Different kinds of fibers, such as carbon or silicon carbide, were added to UHTC matrices to improve the fracture toughness. Several sintering additives were chosen for the densification (ZrSi2, Si3N4 and TaSi2) using various sintering cycles to identify the best temperature allowing densification of the matrix and minimal fiber degradation. The microstructure of the composites was examined through scanning electron microscope (SEM), to study the distribution of the secondary phases, and transmission electron microscope (TEM), to analyse the microstructure at nanoscale level, the evolution of the fiber morphology and the interfaces with the matrix. Subsequently, a thermo-mechanical characterization was carried out. The fracture toughness increased of 20-50% as compared to the unreinforced matrix, whilst the mechanical strength nearly halved owing to the introduction of 100-200 ?m long reinforcement. The room-temperature strength was preserved up to 1200°C, but at 1500°C in air it generally dropped to 80-300 MPa, depending on the sintering additive and fiber type. This study allowed the understanding of the chemical stability of each type of fiber towards different UHTC matrices and suggested possible mechanisms leading to the final microstructure and properties.
Characterization of UHTCs containing various kinds of fibers
L Silvestroni;D Sciti
2014
Abstract
Different kinds of fibers, such as carbon or silicon carbide, were added to UHTC matrices to improve the fracture toughness. Several sintering additives were chosen for the densification (ZrSi2, Si3N4 and TaSi2) using various sintering cycles to identify the best temperature allowing densification of the matrix and minimal fiber degradation. The microstructure of the composites was examined through scanning electron microscope (SEM), to study the distribution of the secondary phases, and transmission electron microscope (TEM), to analyse the microstructure at nanoscale level, the evolution of the fiber morphology and the interfaces with the matrix. Subsequently, a thermo-mechanical characterization was carried out. The fracture toughness increased of 20-50% as compared to the unreinforced matrix, whilst the mechanical strength nearly halved owing to the introduction of 100-200 ?m long reinforcement. The room-temperature strength was preserved up to 1200°C, but at 1500°C in air it generally dropped to 80-300 MPa, depending on the sintering additive and fiber type. This study allowed the understanding of the chemical stability of each type of fiber towards different UHTC matrices and suggested possible mechanisms leading to the final microstructure and properties.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
