Silicon nitride possesses high hardness, high
stiffness and low weight compared to steel. Silicon nitride
performs much better than steel in rolling contact fatigue
making it an ideal rolling element material for bearings.
Silicon nitride is significantly harder, has a 60% lower density
and a 50% higher Young’s Modulus than typical bearing
steels. These properties, combined with a low thermal expansion
and coefficient of friction against steel are essential to
improved rolling element performance in a bearing.
Si3N4 vs. Steel as a
Bearing Material
|
Property
|
Ceramic
|
M50
|
440C Steel
|
Vacuum Melt
|
Air
Melt
|
|
|
Si3N4
|
Steel
|
|
52100
Steel
|
52100
Steel
|
|
Density (g/cc)
|
3.2
|
7.6
|
7.8
|
7.8
|
7.8
|
|
Hardness (Rc)
|
>78
|
64
|
59
|
62
|
62
|
|
Elastic Modulus
(GPa)
|
320
|
190
|
200
|
210
|
210
|
|
PoissonÕs Ratio
|
0.26
|
0.28
|
0.28
|
0.28
|
0.28
|
|
Thermal Expansion
Coefficient
(10-6/C)
(RT to 800C)
|
2.9
|
12.3
|
10.1
|
10.9
|
10.9
|
|
Max Use Temp (C)
|
1000
|
320
|
180
|
180
|
180
|
|
Material Fatigue
Life, Wear
Resistance
|
>100X
|
10X
|
0.8X
|
5X
|
1X
|
|
