What are the preparation methods of silicon nitride products?

 

Silicon nitride products will be corroded by molten solutions such as magnesium, nickel chromium alloy and stainless steel, so we should also keep away from these solutions that will corrode silicon nitride products! Therefore, even if the silicon nitride products are tough, we should pay attention to these details when using the products processed by silicon nitride products, so that the service life of silicon nitride products can be longer.

 

 

 

1、 Reaction sintering

 

 

 

Using the general forming method, first press the silicon powder into the green body with the required shape, and then put the green body into the nitriding furnace for pre nitriding (partial nitriding) sintering treatment. The green body after pre nitriding has certain strength and can be processed by various mechanical processes (such as turning, planing, milling and drilling). Then, the temperature is higher than the melting point of silicon; Again, the green body is completely nitrided and sintered to obtain the product with small size change (i.e. the shrinkage after sintering is very small, and the linear shrinkage is less than 0.11%), which can be used without grinding. Reaction sintering method is suitable for manufacturing parts with complex shape and precise size. It has low cost but long nitriding time.

 

 

 

2、 Hot pressing sintering

 

 

 

The mechanical properties of hot pressing sintered silicon nitride products are better than reaction sintered silicon nitride products, with high strength and high density. However, the manufacturing cost is high and the sintering equipment is complex. Due to the large shrinkage of the sintered body, the dimensional accuracy of the product is limited to a certain extent. Complex parts are difficult to manufacture, only simple parts and products, and the processing of workpieces is also very difficult.

 

 

 

3、 Atmospheric pressure sintering

 

 

 

In terms of increasing the pressure of sintering nitrogen atmosphere, increase the decomposition temperature of Si3N4 (usually, the decomposition starts at 1800 when N2 = 1atm), then sintering at 1700-1800, and then pneumatic sintering at 1800-2000. The purpose of this method is to use air pressure to promote the densification of Si3N4 ceramics, so as to improve the strength of ceramics. The properties of the products obtained are slightly lower than those obtained by hot pressing sintering. The disadvantages of this method are similar to hot pressing sintering.

 

 

 

4、 Pneumatic sintering

 

 

 

In recent years, people have done a lot of research on pneumatic sintering and made great progress. Then Junjie ceramics will share with you here. Then I won't summarize it next. Silicon nitride in pneumatic sintering is carried out at a pressure of 1 ~ 10 MPa and a temperature of about 2000. High nitrogen pressure inhibits the pyrolysis of silicon nitride. Using high temperature sintering can promote the growth of Si3N4 grains with less sintering additives, so as to obtain high toughness ceramics containing long columnar grains grown in situ, with a density of more than 99%. Therefore, pneumatic sintering has attracted more and more attention in laboratory and production. Air pressure sintered silicon nitride products have high toughness, high strength and good wear resistance. It can directly produce all kinds of products with complex shapes close to the later shape, which greatly reduces the production cost and processing cost. Its production process is close to cemented carbide and is suitable for large-scale production.