EOS NickelAlloy IN738 for EOS M 400-4 | 40 µm

The recommended post-processing route for EOS NickelAlloy IN738 includes shot-peening, hot isostatic pressing (HIP) and ageing.

Extra care is required in post-processing since certain geometries printed in EOS NickelAlloy IN738 may be susceptible to formation of macro-cracks upon heat treatment. Geometries with notches or sharp changes of cross-section are particularly vulnerable.

- Shot-peening is recommended to induce compressive residual stress on the surface of the component.
- HIP is recommended to perform the combined stress relief, solution treatment (sub-solvus) and densification steps into a single heat treatment step.
- Ageing is required for precipitation strengthening.

For further details, alternative options, and the recommended order of post-processing operations please refer to the Post-Processing Guide Application Note for EOS NickelAlloy IN738, which can be found on MyEOS.

Shot-peening: 
Use zirconia beads or steel shot as media, and a suitably high pressure, e.g. 4 bar or higher.
Use a suitable stand-off distance of approximately 5 cm and slow travel speed, keeping the angle of incidence roughly perpendicular to the surface of the workpiece. Ensure good coverage of all surfaces, with special focus on overhangs, notches, and changes of cross-section.

HIP:
1. Heat from room temperature to 600°C in 40 mins.​ Increase pressure to ~200 MPa.
2. Hold at 600°C and ~200 MPa for 60 minutes.
3. Heat to 1120°C in 15 minutes. Maintain pressure of 200 MPa.
4. Hold at 1120°C and ~200 MPa for 240 minutes.
5. Cool rapidly to below 300°C within 8 minutes.

Ageing:
1. Heat to 850°C in 60 minutes.
2. Hold at 850°C for 24 hours.
3. Cool from 850°C to <300°C in 20 minutes.