2YSZ – High Fracture Toughness Combined with Superior Shock Absorption

Zirconia is a versatile material with interesting chemical and physical properties. It is particularly useful, when stabilized with yttria, for challenging industrial applications that need fracture-resistance and high strength/wear. 3 mol % yttria-stabilized zirconia (3YSZ) is extensively utilized in structural ceramic applications because of its desirable mechanical properties. These include fracture toughness and high flexural strength.

Innovnano’s Emulsion Detonation Synthesis (EDS) technology can generate an excellent alternative to 3YSZ for structural ceramic applications – 2 mol % yttria-stabilized zirconia (2YSZ) with excellent fracture toughness. This is an exciting new development for the ceramic market.

Maximizing Fracture Toughness

It is common knowledge in the industry that by adjusting the stabilizer content, fracture toughness can be tailored. Usually, reducing the quantity of yttria leads to better fracture toughness. Although, there is a trade-off, with lower yttria-containing powders showing decreased aging resistance and mechanical strength.

Innovnano’s EDS approach has made it possible to produce a higher fracture toughness structural ceramic (2YSZ) alternative to 3YSZ, without compromising the aging resistance and mechanical strength. It involves a predetermined cycle of pressures, high temperatures and rapid quenching in a fully automated system, based on a single step reaction of the detonation of two water-in-oil emulsions.

The energetic nature of EDS adds to the stabilization of the zirconia - an extensively tested process. The powders created have a nanostructure that has a higher specific surface area - to with the improved structural properties of flexural strength, hardness, resistance to thermal shock and fracture toughness.

Innovnano produces a 2YSZ, using EDS, with all of the sought-after characteristics of 3YSZ, as well as the desirable extra benefit of improved fracture toughness, which lower yttria content zirconia possesses. It offers a flexural strength higher than 1000 MPa, with fracture toughness significantly strengthened from 5 to over 14 MPa.m0.5 when compared with 3YSZ.

It provides a great replacement for structural ceramic applications, either as zirconia component in zirconia-toughened alumina/alumina-toughened zirconia (ZTA/ATZ) and cermets or as a ready-to-press powder.

Testing Aging Resistance

To ensure the lower yttria content does not adversely affect principal structural ceramic properties, aging and stability tests have been performed independently.

The test pieces all passed the ISO 13356 standard methodology of 1 million cycles at 320 MPa (maximum) and 20 Hz frequency, without failure when cyclic stress-strain aging tests in saline solution (on Innovnano 2YSZ bars that have undergone cold isostatic pressing (CIP) and conventional sintering) were carried out. The four-point bending strength was determined for 2YSZ bars before and after cyclic stress-strain experiment, and after 106 cycles under the said conditions only 13% of flexural strength was lost.

Additionally, further cyclic stress-strain aging tests were performed successfully (20 Hz, 106 cycles) using 1100 MPa as maximum pressure, showing the exceptional resistance of mechanical aging in Innovnano 2YSZ powders. The superior performance of Innovnano 2YSZ is further exhibited, when compared to studies utilizing 3YSZ in the literature. One study reported that of 13 specimens assessed at a maximum pressure of 650 MPa, none achieved 106 cycles1.

Hydrothermal aging was also analyzed according to ISO 13356:2015 methodology using 2YSZ pellets produced by uniaxial pressing and sintering. To attain the standard, it is necessary for the samples to retain 80% of their flexural strength after five hours at 0.2 MPa and 134 °C. Innovnano 2YSZ exceeded this standard by keeping 85% of its flexural strength.

Testing Shock Absorption

Shock absorption tests were undertaken using standard 3YSZ and Innovnano 2YSZ. YSZ disks were positioned in 3-point support and a pendulum dropped from a certain height (figure 1) to conclude a fracture energy. The fracture energy is the total of the impact energies necessary for disk failure.

Shock absorption testing of Innovnano 2YSZ and benchmark 3YSZ. A 3-point support system (A) was used and a pendulum dropped (B) to obtain fracture energy values at different thicknesses for Innovnano 2YSZ and benchmark 3YSZ (C).

Figure 1. Shock absorption testing of Innovnano 2YSZ and benchmark 3YSZ. A 3-point support system (A) was used and a pendulum dropped (B) to obtain fracture energy values at different thicknesses for Innovnano 2YSZ and benchmark 3YSZ (C).

Figure 1 shows the experimental conclusions using samples of variable thicknesses. Innovnano 2YSZ performed better in the assessed thickness range, by indicating twice the energy absorption capability without failure. So, it is possible to manufacture parts from Innovnano 2YSZ that are 15% thinner, and so with lower material usage, but that still retain the same fracture energy as 3YSZ parts. A recent US patent report showed that the 2YSZ studied demonstrated impact damage at 1.75 J, while the 3YSZ showed damage at 0.85 J2.

Table 1. Properties of benchmark 3YSZ compared to Innovnano 2YSZ.

Performance Benchmark 3YSZ Innovnano 2YSZ
Fracture toughness (MPa.m0.5) 5 14
Flexural strength (MPa) 1200 1200
Hardness (HV10) 1250 1250
Wear-resistance (%ΔP/P) 0.020 0.028
Cyclic fatigue resistance 50 % of static resistance 85 % of static resistance

 

Innovnano using a unique synthesis method, to produce a disruptive product with outstanding potential for structural ceramics applications. It uniquely merges the benefits of high fracture toughness with desirable aging/shock absorption capabilities and scale-up reliability.

References

  1. Renato Chaves Souza, et al. Performance of 3Y-TZP Bioceramics Under Cyclic Fatigue Loading. Materials Research, Vol. 11, No. 1, 89-92, 2008
  2. US patent 2018/0079686 A1

This information has been sourced, reviewed and adapted from materials provided by Innovnano.

For more information on this source, please visit Innovnano.

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