Al2O3/Y-TZP ceramic composite with unidirectional functional gradient

Ceramic composites are developed with the aim of improving the properties of single phase materials, adapting it to the demands of their applications. In this work, composite ceramics with an unidirectional functional gradient based on Al2O3 reinforced with 3, 5, 10 and 15 wt-% of Y-TZP (Yttria stabilized tetragonal zirconia polycrystals) nano-sized particles were prepared, using multilayer deposition and uniaxial compaction. The composites were characterized by their relative density, microstructure, phase composition, hardness and fracture toughness. The results showed the presence of α-Al2O3 and t-ZrO2 as crystalline phases and relative density near to 98%. The hardness varied according to the indented region varying between 1750 and 1540 (HV), for layers containing 3 and 15 wt-% of Y-TZP, respectively. Fracture toughness of the composite layers is also sensitive to the increasing ZrO2 content, presenting average values of 3.2 to 4.8 MPa.m1/2, indicating the influence of toughening mechanisms such as the t → m ZrO2 phase transformation and compressive residual stresses between the α-Al2O3 matrix and the reinforcing t-ZrO2 particles, generated by their thermal mismatch.