The different types of zirconia

Zirconia (TZP)

TZP is a high-performance ceramic that is contained in the tetragonal phase by stabilizing zirconium dioxide (ZrO2) with yttrium oxide (Y₂O3). Undoped zirconia (ZrO2) changes from the tetragonal phase to the monoclinic phase when it cools. This transformation is associated with a change in volume of approximately 4%, which leads to destruction of the component due to crack formation. The doping or stabilization of zirconium oxide is therefore essential for the use of the material.  

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Transformation Toughening

So-called Transformation Toughening is primarily responsible for the outstanding properties of TZP. When a crack forms, there is a stress concentration around the crack tip. This triggers a local transformation from the metastable, tetragonal phase to the monoclinic phase. The conversion requires energy, which reduces the crack energy. In addition, the mentioned volume expansion of around 4% creates compressive stresses at the tip of the crack. This prevents further crack propagation and increases fracture toughness (3, 4).  

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Influence of grain size (Hall-Petch)

Another mechanism for increasing mechanical properties is the grain size of the material. The smaller the particle size, the better the mechanical properties. The particle size depends essentially on the primary powder, the production of the semi-finished product and the sintering conditions. Our TZP is characterized by a small particle size, which is very homogeneous. As a result, we achieve excellent strength values.

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Applications

TZP is used in numerous areas due to its mechanical robustness and biocompatibility

• Medical implants: Dental implants and hip balls benefit from high strength and corrosion resistance (2.4).
• Mechanical engineering: Wear parts such as valves or bearings, nozzles, knives, thread guides for the textile industry, welding pins and pump parts.
• Toolmaking cutting tools due to their high hardness and wear resistance.
• Watch industry/jewelry industry: bezels, buttons or entire cases due to scratch resistance, comfortable wear and outstanding aesthetics

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Challenges

Despite its advantages, TZP is susceptible to low temperature degradation (LTD = low temperature degradation). This occurs during prolonged exposure to moisture and temperatures between 200—300 °C and leads to surface roughness and loss of mechanical properties (2).

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Aluminum reinforced zirconia (TZP-A)

TZP-A is a development of TZP in which a small amount of aluminum oxide (Al2 O3), typically 0.25%, is added. This modification significantly improves long-term stability and resistance to LTD.

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Applications of TZP-A

TZP-A is used in areas where both high strength and long-term stability are required

• Medical implants: Especially in humid environments such as dental implants or orthopedic prostheses.
• Industrial components: Highly stressed parts such as pump components or seals.

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Refinements

The vertical integration of processes allows us to refine components. For example, a wide range of colors is available. This is particularly interesting for applications in the watch and jewelry industry. The color is not obtained retroactively through infiltration, but is an integral part of the starting materials from which the semi-finished or finished product is manufactured. Awalux also offers the development of customer-specific color toner.

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Conclusion

The vertical integration of processes allows us to finish components. For example, a wide range of colors is available. This is particularly interesting for applications in the watch and jewelry industry. The color is not obtained retrospectively through infiltration, but is an integral part of the starting materials from which the semi-finished or finished product is manufactured. Awalux also offers the development of a customer-specific color.

Alumina Toughened Zirconia (ATZ)

Alumina Toughened Zirconia (ATZ) is a high-performance ceramic composite material that is produced by combining zirconium dioxide (ZrO₂) with aluminum oxide (Al₂O³). ATZ typically consists of 80% ZrO2 (stabilized with 3 mol% yttrium oxide) and 20% Al2 O3. This composition combines the high fracture toughness of zirconium oxide with the extreme hardness of aluminum oxide, making ATZ ideal for demanding industrial and medical applications.

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Mechanical properties of ATZ

• Flexural Strength:Up to 1800 MPa (HIP processed)
• Fracture toughness:8 mP/m, significantly higher than pure ZrO₂
• Hardness: 14GPa (Vickers), comparable to tungsten carbide
• Thermal stability: Use up to 1,500 °C thanks to low thermal expansion (6.5—8.9 × 104 K¹)
• Corrosion resistance:Inert to acids, bases and oxidizing media

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Benefits of ATZ

• Transformation toughening: When loaded, the ZrO2 matrix can undergo a stress-induced phase transformation (tetragonal → monocline), which inhibits crack propagation. This is the same mechanism as TZP.
• Crack deflection and crack branching: Al₂O3 particles act as physical barriers to crack propagation. The Al₂O3 particles force the cracks to detours, which increases the required fracture energy. In addition, the crack-Al2 O3 particle interaction can lead to crack branching, which increases the crack front length.
• Residual stresses: The different thermal expansion coefficients of ZrO2 and Al2 O3 generate compressive residual stresses after sintering, i.e. surface compression is increased, which leads to an increase in bending strength.
• Grain refinement of the ZrO2 matrix: Al₂O3 particles suppress grain growth during the sintering process. The smaller grains lead to better mechanical properties (Hall-Petch).
• Low degradation: Al₂O3 addition reduces the vulnerability to low temperature degradation (LTD) in humid environments.
• Wear resistance: ATZ exceeds pure ZrO2 by 3 times in abrasive applications.

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Applications of ATZ

Due to its unique properties, ATZ is primarily used in the following areas

• Medical implants Especially for dental implants but also for hip joints with improved long-term stability
• Industrial components: high-pressure valves that require high resistance to abrasive media (for example in oil production systems). But also guide rails, nozzles, extrusion tools and a wide variety of 3D-printed geometrically complex components with wall thicknesses of up to 20mm.

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Conclusion

The vertical integration of processes allows us to refine components. For example, a wide range of colors is available. This is particularly interesting for applications in the watch and jewelry industry. The color is not obtained retrospectively through infiltration, but is an integral part of the starting materials from which the semi-finished or finished product is manufactured. Awalux also offers the development of customer-specific color shades.

Sources

1. AZom: “An Introduction to Tetragonal Zirconia Polycrystal (TZP)” (2023)
2. Allen Press: “Y-TZP Ceramics: Key Concepts for Clinical Application” (2009)
3. Chevalier et al.: “Low-temperature degradation of zirconia” (J Am Ceram Soc, 2008)
4. Taylor & Francis: “TZP — Knowledge and References

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