Vickers indentation tests were conducted on an Al2O3–TiC composite at different load levels. The ... more Vickers indentation tests were conducted on an Al2O3–TiC composite at different load levels. The crack resistance calculated from the length of the indentation-induced crack exhibits a large scatter. Such a large scatter can be characterized well with Weibull statistics and can be attributed to the effect of microstructural inhomogeneity on the local crack resistance. The effect of the statistical variability
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001
The Vickers hardnesses of a series of Ti(C,N)-based cermets were measured in the indentation load... more The Vickers hardnesses of a series of Ti(C,N)-based cermets were measured in the indentation load range from 1.47 to 40.67 N. It was found that the examined materials exhibit a reversed indentation size effect, i.e. the measured hardness increases with increasing indentation load. Both Meyer's law and the energy balance model can not provide a proper description for the observed experimental phenomena, while the polynomial series representation can describe the experimental data very well. A possible explanation for the cause of the observed reverse indentation size effect was also proposed.
A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holdin... more A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al2O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2O3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21–22 GPa and fracture toughness values of 3.5 ± 0.5 MPa·m1/2 were found for the compacts containing submicrometer-sized Al2O3 grains.
... Maria Teresa Buscaglia1, Vincenzo Buscaglia1,7, Massimo Viviani1, Jan Petzelt2, Maxim Savinov... more ... Maria Teresa Buscaglia1, Vincenzo Buscaglia1,7, Massimo Viviani1, Jan Petzelt2, Maxim Savinov2, Liliana Mitoseriu3,4, Andrea ... grains from 20 to 100 nm can be observed in figure 2), a corresponding ... The dielectric constant (ε) and dielectric losses (tan δ) of the 50 nm BT ...
Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full den... more Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full density by spark plasma sintering (SPS). SPS samples densified at 900° or 950°C exhibit nearly full density and fine grain size (about 300 nm). Compared with samples from conventional sintering (CS), SPS samples show larger permittivity accompanied by a deterioration in dielectric loss and special strain hysteresis loops similar to those of ferroelectric relaxors, with a diffuse AFE–FE phase transition and less field-induced longitudinal strain. The differences in the properties of SPS and CS materials are attributed to the variations of the resultant microstructures, especially the grain size, of the ceramics.
... PHYSICAL REVIEW B 73, 064114 2006 High dielectric constant and frozen macroscopic polarizatio... more ... PHYSICAL REVIEW B 73, 064114 2006 High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics Maria Teresa Buscaglia,1 ... 3 b . Measurements carried out at room temperature showed that tan is of the order of 2% in the range ...
Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural a... more Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural applications. The development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics have good damage tolerance. Until now this has been accomplished by heating the appropriate powder compacts to temperatures above 1,700 degrees C for extended periods. This procedure involves a necessary step of controlling the size and population of seeds added ex situ or formed in situ to ensure selective grain growth. Here we report the very fast (within minutes) in situ formation of a tough interlocking microstructure in Si(3)N(4)-based ceramics. The microstructures are obtained by a dynamic ripening mechanism, an anisotropic Ostwald ripening process that results from the rapid heating rate. The resulting microstructures are uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics. This process is very efficient and opens up new possibilities to optimize mechanical properties and cost-effectively manufacture ceramics.
Vickers indentation tests were conducted on an Al2O3–TiC composite at different load levels. The ... more Vickers indentation tests were conducted on an Al2O3–TiC composite at different load levels. The crack resistance calculated from the length of the indentation-induced crack exhibits a large scatter. Such a large scatter can be characterized well with Weibull statistics and can be attributed to the effect of microstructural inhomogeneity on the local crack resistance. The effect of the statistical variability
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001
The Vickers hardnesses of a series of Ti(C,N)-based cermets were measured in the indentation load... more The Vickers hardnesses of a series of Ti(C,N)-based cermets were measured in the indentation load range from 1.47 to 40.67 N. It was found that the examined materials exhibit a reversed indentation size effect, i.e. the measured hardness increases with increasing indentation load. Both Meyer's law and the energy balance model can not provide a proper description for the observed experimental phenomena, while the polynomial series representation can describe the experimental data very well. A possible explanation for the cause of the observed reverse indentation size effect was also proposed.
A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holdin... more A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al2O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2O3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21–22 GPa and fracture toughness values of 3.5 ± 0.5 MPa·m1/2 were found for the compacts containing submicrometer-sized Al2O3 grains.
... Maria Teresa Buscaglia1, Vincenzo Buscaglia1,7, Massimo Viviani1, Jan Petzelt2, Maxim Savinov... more ... Maria Teresa Buscaglia1, Vincenzo Buscaglia1,7, Massimo Viviani1, Jan Petzelt2, Maxim Savinov2, Liliana Mitoseriu3,4, Andrea ... grains from 20 to 100 nm can be observed in figure 2), a corresponding ... The dielectric constant (ε) and dielectric losses (tan δ) of the 50 nm BT ...
Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full den... more Lanthanum-doped lead zirconate stannate titanate ceramics were successfully compacted to full density by spark plasma sintering (SPS). SPS samples densified at 900° or 950°C exhibit nearly full density and fine grain size (about 300 nm). Compared with samples from conventional sintering (CS), SPS samples show larger permittivity accompanied by a deterioration in dielectric loss and special strain hysteresis loops similar to those of ferroelectric relaxors, with a diffuse AFE–FE phase transition and less field-induced longitudinal strain. The differences in the properties of SPS and CS materials are attributed to the variations of the resultant microstructures, especially the grain size, of the ceramics.
... PHYSICAL REVIEW B 73, 064114 2006 High dielectric constant and frozen macroscopic polarizatio... more ... PHYSICAL REVIEW B 73, 064114 2006 High dielectric constant and frozen macroscopic polarization in dense nanocrystalline BaTiO3 ceramics Maria Teresa Buscaglia,1 ... 3 b . Measurements carried out at room temperature showed that tan is of the order of 2% in the range ...
Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural a... more Ceramics based on Si(3)N(4) have been comprehensively studied and are widely used in structural applications. The development of an interlocking microstructure of elongated grains is vital to ensure that this family of ceramics have good damage tolerance. Until now this has been accomplished by heating the appropriate powder compacts to temperatures above 1,700 degrees C for extended periods. This procedure involves a necessary step of controlling the size and population of seeds added ex situ or formed in situ to ensure selective grain growth. Here we report the very fast (within minutes) in situ formation of a tough interlocking microstructure in Si(3)N(4)-based ceramics. The microstructures are obtained by a dynamic ripening mechanism, an anisotropic Ostwald ripening process that results from the rapid heating rate. The resulting microstructures are uniform and reproducible in terms of grain size distribution and mechanical properties, and are easily tailored by manipulating the kinetics. This process is very efficient and opens up new possibilities to optimize mechanical properties and cost-effectively manufacture ceramics.
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