Abstract
We have used Hertzian and Vickers indentation to investigate contact damage in sintered SiC ceramics, one consisting of uniform, fine-grains and the other a coarse, elongated grain structure. Cracking-resistance measured by Hertzian indentation, showed no discernible difference, nor did the Vickers hardness. However, numerical analysis of the Vickers indentation size effect, performed using the proportional specimen resistance model, indicates 77.3% greater surface energy, mostly realised through cracking, is experienced by heterogeneous SiC per unit area of indentation impression. This is typified by an observable increase in the number of radial cracks generated around Vickers impressions, which has been found to artificially increase the KIC determined by Vickers indentation fracture. Quantitative measurements of pre-existing flaws by Hertzian indentation show that heterogeneous SiC retains a higher density of larger flaws. Relationships between the differences in cracking around Vickers indents and the pre-existing flaw populations of these two SiC ceramics are discussed.
Highlights
Silicon carbide (SiC) ceramics have been increasingly used as structural materials designed to endure a wide range of static/dynamic contact loads, as part of composite armour or as bearings, gaskets and other wear components, largely because of their high hardness, outstanding damage tolerance and low density
The experimental measurements have demonstrated that, despite an almost negligible difference in hardness between the two sintered SiC ceramics tested, a frequently quoted measurement of contact damage resistance, the one with a heterogeneous grain structure displayed a degree of cracking 77.3% higher than that of homogenous SiC
This conclusion is supported by the following findings: (a) The grain structure has no effect on the KIC of SiC ceramics measured by Hertzian indention
Summary
Silicon carbide (SiC) ceramics have been increasingly used as structural materials designed to endure a wide range of static/dynamic contact loads, as part of composite armour or as bearings, gaskets and other wear components, largely because of their high hardness, outstanding damage tolerance and low density. For such applications, hot-pressed SiC would be the favoured material. To date, little work has been done on understanding how such changes influence the resistance to contact damage in ceramics
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