Does a relationship exist between hardness and compression strength for advanced ceramics?

The Knoop hardness (HK) and compression strength (σc) of 23 advanced ceramics were measured to determine if an overarching HK/σc relationship could be identified for ceramics, or if one exists for a specific class of ceramics, similar to the hardness/yield strength relationship (H/Y ≈ 3) identified by Tabor for metals. Compression strength was determined using a dumbbell‐shaped specimen that virtually eliminates the end splitting that occurs when cylinders or cuboids are tested and provides a more representative compression strength value. HK values were obtained over a range of indentation loads between 0.98 and 98N. Four HK values, HK2, load‐independent HK, the hardness from the proportional specimen resistance model, and a brittleness parameter, were obtained and plotted against compression strength. An overarching relationship could not be identified for ceramics in general and the only class of ceramics that had a consistent relationship was tungsten carbide/cobalt that had a HK/σc of approximately 2.5. The consistent relationship for the WC/Co materials is due to the cobalt plastically deforming during the loading processes, something that does not occur in the other ceramics evaluated.