UltraHard Materials LLC
Why UHM’s CeTZP?
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Its Vickers Hardness is substantially higher than any commercial CeTZP currently available.
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Its Vickers Hardness is higher than metals including hardened tool-steel (the hardest known steel). Thus UHM’s CeTZP would wear less and last longer than metals under operational conditions.
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Its fracture toughness is the highest among all of the currently available commercial monolithic engineering ceramics and closer to those of cast iron and some aluminum alloys than other engineering ceramics.
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Its bend and compression strengths are near the top of the range for all of the currently available commercial monolithic engineering ceramics.
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When considering the combination of high hardness, high toughness, high bend strengths and high compression strengths as well as better environmental stability, UHM’s CeTZP is the best candidate material among all of the currently available commercial monolithic engineering ceramics for wear resistance applications under load-bearing conditions.
UHM’s CeTZP engineering ceramic (Ceria stabilised Tetragonal Zirconia Polycrystals) possesses many of the exceptional properties of monolithic engineering ceramics. More importantly, UHM's CeTZP has a relatively high fracture toughness when compared to all the other currently-available commercial monolithic engineering ceramics (such as silicon nitride, silicon carbide, CBN and alumina). Table 1 lists the mechanical properties of UHM's CeTZP. Table 2 lists the thermal properties of CeTZP.
Table 1 - [Note: 1 MPa is approx 145 psi]
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Mechanical Properties
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UHM’s monolithic CeTZP (12 mole% Ceria)
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Conventional monolithic CeTZP (12 mole% Ceria) - (data from references 2,10,12,14)
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Vickers Hardness (GPa)
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9.1 - 13.6
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7 - 9
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Fracture Toughness (MPa-m1/2)
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10 - 15.3
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6 - 10
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Tensile Strength (MPa)
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360 - 420#
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not available
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Bend Strength (MPa)
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1080 - 1260
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400 - 800
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Compression Strength (MPa)
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1045 - 1459
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not available
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Young’s Modulus (GPa)
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190 - 200
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190 - 200
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Density (g/cm3)
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6.1 - 6.2
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6.1 - 6.2
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#estimated from bend strength
[Note: All our mechanical tests were carried out on UHM's CeTZP billets. A LECO test machine for our indentation macrohardness tests utilized 30 kg loads; K1c values were calculated from crack lengths derived from these indentation tests using the equation of Anstis el alia (reference 10)]
Table 2
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Thermal Properties (from references 5,7,15)
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CeTZP
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Thermal Expansion Coefficient (10-6/K)
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10 - 12
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Thermal Conductivity (W/m.K)
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1.9
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Note that the Weibull Modulus "m" of CeTZP (12 mole% Ceria) from three-point bend tests has been determined as 16.54 (references 5,12).
CeTZP vs Other Zirconia Ceramics
YttriaTZP is the zirconia ceramic of choice of most producers. However, YttriaTZP suffers from hydrothermal degradation (even at temperatures as low as 250 C*); that is, it has been shown to be prone to environmental degradation under humid conditions. Similarly, MagnesiaTZP and CalciaTZP require critical control of the annealing conditions and also these powders undergo continuous leaching of the magnesium and calcium ions in aqueous environments. In contrast CeriaTZP (with 12 mole% Ceria) is more environmentally stable and less prone to leaching and degradation of mechanical properties in aqueous environments. (references 5,12) When compared to YttriaTZP (3 mole%), YttriaTZP (6 mole%) and MagnesiaPSZ, CeriaTZP showed the best resistance against cyclic indentation fatigue under the range of indentation loads investigated (reference 7).
*see e.g. A. Feder and M. Anglada Low-temperature ageing degradation of 2.5Y-TZP heat-treated at 1650 °C, Journal of the European Ceramic Society; Volume 25, Issue 13 , August 2005, Pages 3117-3124.