Speaker
Description
Nano-multilayers (NMLs) are functional nano-architectures, which physical properties can be tailored by smart microstructural and interfacial design. Upon thermal treatment, the layered structure of NMLs of immiscible metals degrades. The driving force of the degradation is of capillary nature i.e., the system tends to decrease the energies of interfaces.
In the present work, the degradation upon thermal annealing (400 – 800 °C; duration of 100 min) of sputtered Cu/W NMLs with different nanolayer thicknesses (3, 5, 10 nm) is discussed considering residual stress. The degradation starts only when the major part of initial residual stresses (–0.5 ÷ –3.0 GPa for Cu; –3.0 ÷ –7.0 GPa for W) is released. This can be attributed to the large magnitude of interface stress f, which is defined as the work necessary to strain Cu(111)/W(110) interfaces: the calculated value is 11.25 ± 0.56 J/m2 [1]. The interface stress increases the work required to create the unit of strained Cu/W interface, hindering W/W grain boundary grooving. The magnitude of interface stress f linearly decreases to zero at the temperatures of the onset of NML degradation (700 – 800 °C). The required work is consequently less and the grooving of W/W grain boundaries can then be promoted. Kinetically, the Cu/W NML degradation process was found to be rate-limited by the mobility of W along phase and grain boundaries [2]. Thus, the interplay between the W mobility and the interface stress magnitude can rationalize the experimentally observed “shift” of the NML degradation to higher annealing temperatures.
The reported study was funded by RFBR, project number 19-33-90125.
References:
[1] A.V. Druzhinin et al. Materialia 7 (2019) 100400.
[2] F. Moszner et al. Acta Mater. 107 (2016) 345–353.
| Speaker Country | Russian Federation |
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