Knowledge

The removal of inclusions in high-temperature alloys is a key technology for improving material performance and promoting recycling, especially crucial in high-end manufacturing fields such as aerospace and energy equipment. Currently, mainstream purification processes can be categorized into three major types: physical separation, melting refining, and emerging composite technologies. The following is a comprehensive analysis of the principles, applicable scenarios, and development trends of each type of technology:

 

I. Sources and Classification of Inclusions

The inclusions in high-temperature alloys are mainly classified as follows:

Oxides (such as Al₂O₃, SiO₂)

Sulfides (such as MnS)

Nitrides (such as TiN)

Silicates and complex inclusions (such as Al₂O₃·MgO)

These inclusions disrupt the material's continuity, significantly reducing mechanical properties, fatigue life, and corrosion resistance.

 

II. Comparison of Mainstream Removal Processes and Technologies

(1) Physical Separation Methods

Mechanical Grinding

Principle: Surface impurities are removed through surface grinding.

Characteristics: Low cost, but only suitable for shallow treatment and limited in depth.

Foam Ceramic Filtration

Principle: Micron-sized impurities are intercepted when the melt flows through porous ceramics.

Characteristics: The removal rate of impurities ≤ 50μm is over 80%, but the filter plate is a consumable, increasing costs.

 

(2) Melting and Refining Methods

Vacuum Induction Melting (VIM)

Principle: Reducing oxygen and nitrogen content in a vacuum environment to inhibit the formation of new inclusions.

Characteristics: Can reduce oxygen to the 10 ppm level, but has a weak effect on removing existing inclusions.

Electroslag Remelting (ESR)

Principle: Joule heating generated by current passing through conductive slag melts the electrode and adsorbs inclusions.

Characteristics: Removal rate of large inclusions (>100 μm) is over 90%, but it has high energy consumption and is prone to introducing slag phase contamination.

Electron Beam Melting (EBM)

Principle: High-energy electron beam bombards the raw material, decomposing inclusions (such as Al₂O₃ → Al + O₂↑) under vacuum and high temperature. Features:

It is applicable to high-aluminum/titanium alloys (such as hafnium-containing return materials), with inclusion removal rate > 95%;

It can simultaneously remove high and low density inclusions, and the inclusion content in the ingot is ≤ 0.3 cm²/kg.

 

(3) Flow Field Assisted Techniques

Bottom Blowing Bubble Flotation

Principle: Argon bubbles adsorb inclusions and float to the surface of the melt.

Characteristics: Highly efficient for small-sized inclusions (1–20 μm), but has poor process stability and is easily affected by flow field disturbances.

Electromagnetic Stirring

Principle: Induces melt convection to promote inclusion collision and coalescence.

Characteristics: Often used in conjunction with vacuum melting to enhance the floatation efficiency of impurities.

 

III. Breakthroughs in Cutting-edge Technologies

Composite Process Synergistic Purification

Case Studies:

VIM + ESR + Magnetic Levitation Melting: The three-step method reduces the size of inclusions in powder superalloys by 70% and makes their distribution more uniform.

Electron Beam Droplet Melting + Beam Spot Stirring: Through the temperature gradient, refractory inclusions (such as TiN) are driven to enrich and decompose at the surface in a directional manner.

 

IV. Challenges and Future Directions

Technical Bottlenecks

Current technologies struggle to capture nano-scale inclusions (such as γ' phase precipitates);

Data support for inclusion control in complex alloy systems (such as those with high rhenium and ruthenium contents) is lacking. Development Trends

Short-process composite technology: Develop integrated equipment for "vacuum melting - filtration - electromagnetic refining", reducing energy consumption by 30%;

Intelligent monitoring system: Introduce AI for real-time analysis of melt purity, achieving high dynamic optimization rates.