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Grain boundary grooving under the influence of evaporation (or corrosion)

1979; Elsevier BV; Volume: 79; Issue: 1 Linguagem: Inglês

10.1016/0039-6028(79)90032-3

1879-2758

Vu Thien Binh, Y. Moulin, R. Uzan, M. Drechsler,

Nanofluid Flow and Heat Transfer

Known grain boundary grooving theories have considered three mechanisms—surface diffusion, volume diffusion and evaporation-condensation—acting either alone (Mullins, Robertson) or in concomitance (Mullins, Srinivasan and Trivedi). We present here a grooving theory in which a loss of matter (free evaporation or corrosion) is considered simultaneously with surface diffusion. A dimensionless parameter S is introduced which represents the relative weight of surface diffusion and free evaporation. Surface profile evolutions are calculated as a function of S. As the consequences of the effect of free evaporation: (1) The groove evolution is not any more a steady-state profile evolution. The grooving speed is reduced and the ratio between the ridge height and the groove depth is increased. (2) The groove profile leads to an apparent limiting groove profile whose geometry is a function of S. (3) The time needed for the formation of this apparent limiting groove profile is a function of the diffusion coefficient, the free evaporation rate and the equilibrium groove angle. (4) Thereafter the groove evolution is pseudostationary. Calculations are made for initial plane surface and initial cylindric surface. The former theories (Mullins, Robertson) must be replaced by the described theory in particular if the free evaporation rate (or corrosion), which depends on temperature and substance, is not negligible. The results of the theory are compared with known experimental data, mainly those of Allen. Characteristics of the experimental results can be easily explained by the described theory which should then replace former interpretations for the observed deviations from the steady-state evolution theories. The presented theory opens the possibility to measure the surface diffusion coefficient in regions where evaporation or corrosion occurs and enables one to measure the distribution of parameters of evaporation and corrosion along a great surface area.