Correlation of mechanical properties in bulk metallic glasses with 27Al NMR characteristics

Abstract

We report 27 Al NMR and magnetic susceptibility measurements of Zr and ZrHf-based bulk metallic glasses (BMGs). 27 Al NMR Knight shift shows that there exists a clear correlation between the local electronic properties at Al sites and mechanical properties. In addition, magnetic susceptibility measurements also provide clues on the influence of the electronic states, especially the strong influence of d-orbital characteristics on the mechanical properties of toughness and hardness. bulk metallic glass, nuclear magnetic resonance, knight shift, magnetic susceptibility, mechanical properties Citation: Sandor M T, Kecskes L J, He Q, et al. Correlation of mechanical properties in bulk metallic glasses with 27 Al NMR characteristics.Many families of multi-component bulk metallic glasses (BMGs) have been studied extensively due to their good glass forming ability (GFA) [1-6], thermal stability, as exhibited by their wide supercooled region [2,5,7], and favorable mechanical properties such as high yield strength [5,6]. Earlier studies have discussed correlations of GFA with thermodynamics [8,9], kinetics [8-10], electronic structure [11], and atomic structures [12-14]. To optimize the potential of metallic glasses for engineering applications, an understanding of correlations between electronic structures and mechanical properties can be quite valuable for designing and fine-tuning the properties of BMGs. Previous experimental [15-17] and computational studies of transition metal (TM)-based BMGs [16,18,19] have addressed the issue of the relationship between electronic structures and mechanical properties such as strength and ductility. More experimental evidence would be very useful for further establishing and understanding the correlations between structural properties and electronic properties of BMGs. In this study, we use 27 Al NMR and magnetic susceptibility to show strong correlations between hardness and toughness of Zr and ZrHf-based BMGs and local electronic structures.

On the use of atomistic simulations to aid bulk metallic glasses structural elucidation with solid-state NMR

“…The reader is referred to the supplementary information for detailed results from these tests, and to the Methods section for technical details on our GIPAW simulations. It is especially important to remark that we are presenting here, in an unprecedented way, a quantitative estimate of the nature of the difference between the metallic shifts observed experimentally for pure Al and those of Al-TMs glassy alloys reported in the literature 13 , 14 , 16 , 17 . The quantitative separation of the CS and KS contributions to metallic shifts in the BMGs at issue in the present study, can be roughly estimated from the σ o and σ s values computed for ZrCu 2 Al.…”

“…Notwithstanding these remarks, and besides the aforementioned premise that ssNMR is intrinsically a short-ranged limited characterization technique, we present another argument to justify the use of abstract systems (ASs) to perform our ab initio DFT simulations. The ordinary ssNMR spectra of Al-TMs glassy alloys reported in the literature 13 , 14 , 17 consist of a single distinguishable peak, which is usually broad with widths at half height of about 200 ppm. So, any attempts to correlate ssNMR data with properties of different BMGs reported so far, have been made by comparisons between their spectra.…”

“…However, looking at the respective isotropic chemical shifts ( δ iso ), it becomes clear that the local/semi-local electron density around target Al sites in the ASs B2-Cu 8 Zr 7 Al and B2-Cu 7 Zr 8 Al are completely incompatible with the those on the real BMGs ZCA- x . Recalling that the experimental spectra are broad with widths at half height of about 200 ppm 13 , 14 , 17 , i.e., it would be possible to accept theoretical δ iso values between 100 and 500 ppm. But even so, these two ASs which were also adopted in ref.…”

“…The use of 27 Al ssNMR for the characterization of intermetallic compounds is relatively well established 15 . Recently, it also has been used in a number of studies aimed to establish correlations between peak positions in the measured spectra and mechanical properties of BMGs 13 , 14 , 16 , 17 , or even to understand liquid-liquid transitions in glass forming melts 18 . Nevertheless, as usual and sometimes inevitable in ssNMR studies of glasses, a certain speculative element exists in establishing such relationships in terms of the local/semi-local atomic arrangement and electron density around target sites.…”

Amorphous alloys — A kind of promising high-performance materials

“…The result is a delightful one. We have 17 papers collected in this special issue, which cover broad areas of amorphous alloys, including atomic packing and clusters formation in amorphous alloys [1-3], fragility in glass-forming liquid [4], effects of alloying elements on the glass forming ability of different alloys [5][6][7], deformation behavior and improved mechanical property of amorphous alloys [8][9][10][11], glass-based composites [12,13], high strength metallic glass [14] and functional properties of metallic glasses [15][16][17].…”