Synchrotron X-ray diffractometry and imaging of strains and defects in icosahedral quasicrystal grains

Abstract

In order to better understand the long-range propagation of quasicrystalline order, as well as quasicrystal stability, it is important to know if defects are generated in the quasicrystal grains during their growth. Previously, we studied the degree of perfection of about ten icosahedral quasicrystal grains of various alloys (Al–Pd–Mn, Al–Cu–Fe, Zn–Mg–Y), as grown or annealed, and we disclosed that some of them were much more perfect than the others. In this work we have concentrated on another slice of such a grain of the Al–Pd–Mn alloy. Similarly, we have performed an extensive synchrotron X-ray topographic investigation of strain and defects in this grain, combined with phase-contrast radiography and high resolution X-ray diffraction examinations. Very few two-lobe contrasts associated with pores and no loop-shaped contrasts were observed on the X-ray topographs, but straight line segments and band contrasts have been identified. Line segments could be considered as the result of the climbing of polygonal dislocation loops, as observed by TEM by Caillard and coworkers. This would indicate that most strains and defects observed in quasicrystal grains, at room temperature, are the result of stresses (external and internal) acting after growth.

Acknowledgments

The authors are very grateful to S. W. Kycia for having kindly provided them with this new “highly perfect” grain, to M. Kleman and V. Dmitrienko for helpful discussions and to the technical staffs of the ESRF and ELETTRA for their assistance.