Analyses and interpretations of X-ray diffraction effects in patterns of aged alloys

Abstract

The limitations of the various X-ray diffraction methods which have been used to study the structure of aged alloys are discussed. A method which employs a stationary single crystal and characteristic radiation is described. The method is applied to the structures in aged A1-Ag and A1-Mg-Si alloys. Evidence for one-and two-dimensional diffraction is reported for both alloys. Limitation of particle dimensions is proposed as a ~eneral explanation of the diffraction effects; this is the most suitable explanation for patterns of A1-Mg-Si alloys. Reciprocal-lattice points for thick particles of the precipitate structure evolve from rods for thin platelets, and evolve earlier from planar areas in the reciprocal lattice corresponding to particles that have only one resolvable dimension. A change in structure to that of the precipitate has occurred at the earliest detectable stage. Indefinite periodicities in the matrix structure cannot account for the data for either this alloy or for a previously studied A1-Mg alloy. The interpretation based on particle size is also adequate for other alloy systems, such as A1-Cu and A1-Ag, in which the diffraction effects of the precipitate are more intimately related to those of the matrix. The existence of predominantly one-dimensional particles prior to the platelike particles in the sequence of growth is identified. This is a new concept in the theory of the precipitation process.

The determination of crystallite dimensions using synchrotron-radiation X-ray diffraction photographs

“…1. Similar arguments were brought forward by Geisler & Hill (1948) in the context of interpreting Laue photographs of precipitates of aged alloys. In the upper part of the figure the 410 reciprocal point is elongated due to the fact that the number of reflecting planes is small.…”

Modulated structures in some copper–nickel–iron alloys

“…In particular, it has been shown that the satellites in the diffraction pattern from the modulated lattice lie within the broad envelopes of reflexion which would arise from small independent particles. These considerations suggest that in the case of alloys of the age-hardening type examined by Guinier, Preston and others, and more recently by Geisler & Hill (1948), the difference in the interpretations proposed for the diffraction patterns may be more apparent than real.…”

One dimensional ordering of doping oxygen in HgBa2Cuo4+δ superconductors evidenced by X-ray diffuse scattering

“…Though it has greatly contributed to the understanding of alloys [1,2], ferroelectrics [3] and one dimensional conductors [4], it has not much been used to investigate superconducting cuprates. In the first 15 years after the discovery of high T c superconductivity mainly X-ray diffuse features in the YBCO family were observed and systematically studied [5][6][7].…”