| Thermomechanical processing to extend the range of the glassy state A. Lindsay Greer1; 1UNIVERSITY OF CAMBRIDGE, Cambridge, United Kingdom; PAPER: 248/Molten/Plenary (Oral) SCHEDULED: 15:55/Thu. 24 Oct. 2019/Ambrosia A (77/RF) ABSTRACT: For conventional engineering alloys (which are of course polycrystalline), thermomechanical processing is routinely applied to change their microstructure and optimize their properties. Thermomechanical processing is not applied to conventional glasses, which are generally considered to be brittle. In contrast, metallic glasses formed by liquid quenching have a range of possible states. This range is remarkably extendable by thermomechanical processing [1]. Plastic deformation at room temperature leads to relaxation or rejuvenation. A notched sample in compression shows extreme rejuvenation at the notch root: locally, the hardness and enthalpy match those for a glass cooled at 10<sup>10</sup> K/s, 10<sup>7</sup>-10<sup>8</sup> times faster than for the original glass [2]. Effects of loading in the nominally elastic regime, whether quasi-static or cyclic, are also reviewed [3,4]. Cryogenic thermal cycling (CTC) reduces the initial yield load in nanoindentation and increases plasticity in macroscopic compression, partially reversing the effects of annealing [5]. Yet CTC has little effect on other properties such as elastic moduli. CTC may stimulate soft spots in a matrix that itself is largely unaffected. Combined treatments, e.g. annealing with CTC, can have dramatic effects, e.g. glasses that are harder and stiffer, yet more plastic. Prospects for further modification of metallic glasses will be considered, outlining useful property changes that may be achieved. References: References:<br />[1] Y.H. Sun et al., Thermomechanical processing of metallic glasses: extending the range of the glassy state, Nature Rev. Mater. 1 (2016) 16039.<br />[2] J. Pan et al., Extreme rejuvenation and softening in a bulk metallic glass, Nature Comm. 9 (2018) 560.<br />[3] A.L. Greer & Y.H. Sun, Stored energy in metallic glasses due to strains within the elastic limit, Philos. Mag. 96 (2016) 1643-1663. <br />[4] D.V. Louzguine-Luzgin et al., On room-temperature quasi-elastic mechanical behaviour of bulk metallic glasses, Acta Mater. 129 (2017) 343-351.<br />[5] S.V. Ketov et al., Rejuvenation of metallic glasses by non-affine thermal strain, Nature 524 (2015) 200-203. |
