Investigations of the subcritical crack growth phenomenon and the estimation of lifetime of alumina and alumina–zirconia composites with different phase arrangements

The Constant Stress Rate Test was used to determine subcritical crack propagation of sintered composites in the α-alumina-tetragonal zirconia system. Strength measurements were conducted at different stress rates. Material strength depends on the flaw size. Increasing stress rates led to strength increase as a result of shortening of the time of crack growth.The alumina composite with 5 vol% of zirconia inclusions was prepared as a model of particulate composites with isolated grains of the minor phase. The composite with 15 vol% of zirconia was fabricated as a two-phase material with the minor phase grains content near the percolation point. The third type of a composite containing 35 vol% of zirconia additives was prepared as an example of the composite with typical duplex microstructure. Additionally, α alumina sinters were prepared as a reference material. The performed experiments allowed us to calculate parameters of slow crack propagation and to construct strength-probability-time diagrams for lifetime prediction of ceramic elements.