Crack-Resistant Zirconia-Based Composite Ceramics with Increased Hardness of the Near-Surface Layer

Using a relatively economical method of powder metallurgy, a two-layer composite ceramic based on zirconia stabilized with calcium oxide and alumina toughened (Ca-ATZ) is fabricated. One of the layers contains an additive of silicon dioxide (Ca-ATZ + SiO2). The structure and elemental and phase composition, as well as the set of mechanical properties of the samples in the vicinity of the Ca-ATZ/Ca-ATZ + SiO2 layer interface are studied. It is shown that the presence of a sharp interface between layers with different elemental compositions does not cause structural damage (appearance of pores, cracks, and other macroscopic defects that contribute to deterioration of the strength properties) or changes in the phase composition (more than 90% of zirconia in both layers is in the tetragonal phase, which ensures a high role of the transformation toughening mechanism). The demonstrated preservation of the structural integrity and the ratio of the monoclinic, tetragonal, and cubic phases of zirconia during the formation of a sharp interface between these layers makes it possible to fabricate ceramic based on zirconium dioxide with a thin (100–200 μm) modified layer. Taking into account the difference in the mechanical properties of Ca-ATZ and Ca-ATZ + SiO2 ceramic, this provides a base material (containing SiO2) with increased fracture toughness (not less than 12 MPa m1/2) and a surface layer (containing no SiO2) with nanohardness (no lower than 14 GPa).