Christos Sofras

Biography

Dr. Christos Sofras is a postdoctoral researcher at the Swiss Federal Laboratories for Materials Science and Technology (Empa), specializing in additive manufacturing, alloy design and microstructure engineering. He earned his PhD in Materials Science from EPFL, where his thesis focused on exploiting Laser Powder Bed Fusion to manipulate crystallographic textures in stainless steels and activate deformation mechanisms such as TRIP and TWIP. Before joining EPFL, he obtained his diploma in Mining and Metallurgical engineering from the National Technical University of Athens. His work combines advanced characterization methods, including synchrotron and neutron diffraction, aiming to establish processing–structure–property links.

Abstract

Microstructure as a Design Variable in Laser Powder Bed Fusion

The microstructures produced by Laser Powder Bed Fusion (LPBF) are often regarded as an inevitable consequence of rapid solidification and repeated thermal cycling. This presentation introduces a different perspective: scan strategy is treated as a design variable capable of controlling microstructure - and therefore mechanical behavior - as deliberately as alloy selection or heat treatment. Two case studies, spanning different alloy systems and microstructural length scales, demonstrate the scope of this approach.

In austenitic stainless steels, crystallographic texture strongly influences secondary strain-hardening mechanisms, particularly transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). By controlling the scanning direction, distinct textures can be introduced within selected regions of a component and matched to the local stress state. This allows deformation twinning and martensitic transformation to be promoted where they are most beneficial, increasing strain hardening and energy absorption under complex loading conditions.

The same principle is then extended to a Zr-modified Al-2618 alloy, where scan strategy is used to control grain structure rather than crystallographic texture. Increased melt-pool overlap and repeated local remelting replace the characteristic bimodal grain structure of the alloy with a uniform ultrafine-grained structure directly in the as-built state. The resulting equiaxed grains are approximately 400 nm in size and remain stable during exposure at 400 °C.

Together, these results show that the LPBF procerssing strategy is not merely a route to geometry, but a lever for switching microstructural mechanisms - and the resulting mechanical behavior - on and off within a single build.