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A1-3.85% Cu single crystals were studied by means of the back-reflection divergent X-ray beam method after solution treatment, various modes of quenching and various stages of age-hardening. A complete strain analysis was developed by which the principal strains in a crystal or polycrystalline material can be determined provided the changes of d-spacings of more than six independent (hkl)reflections are recorded. The analysis applied to the various stages of age-hardening of crystals subjected to a fast quench after solution treatment disclosed an anisotropy of strain distribution in the matrix. The maximum strain corresponding to the ageing stage associated with the formation of G. P. zones coincided with one of the [100] directions and shifted about 20 ° when the 0' phase was predominant. The anisotropy of strain distribution was interpreted in terms of a preferred vacancy migration due to thermal and concentration gradients introduced by quenching.

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A method for quantitative determination of local curvature in elastically bent perfect crystals is described. The method is based on X-ray intensity measurements, and a comparison of experimentally determined values with those derived from diffraction theory gives satisfactory agreement. The method was applied to determine the strain gradient and strain concentration in the vicinity of the notch of an elastically bent crystal. The experimental results were compared with those derived from a similar model based on continuum mechanics. Possible applications of the X-ray method are discussed to obtain experimental solutions to strain analyses which, when approached by continuum mechanics, pose formidable mathematical obstacles.

The integrated X-ray reflectivity of elastically bent, but otherwise perfect, crystals are calculated for Lauetype reflections covering the entire curvature range. Anomalous transmission and elastic anisotropy are taken into account, and it is shown that both these effects affect appreciably the reflected intensities for both weakly and strongly bent crystals. The validity of the reflectivity-versus-curvature relation thus obtained is experimentally confirmed for a number of reflections from silicon crystals. The implications of the experimental results to brittle fracture are discussed.

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Lattice defects in quartz induced by fast neutron irradiation were studied by combined methods of x-ray diffraction and transmission electron microscopy. The developed defect structure is characterized by clusters of interstitials enriched in ruptured silicon atoms. The size and density of the defect clusters increase with increasing dose until mutual interaction occurs, resulting in the formation of a stable, hexagonal-like structure resistant to prolonged annealing at 500°C. In thin crystals the size and volume fraction of the defect clusters are dependent on crystal orientation, being related to the open screw channels of the quartz structure. A relationship was established between the total volume fraction of defect clusters and fractional decrease in density induced by neutron irradiation, accounting satisfactorily for the hydrostatic density measurements reported in the literature.

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