X-Ray Scattering from Highly Distorted Lattices Undergoing Phase Separation

Abstract

Calculations by Krivogtaz {xc[1]} dealing with quasiline formation in highly distorted lattices undergoing phase separation have been extended for randomly arranged particles. Qualitative experimental evidence from powder patterns, already in the literature for Cu-Be,Ni-Be,Cu-Ti and Nimonic alloys[2-5], have demonstrated the existence of quasilines. This extended calculation deals with ellipsoids of revolution and allows one to examine different shapes and transformation strains in an anisotropic medium. it is shown that the precipitate transformation strains play a very important role in shaping the Bragg-like profiles. This is most obvious in the intermediate stage which includes Bragg scattering from the lattice, regular static diffuse scattering and the quasiline. For precipitate sizes associated with maximum age hardening, all three normally become scrambled into a broad assymetrically shaped Bragg-like peak. However, a comparison of the theoretical calculations with experimental data from an age hardened Cu-Be alloy shows qualitative agreement, which we believe is due to the non-random nature of precipitation in this system.

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Acknowledgement

The authors would like to acknowledge the National Science Foundation, for funding this research, under Grant No.DMR-8818013. We also express thanks to Dr.B.C.Larson of the Oak Ridge National Laboratory for his stimulating discussions and to Mr.H.Dudley for collecting the data.

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Correspondence to Satish I. Rao.

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Rao, S.I., Wu, C.H. & Houska, C.R. X-Ray Scattering from Highly Distorted Lattices Undergoing Phase Separation. MRS Online Proceedings Library 209, 77–82 (1990). https://doi.org/10.1557/PROC-209-77

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