Zirconia doped with 3% molar of yttria (3Y-TZP) has been widely used in the manufacturing
of medical implants during the last decades, especially thanks to its unique balance of
toughness and strength. At room temperature, these properties are mostly related to
toughening by the stress assisted transformation of the metastable tetragonal phase into
stable monoclinic one in front of a crack tip under stress. This transformation is accompanied
by a volume expansion of 5%, which contributes to prevent material failure by reducing crack
propagation and increasing toughness.
The weak point of 3Y-TZP resides in its environmental sensibility. Indeed, it is prone to Low
Temperature Degradation (LTD), an ageing phenomenon which occurs under humid
atmosphere at relatively low temperatures, being faster around 200°C.
Therefore, this project consists in designing a novel methodology for LTD prevention through
Cerium infiltration into pre-sintered 3Y-TZP porous blanks prior to sintering. The purpose is to
limit the treatment to superficial regions in order to increase the resistance to LTD without
affecting significantly the initial mechanical properties. The control of the infiltration is
performed on specimens by adjusting three parameters: solution viscosity, immersion time
and penetration mechanism (by diffusion or capillarity).
Cerium infiltration appears efficient in regard to LTD prevention, since it is shown that it
prevents degradation after 30h of artificial ageing. Besides, the influence of Cerium on
mechanical properties, such as hardness and fracture toughness, is determined by the
amount and penetration depth of Cerium in 3Y-TZP. By using short immersion times, high
solution viscosities and diffusive penetration mechanisms, the mechanical properties of 3YTZP
are maintained, without significant reduction on hardness or fracture toughness.
Finally, it is proposed another new method to prevent LTD which is based on Cerium
infiltration in combination with sandblasting. |