In recent weeks, quite a few customers have inquired whether we can produce ceramic products made of 5 mol% or 8 mol% yttria-stabilized zirconia (YSZ). While our company frequently produces 3mol YSZ and magnesium-stabilized zirconia, the variations in yttria content have created some confusion. So, what are the actual differences between zirconia stabilized with different mol% of yttria? This article explains the differences between 3mol, 5mol, and 8mol YSZ ceramics, their performance, and typical applications.
Zirconia (ZrO₂) is one of the most widely used ceramic materials. To improve high-temperature performance and mechanical properties, zirconia is stabilized with yttria (Y2O3). YSZ ceramics have three main crystal structures: Monoclinic phase; Tetragonal phase; and Cubic phase The proportion of these phases has a significant impact on its overall properties. Currently, 3Y-TZP (3mol% Y2O3) is the most commonly used YSZ because of its excellent mechanical performance. It has broad application prospects in industries such as chemical processing and machinery. However, even for 3Y-TZP, the performance varies greatly depending on the preparation method. To obtain
zirconia ceramics with higher mechanical properties, approaches such as controlling the sintering temperature and doping can be adopted. The addition of additives can also alter the grain size and phase composition of the material to some extent. Since grain size and phase composition have a significant impact on the physical properties of ceramics, studying their influence is of great importance for exploring ways to enhance the overall performance of zirconia.
1. Effect of Yttria Content on Relative Density
The maximum densification of zirconia corresponds to a yttria content of 3 mol%, where the relative density reaches 98.113%. Before this critical point, the relative density of the samples increases with higher yttria content, while beyond the critical point it gradually decreases. Clearly, sintered bodies with 3 mol% Y₂O₃ exhibit higher relative density than other groups, indicating that Y₂O₃ promotes densification during the sintering of zirconia.
This is because the ionic radius of Y³⁺ (1.06 Å) is larger than that of Zr⁴⁺ (0.87 Å). When Y₂O₃ forms a substitutional solid solution with ZrO₂, it distorts the lattice of the main zirconia phase and increases the number of defects, which facilitates the movement of structural units and promotes sintering, thereby achieving higher densification. However, once the yttria content exceeds the critical value, the beneficial role of Y₂O₃ in the zirconia matrix diminishes, and excessive Y₂O₃ hinders crystallization during the sintering process, leading to a gradual decrease in relative density.
In addition, X-ray photoelectron spectroscopy (XPS) analysis shows that Y³⁺ tends to segregate at the grain boundaries, where it strongly impedes grain boundary migration. This can prevent or delay the separation of pores from grain boundaries, thus allowing the densification process to continue in the later stages of sintering. When the yttria content is 3 mol%, this effect is maximized, resulting in the highest relative density of zirconia ceramics.
2. Effect of Yttria Content on the Mechanical Properties of Zirconia Ceramics
As the molar fraction of yttria increases, the flexural strength of zirconia ceramics rises rapidly, reaching its maximum at 3 mol% Y₂O₃. Beyond this point, further increases in yttria content do not enhance the strength; instead, the strength gradually decreases.
Similarly, the hardness of zirconia ceramics increases with yttria content, reaching its highest value at 3 mol%. After this critical point, the hardness decreases as yttria content continues to increase. At 3 mol% Y₂O₃, the grain size of
yttria-stabilized zirconia is at its minimum, while the material also exhibits high density. At this composition, the microstructure of zirconia contains a certain amount of elongated crystals. These elongated grains form solid bridges between the fine zirconia particles and the bulk matrix, resulting in a tighter bonding and higher cohesion within the material. This structural feature explains why zirconia ceramics achieve their highest hardness at 3 mol% yttria.
Mingrui Ceramics mainly provides custom ceramic parts covering 95%~99.99% alumina, SSiC, Si3N4, Mullite, zirconia ceramic products (including 3 mol% yttria-stabilized zirconia). Contact us today for professional ceramic solutions and quotes.
