ORALS

SESSION: MoltenThuPM2-R1	Angell International Symposium on Molten Salt, Ionic & Glass-forming Liquids: Processing and Sustainability (7th Intl. Symp. on Molten Salt, Ionic & Glass-forming Liquids: Processing and Sustainability).
Thu Oct, 24 2019 / Room: Ambrosia A (77/RF)
Session Chairs: Georges Kipouros; Giancarlo Jug; Session Monitor: TBA

15:55: [MoltenThuPM209] Plenary
Thermomechanical processing to extend the range of the glassy state
A. Lindsay Greer¹ ; ¹University of Cambridge, Cambridge, United Kingdom;
Paper Id: 248 [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 10¹⁰ K/s, 10⁷-10⁸ 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:\n[1] Y.H. Sun et al., Thermomechanical processing of metallic glasses: extending the range of the glassy state, Nature Rev. Mater. 1 (2016) 16039.\n[2] J. Pan et al., Extreme rejuvenation and softening in a bulk metallic glass, Nature Comm. 9 (2018) 560.\n[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. \n[4] D.V. Louzguine-Luzgin et al., On room-temperature quasi-elastic mechanical behaviour of bulk metallic glasses, Acta Mater. 129 (2017) 343-351.\n[5] S.V. Ketov et al., Rejuvenation of metallic glasses by non-affine thermal strain, Nature 524 (2015) 200-203.

SESSION: SISAMFriPM1-R3 E: Complexity in materials	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Fri Oct, 25 2019 / Room: Dr. Christian Bernard
Session Chairs: Mariana Calin; Session Monitor: TBA

14:25: [SISAMFriPM106]
Nanocrystal-amorphous dispersions in Al-based and high-entropy alloys
A. Lindsay Greer¹ ; Akihisa Inoue² ; ¹University of Cambridge, Cambridge, United Kingdom; ²Tianjin University, Tianjin, China;
Paper Id: 250 [Abstract]

We review recent advances in the development of two types of rapidly quenched alloys that show promise as structural materials. In each case, the focus of interest is the dispersions of nanocrystals in the residual amorphous matrix that can be achieved by treating initially fully amorphous melt-spun ribbons.
The first alloy type is Al-based with compositions such as Al₉₀Y₁₀ (at.%) and Al₈₄Y_8.5Ni₄Co₂Pd₁Fe_0.5 [1,2]. Remarkably, when amorphous ribbons are cold-rolled, this induces partial crystallization to nanoscale fcc-Al (alpha-Al). By contrasting this crystallization with the apparently similar crystallization induced by annealing, progress has been made in understanding the mechanisms of hardening and softening. Polymorphic crystallization induced by cold-rolling avoids the formation of compound phases associated with brittleness, and is therefore promising for the development of high-solute Al-based alloys as structural materials.
The second alloy type is metal-metalloid, with a complex (high-entropy) mixture of metals and relatively low metalloid content. An example is the alloy series (Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.125)_86-89B_11-14 [3]. Initially amorphous alloys when annealed show complex crystallization sequences. Nanoscale (5-15 nm) particles of fcc and bcc phases are formed and show very high thermal stability (resistance to coarsening). It is of particular interest that ultrahigh hardness of 1500-1550 Hv can be achieved without the formation of any boride phases. The hardening and thermal stability are unusually high for such low boron content and encouraging for the development of ultrahard coatings.
Prospects for further alloy development are considered.

References:
1. F.F. Han, A. Inoue, Y. Han, F.L. Kong, S.L. Zhu, E. Shalaan, F. Al-Marzouki, A.L. Greer, Novel heating-induced reversion during crystallization of Al-based glassy alloys, Sci. Reports 7 (2017) 46113.\n2. H.W. Bi, A. Inoue, F.F. Han, Y. Han, F.L. Kong, S.L. Zhu, E. Shalaan, F. Al-Marzouki, A.L. Greer, Novel deformation-induced polymorphic crystallization and softening of Al-based amorphous alloys, Acta Mater. 147 (2018) 90-99.\n3. F. Wang, A. Inoue, F.L. Kong, S.L. Zhu, E. Shalaan, F. Al-Marzouki, W.J. Botta, C.S. Kiminami, Yu.P. Ivanov, A.L. Greer, Formation, stability and ultrahigh strength of novel nanostructured alloys by partial crystallization of high-entropy (Fe_0.25Co_0.25Ni_0.25Cr_0.125Mo_0.125)_86-89B_11-14 amorphous phase, Acta Mater. 170 (2019) 50-61.