On the variability of strength to toughness ratio in zirconia-alumina composites

摘要

In his review of available flexure strength/fracture toughness (S/Kc) results for ceramic matrix composites, Rice [1] found it useful to relate the S/Kc ratio of these materials to their microstructures, in particular to the volume fraction of the dispersed phase. In some groups of composites, more detailed analysis of S/Kic plots turned out to be difficult due to significant scatter of the data, as shown in Fig. 1 for ZTA materials. The main reason for this scatter is believed to be the fact that different researchers used different measuring techniques and sample sizes for determination of mechanical properties, in particular the fracture toughness. The technique of measuring fracture toughness was shown to affect the calculated S/Kc values in at least one systematically analysed case of non-transformation toughened particulate composite [2]. In ZTA materials the most significant differences are known to appear between the fracture toughness values measured by single edge-notched beam (SENB), indentation fracture (IF) and indentation strength in bending (ISB) techniques [3-5], not only due to the effects of notch size and shape [4], but also due to mostly undefined local notch/indent tip transformation in non-annealed samples [5], Rice suggested in his analysis [1] that to some extent the variability of SIKC results in ceramic paniculate composites may also be attributed to the size difference of the matrices' grains, and this was also indicated in some other works [3,6-8].