While amorphous phases have been reported in immiscible alloy systems, there is still some controversy regarding the reason for the stabilization of these unusual amorphous phases. In this letter, using three-dimensional atom probe tomography, direct evidence of nanoscale phase separation within the amorphous phase forming in immiscible Cu–Nb alloy thin films has been presented. This evidence clearly indicates that the nanoscale phase separation is responsible for the stabilization of the amorphous phase in such immiscible systems since it substantially reduces the free energy of the undercooled liquid (or amorphous) phase, below that of the competing supersaturated crystalline phases.

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Devitrification in a Ni 60 Nb 35 Sn 5 bulk metallic glass alloy is investigated below the glass transition temperature using cross-correlative TEM and atom probe tomography. As cast and post-anneal (500uC for 2 h) specimens were analysed in both the TEM and the atom probe to determine the extent and nature of any phase separation in the as cast material or devitrification in the annealed material. Furthermore, it was of interest to determine the accuracy of the atom probe reconstructions of both types of material. No significant compositional partitioning was observed in the as cast state, suggesting an amorphous material, and the atom probe reconstructions of these specimens were found to be consistent with the TEM data. The annealed specimens contained Nb and Nb oxide rich regions, Ni 3 Sn nanocrystals, and a significant build-up of oxygen at the boundaries between these nanocrystals and the remaining amorphous matrix regions. These oxygen enriched regions are shown to result in anomalous atom probe reconstructions that are inconsistent with the TEM analyses. It is theorised that the initial crystallisation of Nb and Nb oxide rich regions results in NiSn rich regions, thereby resulting in the formation of Ni and Ni 3 Sn crystalline precipitates.

This study focuses on investigating certain aspects of deformation in bulk metallic glasses (BMGs) based on nanoindentaion and microindentation studies. Using a Berkovich indenter in nanoindentation, the incipient plasticity or early stages of deformation have been studied for a typical BMG, Vitreloy 1. From a critical analysis of the load-displacement curves, the initial displacement burst, often associated with the initiation of shear bands, was found to occur at a value close to the theoretical shear stress of the material. The deformation behavior below these indents, including the formation of shear bands, has been investigated by transmission electron microscopy. The evidence suggests structural changes associated with possible expansion of free volume within the shear bands, especially in the case of deformation under higher loads. Furthermore, while the possibility of nanocrystallization within the shear bands cannot be ruled out, the experimental results do not conclusively indicate the occurrence of such a phenomenon.

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