Novel nanostructured metallic thin films deposited by pulsed laser deposition with improved mechanical properties
Résumé
In recent years, thin metallic films have become increasingly important for several industrial
applications due to the activation of mechanical size effects enabling a mutual combination of
large yield strength and ductility1,2. However, the
correlation between atomic/micro-structure and
mechanical behavior is still not fully grasped and the
research on new nanostructures with improved
mechanical properties is still ongoing. In this context,
pulsed laser deposition (PLD) offers vast and, so far,
poorly exploited possibilities enabling an accurate
control of the film morphology by simply playing with the
deposition pressure. Specifically, films deposited in
vacuum possess a compact morphology due to the
atom-by-atom growth, while the addition of a background gas provide the formation of small
atomic clusters, leading to a nanogranular morphology (cluster-assembled growth)3.
In my project, I will show the potential of PLD for the synthesis and mechanical characterization
of two classes of emerging metallic thin films, namely thin film metallic glasses (TFMGs) and
complex compositional alloy (CCA) thin films.
Firstly, I will cover the results involving the synthesis and the mechanical behavior of ZrCuAlx
TFMGs with different compositions (x = 0,5,8,13 %at.) and morphologies (compact and
nanogranular). I will show that our films are ~10% denser than literature counterparts (8.3 g/cm3 vs
7.4 g/cm3)4, while possessing a unique self-assembled nanolayered structure with local chemical
enrichments, alternating ZrCu and Al rich nanolayers (Figure 1). This leads to a ~30% higher
elastic modulus (E) and hardness (H) compared to sputter-deposited counterparts4 as well as to a
larger onset of crack formation (~1.3%) when deformed in tension on polymeric substrates5.
Micropillar compression tests show that compact ZrCu films have a brittle behavior due to the
formation of shear bands while the nanogranular ones deform homogenously.
In the second part of the talk, I will present preliminary results focusing on AlxCoCrCuFeNi CCA
thin films deposited by PLD with different compositions (x = 0,9,16 %at.) and morphologies, i.e.,
compact and nanogranular. Films possess an FCC nanocrystalline structure with tunable
crystallite size which can be controlled by the deposition parameters and leading to enhanced E
and H vs sputter-deposited counterparts6. In addition, our films report an exceptionally high
(>3.5%) onset of crack formation when deformed on polymer substrate as a result of high energy
of the deposition process, leading to strong adhesion and preventing crack formation.
Overall, the presented results show the potential of PLD to synthetize a novel class of metallic
thin films with tunable mechanical properties and large interest as structural coatings.
References
[1] J. P. Chu et al., Thin Solid Films, 16, 2012; [2] Y. Zou et al., Nat. Commun., 6, 2015;
[3] M. Ghidelli et al,, Acta Mater., 213, 2021; [4] P. Yu et al., Mater. Sci. Eng. a, 45, 2008;
[5] A. Brognara et al., Mater. Des., 219, 2022; [6] B. Braeckman et al., Surf. Coat., 315, 2017.
Figure 1: HRTEM (a) and STEM (b) images of a compact ZrCuAl8 film
highlighting the Al-rich layers (in yellow).