[P1-70] How to improve the ductility of CuZr BMGs based on cyclic pre-straining: MD simulations and mechanical testing
Bulk metallic glasses are currently used as technical materials(e.g.magnetic transmitters, golf clubs, brazing materials) for their high elastic and strength properties, significantly larger than their crystalline counterparts. However, their use is generally limited to elastic engineering applications due to their quasi-brittle behaviour caused by the early initiation of localized shear bands upon plastic deformation.
In this study, we used a combination of atomistic simulations and compressive mechanical testing to investigate the role of mechanical pre-cycling on the stress response and elementary deformation processes of a CuZr glass. In the experiments, unprestrained Zr52.5Cu17.9Ni14.6Al10Ti5(Vitreloy 105) samples show a plastic strain before failure of about 3% strain and a yield strength of about 1900 MPa. After applying a limited number of cycles with a maximum amplitude of 400 MPa (n=2, 4 or 6), the plastic strain increases up to 15%. It remains however in the same low range for higher pre-cycling amplitudes of 700 and 1200 MPa. MD simulations performed on Cu64.5Zr35.5thin films show that (i) unprestrained samples deform due to a local shear banding process, (ii) pre-cycled samples are characterized by the occurrence of homogeneous deformation zones with a concentration that depends on the cyclic stress amplitude i.e.the lower the stress amplitude of the pre-cycles, the higher the proportion of homogeneous deformation. This emphasizes the existence of a critical stress under which the main shearing process of CuZr BMGs changes due to pre-cycling, reducing shear localization and the early occurrence of cracks. These results are confirmed by the statistical analysis of experimental vein patterns on fracture surfaces that show larger cusps (φ>3500 µm2), attributed to highly localized plastic events, only in the cases of samples pre-cycled at high stress amplitude.
In this study, we used a combination of atomistic simulations and compressive mechanical testing to investigate the role of mechanical pre-cycling on the stress response and elementary deformation processes of a CuZr glass. In the experiments, unprestrained Zr52.5Cu17.9Ni14.6Al10Ti5(Vitreloy 105) samples show a plastic strain before failure of about 3% strain and a yield strength of about 1900 MPa. After applying a limited number of cycles with a maximum amplitude of 400 MPa (n=2, 4 or 6), the plastic strain increases up to 15%. It remains however in the same low range for higher pre-cycling amplitudes of 700 and 1200 MPa. MD simulations performed on Cu64.5Zr35.5thin films show that (i) unprestrained samples deform due to a local shear banding process, (ii) pre-cycled samples are characterized by the occurrence of homogeneous deformation zones with a concentration that depends on the cyclic stress amplitude i.e.the lower the stress amplitude of the pre-cycles, the higher the proportion of homogeneous deformation. This emphasizes the existence of a critical stress under which the main shearing process of CuZr BMGs changes due to pre-cycling, reducing shear localization and the early occurrence of cracks. These results are confirmed by the statistical analysis of experimental vein patterns on fracture surfaces that show larger cusps (φ>3500 µm2), attributed to highly localized plastic events, only in the cases of samples pre-cycled at high stress amplitude.