DESIGN OF MIXTURE EXPERIMENTS OF Al2O3-TiB2-TiC COMPOSITES: PART 2: PREDICTION OF VICKERS HARDNESS AND FRACTURE TOUGHNESS

According to the design of mixture experiments, 10 different mixture compositions were established for this study. After spark plasma sintering of these mixtures at 1700°C, 47 MPa and a dwell of 10 minutes, their Vickers hardness and fracture toughness were measured. These experimental results were analyzed in Minitab 17, and then different regression models were obtained for each studied property. The behavior of Vickers hardness and fracture toughness can be explained by two different full cubic models, HV<sub>FC</sub> and FT<sub>FC</sub>. The coefficient of determination (R<sup>2</sup>) of these models are around 60% and 55%, respectively. This suggests that a new design of mixture experiment is needed in order to obtain more adequate models. Despite this, the HV<sub>FC</sub> and FT<sub>FC</sub> models were used for an approximate estimation of the Vickers hardness and fracture toughness, and based on them, contour plots were made for a visual representation of predicted results in the Al<sub>2</sub>O<sub>3</sub>TiB<sub>2</sub>-TiC simplex. These contour plots show the zones corresponding to values of Vickers hardness > 17,9 HV and fracture toughness > 7.00 МPa·m<sup>1/2</sup>. Combining these zones, it was possible to determine the region in the Al<sub>2</sub>O<sub>3</sub>-TiB<sub>2</sub>-TiC simplex, which simultaneously correspond to the Vickers hardness and fracture toughness of sintered samples greater than 17,9 HV and 7.00 МPa·m<sup>1/2</sup>. The obtained HV<sub>FC</sub> and FT<sub>FC</sub> models were additionally tested at three new points, and it was determined that additional experimental values fit well into the predicted by Minitab intervals.