UltraHard Materials Limited
Comparing UHM's CeTZP with Metals
UHM’s CeTZP engineering ceramic has properties that are relatively well suited to some applications that currently use cast iron.
Because of its high hardness, UHM's CeTZP would wear less and last longer than cast iron as well as aluminum and magnesium alloys.
Note that its high hardness (and thus lower wear) together with its very low thermal conductivity make UHM's CeTZP an excellent candidate material for heat engines (see page 8.38 in reference 5).
Table 3
Table 3 lists a summary of the mechanical properties of UHM’s CeTZP compared to cast iron, aluminum and magnesium alloys.
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Mechanical Properties
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UHM’s CeTZP
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Cast Iron
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Aluminum Alloys (wrought)
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Magnesium Alloys (wrought)
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Vickers Hardness (GPa)
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9.1 - 13.6
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0.66 - 3.09
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0.19 - 1.51
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0.45 - 1.3
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Fracture Toughness (MPa.m1/2)
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10 - 15.3
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12 - 25
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28 - 42
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16 - 22
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Tensile Strength (MPa)
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360 - 420#
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400 - 1200
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58 - 575
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200 - 472
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Bend Strength (MPa)
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1080 - 1260
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600-1800*
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87 - 860*
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300 - 710*
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Compression Strength (MPa)
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1045 - 1459
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260 - 1030
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40 - 510
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120 - 440
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Young’s Modulus (GPa)
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190 - 200
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152 - 193
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68 - 78.5
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42 - 45
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Density (g/cm3)
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6.1 - 6.2
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6.9 - 7.8
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2.52 - 2.84
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1.74 - 1.88
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#estimated from bend strength *estimated from tensile strength
Note: 1 MPa is approx 145 psi
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)
Summary:
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The bend and compression strengths of UHM’s CeTZP are almost similar in magnitude to each other, a feature that has more in common with metals than ceramics. Other monolithic engineering ceramics have compression strengths usually two to ten times their bend strengths.
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This could mean that materials engineers might not need to restrict designs using UHM’s CeTZP components to a compressive mode, a design constraint often required when other monolithic engineering ceramics are used.
Table 4 lists the thermal properties of CeTZP engineering ceramic compared to cast iron, aluminum and magnesium alloys (references 7 and 15).
Table 4
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Thermal Properties
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CeTZP
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Cast Iron
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Aluminum Alloys (wrought)
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Magnesium Alloys (wrought)
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Thermal Expansion Coefficient (10-6/K)
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10 - 12
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10.6 - 13.5
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22 - 24.1
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50 - 126
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Thermal Conductivity (W/m.K)
|
1.9
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18 - 34
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116 - 237
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24.6 - 27.9
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For purposes of material substitution, it is important to note that the thermal expansion coefficient of CeTZP is similar to cast iron. Also, the very low thermal conductivity of CeTZP engineering ceramic makes it a good heat insulator.
An example of combining the exceptional properties of UHM’s CeTZP in high performance applications would be a disk brake caliper piston. When brakes are applied forcefully, a large quantity of heat is generated. A CeTZP brake caliper piston should deform less and should transfer less heat to the hydraulic oil and should thus reduce brake fade and sponginess. Also, the better corrosion resistance of CeTZP will reduce maintenance requirements.
Friction of Metal Sliders on CeTZP
A study on the dynamic friction of metal sliders on CeTZP (reference 6) was carried out between temperatures of 298 and 973K. Given in Table 5 is a summary of its results.
Table 5 (data obtained from reference 6)
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Property
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Aluminum (HE9)
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Copper (HDHC)
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Medium Carbon Steel (EN8)
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Stainless Steel (AISI 304)
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| Vickers Hardness (GPa) |
0.71
|
1.11
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2.53
|
2.35
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| Friction Coefficient at room temperature (Approx values) |
0.13
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0.14
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0.15
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0.15
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Friction Coefficient at elevated temperature (Approx values)
|
>0.5
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>0.5
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>0.5
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>0.5
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This study indicated that, at room temperature, CeTZP could be used with any of the metals given in Table 5 in un-lubricated applications where steel-steel components are currently utilized, with probably a very low wear rate of CeTZP because of the latter's relative hardness (reference 6).
Note that room temperature steel-steel friction coefficient values are approximately the same (i.e. ~0.1 to 0.15).