Microstructures and properties of high-entropy alloys

Electrospinning: a fascinating fiber fabrication technique.

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Plasticity in small-sized metallic systems: Intrinsic versus extrinsic size effect

/pdf/phase-stability-in-high-entropy-alloys-formation-of-solid-54ci0ongt4.pdf

Phase stability in high entropy alloys: Formation of solid-solution phase or amorphous phase

Deformation of metallic glasses: Recent developments in theory, simulations, and experiments

We report a composite material consisting of precipitated micron-scale Ta-rich solid solution particles distributed in a bulk metallic glass matrix. The reinforcing ductile particles are precipitated during melting of the master alloy of glass-forming (Zr70Ni10Cu20)82Ta8Al10, by using previously prepared metastable Zr–Ta solid solution binary ingots. Upon cooling from the melt, the matrix undergoes a glass transition to produce an amorphous phase while the particles of precipitated Ta solid solution are distributed in the glass matrix. The resulting material not only shows high strength (∼2.1 GPa), but also has dramatically enhanced plastic strain to failure in uniaxial compression relative to single-phase bulk metallic glasses. The composite also displays limited tensile ductility.

Metallic glass matrix composite with precipitated ductile reinforcement

Bulk metallic glasses subjected to quasistatic uniaxial compression at room temperature typically display large elastic strains but limited plastic flow of 0--2% before failure. We have developed an amorphous alloy, ${\mathrm{Zr}}_{59}{\mathrm{Ta}}_{5}{\mathrm{Cu}}_{18}{\mathrm{Ni}}_{8}{\mathrm{Al}}_{10},$ which experiences an average macroscopic plastic strain of 4.5% before failure. The as-cast alloy shows no evidence for the presence of crystalline phases, and displays a distinct glass transition temperature and a wide supercooled liquid region. Upon compression beyond the yield point, the alloy develops shear bands which show a pronounced tendency for branching. We propose that this shear band branching distributes the plastic strain on the shear band, thereby suppressing crack initiation and allowing the material to experience a large macroscopic plastic strain before failure.

Enhanced plastic strain in Zr-based bulk amorphous alloys

We have compared the structure of shear bands with that of undeformed regions of a metallic glass. Using quantitative high-resolution electron microscopy, we observed void-like defects, approximately 1 nm in diameter and at a concentration of one in 100nm3, which are generated as a result of plastic deformation in the shear bands. These defects may result from the coalescence of excess free volume upon cessation of the flow. By comparing the free energy of the shear band containing uniformly distributed free volume with that of the relaxed shear band with voids present, we show that the coalescence is thermo-dynamically possible.

Todd C. Hufnagel

Papers

Mechanical behavior of amorphous alloys

Deformation of metallic glasses: Recent developments in theory, simulations, and experiments

Metallic glass matrix composite with precipitated ductile reinforcement

Enhanced plastic strain in Zr-based bulk amorphous alloys

Nanometre-scale defects in shear bands in a metallic glass