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.

( Ti 0.705 Fe 0.295 ) 100 − x Sn x (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 εf=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.

Microstructural investigation of a deformed Ti 66.1 Cu 8 Ni 4.8 Sn 7.2 Nb 13.9 nanostructure-dendrite composite using transmission electron microscopy (TEM) reveals heterogeneous propagation and interaction of the shear bands, depending on the geometry of the interfaces between the nanostructured matrix and dendrites. The geometrical effect on the propagation and interaction of the shear bands is presented by the different morphology of the interfaces i.e. stepped and smooth interfaces suggesting a different amount of accumulated shear strains at the interfaces between the nanostructured matrix and the dendrites.

Alloys. -An ultra-fine eutectic structure is prepared in the Ti 70.5 Fe 29.5 binary alloy by slow cooling from the melt through arc melting and cold crucible rod casting. High strength-ductile bulk specimens with ultrafine eutectic microstructure are obtained after addition of the rather cheap element Sn to the binary Ti70.5Fe29.5 alloy. The ternary alloy exhibits a significant improvement of the plastic deformability. The ingot of Ti67.79Fe28.36Sn3.85 alloy solidified at a low cooling rate shows the high processability of this ductile alloy in bulk scale without any micrometer-size second phase dispersions. -(DAS*, J.; KIM, K. B.; BAIER, F.; LOESER, W.; GEBERT, A.; ECKERT, J.; J.

In this paper, details are given for the structural evolution of (Ti amorphous alloys, part of wider program of alloy development by equiatomic substitution. All three alloys initially crystallize by forming a nanoscale icosahedral phase. However, at higher temperatures, their decomposition sequences differ significantly. The nanoscale icosahedral phase in the (Ti 33 Zr 33 Hf 33 ) 70 (Ni 50 Cu 50 ) 20 Al 10 alloy decomposes into a mixture of Zr 2 Cu-type and icosahedral phases. This icosahedral phase still exists after heating up to 970 K, indicating a high thermal stability of this phase. The nanoscale icosahedral phase in the (Ti 33 Zr 33 Hf 33 ) 70 (Ni 33 Cu 33 Ag 33 ) 20 Al 10 alloy also transforms into a mixture of Zr 2 Cu-type and icosahedral phase during the second exothermic reaction but then transforms into a mixture of Zr 2 Cu-type and Ti 2 Ni-type phases. The nanoscale icosahedral phase in the (Ti 25 Zr 25 Hf 25 Nb 25 ) 70 (Ni 50 Cu 50 ) 20 Al 10 alloy decomposes into a mixture of Ti 2 Ni-type and MgZn 2 -type phases during the second exothermic reaction. It is concluded that the formation of the Zr 2 Cu-type phase retards the decomposition of the nanoscale icosahedral phase, which increases the thermal stability. In contrast, formation of Ti 2 Ni-type and MgZn 2 -type phases accelerates the decomposition of the nanoscale icosahedral phase, which decreases its thermal stability.