Load-dependence of Knoop hardness of Al2O3–TiC composites

Nine samples of Al2O3–30 wt.% TiC composites were prepared by hot-pressing the Al2O3 powder mixed with TiC particles. The average sizes of the TiC particles used for preparing the nine samples were different with each other. Knoop hardness measurements were conducted on these nine samples, respectively, in the indentation load range from 1.47 to 35.77 N. For each sample, the measured Knoop hardness decreases with the increasing indentation load. The classical Meyerʹs power law and an empirical equation proposed originally by Bückle were verified to be sufficiently suitable for describing the observed load-dependence of the measured hardness. Analysis based on Meyerʹs law can not provide any useful information about the cause of the observed ISE while true hardness values, which are load-independent, can be deduced from the Bückleʹs equation. It was found that the deduced true hardness increases with the average size of TiC particles existing in the sample.