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Results of a Debye-Scherrer X-ray investigation are given which show that the order-disorder transformation is a first-order or heterogeneous reaction in Cu-Au alloys with compositions near CuAu. Evidence was found for conventional tie-line segregation across a usual type of two-phase field separating the ordered and disordered fields in the Cu-Au equilibrium phase diagram. The horizontal and vertical widths of the two-phase fields are about 3 atomic pct and 20°C, respectively, at 43 and 54 atomic pct Au. No evidence for the existence of an ordered structure based on a stoichiometric composition of Cu3Au2 could be found.

The alloy Cu4Pd has a disordered face-centered-cubic structure when quenched from temperatures between 478°C and the melting point (about 1100°C). Below 478°C an ordered phase is stable. The results of a Debye-Scherrer X-ray analysis indicate that the ordered phase has a tetragonal unit cell described by the space group C24h − P 42/m with 2 Cu in 2a, 2 Cu in 2f, 4 Cu in 4j (x = 0.2, y = 0.6), 4Pd in 4j (x = 0.4, y = 0.2), and 8 Cu in 8k (x = 0.1, y = 0.3). The orientation relationship between the face-centered-cubic phase and the ordered tetragonal phase is given by: The behavior of Cu4Pd is typical of ordering alloys except that the transformation is very sluggish. The increase in hardness and the microstructural and X-ray diffraction effects are interpreted in terms of coherency strains caused by the ordering.

The precipitation process in a Cu-2.5 pct Fe alloy was studied experimentally by means of X-ray diffraction and hardness measurements and light and electron microscopic observations. It was concluded that γ-Fe and α-Fe precipitate simultaneously, γ-Fe dominating in the early stages. During later stages, the particles of γ-Fe dissolve, providing the copper lattice with iron atoms which diffuse to the more stable α-Fe particles. The α-Fe particles continue to grow until all evidence of the γ-Fe is gone.

A new method for preparing divergent beam x‐ray photographs of crystals is presented. This employs the usual Laue transmission camera and a collimated primary beam of x‐rays. Fluorescent radiation originating either in the crystal sample or at a radiator in front of the crystal is used as the source of divergent x‐rays. Some applications of the technique to determinations of orientation, lattice parameters, and crystal perfection are illustrated.

The structural aspects of the precipitation of MgFa in LiF have been studied in LiF crystals containing up to 3 wt. % MgFs. The precipitate particles appear to be rodlike, having a sawtooth morphology. The rods lie in two directions on matrix planes which are close to but not precisely {111}LIF.The lattice orientation relationship between MgF2 and LiF has been established by X-ray techniques as(111)LIF‖(100)MgF2Laue photographs of slowly cooled crystals show diffuse X-ray scattering effects which are associated with the precipitation process.Excellent matching of atoms at the interfaces between the precipitate and matrix is postulated on the basis of a hard-sphere atomic model. The results suggest that phase coherency obtains during the early stages of growth, and that growth is controlled by dislocation interfaces.Rapid quenching retains all MgF2 in solution. Upon subsequent aging a transition structure forms which is based essentially on the LiF lattice but with a cell size of 8.20 Å, roughly double that of LiF. With further aging the transition structure is replaced by the normal MgF2 tetragonal structure.

The Decker, Asp, and Harker technique and the Schultz technique for obtaining pole figure x‐ray data in the transmission and back‐reflection regions, respectively, are shown to give sufficient data for a complete pole figure, with consistent intensity contours in a 15° annulus of overlap. An improved integrating specimen holder, based on the design of Geisler, was found to perform satisfactorily for transmission and back‐reflection operation.A powder method for making all‐metal sheet specimens with randomly oriented crystals is described. The use of this type of random sample for establishing background and 1X intensity levels for a corresponding textured specimen is shown to give results which are only semiquantitative when normal filtered radiation is used.

The order-disorder phenomenon in alloys near CoPt composition was studied during the progress of the ordering reaction. The changes in hardness, electrical resistance, X-ray diffraction, and microstructure which accompany the transformation at various temperatures were found to be similar to those characteristic of conventional heterogeneous precipitation reactions. The transformation is discussed in terms of four distinct processes which can appear in the reaction.

Some of the variants of the original Berg method for making topographical images of single crystal specimens, using Bragg diffraction of X-rays, are discussed. Topographical images reveal dislocations, inclusions, remains of scratches, and other regions of crystalline imperfections. The principles, as well as the major features and limitations of each of the diffraction microscopy methods, are reviewed briefly. A reference is cited in which these X-ray methods and examples of their applications are described in detail.

