Distributed-activation kinetics of Heterogeneous Martensitic Nucleation
| Autor: | Morris Cohen, Gregory B. Olson, Minfa Lin |
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| Rok vydání: | 1992 |
| Předmět: | |
| Zdroj: | Metallurgical Transactions A. 23:2987-2998 |
| ISSN: | 2379-0180 0360-2133 |
| DOI: | 10.1007/bf02646117 |
| Popis: | Martensitic nucleation under normal circumstances is a heterogeneous process, and the heterogeneity can be explained by the potency distribution of defects that provide the nucleation sites, including both preexisting and autocatalytically generated defects. The potency distribu- tion of the preexisting defects has been shown earlier by small-particle studies to follow an exponential function, whereas that of the autocatalytic defects is found in the present work to obey a Gaussian function. A major distinction between these two distributions is that the number density of thepreexisting defects increases monotonically with decreasing defect potency, while the number density of theautocatalytic defects is distributed about a mode, giving a saturation level of its cumulative distribution. As a result of these potency distributions, the nucleating sites of both origins exhibit distributions in their activation energies for nucleation, and a distributed- activation kinetic model is now proposed to take these variations into account for martensitic transformations. The features of this model are tested with considerable success in experiments on an Fe-32.3Ni alloy, leading to calculations of the entire course of martensitic transformation curves (including the athermal, anisothermal, and isothermal contributions), the changing shapes of time-temperature-transformation (TTT) diagrams for a range of Fe-Ni compositions, and the grain-size dependence of “bursting” behavior. |
| Databáze: | OpenAIRE |
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