Measurement of Vickers hardness on ceramic floor tiles

In this paper, Vickers macro- and micro-hardness of ceramic floor tiles samples made from two types of clay materials, kaolinite and illite–carbonate raw materials, were presented. The samples, designed separately, from both types of clay materials were shaped by dry pressing at 25 MPa, then fired at 960 and 1050 °C in laboratory conditions and exposed to freezing/thawing cycles with the aim to compare the hardness before and after cycling and correlate it to their microstructure. The results showed that Vickers macrohardness increases with the increasing of the firing temperature, although the expected microstructure is not achieved. The results obtained after freezing and thawing follow the same trend. In addition, the indentation size effect (ISE) in the case of low-load hardness testing was analysed. It should be noticed that the samples based on illite–carbonate clay material after the freezing/thawing cycles showed an unexpected increasing of hardness. The obtained results might be the consequence of the calcium silica hydrates formation during cycling treatment, causing a different behaviour of this kind of systems under low-loading. The ISE was described through the application of the Mayer's law, proportional specimen resistance (PSR) model and modified PSR model. The best correlation between measured values and used models was achieved in the case of modified PSR model. The most reliable results for the load independent hardness, H LIH, were obtained in the case of Vickers hardness measurement HV1.