F. Baier

Heterogeneity of a Cu47.5Zr47.5Al5 bulk metallic glass

Microstructural investigation of an as-cast Cu47.5Zr47.5Al5 bulk metallic glass (BMG) reveals two amorphous phases formed by liquid phase separation. The morphology of the phase separated amorphous regions is spherical with 10–20nm in size. These areas are homogeneously distributed throughout the sample. Moreover, a macroscopic heterogeneity also occurs along with the nano-scale liquid phase separation. The macroscopic heterogeneity can be distinguished from the different degree of the chemical fluctuations in the sample, and the existence of nano-scale crystals of less than 5nm in size. Presumably, both the macroscopic heterogeneity and the nano-scale phase separation enhance branching of the shear bands during deformation in the Cu47.5Zr47.5Al5 BMG.

High-strength Ti-base ultrafine eutectic with enhanced ductility

(Ti0.705Fe0.295)100−xSnx (x=0 and 3.85) ultrafine eutectics were prepared by slow cooling from the melt through cold crucible casting. The addition of 3.85 at. % Sn to the binary Ti–Fe eutectic decreases the strength slightly but considerably improves the plastic deformability under uniaxial compressive loading from ef=2.1% to 9.6% strain to failure. The change in the morphology of the eutectic and the distribution of the FeTi phase are suggested as origin of the improvement of the mechanical properties.

Propagation of shear bands in Ti66.1Cu8Ni4.8Sn7.2Nb13.9 nanostructure-dendrite composite during deformation

During deformation of Ti66.1Cu8Ni4.8Sn7.2Nb13.9 nanostructure-dendrite composite, primary and secondary shear bands form under perpendicular orientation. Detailed investigation of the microstructure of deformed specimens reveals deformed body-centered-cubic (bcc) β-Ti dendrites forming a stepped morphology at the interfaces between the bcc β-Ti dendrites and the nanostructured matrix, consisting of hexagonal close packed (hcp) α-Ti and body-centered-tetragonal (bct) Ti2Cu phases. In the nanostructured matrix, the primary shear bands pass through coherent grain boundaries between the hcp α-Ti and the bct Ti2Cu phases. In contrast, the secondary shear bands in the nanostructured matrix are arrested by sandwiched nanoscale grains of the hcp α-Ti and bct Ti2Cu phases.

Lattice distortion∕disordering and local amorphization in the dendrites of a Ti66.1Cu8Ni4.8Sn7.2Nb13.9 nanostructure–dendrite composite during intersection of shear bands

The dendrites in the Ti66.1Cu8Ni4.8Sn7.2Nb13.9 nanostructure–dendrite composite deformed up to 25% reveal an interaction of primary and secondary shear bands. A detailed analysis of the lattice images of the interaction regions in the dendrites using high resolution transmission electron microscopy indicates local amorphization and lattice distortion∕disordering near to the apex of the primary shear bands in the dendrite. Furthermore, moire fringes are formed at the edge of the interaction regions between the primary and secondary shear bands suggesting gradual structural changes in the dendrites.

Toughening mechanisms of a Ti-based nanostructured composite containing ductile dendrites

The compressive deformation behavior of a multi-component Ti-Cu-Ni-Sn-Nb composite containing ductile dendritic precipitates embedded in a nanostructured matrix was investigated. The Ti-based composite not only displays a high compressive plasticity of approximate to 21 %, but also exhibits a high fracture strength of approximate to 1.8 GPa, which is comparable to that of monolithic bulk metallic glasses. Pronounced work hardening was observed after yielding. The surface deformation morphology reveals that the work-hardening behavior of the composite is related to the plastic deformation of the dendritic phase and the interaction of shear bands in the nanostructured matrix with the hardened dendrites. At the final stage of compression, most of the dendrites are work hardened, whereby the propagation of the shear bands in the matrix is retarded. The strong interaction between the dendrites and the matrix contributes to the high strength and plastic deformation capability of the composite. The fracture surface exhibits viscous flow traces, indicating that softening or melting of the composite occurs at the moment of fracture, due to the release of the high elastic energy stored in the specimen.