Correlations between the ductility and medium-range order of bulk metallic glasses

Abstract

Understanding ductility or brittleness of monolithic bulk metallic glasses requires detailed knowledge of the amorphous structure. The medium-range order (MRO) of ductile Pd40Ni40P20 and brittle Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) was characterized prior to and after notched three-point bending tests using variable-resolution fluctuation electron microscopy. Here, we show the presence of a second larger MRO correlation length in the ductile material, which is not present in the brittle material. The second larger correlation length accounts for an increased heterogeneity, which seems to enable an easier shear band formation and thus explain the difference in deformability.

Impact of Severe Deformation by HPT at Room Temperature on the Relaxation of the Glassy and the Supercooled Liquid States of PdNiP

“…FEM is a microscopic technique which has been shown to be sensitive to higher order correlation functions such as g 3 and g 4 and hence to MRO in disordered materials 7,8,20,23,[26][27][28][29][30][31]46 . A statistical analysis of the diffracted intensities I( k, R, r) from nanometer-sized volumes was used by utilizing STEM microdiffraction 25 , where k is the scattering vector, R is the probe size and r is the position on the sample.…”

“…A more detailed and recent discussion on different models for describing FEM-based data can be found in Ref. 7 . Moreover, in order to elucidate subtle differences in the amorphous structure between the individual materials' states differential curves ∆V(k,R) of the normalized variances are analyzed.…”

“…Eutectic alloys, such as Pd 40 Ni 40 P 20 having a deep melting point, are predestined to produce bulk metallic glasses (BMGs) since slower cooling rates (∼ 10 1 K/s) lead to the desired glassy state [1][2][3][4] . Moreover, Pd 40 Ni 40 P 20 exhibits good glass-forming ability [3][4][5] and mechanical properties (ductility) [6][7][8] . Depending on the cooling rate, the cast-material inherently attains variations of local atomic structures corresponding to higher and lower energy states 9 .…”

“…Low-temperature heat capacity measurements (PPMS) were performed in order to reveal changes in the atomic vibrational spectra which are related to the excess free volume distribution 18,19 and thus atomic arrangements. To investigate the corresponding amorphous structure in detail, fluctuation electron microscopy (FEM) was employed to determine the MRO fingerprint (size 7,20 , relative volume fraction 21,22 and types 23,24 ) of each materials' state 20,[25][26][27][28][29][30][31] . Finally, these findings are discussed in terms of a PEL scheme offering a new approach for MRO engineering of glasses.…”

Comparison of Experimental STEM Conditions for Fluctuation Electron Microscopy

“…Comprehensive MRO studies on the PdNiP system using the current setup were recently reported in Hilke et al (2020) and Davani et al (2020aDavani et al ( , 2020b.…”