http://nanomechanics.mit.edu/sites/default/files/documents/Kumar_03.pdf

Mechanical behavior of nanocrystalline metals and alloys

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

Journal of Physics Condensed Matter: Preface

Alloys with composition of AlCoCrFeNiTix (x: molar ratio; x=0,0.5,1,1.5) were designed by using the strategy of equiatomic ratio and high entropy of mixing. The alloy system is composed mainly of body centered cubic solid solution and possesses excellent room-temperature compressive mechanical properties. Particularly for AlCoCrFeNiTi0.5 alloy, the yield stress, fracture strength, and plastic strain are as high as 2.26GPa, 3.14GPa, and 23.3%, respectively, which are superior to most of the high-strength alloys such as bulk metallic glasses.

Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties

The case for bulk metallic glass

Single-phase nanocrystalline materials undergo inhomogeneous plastic deformation under loading at room temperature, which results in a very limited plastic strain (smaller than 0–3%). The materials therefore display low ductility, leading to catastrophic failure, which severely restricts their application. Here, we present a new in situ-formed nanostructured matrix/ductile dendritic phase composite microstructure for Ti-base alloys, which exhibits up to 14.5% compressive plastic strain at room temperature. The new composite microstructure was synthesized on the basis of the appropriate choice of composition, and by using well-controlled solidification conditions. Deformation occurs partially through dislocation movement in dendrites, and partially through a shear-banding mechanism in the nanostructured matrix. The dendrites act as obstacles restricting the excessive deformation by isolating the highly localized shear bands in small, discrete inter-dendritic regions, and contribute to the plasticity. We suggest that microscale ductile crystalline phases might therefore be used to toughen nanostructured materials.

Novel Ti-base nanostructure-dendrite composite with enhanced plasticity.

by optical microscopy and scanning electron microscopy. From the measured interlamellar spacings ranging from λ = 0.18 to 0.5 µm, the solidification front velocities and the cooling rates at different positions in the as-cast samples are derived. The decisive effect of the diameter of cast rods is confirmed. For a centrifugal casting technique, the maximum cooling rate decreases from 730 to 95 K/s when the diameter increases from 2 to 5 mm. Moreover, it is revealed that the local cooling rates decrease significantly from the bottom towards the top of the rods. From the estimated cooling rates at a fixed rod diameter the centrifugal casting technique is assessed as superior to other methods applied, namely copper-mould casting and suction casting. The estimated cooling rates are compared with literature data for glass-forming alloys.

https://www.jstage.jst.go.jp/article/matertrans/43/7/43_7_1670/_pdf

Cooling Rate Evaluation for Bulk Amorphous Alloys from Eutectic Microstructures in Casting Processes.

Vertical optical floating zone furnace: Principles of irradiation profile formation

Crystal growth of rare earth-transition metal borocarbides and silicides

A group of novel nanostructured composites fabricated by different casting methods is presented. Nb, Ta and Mo are added into Ti-base bulk metallic glass (BMG)-forming alloys and Nb is added to the Zr-base BMG-forming alloy to induce the formation of dendrite/ nanostructured matrix composites. These composites exhibit high fracture strength of up to 2400 MPa. Both Nb-bearing Ti- and Zr-base composites exhibit over 14% plastic strain upon room temperature compression. The Ti60Cu14Ni12Sn4Nb10 composite also exhibits over 7% room temperature tensile plastic strain. The high strength of the composites is attributed to the nanostructured matrix. The large plasticity is due to the retardation of excessive localized shear banding in the matrix by the presence of the ductile dendrites. The significant work hardening before fracture is attributed to the deformation behavior of the dendritic solid solution.

https://www.jstage.jst.go.jp/article/matertrans/44/10/44_10_1999/_pdf

Wolfgang Löser

Papers

Novel Ti-base nanostructure-dendrite composite with enhanced plasticity.

Cooling Rate Evaluation for Bulk Amorphous Alloys from Eutectic Microstructures in Casting Processes.

Vertical optical floating zone furnace: Principles of irradiation profile formation

Crystal growth of rare earth-transition metal borocarbides and silicides

Nanostructured Composites in Multicomponent Alloy Systems