Research on Friction Characteristics and Damage Behavior of Silicon Nitride Ceramics

Silicon nitride ceramics (Si3N4) has high strength, high wear resistance, high temperature resistance, corrosion resistance, acid and alkali resistance, can be used for a long time in seawater, and has good electromagnetic insulation properties. It is widely used in various types of high In precision bearings.

In this experiment, Si3N4 ceramic balls prepared with different formulations and different processes were selected, and bearing steel was used as the auxiliary material to investigate the fretting friction and wear behavior of Si3N4 ceramic balls and bearing steel under non-lubricated conditions, and to reveal the surface damage characteristics of Si3N4 ceramic balls. The influence of additive formula and sintering process on the fretting surface damage characteristics of Si3N4 ceramic balls provides theoretical basis and guidance for optimizing the preparation process of Si3N4 ceramic balls.

Experimental preparation

The specific sintering aid numbers and corresponding contents and formulas of the 7 different sintering aid formulations used in this article are shown in Table 1. The corresponding Si3N4 ceramic sphere optical photo is shown in Figure 1, showing the types of rare earth oxide sintering aids Affect the color of Si3N4 ceramic balls, and the higher the content, the darker the color. The preparation process of Si3N4 ceramic balls involves gas pressure sintering (GPS) and two-step sintering method (GPS+HIP) of gas pressure sintering and hot isostatic pressing sintering at different temperatures. The sintering method and the expression method of sintering temperature are used in the text. For example, GPS1750 refers to Air pressure sintering at 1750°C. The bearing steel used in the test is the raceway material of rare earth high carbon chromium bearing steel (hardness 744.71±28.11HV). Before the test, the bearing steel was processed into a block of φ24×7.8mm, and the surface was pre-grinded and polished, and the Si3N4 ceramic balls and bearing steel were cleaned with acetone to remove surface oil stains.

Use the fretting friction and wear test machine to carry out the fretting friction and wear test of Si3N4 ceramic ball and bearing steel under no lubrication conditions. The applied load is 162N (maximum contact stress is 2.5GPa), the fretting stroke is set to 0.5mm, and the frequency is 15Hz. The test duration is 3600s.

Characterization of damage and degree of damage

Result analysis

1、The influence of sintering aids on the fretting friction and wear of Si3N4 ceramic balls

2、Effect of Sintering Process on Friction and Wear of Si3N4 Ceramic Ball

3、Wear of Si₃N₄ ceramic ball on bearing steel

4、Si₃N₄ The fretting damage characteristics and damage mechanism of ceramic balls

Conclusion

(1) The formula and content of sintering aids have a significant impact on the fretting wear of Si3N4 ceramic balls. Under the same sintering process, Si3N4 ceramic balls formulated with 5AlEr and 3AlY additives have a more stable friction state and lower wear. degree.

(2) Increasing the air pressure sintering temperature can alleviate the fretting damage behavior of the Si3N4 ceramic ball, thereby reducing its damage; however, after the hot isostatic pressing sintering process is introduced again on the basis of the air pressure, although the damage behavior can be further milder, However, the wear resistance of Si3N4 ceramic balls is generally weakened.

(3) The fretting damage mechanism of Si3N4 ceramic balls and bearing steel under unlubricated conditions is mainly multi-factor damage behavior combining abrasive wear, adhesive wear and fatigue damage. The main damage forms are friction damage, spalling and fatigue cracks. At the same time, due to the effect of frictional heat, there is also the existence of tribochemical reactions.