Need to measure the residual stress measurements for the additively manufactured Inconel 718 alloy.
What would be the correct procedures to measure the residual stress using XRD for the alloy for checking two different scan strategies and laser parameters?
1. Print two samples with the same support parameters and build one layer for XRD residual stress measurements.
2. Print two samples with the same support parameters and build five layers for XRD residual stress measurements- The idea is to avoid the effects of the support structure used.
Or it would be another option to do
With XRD technique RS can be measured in homogeneous materials, with crystalline lattice, near the surface (up to a depth of 0.01mm). Given the technology of obtaining the material, I think that XRD technique is not appropriate in this case. Of course, the physical properties of this material represent a challenge for any RS measurement technique. However, for this material I would choose the method with strain gauges (the drilled strain rosette, see ASTM E837). Maybe a destructive method (removal of layers and strain or deflection measurement) would yield acceptable results.
Are you planning to use synchrotron high-energy x-rays or laboratory x-rays? I am asking because in the latter case you are going to be very susceptible to surface artifacts, plus these materials will be very inhomogeneous - with interesting distributions of precipitates, porosity, spatial variations of grain size/shape, etc.
So be careful interpreting your data.
There is a fair amount of publication on this topic, so you can be reasonably prepared once you have done a recent literature survey.
Sincerely I suggest you read these articles:
- Understanding processing parameters affecting residual stress in selective laser melting of Inconel 718 through numerical modeling (2019)
- Transient development of residual stresses in laser beam melting – A neutron diffraction study (2018)
- Residual stresses in selective laser sintering and selective laser melting (2006)
- Study on the microstructure, mechanical property and residual stress of SLM Inconel-718 alloy manufactured by differing island scanning strategy (2015)
Also, there are many other articles in this area.
Edward Andrew Payzant : We are using the normal laboratory x-rays, as the aim is to obtain the rough residual stress values (surface only) in response to various laser parameters.
What if we select 4 to 5 regions with fewer surface irregularities and average the stress values, would that be a fair representation?
The AM Bench Conference that was held in June of 2018, included comparisons of measurements and modeling of residual stresses in identical builds of IN625. The results of these comparisons are being published in the TMS/Springer journal "Integrating Materials and Manufacturing Innovation." This included x-ray, neutron, and sectioning methods for residual stress measurements and the publications should include the details of interest to you. Information on this conference can be found at the AM Bench website (https://www.nist.gov/ambench) which will be updated soon to reflect the publication of the results from 2018. It has been proposed that the next iteration of this conference series should be held in June 2021 and include residual stress measurements on IN718 builds.
Dear Sebastian,
Practical method :
A colleague of mine print an entire little part on supports with low stress, she cut the supports and measure the part deformation. No need for x-rays and laboratory.
Best regards,
Daniel FRAGNIER
That was also covered in the IMMI paper. In fact, it is in the title of the paper: Phan et al., "Elastic Residual Strain and Stress Measurements and Corresponding Part Deflections of 3D Additive Manufacturing Builds of IN625 AM-Bench Artifacts Using Neutron Diffraction, Synchrotron X-Ray Diffraction, and Contour Method," Integ Mater Manuf Innov. doi: 10.1007/s40192-019-00149-0
With XRD technique RS can be measured in homogeneous materials, with crystalline lattice, near the surface (up to a depth of 0.01mm). Given the technology of obtaining the material, I think that XRD technique is not appropriate in this case. Of course, the physical properties of this material represent a challenge for any RS measurement technique. However, for this material I would choose the method with strain gauges (the drilled strain rosette, see ASTM E837). Maybe a destructive method (removal of layers and strain or deflection measurement) would yield acceptable results.
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