Master Thesis Announcement

Re-use of Metal Powders for Additive Manufacturing Processes

Background
Selective laser melting (SLM) is an additive manufacturing process in which the thermal energy
of a laser beam melts and fuses areas of the powder bed. This technology allows manufacture
the near-net-shape components. In many cases only a small portion of the powder is actually
melted and solidified into a component. Most is left after the build. Since the powder used in
SLM is costly and waste should be avoided. The un-melted powder is therefore recycled and
reused in the subsequent process.

Due to the heating effect originated from the laser beam and the interaction with the surrounding
atmosphere, the un-melted metal powder becomes aged gradually. Correspondingly, the surface
morphology and chemistry, the shape and size distribution as well as the flowability of the
particles are modified. The aged powders may affect the final properties of the printed
component negatively, making the number of times that metal powder can be cycled in an SLM
process limited. It is thus of great importance to establish relevant methods for estimating the
utilization limit of the reused powder. From the economic point of view, it is also of urgent
interest to develop a recycling methodology to reuse the metal powder.
Objectives

The objective is to a) Determine the utilization limit – “lifetime” of the initial powder material
in the SLM process; b) Develop a methodology which is sensitive, reliable and easy enough
to monitor the progress of the “lifetime” of the metal powder; c) Develop a strategy to reuse
the metal powder by keeping the metal powder as close to the “virgin” condition as possible
by certain post process steps.

Work Description
This work will be performed in close collaboration between Uddeholm, the world’s leading
manufacturer of tool steel, and the Department of Industrial and Materials Science at
Chalmers University. The following packages are included:
• Literature study
• Simulate the aging process during SLM by heat-treating powder in a furnace with
controlled atmosphere under certain time.
• Post processing of aged powder for recycling, e.g., by milling or reduction annealing
• Surface morphology and chemistry (Optical Microscopy, Scanning Electron
Microscopy, X-ray diffraction, and X-ray Photoelectron Spectroscopy)
• 3D printing by SLM and material testing, e.g., impact toughness
Qualification
We are looking for you who are studying towards a Master of Science degree in the field of
material science, applied physics or mechanical engineering.
Start of the thesis work:

Contact: Docent Yu Cao (yu.cao@chalmers.se ); Academic supervisor and examiner
Dr Christos Oikonomou (christos.oikonomou@uddeholm.com); Industrial
supervisor