Wednesday, October 05, 2005

Vacancies and stress relaxation!

Zhang, Johnson and Dahmen have recently published a paper in Acta Materialia on vacancy mediated elastic stress relaxation. Zhang et al use in-situ transmission electron microscopy to study the solidification of lead, lead-cadmium, and lead-indium particles embedded in aluminum. The elastic stresses that develop due to the shape and volume changes during the solidification are relaxed by ferrying vacancies to the precipitate-matrix interface from the bulk. The experiments are done on inclusions well inside the matrix; that would mean transmission electron microscopy on samples of thickness of the order 100-200 nm. I found no explicit mention of that information in the paper, though, I understand that with microscopes that operate at higher voltages, it indeed is possible to study specimens that thick. The experiments are isothermal and hence the thermal strains are ruled out. The micrographs in Figures 2 and 4, and the (schematic in) Figure 4 are sort of neat; a paper worth taking a look at.

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