Y-TZP nanostructures with non-homogeneous yttria distribution for improved hydrothermal degradation resistance and mechanical properties

Cyclic fatigue behavior of Y‐TZP nanostructures with non‐homogeneous yttria distribution

“…This is linked to the improved microstructure provided by the adopted ceramic processing method, as discussed previously, and the effects of nanometric grains and the non-homogeneous yttria distribution. 29 In contrast, despite the increased mechanical strength, the variability of the dip coating process led to a higher scatter of strength data, as indicated by the minimum and maximum biaxial flexural strength values of 1 484 and 2 119 MPa, respectively, and consequently the lower Weibull modulus. Nonetheless, the minimum biax- ial flexural strength result is still higher than the maximum values from the other groups of 1 155 and 1 420 MPa for CS and NNHYD, respectively.…”

“…The volume expansion generated by the forced 𝑡→𝑚 transformation in the artificial aging leads to a surface toughening effect, which is beneficial for CS 3Y-TZP 44 in experimental conditions, as indicated by the increase in characteristic strength for the aged CS group, with no significant impact on the Weibull modulus. On the other hand, this effect can be detrimental to nanostructured Y-TZP materials 29 since the amount of the monoclinic phase formed is more restricted to the near-surface region (Figure 4), which can cause microcracking due to the excessive stresses localized in a smaller volume. This is noticeable by the reduction in characteristic strength of aged NNHYD and DC-NNHYD samples, and even more evident in the leveling down of BFST results of aged DC-NNHYD samples, resulting in a very high Weibull modulus (Table 4).…”

“…The properties of each powder are available in ref. 29 The identification and characteristics of the different groups of samples are summarized in Table 1. Samples were formed by slip casting of aqueous ceramic suspensions in plaster molds, as described in details elsewhere.…”

“…Samples were formed by slip casting of aqueous ceramic suspensions in plaster molds, as described in details elsewhere. 29 The green density was determined by the weight and geometric volume of the powder compacts, using an analytical balance (AUX 320, Shimadzu) and a digital micrometer (Mitutoyo). After forming, DC-NNHYD samples were subjected to a pre-sintering step in an electrical furnace (LHT 03/17D, Nabertherm) with a heating rate of 10 • C/min up to 1000 • C with a dwell time of 30 min followed by cooling with a rate of 10 down to room temperature.…”

“…28 Thus, an ideal balance between strength, toughness, and LTD resistance must be achieved to improve the lifetime of zirconia-based biomaterials. 27 In a previous work, 29 our group tested the hypothesis that nanostructured Y-TZP ceramics with nonhomogeneous yttria distribution could exhibit high toughness and strength combined with resistance to LTD. Nanostructured 3Y-TZP materials presented no signs of LTD after 20 h of accelerated hydrothermal aging in autoclave at 134 • C under 2 bar, but presented reduced mechanical properties when compared to conventional submicrometric (CS) 3Y-TZP, due to the phase-stabilizing effect of small grain sizes. The introduction of the nonhomogeneous yttria distribution by mixing zirconia powders with different yttria contents (0 and 3 mol%) generated nanostructures with higher strength and toughness.…”