PREAMPA

PREcision Additive Manufacturing of Precious metals Alloys

Selective laser melting (SLM) is a powder bed additive manufacturing (AM) technology which allows building components from an alloy powder with complex 3D geometries layer by layer. The application of this technology to precious metals based alloys has been shown to face several challenges, related to their particular combination of optical, thermal and mechanical properties. Resulting parts are notoriously porous, and have low dimensionnal accuracy.

Machine combining Selective Laser Melting (SLM) and Laser Shock Peening (LSP), Source: EPFL

The project consortium aims to improve significantly the processing of these alloys by using lasers with different wavelengths, changing the reflectivity of powders through sacrificial coating and combining the SLM process with a Laser Shock Peening (LSP) treatment. These efforts will be complemented by the development of novel methods for the control and measurement of residual stresses, which are a major cause of process failure and geometrical distortions.

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Scope of Research Activities
Material development

• Cataloguing precious metal alloys candidates for Selective Laser Melting (SLM),
  including metallic glasses and high entropy alloys
  
• Alloying with trace elements
• Sacrificial coating of metal powders

SLM process development

• SLM with selected alloys
• Process development using two lasers with different wavelengths
• In situ monitoring based on acoustic emissions for defects detection
• Reflective anisotropy spectroscopy (RAS) for residual stress mapping
• Combination of SLM with Laser Shock Peening (LSP)

Advanced in situ and ex situ characterization

• Quantification of porosities and cracks
• Residual stresses, crystallographic phases, texture 
• Crystallinity, local structure, pair distribution function, excess free volume
• In situ fast heating and cooling, in situ SLM

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Key Technical Problems to Solve

• The high reflectivity and thermal conductivity of PMs makes them difficult to be consolidated by standard SLM, and parts are often porous and rough with a rather poor reproducibility.
  
• Residual stresses that build up during SLM reduce the geometrical accuracy and may lead to damage / cracking, which prevents some alloys to be considered as potential candidates for mm to cm parts.
  
• The good combination of hardness and ductility is often not obtained with standard precious alloys, and traditional thermomechanical treatments.
  

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Demonstrators

• Small cubes
  
• Little cylinders (on which compression tests can be performed)
  
• Parts representative of the challenges faced by the watch industry
  
  

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Linked Scientific Publications

• Hocine, S., S. Van Petegem, U. Frommherz, G. Tinti, N. Casati, D. Grolimund and H. Van Swygenhoven (2020). "A miniaturized selective laser melting device for operando X-ray diffraction studies." Additive Manufacturing 34: 101194.
• Hocine, S., H. Van Swygenhoven and S. Van Petegem (2021). "Verification of selective laser melting heat source models with operando X-ray diffraction data." Additive Manufacturing 37: 101747.
• Hocine, S., H. Van Swygenhoven, S. Van Petegem, C. S. T. Chang, T. Maimaitiyili, G. Tinti, D. Ferreira Sanchez, D. Grolimund and N. Casati (2020). "Operando X-ray diffraction during laser 3D printing." Materials Today 34: 30-40.
• Kurtuldu, G. and J. F. Löffler (2020). "Multistep Crystallization and Melting Pathways in the Free-Energy Landscape of a Au–Si Eutectic Alloy." Advanced Science 7(12): 1903544.
• Kurtuldu, G., K. F. Shamlaye and J. F. Löffler (2018). "Metastable quasicrystal-induced nucleation in a bulk glass-forming liquid." Proceedings of the National Academy of Sciences 115(24): 6123.
• Lindström, V., O. Liashenko, K. Zweiacker, S. Derevianko, V. Morozovych, Y. Lyashenko and C. Leinenbach (2020). "Laser Powder Bed Fusion of Metal Coated Copper Powders." Materials 13(16).
• Sohrabi, N., J. Jhabvala, G. Kurtuldu, M. Stoica, A. Parrilli, S. Berns, E. Polatidis, S. Van Petegem, S. Hugon, A. Neels, J. F. Löffler and R. E. Logé (2021). "Characterization, mechanical properties and dimensional accuracy of a Zr-based bulk metallic glass manufactured via laser powder-bed fusion." Materials & Design 199: 109400.
• Sohrabi, N., R. S. Panikar, J. Jhabvala, A. R. Buch, S. Mischler and R. E. Logé (2020). "Laser coating of a Zr-based metallic glass on an aluminum substrate." Surface and Coatings Technology 400: 126223.
• Yan, W., I. Richard, G. Kurtuldu, N. D. James, G. Schiavone, J. W. Squair, T. Nguyen‐Dang, T. Das Gupta, Y. Qu, J. D. Cao, R. Ignatans, S. P. Lacour, V. Tileli, G. Courtine, J. F. Löffler and F. Sorin (2020). "Structured nanoscale metallic glass fibres with extreme aspect ratios." Nature Nanotechnology 15(10): 875-882.
  

Leading Principal Investigator

Prof. Dr. Roland Logé
Laboratory of Thermomechanical Metallurgy, EPF Lausanne

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Project Consortium

• Dr. Christian Leinenbach, Laboratory for Advanced Materials Processing, Empa
  
• Prof. Dr. Jörg F. Löffler, Laboratory of Metal Physics and Technology, ETH Zürich
  
• Prof. Dr. Ralph Spolenak, Laboratory of Nanometallurgy, ETH Zürich
  
• Prof. Dr. Helena Van Swygenhoven, Photons for Engineering and Manufacturing Group, PSI
  
• Dr. Antonia Neels, Center for X-Ray Analytics, Empa