Different tungsten powder metallurgical processes have a significant impact on the performance of tungsten electrodes, especially in terms of electron emission ability, crack resistance, ablation resistance, arc stability, etc. Tungsten electrodes are usually made through powder metallurgy processes, and differences in milling, pressing, sintering, and subsequent processing processes can directly affect the microstructure and performance of the final electrode.
The following is an analysis of the main tungsten powder metallurgical processes and their impact on the properties of tungsten electrodes:
- Particle Size And Distribution Of Tungsten Powder
Influencing factors: particle size controlled by reduction process (hydrogen reduction) or spray drying;
Impact performance:
The finer the particle size, the higher the sintering density and uniform structure.
Uneven particle size or coarse particles can form porous or tissue weaknesses, leading to electrodes prone to cracking or burning;
Uniform fine particles contribute to the formation of dense electrodes, enhancing resistance to high temperatures and ablation.
- Forming Method (cold Pressing/isostatic Pressing)
Cold pressing:
The pressure distribution is uneven, which is prone to density gradients.
The structure is not uniform after sintering, which may cause cracks or unstable properties.
Isostatic Pressing (CIP):
The pressure acts evenly on the powder, and the density is good;
It is conducive to obtaining isotropic structure, improving mechanical strength and heat resistance;
The crack resistance of the electrode is better than that of cold pressing.
- Sintering Process
Common methods: vacuum sintering or hydrogen atmosphere sintering;
Key parameters: sintering temperature, time, heating rate;
Impact performance:
Full sintering at high temperature can form a dense structure with good grain bonding, high electrode strength and long life.
Insufficient sintering leads to many pores, brittleness, easy oxidation and cracking;
Too high a sintering temperature may cause the grains to grow and reduce arc concentration.
- Subsequent Processing (forging, Tempering, Grinding)
Machining (e.g. forging):
Improve the consistency of grain direction, improve conductivity and strength;
At the same time, some pores and microcracks are eliminated;
Heat treatment (e.g. annealing):
Eliminate internal stress and improve thermal crack resistance;
Grinding treatment:
Proper grinding helps the electrode arc stabilization;
Improper grinding can introduce stress concentrations or surface microcracks.
- Doping Technology (composite Powder Metallurgy)
Rare earth oxides (such as ThO₂, La₂O₃, CeO₂, ZrO₂) are mixed with tungsten powder for metallurgical processing.
This process ensures uniform distribution of doped phases and enhances the electrode’s electron emission performance and ablative resistance.
The higher the uniformity of the doped powder, the more stable the final performance.
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