Nucleation in solids: The induction and steady state effects

Discontinuous reactions are solid state moving boundary phase transitions characterised by a discontinuous or abrupt change in orientation and composition between the matrix phases in the reactant and product aggregate across the migrating boundary or reaction front that provides a short circuit path of diffusion. The reactions include discontinuous precipitation, discontinuous coarsening, discontinuous dissolution, and diffusion induced grain boundary migration. All these reactions may account for a substantial change in microstructure, composition, and material properties, and hence, deserve adequate scientific attention for a better understanding. The present review provides a comprehensive discussion on the current status of understanding about nucleation and growth mechanisms, genesis and driving force, product morphology and distribution, kinetic growth models, and related experimental techniques, and above all, the unresolved questions concerning these discontinuous reactions. In addition, ...

https://www.skpabi.com/documents/skp%20publications/67%29%20Internat%20Met%20Rev%20%282000%29.pdf

Discontinuous reactions in solids

Experimental data on the temperature dependence of solute segregation to grain boundaries in polycrystalline metals does not appear to be adequately explained by a single binding energy between solute atoms and grain boundary sites. The extent of segregation in a given alloy appears to decrease more slowly with increasing temperature than is consistent with a theory based on such a single binding energy. This behavior can be explained however, if a spectrum of binding energies is assumed to exist. Such a binding energy spectrum presumably results from the site-to-site variation in the solute environment at the grain boundary. The present paper considers the elastic interaction between solute atoms and tilt boundaries in order to estimate the spectrum of binding energies for such boundaries. The extent of solute segregation to these boundaries is then calculated for several sets of parameters that determine the nature of the solute and the grain boundary.

The spectrum of binding energies approach to grain boundary segregation

Copper and its alloys generally display a severe reduction in ductility between roughly 300 and 600 degrees C, a phenomenon variously called 'intermediate temperature embrittlement' or 'ductility trough behaviour'. This review of the phenomenon begins by placing it in the wider context of the high-temperature fracture of metals, showing how its occurrence can be rationalised in simple terms on the basis of what is known of intergranular creep fracture and dynamic recrystallisation. Data in the literature are reviewed to identify main causes and mechanisms for embrittlement, first for pure copper, and then for monophase and multiphase copper alloys. Coverage then turns to the 'grain boundary embrittlement' phenomenon, caused by the intergranular segregation of even minute quantities of alloying additions or impurities, which appears to worsen dramatically the intermediate temperature embrittlement of copper alloys. Finally, metal-induced embrittlement, including in particular liquid metal embrittlement, is presented as a second mechanism leading to an exacerbation of the intermediate temperature embrittlement of copper and its alloys.

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S.P. Clough

Papers

A study of sulfur embrittled oxygen free copper

Comment on “The role of special high angle grain boundaries in precipitate nucleation” by P.H. Pumphrey

Partitioning of alloying elements during discontinuous precipitation in AlZnX alloys