Structural Features and Related Properties of Amorphous Alloys with High Defect Densities/ Interfaces Densities

• Applicant: Professor Dr.-Ing. Horst Hahn
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 323543657

• Final Report Year: 2022

Final Report Abstract

The structural features as well as mechanical properties of several amorphous alloys such as Zr62Cu22Al10Fe5Dy1, Zr52.5Cu17.9Ni14.6Al10Ti5 (Vitreloy 105), Ti50Ni25Cu25 and Cu50Zr50 (at. %) with high density of defects introduced by severe plastic deformation by high pressure torsion (HPT) had been studied by means of X-ray diffraction, transmission electron microscopy (TEM), atom probe tomography and nanoindentation. It was found that HPT leads to an increase of the free volume in all studied alloys for 1-2% due to extensive formation of shear bands (SBs). In this respect HPT-processed bulk metallic glasses (BMGs) are similar to nanoglasses, produced by inert gas condensation and sputtering. For the first time the local chemical–structural modifications associated to shear banding in the HPT-deformed samples of Vitreloy 5 BMG alloy were studied by means of 4D-STEM followed by an on-site developed method for phase mapping of nanostructured amorphous materials. This method allowed to unambiguously recognize shear bands, whereas they were practically invisible in conventional TEM imaging modes. It was found that in a narrow SB area, confined to a few nanometers, a reduction of geometrically favored motifs (GFMs, tetrahedrally closepacked polyhedral structural units building the atomic structure of metallic glasses), and a formation of geometrically unfavorable motifs (GUMs) occurred. Furthermore, an abrupt segregation of Zr and Cu at opposite sides inside the SB was observed. In the vicinity of the SB, the antisymmetric shear band affected zone extending several hundred nanometers away from the SB, was formed. Further investigations showed that the formation of GUMs led to increased plasticity, which was manifested by the absence of serrations in the nanoindentation curves along with an increased strain rate sensitivity of HPT-processed metallic glasses. Such behavior resembles that of nanoglasses. It was proposed that the plasticity of BMGs may be enhanced by alloy design that includes selecting atomic species having enough flexibility to rearrange their local chemical structure because the GUMs and GFMs prefer different elemental composition.

Publications

• HPT-induced shear banding and nanoclustering in a TiNiCu amorphous alloy. Materials Letters 209 (2017) 327-329
  E.V. Ubyivovk, E.V. Boltynjuk, D.V. Gunderov, A.A. Churakova, A.R. Kilmametov, R.Z. Valiev
  
• Cluster structure in amorphous Ti-Ni-Cu alloys subjected to high-pressure torsion deformation. Journal of Alloys and Compounds 749 (2018) 612-619
  D.V. Gunderov, E.V. Boltynjuk, E.V. Ubyivovk, A.V. Lukyanov, A.A. Churakova, A.R. Kilmametov, Yu.S. Zamula, R.Z. Valiev
  
• Enhanced strain rate sensitivity of Zr-based bulk metallic glasses subjected to high pressure torsion. Journal of Alloys and Compounds 747 (2018) 595-602
  E.V. Boltynjuk, D.V. Gunderov, E.V. Ubyivovk, M.A. Monclús, L.W. Yang, J.M. Molina- Aldareguia, A.I. Tyurin, A.R. Kilmametov, A.A. Churakova, A.Yu. Churyumov, R.Z. Valiev
  
• Consolidation of the Amorphous Zr50Cu50 Ribbons by High-Pressure Torsion. Adv. Eng. Mater. 2019, 1900694
  D. Gunderov, E. Boltynjuk, E. Ubyivovk, A. Churakova, A. Kilmametov, R. Valiev
  
• Accumulative HPT of Zr-based bulk metallic glasses. Materials Letters 261 (2020) 127000
  D.V. Gunderov, A.A. Churakova, V.V. Astanin, R.N. Asfandiyarov, H. Hahn, R.Z. Valiev
  
• Unveiling the Local Atomic Arrangements in the Shear Band Regions of Metallic Glass. Adv. Mater. 33 (2021) 2007267
  X. Mu, M. R. Chellali, E. Boltynjuk, D. Gunderov, R.Z. Valiev, H. Hahn, C. Kübel, Yu. Ivanisenko, L. Velasco