Zirconia-toughened alumina (ZTA)

Question 1

What is the result of the presence of (un-doped) zirconia grains in a polycrystalline Al2O3 matrix?

Answer 1

~ significantly increases the fracture toughness and strength over pure Al2O3

~ optimum of 15vol% ZrO2

Question 2

How does strength enhancement occur?

Answer 2

~ via t–>m transformation freely occurring in dispersed pure ZrO2 grains during cooling from sintering heat treatment

~ associated volume expansion facilitates microcracking in the surrounding matrix. A propagating fracture crack can be bifurcated (divided into branches/forks) when encountering the ZrO2 particle and its associated microcracks

~ microcracking has been shown to substantially improve thermal shock resistance of ZTA over pure Al2O3

~ this strengthening mech is not elevated temp-degraded as is the case of PSZ/ZTA transformation toughening