Stability of nanocrystalline spark plasma sintered 3Y-TZP

Spark plasma sintered 3Y-TZP has been investigated with respect to hydrothermal ageing and grinding. The sintering was performed between the temperatures of 1,100 and 1,600 °C for a soaking time of 5 minutes and the resulting materials were obtained with grain sizes between 65 to 800 nm and relative densities between 88.5 to 98.8%. Experiments on hydrothermal ageing in water vapour at 131 °C, 2 bars during 60 hours shows that phase stability is retained, elastic modulus and hardness of near surface region measured by nanoindentation does not change in fine grain (<200 nm) materials, in spite of porosity. In ground specimens, very small amount of transformation was found for all grain sizes studied.Peer ReviewedPostprint (published version

Influencia de la degradación hidrotérmica en la resistencia mecánica y comportamiento al desgaste de 3Y-TZP

En este trabajo se realiza un estudio comparativo de la influencia de la degradación hidrotérmica a baja temperatura de circona tetragonal estabilizada con el 3% molar de Itria (3Y-TZP) en la resistencia mecánica a flexión y en el comportamiento bajo cargas de indentación esférica. Se presentan resultados de resistencia mecánica a flexión y de indentación esférica monotónica así como de ensayos de rayado en probetas artificialmente degradadas durante diferentes períodos de tiempo. Se pone de manifiesto que la resistencia mecánica a flexión es poco sensible a la degradación; por el contrario, los ensayos superficiales ponen claramente de manifiesto la presencia de degradación en sus etapas iniciales. Se constata la fuerte sensibilidad de la resistencia al desgaste y de la fatiga por contacto a la presencia de degradación hidrotérmica a baja temperatura. Los resultados se analizan en términos de la capa degradada de estructura monoclínica que se forma durante la degradación.Postprint (published version

Determination of the intrinsic fracture toughness from the COD analysis of indentation cracks in Spark Plasma Sintered 3Y-TZP reinforced with MWCNT

El método de la indentación para medir la tenacidad de fractura ha sido ampliamente utilizado en materiales frágiles debido a su sencillez y a que puede realizarse en volúmenes pequeños de material. Especialmente en estos casos, las tenacidades de fractura obtenidas mediante el método de indentación pueden llegar a ser muy distintas de los valores reales obtenidos mediante métodos rigurosos basados en un conocimiento preciso de todos los parámetros que intervienen en la fractura. Esto ha llevado a desarrollar métodos que relacionan el perfil de la abertura de la grieta de indentación con la tenacidad intrínseca de fractura KI0. En este trabajo se ha estudiado la cerámica 3Y-TZP y el material compuesto formado por 3Y-TZP y 2% en volumen de nanotubos de carbono con paredes multicapa (MWCNT) ambos producidos por Spark Plasma Sintering (SPS). El método de análisis del COD permitió comprobar que la adición de este contenido de MWCNT no afecta prácticamente al COD medido experimentalmente y que la tenacidad intrínseca KI0 es por tanto muy similar para ambos materiales. Estas observaciones en principio no justifican las diferencias en tenacidad de fractura determinadas por el método clásico de tenacidad de fractura por indentación en los materiales estudiados. // The indentation method has been widely used to measure the fracture toughness in fragile materials due to its simplicity and that only needs of a small sample. However, it is well known that the fracture toughness values obtained by indentation methods can be substantially different from the values obtained from more rigorous methods which are based on a precise knowledge of all parameters involved in fracture. This situation has lead to the development of new methods that investigate the crack opening displacement (COD) and relate it to the intrinsic fracture toughness KI0. In the present work, a 3Y-TZP ceramic has been studied together with a composite containing 2% vol. of multiwall carbon nanotubes (MWCNT); both of which were produced by Spark Plasma Sintering (SPS). The COD method showed that the addition of MWCNTs did not effectively affect the COD and the intrinsic fracture toughness KI0 was thus very similar in both materials. These observations in principle do not justify the differences determined by the classical indentation fracture toughness method on the present materials.Peer Reviewe

Influence of hydrothermal degradation on wear behaviour of Zirconia tetragonal polycrystals doped with 3% molar of yttria

The goal of this work is to analyse the influence of hydrothermal degradation on wear behaviour on samples of tetragonal polycrystals doped with 3% molar of yttria in air under dry sliding conditions on samples artificially aged at 0, 10 and 60 hours in autoclave at 131°C. The samples were prepared by conventional compaction and sintering at 1450°C. The study was carried out by performing scratch tests and ball on disc experiments against 3Y-TZP balls. At low loads the damage was not distinctive, but under high loads the damage mechanisms were different suggesting a clear effect of degradation after long ageing times. On the contrary, in samples degraded during 60 hours the wear rates in both experiments were initially higher than on non-aged specimens and decreased with increasing load and/or sliding distance.Peer Reviewe

Influence of hydrothermal degradation on wear behaviour of zirconia tetragonal polycristals doped with 3% molar of yttria

