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After some experimenting this is the most reliable sintering procedure we settled on:
| Ramp K/min | Target Temp °C | Hold time min | Reason / Comment |
|---|---|---|---|
| 5 | 100 | 10 | Drying |
| 5 | 600 | 120 | Burning off Binder |
| 15 | 1350 | 180 | Sintering |
| 40 | 200 | 0 | Cooldown |
Gas is turned on at 200 °C, and the Cooldown step is necessary to keep gas flowing during cooldown, otherwise the oven would close its valve as soon as the 180 min sintering step is over.
The oven only opens back up once it has reached 200 °C.
Gas flow should be at least 2.0 SLPM, as below that oxidation becomes very evident and parts become brittle.
At ~2.5 SLPM parts come out with partially metallic looking surfaces, maybe testing at even higher flow rates will yield interesting results.
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Sintering under vacuum instead of the reducing atmosphere yields good results, but the parts are even more prone to breaking.
Presumably the carbon crucible used in the DIY SIntering Oven V1 creates a reducing atmosphere by consuming all remaining oxygen.
When sintering under vacuum it is evident that some copper boils off the alloy, not sure how that affects mechanical strength or similar.