MAPP Lecture Series - Professor Nick Lavery

Professor Nick Lavery, Director of the Materials Advanced Characterisation Centre (MACH1) and lead academic of the Swansea Manufacturing Research (SAMR) group will be joining us online to speak about Developing High Entropy Alloys for Additive Manufacturing.

Abstract

A new high entropy alloy based on five primary elements(Al-Cr-Fe-Mn-Ni) has been designed specifically for use in powder form in additive manufacturing processes, as a lighter alternative to stainless steels, such as 316L, designed to have good properties in as-built form.

The alloy elements were initially selected using a top-down approach based on cost and environmental indices which resulted in millions of possibilities.

A Hume-Rothery approach, [1], was then used to determine possible phases within aspecific density range, reducing the choices to thousands of possibilities, and then for optimum elemental percentages and potential hardness to further reduce the choices to hundreds of possibilities. Further down-selection was achieved using a combination of laboratory synthesis and manufacturing considerations of elemental limits (e.g. Al and Mn) during gas atomisation, effectively narrowing down the choices to just a few winning compositions.

After two years of work on the COMET (CombinatorialMetallurgy) project the alloy was produced in powder form by Sandvik-Osprey at the plant in Neath, South Wales in August 2020. The composition was achieved within set tolerances, as were size distributions and powder morphology. The entire gas atomised batch (300kg) was split into three sizes, oversized (150 μm), laser powder bed fusion (15-45 μm) size, and fines (<15 μm)sizes. The powder was then used across a wide range of different processes, Spark Plasma Synthesis, Laser Powder Bed Fusion, Blown Powder and MaterialBinder Jet.

This alloy was specifically designed to be 7% lighter than standard stainless steels but with similar or better mechanical and corrosion-resistant properties, by aiming for a high proportion of the FCC phase and higher hardness than 316L.

This talk will highlight the development path of this alloy, and a few of the more recent results as we compare mechanical properties across a range of AM/PM processes. The development process is also being applied to other families of HEAs, such as lightweight systems for aerospace and high-hardness, refractory based systems.

[1] Calvo-Dahlborg, M. and Brown, S.G., (2017).Hume-Rothery for HEA classification and self-organizing map for phases and properties prediction. Journal of Alloys and Compounds, 724, 353-364.