What are the differences in the performance changes of materials between vacuum sintering and atmosphere sintering?

1. Mechanical Properties

1. Strength

Vacuum sintering: Effectively removes impurities and gases from the material, resulting in higher density and lower porosity of the sintered body, thereby significantly improving the material's strength. For example, vacuum-sintered metal ceramic tools can have flexural strength 20% to 30% higher than similar products sintered in an atmosphere.

Atmosphere sintering: By selecting an appropriate atmosphere, the sintering performance of the material can be improved, thereby increasing the material's strength to some extent. However, improper atmosphere control may cause defects such as pores and inclusions in the material, reducing its strength.

2. Hardness

Vacuum sintering: Due to high material density and fine, uniform grains, hardness is generally higher. For example, vacuum-sintered cemented carbide tools can have hardness 1 to 2 HRA units higher than those sintered in an atmosphere.

Atmosphere sintering: The effect of atmosphere on material hardness is complex. In some cases, such as sintering in a reducing atmosphere, oxides in the material can be reduced, increasing purity and thus hardness; however, if the atmosphere contains impurities or reaction products, it may reduce the material's hardness.

3. Toughness

Steam sintering: The material's internal structure is uniform with few defects, resulting in relatively good toughness. For example, vacuum-sintered titanium alloy materials can have impact toughness 15% to 20% higher than those sintered in an atmosphere.

Atmosphere sintering: Improper atmosphere selection or control may cause defects such as cracks and pores in the material, reducing toughness. However, under certain special atmospheres, such as using special mixed atmospheres, toughness can be improved by adjusting the material's microstructure.

2. Physical Properties

1. Density

Vacuum sintering: The vacuum environment favors densification of the material and effectively removes gases from pores, resulting in higher density of the sintered body. For example, vacuum-sintered ceramic materials can achieve a relative density of over 98%.

Atmosphere sintering: The effect of atmosphere on material density depends on the nature of the atmosphere and the sintering process. Generally, sintering in an inert atmosphere can also increase material density, but the improvement may not be as significant as vacuum sintering.

2. Electrical and Thermal Conductivity

Vacuum sintering: Due to high material purity and fewer internal defects, electron and heat transfer are smoother, resulting in good electrical and thermal conductivity. For example, vacuum-sintered copper-based composites can have electrical conductivity 10% to 15% higher than those sintered in an atmosphere.

Atmosphere sintering: If the atmosphere contains impurities or reaction products, it may affect electron and heat transfer, reducing electrical and thermal conductivity. However, in some cases, such as using special doping atmospheres, electrical and thermal conductivity can be improved by adjusting the material's microstructure.

3. Chemical Properties

1. Oxidation Resistance

Vacuum sintering: Materials sintered in a vacuum environment are less likely to form oxide films on the surface, thus exhibiting better oxidation resistance. For example, vacuum-sintered stainless steel materials show significantly better oxidation resistance at high temperatures compared to those sintered in an atmosphere.

Atmosphere sintering: Using inert or reducing atmospheres during sintering can reduce oxidation of the material, improving oxidation resistance to some extent. However, improper atmosphere control may cause oxidation during sintering or subsequent use.

2. Corrosion Resistance

Vacuum sintering: High material purity and fewer internal defects result in a denser and more uniform oxide film on the surface, providing good corrosion resistance. For example, vacuum-sintered nickel-based alloys exhibit stronger corrosion resistance in corrosive media than those sintered in an atmosphere.

Atmosphere sintering: The effect of atmosphere on corrosion resistance is similar to that on oxidation resistance. Appropriate atmospheres can improve corrosion resistance, but if the atmosphere contains impurities or reaction products, corrosion resistance may be reduced.

The differences between vacuum sintering and atmosphere sintering in material properties mainly lie in density, purity, mechanical properties, chemical stability, and thermal properties. Choosing the appropriate sintering method depends on the specific material requirements and application scenarios.