Role of t-ZrO₂ stabilization methods in phase composition, structure and properties of ZTA ceramics

In this study, alumina–zirconia ceramics with ZrO₂ components obtained using different methods were investigated. Synthesized undoped ZrO₂ powder, commercial powder of ZrO₂, doped with 3 mol% Y₂O₃ and commercial powder of monocline zirconia doped with 2 mol% ceria were used. Highly dispersed (D50 < 100 nm) undoped zirconia was synthesized by precipitation from 1 M aqueous solution of ZrOCl₂-8H₂O with 25% aqueous ammonia solution. The resultant products were treated with water and isopropyl alcohol. Thermal treatment of the powder was carried out in a chamber furnace at a temperature beginning at 450 °C. Increasing the content of undoped ZrO₂ synthesized using the precipitation method increased the average size of ZrO₂ grains from 370 ± 20 nm to 560 ± 25 nm. During sintering of alumina-zirconia ceramics containing 20 vol% highly dispersed undoped zirconia, clusters of ZrO₂ particles unite to form large grains (800–1100 nm). Zirconia crystals with sizes less than 300 nm in the ceramic structure are observed inside and in the joints of Al₂O₃ grains. With the increase in total undoped zirconia content from 10 to 20 vol% in alumina–zirconia ceramics, the proportion of t-ZrO₂ remaining during sintering decreases from 6 to 2 vol%. The introduction of cerium nitrate into a suspension of monoclinic zirconia at the stage of dispersion leads to the formation of ceramic CeAl₁₁O₁₈ platelets with length of up to ~ 2 μm and width of ~ 0.15 μm. The bending strength is 800 ± 50 MPa and fracture toughness is 5.4 ± 0.7 MPa*m^1/2 in Al₂O₃–ZrO₂ ceramics containing 15 vol% zirconia doped with 2 mol% ceria.