Zirconia (ZrO2) Machining Techniques – Process, Applications and Benefits

Zirconia (ZrO2) is best known among ceramics as being both hard and fracture-tough at room temperature. Additionally, its fine (sub-micron) grain size enables excellent surface finishes and the ability to hold a sharp edge.

Although it retains many properties including corrosion resistance at extremely high temperatures, zirconia does exhibit structural changes that may limit its use to perhaps only 500°C. It also becomes electrically conductive as this temperature is approached.

Zirconia is commonly blended with either MgO, CaO, or Yttria as a stabilizer in order to facilitate transformation toughening. This induces a partial cubic crystal structure instead of fully tetragonal during initial firing, which remains metastable during cooling. Upon impact, the tetragonal precipitates undergo a stress induced phase transformation near an advancing crack tip. This action expands the structure as it absorbs a great deal of energy, and is the cause of the high toughness of this material. Reforming also occurs dramatically with elevated temperature and this negatively affects strength along with 3-7% dimensional expansion. The amount of tetragonal can be controlled by additions of the blends above to balance toughness against loss of strength.

Cubic Zirconia

Cubic Zirconia: This single crystal optically clear form of ZrO2 has a relatively low fracture toughness and strength, but very high thermal shock resistance.

Partially Stabilized Zirconia PSZ

Partially Stabilized Zirconia or PSZ: Cream colored blends with approximately 10% MgO, called partially stabilized zirconia (PSZ), are high in toughness, and retain this property to elevated temperatures. They are somewhat lower in cost but also have larger grain structure.

Tetragonal Zirconia Polycrystals TZP

Tetragonal Zirconia Polycrystal or TZP: Yttria blends of approximately 3% are called tetragonal zirconia polycrystal (TZP) and have the finest grain size. These grades exhibit the highest toughness at room temperature, because they are nearly 100% tetragonal, but this degrades severely between 200 and 500°C as these irreversible crystal transformations also cause dimensional change.

Mechanical Properties of Zirconia

Table 1. Mechanical properties of zirconia

Property

Value

Units

Density

5.75

gm/cc

Hardness

1120-1300

Knoop

Tensile Strength

65

kpsi

Modulus of Elasticity

29-30

psi x 106

Flexural Strength

100

kpsi

Poisson’s Ratio

0.23-0.31

-

Compressive Strength

268

kpsi

Fracture Toughness

12

MPa m1/2

Electrical Properties of Zirconia

Table 2. Electrical properties of zirconia

Property

Value

Units

Dielectric Strength

250

Ac volts/mil

Dielectric Constant

-

@ 1MHz

Volume Resistivity

>108

ohm-cm2/cm

Thermal Properties of Zirconia

Table 3. Thermal properties of zirconia

Property

Value

Units

Coefficient of Thermal Expansion

10.1

X10-6/°C

Thermal Conductivity

1.8-3.0

W/m°K

Specific Heat

0.1

cal/g°C

Max Working Temp

1100

°C

Shock Resistance

400

°C diff

All properties are at room temperature unless otherwise noted.

Engineering data are representative, and are not intended as absolute nor warrantable. Manufacturer’s Data shown is blended from multiple sources and therefore illustrates the marketplace.

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

For more information on this source, please visit INSACO Inc.

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