Will tungsten discharge needles migrate or deform in long-term high-voltage applications

Structural stability characteristics of tungsten metal

Tungsten is a body-center cubic structure (BCC) refractory metal with extremely high melting point (3410°C), high strength, high elastic modulus (approximately 400 GPa), and low self-diffusion rate. These physical properties determine that tungsten has good structural stability in high temperature and high pressure environments. However, long-term exposure to high-voltage electric field and high-temperature discharge environments, the tungsten needle tip material may still experience slow migration or microdeformation, affecting the discharge performance and life.

The driving mechanism of high-voltage electric field to the migration phenomenon of tungsten needle

Under the action of a strong electric field, there is an extremely strong electric field gradient at the tip of the tungsten discharge needle, which can usually reach more than 10⁷ V/m. This electric field will produce an electromigration effect, causing tungsten atoms to migrate slowly along the current direction. This phenomenon is particularly evident under high DC voltage and continuous discharge conditions, especially when the needle tip temperature is above 800°C, the atomic movement speed under the electric field drive will significantly accelerate, eventually causing structural rearrangement or local depression.

Thermal migration and thermal gradient-induced deformation mechanism

Long-term high-voltage pulses or arc discharges will cause non-uniform heating to the tip of the tungsten discharge needle, resulting in a significant thermal gradient distribution. In high-temperature areas, the diffusion capacity of tungsten atoms is enhanced, migrating to low-temperature areas, forming thermal migration (Thermomigration). This process will cause the local mass of the needle tip to decrease, collapse, passivation, and even asymmetric deformation, which will affect the concentration of the electric field and discharge efficiency.

Effect of discharge ablation on the geometric shape of needle tips

During the high-voltage breakdown, microplasmon formation and arc channel release are accompanied by. This process will cause ablation of the surface material of the tungsten discharge needle, especially the formation of repeated ablation pits at the discharge start point, gradually changing the needle tip geometry. This electrocorrosion is one of the important sources of deformation and is closely related to the discharge frequency, gas medium, and voltage waveform. After a long period of operation, the radius of curvature of the tip increases, resulting in an increase in discharge voltage and a decrease in discharge efficiency.

Lattice rearrangement and microplastic deformation

Mechanical and thermal stresses caused by high-pressure pulses will induce lattice slip, dislocation aggregation and sub-grained recombination on the surface of the tungsten discharge needle. Under the action of cyclic stress, some tungsten grains may rotate or recrystallize in an orientation, forming grain boundary migration and stress concentration zones. This process triggers a microplastic flow of the material, especially in fine needle structures and microdischarge systems, and ultimately manifests as a slight offset or ellipticization of the needle tip.

The difference between vacuum and gas environment on deformation behavior

When used in a vacuum environment, the heat dissipation efficiency is lower, the needle tip temperature rises faster, and the material migration speed increases. In contrast, when discharged in an inert gas environment such as argon and nitrogen, the heat is partially absorbed and the migration speed is reduced, but physical ablation caused by the arc still exists. Therefore, different atmospheres have different leading factors on the deformation mechanism of tungsten needles, and engineering design needs to be precisely matched according to the application environment.

Deformation risks caused by surface oxidation and material desorption

During long-term use in open air or oxygen-containing gases, tungsten oxide (WO₃) may gradually form on the tungsten surface and sublimate or fall off at high temperatures. This process causes the continuous loss of surface substances, causing the shape of the tip to gradually change, especially the formation of "erosion pits" or "annular steps" in the tip area, which in severe cases may even cause distortion of the electric field and unstable discharge.

Engineering countermeasures and design optimization suggestions

In order to reduce the migration and deformation of tungsten discharge needles during long-term high-voltage use, the following technical measures can be taken:

Choose high-purity tungsten materials with small grains and stable texture to enhance their migration resistance

Passivation treatment or doping rare earth elements (such as thorium, cerium) to improve thermal stability and electromigration resistance

Optimize electrode geometric design to reduce tip heat concentration

Operate the system in a sealed inert gas environment to slow down oxidation rates and ablation processes

Set up a periodic maintenance inspection system to conduct microscopic imaging analysis of tip morphology

Introduce automatic alignment device to ensure that the needle tip is neutral and does not deviate after long-term use.

Lifetime performance in application examples

In high-frequency discharge equipment, electrostatic spray systems and microplasma generators, the tungsten discharge needles that have been structurally optimized and environmentally controlled have maintained stable geometric structure and discharge performance in more than 10⁶ discharge cycles. Comparative experiments show that after 72 hours of continuous operation, the untreated tungsten needle has obvious tip offset and ablation pit structure, while the doped and surface-treated tungsten alloy discharge needle remains intact, effectively improving the system discharge stability and product life.