Abstract
In this work, the flexure strength and fracture propagation mechanisms in yttria tetragonal zirconia (3YTZP) dense composites with 1 and 5 vol.% exfoliated graphene nanoplatelets (e-GNP) were assessed. The composite powders were processed by dry planetary ball milling to exfoliate the as-received GNP, and then densified by spark plasma sintering (SPS). The hardness and Young’s modulus were measured by Vickers indentation and the impulse-echo technique, respectively. Flexural strength and modulus were estimated by four-point bending tests. Finally, cracks originated by Vickers indentations were analyzed by scanning electron microscopy (SEM). The Raman spectra and SEM observations showed a reduction in the number of graphene layers and most remarkably in the lateral size of the e-GNP, achieving a very homogeneous distribution in the ceramic matrix. The hardness, elastic modulus, and flexural strength of the 3YTZP matrix did not vary significantly with the addition of 1 vol.% e-GNP, but they decreased when the content increased to 5 vol.%. The addition of e-GNP to 3YTZP increased its reliability under bending, and the small lateral size of the e-GNP produced isotropic fracture propagation. However, the energy dissipation mechanisms conventionally attributed to the larger GNP such as fracture deflection or blocking were limited.
Highlights
Ceramics are intrinsically fragile, but they possess unique properties such as hardness, thermal stability, resistance to corrosion, etc. that make them very attractive for structural applications; the search for possible reinforcements is always interesting
The hardness, elastic modulus, and flexural strength of the 3YTZP matrix did not vary significantly with the addition of 1 vol.% exfoliated graphene nanoplatelets (e-graphene nanoplatelets (GNPs)), but they decreased when the content increased to 5 vol.%
5 vol.% e-GNP nominal content, which means that no losses of ceramic or GNP took place during the powder processing
Summary
But they possess unique properties such as hardness, thermal stability, resistance to corrosion, etc. that make them very attractive for structural applications; the search for possible reinforcements is always interesting. The use of secondary phases to reinforce ceramics has been extensively studied; only in the last few decades, the possibility of using nano-sized reinforcements as an alternative to fibers, whiskers, and conventional second phases has been considered. Among these nano-sized reinforcements, two-dimensional graphene-based nanomaterials (GBNs) are interesting, because of the high surface area of graphene (~2600 m2 ·g−1 ) [1], and because of its extremely high tensile strength (130 GPa) and Young’s modulus (1 TPa) [2]. Its extraordinary electrical and thermal conductivities can be useful for functional composites. The GBNs typically used as fillers in composites include multilayer graphene (up to 10 layers), few-layer graphene (n < 5) and cost-effective stacking of n > 10 graphene layers, known as graphene nanoplatelets (GNPs) [3,4,5].
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