What gases can be used in a vacuum sintering furnace?

The vacuum sintering furnace can introduce various gases during the sintering process according to the material characteristics and process requirements, with the main purpose of controlling the atmosphere environment inside the furnace and optimizing the sintering effect. The following are common gas types and their specific application scenarios and functions:

1. Inert gas (protective gas)
Representative gases: argon (Ar), helium (He)
Application Scenario:
Activated metal sintering: such as titanium (Ti), zirconium (Zr), hafnium (Hf), etc., are prone to react with oxygen and nitrogen at high temperatures. Introducing argon gas can isolate the air, prevent oxidation or nitridation, and maintain the purity of the material.
Precious metal processing: such as gold (Au), silver (Ag), platinum (Pt), etc. Argon gas can prevent surface oxidation, maintain luster, and reduce subsequent polishing processes.
High temperature sintering: Argon gas has high thermal conductivity and can uniformly transfer heat, making it suitable for sintering high-temperature alloys (such as nickel based alloys) or ceramic materials.
Function: To provide an oxygen free and nitrogen free protective environment, prevent material oxidation, nitriding, or volatilization, and ensure component stability.

2. Reductive gases
Representative gases: hydrogen (H ₂), carbon monoxide (CO)
Application Scenario:
Metal oxide reduction: For oxides such as copper (Cu) and iron (Fe), hydrogen can reduce them to metals while removing the surface oxide layer.
Powder metallurgy: When sintering iron-based and copper based powder metallurgy parts, hydrogen can reduce the oxide on the surface of particles, promote particle bonding, and increase density.
Carbide sintering: In the sintering of hard alloys (WC Co), hydrogen can reduce the oxide of cobalt (Co), avoiding cobalt volatilization and maintaining material hardness and toughness.
Function: Remove oxides through reduction reactions, purify material surfaces, and promote densification.

3. Nitrogen (N ₂)
Application Scenario:
Non active metal sintering: such as stainless steel, aluminum alloys, etc., nitrogen can provide an inert environment to prevent oxidation, while the cost is lower than argon.
Sintering of nitride ceramics: such as silicon nitride (Si ∝ N ₄), aluminum nitride (AlN), etc., nitrogen gas is the reaction gas, participates in the nitriding reaction, and forms the target compound.
Partial high-temperature alloys: At specific temperatures, nitrogen can suppress element volatilization, such as sintering of certain nickel based alloys.
Function: As a protective or reactive gas, it controls the composition and structure of materials.

4. Mixed gas
Representative combinations: Argon+Hydrogen (Ar-H ₂), Nitrogen+Hydrogen (N ₂ – H ₂)
Application Scenario:
Sintering of complex materials: For example, in titanium alloys, it is necessary to avoid both oxidation and nitridation at the same time, and a mixed gas of argon gas as the main and hydrogen gas as the auxiliary can be used.
Carbide/nitride co firing: For example, titanium carbide nitride (TiCN) ceramics require nitrogen gas and carbon sources (such as methane) to participate in the reaction and form the target phase structure.
Function: Integrating the advantages of multiple gases to achieve more precise atmosphere control.

5. Special gases (customized as needed)
Representative gases: methane (CH4), ammonia (NH3), carbon dioxide (CO ₂)
Application Scenario:
Carbonization reaction: Introducing methane can introduce a carbon source for the carbonization process of materials such as silicon carbide (SiC) and tungsten carbide (WC).
Nitriding reaction: Ammonia gas decomposes into nitrogen gas and hydrogen gas, which are used for sintering nitrides such as aluminum nitride (AlN) and boron nitride (BN).
Carbonization treatment: After sintering of steel parts, CO ₂ or methane is introduced for carburizing to improve surface hardness.
Function: As a reactive gas, participate in material synthesis or surface modification.

Core principles of gas selection
Material compatibility:
Active metals such as Ti and Zr should strictly avoid oxygen and nitrogen, and prioritize argon or hydrogen.
Precious metals such as Au and Ag can be selected with argon or nitrogen gas, which has a lower cost.
Ceramic materials (such as Al ₂ O ∝, Si ∝ N ₄) require the selection of nitrogen, hydrogen, or mixed gases based on the target phase.
Process objective:
Pure protection: Choose inert gases (argon, nitrogen).
Reduced oxide layer: Choose hydrogen gas or mixed gas (Ar-H ₂).
Synthesis of compounds: Select reaction gases (such as CH4, NH3).
Cost and safety:
Hydrogen is flammable and explosive, and explosion-proof devices are required; Argon gas has high cost but good safety.
Nitrogen has a low cost, but it may react with some metals (such as nitridation of Ti at high temperatures) and should be used with caution.

Typical application cases
Sintering of titanium alloy implants:
Gas: Argon (purity ≥ 99.999%).
Function: Prevent titanium from reacting with oxygen and nitrogen, and maintain biocompatibility.
Sintering of hard alloy cutting tools:
Gas: Hydrogen gas (or Ar-H ₂ mixed gas).
Function: Reduces cobalt oxide, prevents cobalt volatilization, and improves tool hardness and toughness.
Sintering of silicon nitride ceramic bearings:
Gas: Nitrogen (or N ₂ – H ₂ mixed gas).
Function: Promote nitriding reaction and form high-strength and wear-resistant Si ∝ N ₄ phase.