Effect of loading conditions on the fracture toughness of zirconia

Abstract Purpose A Vickers hardness indenter was pressed into yttria-stabilized zirconia (Y-TZP) by the indentation fracture method (IF method). Methods The effect on the calculated Vickers hardness, fracture toughness values, and indentation fracture load (9.8, 49, 98, 196, and 294N) was examined to deduce the optimum conditions of the IF method. Calculated Vickers hardness and fracture toughness values were analyzed with one-way analysis of variance and then multiple comparisons (Scheffe). The appearance of on indentation and cracks was also evaluated using a scanning electron microscopy (SEM). Results Indentation of Y-TZP was generated by 9.8 and 49N of indentation fracture load, however cracks could not be confirmed with the microscope attached to the Vickers hardness tester. Both indentation and cracks were observed at 98, 196 and 294N of indentation fracture load obtained values of 7.1 and 6.8MPam 1/2 . Cracks noted at the 98N were not clear, whereas the 196 and 294N showed especially clear cracks. Due to the hardness of zirconia and the light loads, fracture toughness values for 9.8, 49, and 98N could not be calculated. There was no significant difference between 196 and 294N, when calculated fracture toughness values were analyzed with multiple comparisons. SEM revealed clear indentation and cracks, that extended linearly, but no chips or fractures were observed. Surface changes were observed at 196 and 294N that are presumed to be accompanied by phase transition around the cracks. Conclusions Optimum experimental conditions of the indentation fracture load in the IF method were determined as 196 and 294N.