ISSN:
1432-2021
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
Abstract Creep tests were performed on cylindrical cold-pressed polycrystalline specimens of pure NH4NO3 and KNO3 while the specimens were simultaneously cycled through the known phase transformations. The observed deformation behaviour and the transformation strains were both qualitatively and quantitatively consistent with the Greenwood and Johnson (1965) theory of transformational plasticity, which applies to external stresses less than the yield stress of the weaker phase. A new and simpler development of this theory is given in the Appendix. The transformation strains observed in composite specimens, in which only one component transformed, were all significantly less than those observed in the pure materials. This behaviour is observed even in specimens where the volume fraction of the marginally-stronger non-transforming phase is too small to form a continuous framework in the specimen. It is suggested that the stress associated with the difference in thermal expansion of the two components, especially during a phase transformation, leads to the nucleation of a high density of tangled, essentially immobile, dislocations in the transforming component, similar to work-hardening. The relevance of these observations to the possibility of transformation plasticity as an important deformation mechanism in the Earth is discussed.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00202030
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