Elaboration de monocristaux de zirconium α et etude de leur perfection cristalline

The methods depending on critical straining followed by α-phase annealing, or on thermal cycling across the allotropie transformation temperature, do not enable the production of large zirconium crystals of predetermined orientation. A method based on localised phase transformation in a controlled thermal gradient has been successfully developed: it permits the preparation of crystals up to 100 mm long in favourable cases. A study of the mechanism of formation of an α monocrystal from a β monocrystal has led to a recognition of the parameters which determine the growth of the desired monocrystals. An analysis of the crystal orientations obtained has established the optimal conditions for obtaining orientations close to a desired one. X-ray methods have been used to examine the perfection of the crystals: some were strongly polygonised but others had overall misorientations of less than 10^?2 degree.