Knowledge of sintering atmosphere in metal powder metallurgy

Metal powder metallurgy is the process of forming and sintering metal or alloy parts from metal powders (or mixtures of metal powders and non-metal powders) as raw materials.This technology can directly produce porous, semi-dense or fully dense materials and products, so it is widely used. In the sintering of metal powder metallurgy products, the sintering atmosphere is one of the important factors affecting the properties of sintered products.The powder sintering atmosphere refers to the actual atmosphere in the sintering furnace when the powder metallurgy products are sintered.Here's a look:

Firstly: Protective atmosphere: protective atmosphere is divided into reducing atmosphere and neutral atmosphere, reducing atmosphere is divided into hydrogen and ammonia decomposition.In the sintering process, the main role of protecting atmosphere is to protect sintered products from oxidation. Hydrogen has a strong permeability at a certain temperature and is a non-toxic gas with strong chemical activity. It is often used as a protective atmosphere in the sintering of tungsten, cemented carbide, stainless steel and other refractory powder metallurgy products.

Decomposition of ammonia liquid ammonia is obtained after thermal decomposition by the combination of hydrogen and nitrogen mixture gas, can be in powder metallurgy as a reducing agent, also used as a sintering atmosphere, except for some products containing nitrogen composition with the atmosphere produces chemical reaction can't use this sintering atmosphere, most of the metal can use this to sintering atmosphere.

Neutral atmosphere: the neutral atmosphere mainly includes nitrogen, ammonia and vacuum, among which the vacuum atmosphere is the most widely used. 

Secondly: Controlled atmospheres: these atmospheres are exothermic (without external heating) and endothermic (without external heating), both of which are converted from hydrocarbons.

Exothermic type can be used to control the carbon content of sintered products of powder metallurgy (including injection molding). It can be divided into light type and thick type atmosphere. The carbon potential of light type exothermic atmosphere is very low.The concentrated exothermic atmosphere has a higher carbon potential, which can be used to prevent the oxidation of powder metallurgy iron base and copper base parts and reduce the decarburization of iron base parts. Compared with exothermic atmosphere, the endothermic atmosphere is a controlled atmosphere with stronger

reducibility and higher carbon potential.

Thirdly: Air atmosphere: this sintering atmosphere is mainly through a certain air gas in the sintering furnace, can also be regarded as sintering under normal pressure, generally used in metal composite materials and ceramic materials sintering products.

Conclusion: in the sintering process of metal powder metallurgy products, the selection of suitable atmosphere sintering is helpful to improve the densification degree of products and obtain products with good properties.