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.

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

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.

Demonstrators

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

Leading Principal Investigator

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

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