Mechanical properties of high entropy alloy-metallic glass composites

Date

2024-8-14

Author

Fadaie, Amir

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Nanolayers of metallic glasses (MG) and high-entropy alloys (HEA) provide an effective model system for studying mechanical behavior and length scale effects in confined geometries. This study investigates the structure-property relationships in CuZr/NbMoTaW nanolayers, prepared by magnetron sputtering with layer thicknesses ranging from 5 to 200 nm. Mechanical properties were evaluated using nanoindentation to measure elastic modulus, hardness, and yield strength, along with energy-based fracture toughness assessments. Results showed that HEA exhibited higher stiffness and hardness than MG, with multilayered samples displaying intermediate values. Notably, the 5 nm layers demonstrated significantly higher hardness. XRD and TEM analyses confirmed the amorphous nature of CuZr and the BCC structure of NbMoTaW with (200) texture switching to (211) texture in nanolayers. Confined Layer Slip (CLS) model with an effective shear modulus was utilized and the composite CLS model was developed in this work. CLS model underestimated hardness for h≥30 nm but aligned with experimental data at 5-10 nm, showing peak hardness of 12.9 GPa at h=2.9 nm. Composite CLS model predicted a peak hardness of 12.2 GPa at h=2.8 nm and provided accurate estimates over a broader thickness range (h=5-100 nm), slightly underestimating hardness at h=200 nm. Experimental data was closer to the Reuss estimate, suggesting an iso-strain behavior. The composite CLS model fitted better with λ=13.4, achieving a peak hardness of 12.0 GPa at h=2.7 nm. These findings are useful for optimizing the structure of MG/HEA nanolayers toward the development of advanced composites that combine high strength and toughness.

Subject Keywords

Metallic glasses, High entropy alloys, Nanolayered metals, Mechanical properties, Nanoindentation

URI

https://hdl.handle.net/11511/112229

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Graduate School of Natural and Applied Sciences, Thesis