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Comparing UHMís CeTZP with Various Steels

Wear is a major cause of equipment failure and downtime in industry and in the military as well as with commercial products (page 8.8 in reference 7). This is reflected in the very large market for replacement parts due to wear which has been estimated at $60 billion in the US in 1998 (1% of GDP). 

Ceramics are currently considered the best candidate material for reducing wear and friction in a variety of applications in this market. This is because ceramics are much harder than metals and would thus last longer. 

Zirconia cutting blades, for example, last 90 times longer than steel blades. In addition, zirconia cutting blades have very sharp edges and resist corrosion and oxidation especially in harsh environments (from page 8.74 in reference 7 and references 3 and 5).

Note that ceramics are much less vulnerable to chemical and galvanic attack than bonded tungsten carbide and steel (references 5,7,9,12).

Table 6

Table 6 lists the mechanical properties of UHMís CeTZP compared to various steels.

Mechanical Properties

UHMís CeTZP ceramic

Low Carbon Steel

High Carbon Steel

Pressure Vessel Steel (e.g. HY130)

Stainless Steel (316)

Vickers Hardness (GPa)

9.1 - 13.6

0.8 - 1.8

1.2 - 3.9

2.0 - 5.4

0.7 - 1.0

Fracture Toughness (MPa.m1/2)

10 - 15.3

50 - 80

20 - 80

80 - 181

75 - 100

Tensile Strength (MPa)

360 - 420#

500 - 800

600 - 1880

1200 - 2000

540 - 617

Bend Strength (MPa)

1080 - 1260

750-1200 *

900-2820 *

1800-3000 *

810-930 *

Compression Strength (MPa)

1045 - 1459

190 - 500

400 - 1300

1500 - 1900

185 - 277

Youngís Modulus (GPa)

190 - 200

196 - 211.4

196 - 210

200 - 210

215

Density (g/cm3)

6.1 - 6.2

7.82 - 7.87

7.80 - 7.82

7.80 - 7.85

7.8 - 7.9

#estimated from bend strength                                                        

* estimated from tensile strength

[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)]

Two properties clearly distinguish UHMís CeTZP from the various steels given here. They are:

  • Vickers Hardness of UHM's CeTZP are several times higher than, say, low carbon steel. Thus UHM's CeTZP would wear less and should last longer than the various steels.
     

  • Compression strength of UHM's CeTZP are higher than the various steels (except for pressure-vessel steel).

Table 7

Table 7 lists the thermal properties of CeTZP compared to the various steels (references 7,15). 

Thermal Properties

UHMís CeTZP ceramic

Low Carbon Steel

High Carbon Steel

Pressure Vessel Steel (e.g. HY130)

Stainless Steel (316)

Thermal Expansion Coefficient (10-6/K)

10 - 12

12 - 13

12 - 15

12 - 14

14 - 17

Thermal Conductivity (W/m.K)

1.9

40 - 70

38 - 46

30 - 46

14 - 16

Compared to the various steels, the thermal conductivity of UHMís CeTZP is clearly very low while its thermal expansion coefficient is similar in magnitude.

Note also 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 e.g. page 8.38 in reference 5).

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. 

Table 5

Given in Table 5 is a summary of its results.

Property 

Aluminum (HE9)

Copper (HDHC)

Medium Carbon Steel (EN8)

Stainless Steel (AISI 304)

Vickers Hardness (GPa)

0.71

1.11

2.53

2.35

Friction Coefficient at room temperature (Approx values)

0.13

0.14

0.15

0.15

Friction Coefficient at elevated temperature (Approx values)

>0.5

>0.5

>0.5

>0.5

This study indicated that, at room temperature, CeTZP could be used with any of the metals given in Table 5 in unlubricated applications where steel-steel components are currently utilised, 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).


 

 

UHM

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