters and the choice of the fibers are crucial to obtain full densification without jeopardizing the fibers integrity and permit adequate load transfer.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Abstract Simple hot pressing and vacuum pre-treatment at 1600°C followed by hot pressing were used for obtaining dense composites of ZrB2–15 vol% SiC– 5 vol% Mo2C. The room temperature strength was around 820 MPa for the hot-pressed... more
Abstract Simple hot pressing and vacuum pre-treatment at 1600°C followed by hot pressing were used for obtaining dense composites of ZrB2–15 vol% SiC– 5 vol% Mo2C. The room temperature strength was around 820 MPa for the hot-pressed material and 650 MPa for the material obtained by use of thermally treated powders. At 1800°C, the strength converged to 154 and 182 MPa, respectively, as was mostly driven by SiC grain sliding. Oxidation in static air at 1600°C for 2 hours showed the formation of a 3-layered scale for both materials but with different thickness. The outermost layer was a borosilicate glass; the intermediate layer consisted of a phase based on zirconium oxide, silicon oxide, molybdenum boride and oxide; and the last layer was a silicon-depleted boride matrix. The two-step processing route resulted in a material with higher oxidation resistance, due to coarser grain size and higher amount of (Mo,Zr)B phase, which remained stable as solid compound in the sub-scales.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Luca Zoli, CNR-ISTEC, National Research Council of Italy Institute of Science and Technology for Ceramics, luca.zoli@istec.cnr.it Laura Silvestroni, National Research Council of Italy Institute of Science and Technology for Ceramics,... more
Luca Zoli, CNR-ISTEC, National Research Council of Italy Institute of Science and Technology for Ceramics, luca.zoli@istec.cnr.it Laura Silvestroni, National Research Council of Italy Institute of Science and Technology for Ceramics, Paola Pinasco, National Research Council of Italy Institute of Science and Technology for Ceramics, Diletta Sciti, National Research Council of Italy Institute of Science and Technology for Ceramics
Research Interests:
Abstract The reactivity behaviour between a MAX phase and ZrB2 or WC was explored with the aim of developing novel composites by merging the benefits of the individual constituents. Hot pressing of Ti3SiC2 with 30 vol% ZrB2 at 1450 °C led... more
Abstract The reactivity behaviour between a MAX phase and ZrB2 or WC was explored with the aim of developing novel composites by merging the benefits of the individual constituents. Hot pressing of Ti3SiC2 with 30 vol% ZrB2 at 1450 °C led to notable microstructure re-assessment with formation of inter-locked sub-micrometric boride grains. This composite displayed enhanced hardness and showed a strength over 430 MPa up to 1200 °C, which is a great achievement considering the ductile behaviour of typical pure MAX compounds. However, addition of WC led to a highly porous composite with poor performance. These findings set a first basis for the progress of original light ceramics with combined hardness and failure tolerance over a broad temperature range.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The materials currently used in aerospace and aviation, such as C/C and C/SiC composites, possess excellent mechanical properties but are limited to a maximum operational temperature of 1600°C (C/SiC) and poorly oxidizing environments... more
The materials currently used in aerospace and aviation, such as C/C and C/SiC composites, possess excellent mechanical properties but are limited to a maximum operational temperature of 1600°C (C/SiC) and poorly oxidizing environments (C/C). For more demanding applications, new materials able to withstand extreme temperatures without recession are required. In the framework of the C3harme project, a new class of materials labelled UHTCMCs, consisting of a UHTC matrix reinforced with carbon fibers, has been developed and characterized in order to overcome these challenges. Different fiber reinforcements and sintering parameters have been investigated from the microstructural point of view. The composites were fabricated via slurry infiltration of fiber, using a powder mixture of ZrB2 and SiC; the green pellets were then sintered via hot pressing. Extensive microstructural analysis was carried out on the sintered samples, showing how the sintering parameters and the choice of the fibe...