Zirconia Toughened Alumina

Zirconia toughened alumina (ZTA) is an advanced ceramic material widely used in valve seals, bushings, pump components and cutting tools due to its strength and chemical stability – as evidenced by its ability to withstand heavy loads without significant degradation.

ZTA boasts impressive thermal shock resistance and can withstand sudden shifts in temperature changes, as well as rapid temperature swings. Read on to learn more about its mechanical properties!

Hardness

Zirconia added to an alumina matrix increases its hardness, fracture toughness and flexural strength while increasing resistance to wear and erosion. The mechanism typically involved is phase transformation followed by microcrack formation but may also involve stress theory theories as applicable.

Metastable tetragonal zirconia precipitates that form fine dispersion within an alumina matrix can undergo spontaneous transformation into monoclinic forms when their constraint is lifted during crack propagation, providing energy against stress fields driving crack propagation.

ZTA ceramic has superior fracture toughness and hardness compared to other oxide-based engineering ceramics, as well as twice the cyclic fatigue strength of Y-TZP. As such, its properties make it suitable for applications requiring extreme wear resistance, chemical inertness and low friction as well as high strength and stiffness.

Flexural Strength

ZTA ceramics can be made by altering the ratio of yttria stabilized zirconia (Y-TZP) within an alumina matrix using hot isostatic pressing, to optimise hardness-fracture toughness-flexural strength combinations that result in unparalleled cyclic fatigue resistance surpassing most advanced technical ceramics.

Metastable Y-TZP in an alumina matrix results in the formation of tetragonal-monoclinic transformation phase agglomerates which increase fracture toughness through phase transformation stiffening (Claussen 1976). Preferentially crossing cracks, these transition agglomerates will compress the zone ahead of the crack front and reduce its progression, ultimately increasing fracture toughness.

This material structure has led to the creation of alumina-zirconia composites such as BIOLOX Delta, used extensively for total hip replacements and other load-bearing orthopedic components. This ceramic biomaterial features outstanding wear resistance, chemical inertness at room temperature, thermal shock resistance and excellent chemical inertness at all temperatures.

Corrosion Resistance

Chemically inert and resistant to high temperatures and wear, it provides superior performance compared to 99 alumina ceramics and is more cost-effective as well.

Zirconia also boasts impressive tensile strength, flexural and elasticity properties and biocompatibility – making it ideal for medical uses like hip replacements. Due to transformation toughening under stress conditions, zirconia particles change from metastable tetragonal form into monoclinic form, helping close cracks more efficiently while increasing fracture toughness.

CeramTec (Biolox Delta) commercializes an alumina-zirconia composite where unstabilized zirconia remains in tetragonal phase to manage this transformation and provide crack tip blunting and crack deviation, improving toughness of alumina matrix. Zirconia content of material can be altered through powder preparation and densification techniques.

Thermal Shock Resistance

Zirconia added to a primary alumina matrix during sintering can significantly enhance its strength and toughness, creating what’s known as ZTA (Zirconia Toughened Alumina), outperforming regular alumina ceramics in both mechanical and wear applications.

Zirconia toughened alumina is noted for its exceptional properties such as high hot hardness and rapture strength, chemical inertness at room temperature, low thermal expansion rates and excellent thermal shock resistance – ideal properties for milling components as well as wear parts requiring cooling mechanisms.

CeramTec markets a ZTA called Biolox delta that features an alumina matrix with dispersed Y-TZP particles (17 weight/wt%) and strontium aluminate platelets (0.5 weight/wt%), providing an effective combination of tetragonal-to-monoclinic phase transformation mechanisms and crack deflection mechanisms to provide improved toughness, which makes this ideal for primary THA procedures on femoral bearing surfaces.

Electrical Insulation

Zirconia-toughened alumina can withstand thermal shock without cracking or breaking under sudden changes in temperature, thanks to dispersed alumina particles dispersed within its matrix that absorb the thermal energy and generate compressive stresses that prevent fractures.

Alumina-zirconia ceramic is more dense than its pure zirconia counterpart, making it ideal for electrical insulation applications. Furthermore, its lower thermal expansion than zirconia makes it suitable for parts requiring cooling.

Transformation toughening of Alumina-zirconia composites offers additional advantages; here, zirconia grains in an alumina matrix undergo a metastable phase where their grains undergo transformation from tetragonal to monoclinic structures, thus decreasing stress-induced cracking by increasing resistance against abrasion and impact. Alumina toughened zirconia typically occurs through pyrophoric reaction involving Zirconium(IV) oxide octahydrate, Aluminium Nitrate Nanohydrate Triethylamine and HNO3(Nitric Acid); increasing particle sizes further aid dispersion of metastable zirconia grains.