Deformation induced microstructural instability in the PbSn eutectic

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The influence of deformation on the microstructural stability of a directionally solidified PbSn lamellar eutectic was studied. Direct observations of coarsening and microstructural changes of as-grown and deformed specimens, annealed at 93% of the absolute eutectic temperature, were made and the results quantitatively compared with values predicted by a two-dimensional fault migration coarsening model. The structural faults responsible for coarsening include as-grown faults as well as terminations resulting from recovery processes as proposed by Nakagawa and Weatherly. The number of such terminations increases generally with increasing prior deformation. For specimens with prior deformation less than 50% reduction-in-area by rolling, good agreement between the experimental and predicted coarsening rates was observed. The coarsening of heavily deformed specimens (60% and 70% R.A. by rolling) is not described by the simple model utilized in this work because the actual microstructure is not emulated by the modeled one. However, the basic concepts describing the initial rate of coarsening in heavily deformed materials are probably similar to those in lightly deformed ones. The fault migration velocity obtained from coarsening data in this study compares well with theoretical and previously observed values of this velocity. © 1977.

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Acta Metallurgica