Planar Growth Faults in Nb3Al

Abstract

A transmission electron microscopy study of planar growth faults in the A15 intermetallic phase Nb3Al is presented. These faults are not observed in plasma melted material but a high density of these features is observed in arc-melted material which is cooled more slowly. The faults are found most frequently on planes {100}, often changing from one plane to another along their length. It has not been possible to obtain a full diffraction contrast analysis from the faults but HREM images indicate that they are intrinsic with a displacement vector R=1/4<120>. Since this vector does not lie in the plane, they cannot form by glide processes alone and therefore probably arise when vacancies coalesce into sheets on {100}. Since this value of R is consistent with the removal of an Al-rich plane {004}, it is argued that the formation of these faults may help to stabilise the A15 phase to Nb-rich compositions.

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Acknowledgements

This work has been carried out with financial support from SERC. The authors would like to thank Dr. J. Shyue, Prof. H.L. Fraser and Prof. M.H. Loretto for helpful discussions. Financial support to attend this meeting was provided by the Institute of Physics EMAG group (LSS + MA), C.R. Barber Trust Fund (LSS) and the Institute of Materials Andrew Carnegie Grant Scheme (LSS).

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Smith, L.S., Cheng, TT. & Aindow, M. Planar Growth Faults in Nb3Al. MRS Online Proceedings Library 288, 263–268 (1992). https://doi.org/10.1557/PROC-288-263

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