CERAMIC BEARINGS - Silicon Nitrides For Bearings
CERAMIC BEARING Balls are made from two types of silicon nitrides made by Ceramics: NBD200 and SN101C. Both are qualified by bearing companies worldwide and meet all the essential requirements of a bearing grade silicon nitride. They are both fabricated using glass encapsulation HIPing which assures 100% density, high beta phase content, micron-sized grains, and minimal levels of glass phase. The attached TABLE 1 shows the typical properties for NBD200 and SN101C silicon nitrides.
The NBD200 is a “Magnesia” doped material, whereas SN101C is a “Yttria” doped material. Both are Hot Isostatically Pressed (HIP) and meet the demanding requirements of ball bearing and check valve applications. Due to the HIP processing, they have zero porosity, fine grain microstructures, minimal level of dopant, and appropriate levels of strength, hardness, toughness, and rolling contact fatigue behavior to work exceptionally well in ball bearing and check valve applications. The dopant or “sintering aid” is the controlling factor concerning corrosion resistance. Both Magnesia and Yttria based silicon nitrides are highly inert in most liquids and gases. For example, no organic solvent is known to corrode silicon nitride at all.
The attached TABLE 4 shows typical behavior of HIPed silicon nitride in a variety of acid and alkali solutions, gases, molten salts / akalies, and molten metals / alloys / oxides.
This table can be used as a general guide for applications.
In general, Magnesia and Yttria based silicon nitrides behave the same in various environments. Some exceptions do exist. For example, Yttria based silicon nitrides are more resistant to hydrofluoric (HF) acid solutions than Magnesia based silicon nitrides, however factors such as the part size, geometry, and surface finish, as well as the concentration of the HF. Tests have shown that both NBD200 and SN101C work in HF at low concentration levels.
Advanced Ceramics Bearing Materials - Typical Properties
| Density [g/cm3] (% Theoretical) |
3.16 [>99.9%] |
3.21 [>99.9%] |
| RT Flexural Strength [MPa] |
>900 |
>1000 |
| Weibull Modulus |
>15 |
>25 |
| Elastic Modulus [GPa] |
320 |
310 |
| Poisson’s Ratio |
0.26 |
0.27 |
| Vicker’s Hardness HV10 |
1550 |
1600 |
| Fracture Toughness [MPa * m1/2] |
>5.5 |
>6.5 |
| Thermal Expansion Coeff. 10-6/°C; [RT-1000?C] |
2.9 |
3.7 |
| Thermal Conductivity [W/mK] @ 25°C |
29 |
34 |
| Electrical Resistivity [Ω-cm] |
1014 |
1014 |
| Dielectric Constant @ 1MHz |
8.0 |
8.0 |
| Corrosion 5% HF Solution, 500 Hours Weight Loss/ Surface Area [g/cm2] |
0.68 |
0.10 |
| Corrosion 5% HCL Solution, 500 Hours Weight Loss/ Surface Area [g/cm2] |
0.0002 |
0.0036 |
SN-101C Material Testing By Clients
| CERBEC Customer Location |
Japan |
United Kingdom |
USA |
| Test Type |
Rolling Contact Fatigue |
Rolling Contact Fatigue |
Rolling Contact Fatigue |
| Description |
3/8" SN-101C Balls on Cr Steel Plates |
Cr Steel Discs on SN-101C Rods |
Cr Steel Balls on SN101C Rods |
| Number of Tests |
5 |
10 |
8 |
| Contact Stress GPa (ksi) |
5.9 (862) |
4.8 (700) |
6.9 (1006) |
| Speed (RPM) |
1,200 |
12,500 |
3,600 |
| Lubricant |
Oil |
Oil |
Oil |
| Test Target (No Failure) |
>400 hours |
>72 [10]6 cycles |
>30 [10]6 cycles |
| Results |
All Tests>400 hours |
All Tests>72 [10]6 cycles |
All Tests>30 [10]6 cycles |
SN-101C Grade 5 Balls - Bearing Fatique Tests by Clients
| CERBEC Customer Location |
Japan |
Germany |
USA |
| Bearing Type |
Thrust |
Angular Contact |
Radial |
| Ball Size mm (in.) |
9.525mm (3/8") |
7.937mm (5/16") |
11.112mm (7/16") |
| Bearings Tested |
4 |
4 |
18 |
| Balls Per Bearing |
9 |
15 |
9 |
| Contact Stress GPa (ksi) |
3.7 (540) |
2.9 (423) |
3.6 (525) |
| Speed (RPM) |
2,000 |
12,000 |
3,000 |
| Test Target (Hours) |
500 |
1,000 |
700 |
| Results |
All Bearings>500 hours
SN-101C Qualified |
All Bearings>1,000 hours
SN-101C Qualified |
All Bearings>2,000 hours
SN-101C Qualified |
Figure 1 shows Ball Crush Strength for SN-101C and NBD-200 for your reference.
Figure 1
Typical Chemical Corrosion of Silicon Nitride
| SPECIES |
Concentration
(%) |
Exposure Time
(Hrs) |
Temperature
(°C) |
Reaction |
| None |
Weak |
Strong |
| ACIDS & ALAKALIES |
| Hydrochloric Acid |
20 |
500 |
Boiling |
X |
|
|
| Nitric Acid |
65 |
500 |
Boiling |
X |
|
|
| Sulphuric Acid |
10 |
500 |
70 |
X |
|
|
| Sulphuric Acid |
85 |
500 |
20 |
X |
|
|
| Orthophosphoric Acid |
|
500 |
20 |
X |
|
|
Pyrophosphoric Acid
Hydrofluoric Acid |
Conc. |
500 |
20 |
X |
|
|
| 192 |
Boiling |
|
|
X |
| Sodium Hydroxide |
20 |
500 |
20 |
X |
|
|
| Sodium Hydroxide |
50 |
115 |
Boiling |
X |
|
|
| Hydrofluoric & Nitric Acids |
Conc. |
68 |
Boiling |
|
|
X |
| GASES |
| Oxygen |
Air |
|
500 |
X |
|
|
| Oxygen |
|
|
700 |
|
X |
|
| Oxygen |
|
|
1200 |
|
|
X |
| Chlorine |
|
500 |
900 |
X |
|
|
| MOLTENS SALTS / ALKALIES |
| Sodium Hydroxide |
|
|
400 |
|
X |
|
| Sodium Sulfate |
|
|
1000 |
|
|
X |
Sodium &
Potassium Chloride |
|
|
900 |
|
|
X |
Sodium &
Zirconium Fluoride |
|
|
650 |
|
|
X |
| MOLTEN METALS / ALLOYS / OXIDES |
| Copper |
|
7 |
1150 |
|
|
X |
| Zinc |
|
500 |
550 |
X |
|
|
| Magnesium |
|
500 |
750 |
|
X |
|
| Aluminum |
|
1000 |
950 |
X |
|
|
| Tin |
|
144 |
300 |
X |
|
|
| Iron |
|
2 |
1450 |
|
|
X |
|
NBD200 Microstructure 
SN101C Microstructure 
SN101C Microstructure