The primary manufacturing techniques for W-Cu alloys include powder metallurgy, infiltration, injection molding, and copper oxide reduction, with powder metallurgy being the most widely applied and mature method. The specific process flow and key points are outlined below:
I. Powder Metallurgy Process Flow
1. Powder Preparation
- High-purity tungsten (W) powder (≥99.9%) and copper (Cu) powder (≥99.95%) are used, prepared via mechanical alloying or chemical reduction to produce ultrafine powders for enhanced sintering activity.
- Tungsten powder particle size: 1–5 μm; copper powder particle size: 0.5–2 μm. Mixing powders with multiple particle sizes improves sintering performance.
2. Blending and Mixing
- Precise weighing of W and Cu powders according to target compositions (e.g., WCu7, WCu10). A small amount of nickel (Ni) powder (≤3%) may be added as an activator for activated sintering.
- Thorough mixing using ball mills or three-dimensional mixers ensures compositional uniformity.
3. Pressing
- The mixed powder is loaded into a die and cold isostatically pressed (CIP) at 150–400 MPa to form high-density compacts (relative density ≥65%).
- Pressing pressure must be adjusted based on powder particle size and shape to avoid delamination or cracking.
4. Sintering and Infiltration
- High-Temperature Liquid-Phase Sintering: The compact is sintered at 1300–1500°C, where copper melts into a liquid phase to fill tungsten grain boundaries, promoting densification.
- Activated Sintering: With Ni addition, sintering occurs at 1180–1200°C, reducing the sintering temperature and achieving high density (≥99%).
- Infiltration Method: A porous tungsten skeleton (porosity 20–30%) is first sintered, followed by copper infiltration at 1200–1300°C, suitable for low-Cu-content products (e.g., WCu5–WCu20).
5. Cold Working
- Post-sintering materials undergo machining (turning, grinding, or electrical discharge machining, EDM) to achieve final dimensional accuracy and surface quality.
- Surface coatings (e.g., gold, silver, or nickel plating) enhance corrosion resistance and weldability.
II. Key Process Parameter Control
1. Powder Characteristics
- Finer powders exhibit higher sintering activity but are prone to agglomeration, requiring optimized blending processes.
- Spherical powders offer better flowability for automated pressing, while irregular powders demand higher pressing pressures.
2. Sintering Temperature and Time
- Insufficient temperature leads to inadequate density (<98%), while excessive temperature may cause tungsten grain coarsening, reducing strength.
- Sintering time is adjusted based on material thickness, typically ranging from 2–8 hours.
3. Atmosphere Control
- Sintering is conducted in a hydrogen or vacuum environment to prevent oxidation.
- For infiltration, copper liquid flow must be controlled to avoid leakage or porosity.
III. Process Optimization Directions
1. Density Enhancement
- Hot isostatic pressing (HIP) post-treatment eliminates closed porosity, achieving densities up to 99.9%.
- Optimized infiltration processes, such as staged heating or pressure infiltration, improve copper filling rates.
2. Performance Uniformity Improvement
- Nanocrystalline powders prepared via mechanical alloying refine microstructures.
- Gradient sintering techniques reduce thermal stress-induced cracking.
3. Cost Reduction
- Development of low-cost raw materials (e.g., recycled tungsten powder) and short-flow processes (e.g., spark plasma sintering, SPS).
- Optimized mold designs improve material utilization.
IV. Typical Applications
1. Electrical Contact Materials
- Used in high-voltage switches (e.g., 128 kV SF6 circuit breakers), requiring arc erosion resistance and anti-welding properties.
- Typical composition: WCu70–WCu85, density ≥99%, flexural strength ≥667 MPa.
2. Electrical Discharge Machining (EDM) Electrodes
- Used for machining hard-to-cut materials like cemented carbides and die steels, requiring high electrical conductivity and erosion resistance.
- Typical composition: WCu20–WCu30, thermal conductivity ≥170 W/(m·K), electrode wear rate <5%.
3. Aerospace Components
- Used in rocket nozzle throats and gas vanes, requiring high-temperature resistance (3000–5000 K) and transpiration cooling effects.
- Typical composition: WCu10–WCu20, where copper evaporation absorbs heat to reduce surface temperature.
4. Electronic Packaging Materials
- Used for chip carriers and microwave device substrates, requiring thermal expansion coefficient matching with silicon (CTE ≈ 4–7 × 10⁻⁶/°C).
- Typical composition: WCu75, thermal conductivity ≥200 W/(m·K), capable of withstanding 2000°C.