Synthesis and mechanical behavior of nanostructured high entropy alloy thin films by pulsed laser deposition
Résumé
High entropy alloy thin films (HEA-TFs) have become object of intense research in the last years
due to the mutual combination of large strength and ductility, overcoming traditional bulk
materials [1]. However, the field of thin film HEAs is still at its early stage and the effects of
nanostructure on mechanical behavior have not been studied yet. In this context, pulsed laser
deposition (PLD) offers the ability to control the morphology of the films by simply playing with
the pressure during the deposition by adding an inert gas or by changing the laser wavelength
and fluence (J/cm2) [2]. Here, we investigate the structure and mechanical properties of
AlxCoCrCuFeNi thin films
deposited by PLD investigating
the effects of laser wavelength
(1064 and 532 nm), deposition
pressure (vacuum and 5 Pa He) as
well as the Al content (from 0 up
to 16 %at.). In addition, a second
series of samples was grown by
magnetron sputtering for
comparison purposes. We show in
Fig. 1 that CoCrCuNiFe films deposited in vacuum and at 5 Pa He are, respectively, compact and
nanogranular. Moreover, we show that addition of Al (AlxCoCrCuFeNi) is responsible of a phase
transition from FCC to BCC (at 16% at. Al), possessing a unique atomic structure alternating Alrich
and CoCrCuNiFe nanolayers. The Young’s modulus and hardness of PLD films (175 and 10.8
GPa) are ~10% larger than magnetron sputtered films with a slightly decrement by addition of
Al and for nanogranular film [3]. Tensile test on polymeric substrate (Kapton®) show that
compact films have an outstanding onset of crack initiation up to ~3.5% which is higher vs
literature (~2% [4]) and slightly decreasing by adding Al. The larger mechanical properties of PLD
films can be related to the high energies of deposition and nanolayered structure. Overall, we
show that PLD has the potential to synthetize a novel class of HEA-TFs with tunable mechanical
properties and potential interest as structural coatings.
References
[1] Zou, Y. et al., Nat. Commun. 6, 2015. [2] M. Ghidelli et al., Acta Mater. 213, (2021).
[3] Braeckman, B., Ghent University, (2016). [4] Li, C. et al., Surf. Coat. 402, (2020).