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- ItemRejuvenation through plastic deformation of a La-based metallic glass measured by fast-scanning calorimetry(Amsterdam : Elsevier B.V., 2020) Meylan, C.M.; Orava, J.; Greer, A.L.We explore the glassy states achievable after a metallic glass is formed on liquid quenching. Samples of La55Al25Ni20 (at.%) metallic glass (rod and ribbon) are studied. The extent of structural relaxation at room temperature is characterized for this low-glass-transition temperature glass. Plastic deformation (uniaxial compression) rejuvenates the glass to states of higher enthalpy characteristic of glass formation at high cooling rate. Deformation increases the heterogeneity of the glass, widening the spectrum of relaxation times. The extent of rejuvenation in samples of low aspect ratio is compared with that under conditions of high constraint in notched samples. The deformation-induced rejuvenation is particularly susceptible to reduction on subsequent ageing. Fast-scanning calorimetry is useful in characterizing the dynamics of structural relaxation. The shadow glass transition is more evident on fast heating, and is observed in this glass for the first time. A new excess exothermic effect is observed before the glass transition.
- ItemStabilization of the ζ-Cu10Sn3 Phase by Ni at Soldering-Relevant Temperatures(Heidelberg : Springer Verlag, 2020) Wieser, C.; Hügel, W.; Martin, S.; Freudenberger, J.; Leineweber, A.A current issue in electrical engineering is the enhancement of the quality of solder joints. This is mainly associated with the ongoing electrification of transportation as well as the miniaturization of (power) electronics. For the reliability of solder joints, intermetallic phases in the microstructure of the solder are of great importance. The formation of the intermetallic phases in the Cu-Sn solder system was investigated for different annealing temperatures between 472 K and 623 K using pure Cu as well as Cu-1at.%Ni and Cu-3at.%Ni substrate materials. These are relevant for lead frame materials in electronic components. The Cu and Cu-Ni alloys were in contact to galvanic plated Sn. This work is focused on the unexpected formation of the hexagonal ζ-(Cu,Ni)10Sn3 phase at annealing temperatures of 523–623 K, which is far below the eutectoid decomposition temperature of binary ζ-Cu10Sn3 of about 855 K. By using scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction and X-ray diffraction the presence of the ζ phase was confirmed and its structural properties were analyzed.