The goal of this work is to analyse the influence of hydrothermal degradation on wear behaviour on samples of tetragonal polycrystals doped with 3% molar of yttria in air under dry sliding conditions on samples artificially aged at 0, 10 and 60 hours in autoclave at 131°C. The samples were prepared by conventional compaction and sintering at 1450°C. The study was carried out by performing scratch tests and ball on disc experiments against 3Y-TZP balls. At low loads the damage was not distinctive, but under high loads the damage mechanisms were different suggesting a clear effect of degradation after long ageing times. On the contrary, in samples degraded during 60 hours the wear rates in both experiments were initially higher than on non-aged specimens and decreased with increasing load and/or sliding distance.Peer Reviewe

Relationship between density and mechanical properties of spark plasma sintered zirconia ceramics

Zirconia ceramics stabilized with 3 mol % Yttria were produced by spark-plasma sintering. Toughness, Vickers hardness, nanoindentation elastic modulus and Berkovich hardness were determined in terms of the final density and sintering temperature. Very fine grain materials from 65 to 800 nm were obtained with relative densities ranging from 88 to 99.5%. Results show lower elastic modulus and hardness in low dense specimens compared to fully dense specimens, also indentation fracture toughness changes with density and grain size. Specimens investigated under hydrothermal degradation at 131ºC for 60 hours show that mechanical properties are not affected by this treatment in low density and low grain size specimens, but affects strongly the elastic modulus and contact hardness of specimens of near full density and large grain size. The results are discussed in terms of density, grain size and t-m transformability.Peer ReviewedPostprint (published version

Influence of hydrothermal degradation on wear behaviour of Zirconia tetragonal polycrystals doped with 3% molar of yttria

The goal of this work is to analyse the influence of hydrothermal degradation on wear behaviour on samples of tetragonal polycrystals doped with 3% molar of yttria in air under dry sliding conditions on samples artificially aged at 0, 10 and 60 hours in autoclave at 131°C. The samples were prepared by conventional compaction and sintering at 1450°C. The study was carried out by performing scratch tests and ball on disc experiments against 3Y-TZP balls. At low loads the damage was not distinctive, but under high loads the damage mechanisms were different suggesting a clear effect of degradation after long ageing times. On the contrary, in samples degraded during 60 hours the wear rates in both experiments were initially higher than on non-aged specimens and decreased with increasing load and/or sliding distance.Peer Reviewe

Influence of hydrothermal degradation on wear behaviour of Zirconia tetragonal polycrystals doped with 3% molar of yttria

The goal of this work is to analyse the influence of hydrothermal degradation on wear behaviour on samples of tetragonal polycrystals doped with 3% molar of yttria in air under dry sliding conditions on samples artificially aged at 0, 10 and 60 hours in autoclave at 131°C. The samples were prepared by conventional compaction and sintering at 1450°C. The study was carried out by performing scratch tests and ball on disc experiments against 3Y-TZP balls. At low loads the damage was not distinctive, but under high loads the damage mechanisms were different suggesting a clear effect of degradation after long ageing times. On the contrary, in samples degraded during 60 hours the wear rates in both experiments were initially higher than on non-aged specimens and decreased with increasing load and/or sliding distance.Peer ReviewedPostprint (published version

Influence of hydrothermal degradation on wear behaviour of zirconia tetragonal polycristals doped with 3% molar of yttria

The goal of this work is to analyse the influence of hydrothermal degradation on wear behaviour on samples of tetragonal polycrystals doped with 3% molar of yttria in air under dry sliding conditions on samples artificially aged at 0, 10 and 60 hours in autoclave at 131°C. The samples were prepared by conventional compaction and sintering at 1450°C. The study was carried out by performing scratch tests and ball on disc experiments against 3Y-TZP balls. At low loads the damage was not distinctive, but under high loads the damage mechanisms were different suggesting a clear effect of degradation after long ageing times. On the contrary, in samples degraded during 60 hours the wear rates in both experiments were initially higher than on non-aged specimens and decreased with increasing load and/or sliding distance.Peer Reviewe

Relationship between density and mechanical properties of spark plasma sintered zirconia ceramics

Zirconia ceramics stabilized with 3 mol % Yttria were produced by spark-plasma sintering. Toughness, Vickers hardness, nanoindentation elastic modulus and Berkovich hardness were determined in terms of the final density and sintering temperature. Very fine grain materials from 65 to 800 nm were obtained with relative densities ranging from 88 to 99.5%. Results show lower elastic modulus and hardness in low dense specimens compared to fully dense specimens, also indentation fracture toughness changes with density and grain size. Specimens investigated under hydrothermal degradation at 131ºC for 60 hours show that mechanical properties are not affected by this treatment in low density and low grain size specimens, but affects strongly the elastic modulus and contact hardness of specimens of near full density and large grain size. The results are discussed in terms of density, grain size and t-m transformability.Peer Reviewe