Chemical etching behaviour of BeO crystals was investigated for selected etchants ranging from basic to acidic in nature. Surface-emergent defects (dislocations, enclosed platinum crystals, point-defect concentrations, surface mechanical damage, twin boundaries) give rise to recognisable etch figures that are characteristic of etchant, defect type, and orientation of emergence face. Gross etching rates (in the absence of surface-emergent defects) are strongly anisotropic for both basic and acidic etchants, reflecting the crystallographic polarity of the BeO crystal structure; intermediate etchants give nearly isotropic etching. The details of gross and figure etching are described.

In recent years, a number of experimental X-ray diffraction techniques have been developed by which a topographical display of the microscopical defects in a crystal can be obtained. This brief review of the most useful of these techniques is intended to summarize the elements of the various methods and to compare their respective features and limitations. Contrary to microradiographic methods, in which image contrast is due entirely to variations in X-ray absorption from point to point in the specimen, X-ray diffraction topography is concerned with point-topoint variations in the directions or the intensities of X-rays that have been diffracted by crystals. From these variations the defect structure of the crystal may be examined. Methods that mainly measure local variations in the direction of the diffracted beam are useful for the detection of gross misorientations such as subgrains or grains (methods of Gui nier and Tennevin, Schulz, Weissmann). Intensity mapping methods are chiefly concerned with individual defects such as dislocations, stacking faults, etc. In both groups there are experimental arrangements with both Laue-case (transmission) and Bragg-case (back reflection) geometry.

A new method is proposed for predicting the ō-phase susceptibility of high-temperature superalloys. It is based on modifications of previous methods which involve electron-vacancy correlations. A calculated critical electron-vacancy number unique to each residual matrix composition is compared to the total electron-vacancy concentration (NV) for the residual matrix. The new method has been applied to experimentally determined residual matrix compositions (i.e. the composition of a matrix after all early precipitates have formed) of nickel-and cobalt-base superalloys. The modification exhibits a greater range of applicability to various austenitic alloy compositions than do current electron-vacancy tools.

The equilibria between phases in platinum alloys containing 42, 48, and 54 atomic percent cobalt were determined at temperatures below 1000°C. This system of alloys exhibits an order‐disorder transition analogous to that for CuAu. A temperature range in which ordered and disordered phases coexist in equilibrium was determined for each alloy. These data were incorporated in the phase diagram. The Co‐Pt system is the first ordering alloy system in which it has been shown that this reaction is a true phase transformation contrary to the prevalent concepts of the phenomena.

The quality and interpretation of diffraction topographic images are strongly dependent on. the detailed laboratory techniques that are used in making them. In this paper practical instructions are given for the preparation of Berg-Barrett and Lang topographs. It is hoped that these suggestions will enable the novice in the field of X-ray topography to produce high quality images and to interpret them with a minimum of learning time. The topics treated include adjustment of the critical conditions for attaining highest resolution, choice of radiation and the specific hkl planes to be used, conditions limiting the size of the image, cause and avoidance of image distortion, choice of photographic emulsions, plate processing for best contrast and resolution, photomicrographs of the original image, and plate preservation.

X-ray, and optical and electron microscopy studies have been made of precipitation in single crystals of LiF doped with MgF2. MgF2 was found to nucleate only with difficulty, which probably accounts for the large MgF2 precipitates that were observed. However, a metastable phase was discovered which readily nucleated, and, at low concentrations (e.g. 0.045 mol % MgF2), it formed even on slow cooling. Its structure appears to be similar to that proposed by Suzuki for the NaCl/CdCl2 system. The morphology of the metastable phase was seen by electron microscopy to be intersecting {100} platelets. On holding crystals containing the metastable phase at temperatures of about 300° C, particles of MgF2 nucleated at, and grew at, the expense of the metastable phase. The observation of precipitation of the metastable phase at low Mg++ ion concentrations is notable, for precipitation has almost certainly occurred during other studies of ionic conductivity, dielectric loss, and colour centres, etc., where crystals have been held at temperatures below 250° C. Solid-solubility measurements have been made to establish the MgF2 solvus line at concentrations up to 6.5 mol % MgF2 and the metastable phase solvus line up to 0.225 mol % MgF2. Kinetic measurements indicate that the growth of the metastable phase is controlled by bulk diffusion of Mg++ ions, whereas the growth of MgF2 appears to be controlled by the motion of vacancy pairs.

Perinatal obstetricians, surgeons, ultrasonographers, pediatricians, bioethicists, and physiologists from centers active in fetal treatment (13 centers in 5 countries) gathered at Santa Ynez Valley...

The Denver X-ray Conferences are known to X-ray analysts all over the world and the August meetings are looked forward to with cosiderable entusiasm by the conference regulars. Even those who have never been fortunate enough to attend one of the meetings are able to follow the presentations by means of the excellent conference books Advances in X-ray Analysis which appear in the Spring following the meeting. The following contribution has been prepared by Professor Newkirk of the University of Denver, who has been active for a number of years on the local Denver Conference committee. Professor Newkirk gives a short history of the conferences and includes some interesting insights into the technical and doemstic arrangements.