ANR Project MICRO-HEAs

MICRO-scale mechanical characterization of thin film High Entropy Alloys (Micro-HEAs), ANR-21-CE08-0003-01

High entropy alloys thin films (HEAs-TF) are a relatively new class of materials with potential industrial and technological applications such as hard coatings, MEMS, etc. However, the development of new microstructures with tailored nano- and microscale features (grain size, density of interfaces etc.) is one of the current challenges, especially targeting mutually exclusive mechanical properties such as high yield strength-plasticity and thermal stability.

For this reason, the objectives of the ANR MICRO-HEAs project are to synthesize nanostructured HEA-TFs by exploiting the potential of both Pulsed laser deposition (PLD) and magnetron sputtering. More specifically, PLD was used to synthesize model nanocrystalline CoCrCuFeNi HEAs exploiting cluster-assembled growth resulting in large hardness (~11 GPa) and yield strength (2.2 GPa), while maintaining high plastic deformability (without failure up to 30 %, see Figure 1) and thermal stability (onset of grain growth at 49% or the melting temperature).

Moreover, within MICRO-HEAs we focus on the synthesis of HEA-based nanolaminates (NLs), aiming to improve the strength by blocking the propagation of dislocations due to the presence of nanointerfaces while keeping large plastic deformability by the addition of Al layers. Specifically, we used magnetron sputtering for the synthesis of Al/Alx(CoCrCuFeNi)100-x NLs, controlling the layer thickness and the  as well as the composition of the HEAs-TF synthetizing  both FCC/FCC and FCC/BCC NLs, while tailoring the mechanical behavior (Fig. 2). Moreover, we also exploit the potential of PLD to synthesize Al/CoCrCuFeNi NLs with ultrafine bilayer periods (down to 2.5 nm), enabling superior hardness (up to ~10 GPa) and high yield strength (up to 3.3 GPa).

Finally, MICRO-HEAs supported the development of experimental micromechanical capabilities of LSPM, by financing the acquisition of the FemtoTools (FT-NMT04) in situ SEM nanoindenter.