Specification for Tungsten heat treatment for stress relief

[Jboezi]

I have a group of tungsten pins used in an application like a single cathode. They are 2% lanthanum doped. We have noticed that when an arc is generated in our product the cathodes tend to warp. This is causing instability. We believe this warping to be due relief of stress due to material processing. Our supplier has recommended heat treating at 1900C for 2-3 minutes. I would like to find some references to verify this is correct. Does anyone have experience specifying heat treatment for tungsten rod/wire? I have seen "annealed" tungsten wire available for purchase but not the time and temp they were processed at.

Thank you,
John

 

[CoryPad]

THe ASM Handbook lists stress relief annealing temperature as 1100 [°]C to 1200 [°]C and recrystallization annealing as 1250 [°]C to 1350 [°]C. The time would be around 1 hour in a furnace. I wonder if the 1900 [°]C for 2 minutes is from induction heating.

 

[EdStainless]

The stress relief temp should be below the anneal temp, so the 1900F sounds reasonable. You do want to keep the time short to minimize surface damage from oxidation.
Probably the most critical aspect is that they cool uniformly. No fans, not laying on a surface, maybe hold them with SS wire and let them cool in still air.
It would be easy enough to test.

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Plymouth Tube

 

[kumkumvijay]

I would like to share my opinion as below:
1. Stress relieving for 2-3 minutes might have suggested with an intention to avoid change of mechanical properties due to re-crystallization.
2. Small section parts are highly deformed in the manufacturing process, so generally the part supplier must ensure that the required heat treatment is done and mechanical properties are guaranteed.
3. If the part supplier skipped annealing or required heat treatment process of his raw material then the total stress in the final part can be high enough to create problem.
4. Stress relieving of Tungsten need special atmosphere and cycle carefully prepared to avoid oxidation or nitriding or carburizing.
5. Impurities in the tungsten also cause issue like you have mentioned.