Quantum mechanically guided design of ultra strong and damage tolerant glasses
Final Report Abstract
Metallic glasses are amorphous materials with outstanding mechanical properties such as high damage tolerance, which is the combination of high fracture-toughness and strength. In the SPP-1594, knowledge-based design proposals for fracture toughness, stiffness and thermal expansion of metallic glasses have been developed, to enable the prediction ab initio of these properties based on their electronic structure. This allows for a more efficient development of metallic glasses by computationally screening the properties of metallic glasses and focusing synthesis on the most promising alloy compositions. The present project set out to validate the design proposals named above, whereby the focus was on the fracture toughness. With bending experiments on micro-meter sized cantilevers that contained a pre-notch, the fracture toughness can be determined given a negligible plastic deformation of the sample. However, the investigated samples of PdAlY-Ir, PdAlY-Au and PdAlY-Ni metallic glasses all exhibit significant plastic deformation and do not break until the maximum displacement of the intender was reached. Hence, linear elastic fracture mechanics cannot be applied to determine the fracture toughness of these glasses. Analysis of the stiffness in the unloading segments during the bending experiment showed an increase in stiffness with increasing displacement of the indenter, which is opposite to the decreasing stiffness expected for a growing crack. Thus, also elasto-plastic fracture mechanics is not applicable to this samples and values of fracture toughness cannot be obtained with this state-of-the-art method. However, during loading of these three metallic glass systems, shear bands evolve on both sides of the cantilever, being under compressive and tensile stress, respectively. The shear bands do not cross the neutral axis of the cantilever; therefore, they are confined by the stress field inside the cantilever. Although not giving a quantitative fracture toughness, the micro-mechanical tests reveal a significant plasticity in these PdAlY-based metallic glasses. To bridge the gap between metallic glasses and oxide glasses, the AlSiO system with varying oxygen content was investigated. However, as this system becomes an isolator with increasing oxygen content, only cantilevers from a sample with a low oxygen content could be prepared. This cantilever fractured brittle. However, for systematic study, the synthesis process requires optimization to provide high quality samples that allow to address the charging issues during sample preparation. In addition, the fingerprint for electrical resistivity of metallic glasses in the electronic structure has been revealed based on the PdAlY-M system. For the electrical resistivity, the electronic states around the Fermi-level are decisive. Based on the analysis of the Crystal Orbital Hamilton Population (COHP), which is a measure of the contribution of the electronic states to the bond energy, it has been shown that the electrical resistivity at room temperature scales with the COHP integrated around the Fermi level. Hence, the stronger the electrons are bond, the higher the electrical resistivity at room temperature. In the future, new characterization techniques for tough metallic glasses need to be developed to characterize the alloys suggested by the knowledge-based design proposals to contain promising properties. Then, these compositions with a high fracture toughness will be promising for industrial applications, especially in micro electro-mechanical devices or medical instruments, where small component size are required.
Publications
- Effect of hybridization in PdAlY-(Ni/Au/Ir) metallic glasses thin films on electrical resistivity
H. Bishara, G. Dehm, J. M. Schneider, S. Evertz,
(See online at https://doi.org/10.2139/ssrn.3951676) - Electronic hybridisation implications for the damage-tolerance of thin film metallic glasses, Sci. Rep. 6 (2016) 36556
V. Schnabel, B. Nagamani Jaya, M. Köhler, D. Music, C. Kirchlechner, G. Dehm, D. Raabe, and J. M. Schneider
(See online at https://doi.org/10.1038/srep36556) - Nano-laminated thin film metallic glass design for outstanding mechanical properties, Scripta Mater. 155 (2018) 73-77
P. Kontis, M. Köhler, S. Evertz, Y.-T. Chen, V. Schnabel, R. Soler, J. Bednarick, C. Kirchlechner, G. Dehm, D. Raabe, J.M. Schneider, B. Gault
(See online at https://doi.org/10.1016/j.scriptamat.2018.06.015) - Electronic structure based design of thin film metallic glasses with superior fracture toughness, Mater. Des. 186 (2020) 108327
S. Evertz, I. Kirchlechner, R. Soler, C. Kirchlechner, P. Kontis, J. Bednarcik, B. Gaultb, G. Dehm, D. Raabe, J. M.Schneider
(See online at https://doi.org/10.1016/j.matdes.2019.108327) - Review on quantum mechacnically guided design of ultra-strong metallic glasses, Frontiers Mater. 7 (2020) 89
S. Evertz, V. Schnabel, M. Köhler, I. Kirchlechner, P. Kontis, Y.-T. Chen, R. Soler, B. N. Jaya, C. Kirchlechner, D. Music, B. Gault, J. M. Schneider, D. Raabe and G. Dehm
(See online at https://doi.org/10.3389/fmats.2020.00089)
