Texture study of two molybdenum shaped charge liners by neutron diffraction

The textures of two different conical shaped liners, fabricated by the same forging processes from arc-cast and powder-sintered ingots, were investigated by using neutron-diffraction measurements and three-dimensional orientation-distribution-function (ODF) analysis. The major textures of both liners could be described by the (1 1 1) uv w and (1 0 0) u v w type. The two liners had essentially identical texture at the 8 cm position (measured from the base of the cone) with strong sheet-type texture components, i.e. (1 1 1) ¯1 0 1, (1 1 1) ¯1 1 0 and (1 0 0) 0 1 1. However, the dominant textures at the 3 cm positions were 1 1 1 and 1 0 0 fibre textures with the fibre axes oriented parallel to the normal direction in both liners. A strong cube texture was observed at the 3 cm position of the arc-cast liner but it was not observed for the powder-sintered liner. The arc-cast liner had a generally higher degree of texture than the powder-sintered liner.     

Relationship between deposition and recrystallization textures of copper and chromium electrodeposits

The 100, 111 and 110 textures of copper electrodeposits obtained from copper sulfate baths changed to the 100, 100 and textures, respectively, after recrystallization. The textures of chromium electrodeposits obtained from the standard Sargent bath remained unchanged after recrystallization. The results are in agreement with the prediction of the strain energy release maximization model, in which the recrystallized grains orient themselves so that their minimum elastic modulus direction can be parallel to the absolute maximum internal stress direction due to dislocations in the non-recrystallized grains.     

Investigation of energy-gap anisotropy in superconducting aluminum,cadmium, and zinc

Measurements of the low-temperature specific heat of the pure metal and dilute nonmagnetic alloys of Al, Cd, and Zn are described. The washing out of the energy gap anisotropy with increasing impurity as predicted by Anderson was observed in aluminum-magnesium alloys, and the mean-squared anisotropy parameter a ² was measured to be a ²0.010. Values deduced from measurements on Zn and Cd and their corresponding alloys with 1₀ gave a ²0.02 for Zn and a ²0.05 for Cd. Values of the gaps determined by fitting to a two-gap model are given and compared to those deduced from previous work.     

Standard Gibbs' energies of formation of BaCuO2, Y2Cu2O5 and Y2BaCuO5

The Gibbs' energies of formation of BaCuO₂, Y₂Cu₂O₅ and Y₂BaCuO₅ from component oxides have been measured using solid state galvanic cells incorporating CaF₂ as the solid electrolyte under pure oxygen at a pressure of 1.01×10⁵ Pa BaO + CuO BaCuO₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=–63.4–0.0525T(K) Y₂O₃ + 2CuO Y₂Cu₂O₂ G _f,ox ^o (± 0.3) (kJ mol^–1)=18.47–0.0219T(K) Y₂O₃ + BaO + CuO Y₂BaCuO₅ G _f,ox ^o (± 0.7) (kJ mol^–1)=–72.5–0.0793T(K) Because the superconducting compound YBa₂Cu₃O_7– coexists with any two of the phases CuO, BaCuO₂ and Y₂BaCuO₅, the data on BaCuO₂ and Y₂BaCuO₅ obtained in this study provide the basis for the evaluation of the Gibbs' energy of formation of the 1-2-3 compound at high temperatures.     

On the mechanism of feathery crystallisation of aluminium

The growth of twinned crystals of aluminium on solidification is discussed with reference to the structure of the growing tip. It is shown that one must differentiate between two types of 112 growth directions in the twin boundary. Normally, all the tips grow in the same type of 112 growth direction and this particular type may give the tip a favourable shape, possibly by producing a sharp edge. If a tip is growing in a less favourable 112 direction, the favourable type can be established by the twins changing sides. This is observed to occur regularly in the continuous casting method according to Hunter. The re-entrant edge mechanism is not supported by the present results.     

Deformation and recrystallization textures of copper single crystals and bicrystals

Recrystallization textures in rolled copper specimens have been investigated so as to elucidate the mechanisms of cube texture formation. The specimens are single crystals with the orientations corresponding to the main components of the rolled textures, such as {112}111,{110}112, etc. and bicrystals consisting of such oriented crystals. The cube texture was not observed in any single crystal specimens, but observed in only two bicrystal specimens with {112}/111{100}001 and {110}112/{100}001 orientations. The formation of cube texture seems to require the existence of a cube oriented region in the deformed state, and the favourable oriented matrix to allow the growth of such nuclei.     

Measurements of chemical potentials in superconducting tin whiskers

A superconductor / normal conductor potential probe pair was used to measure differences between the time-averaged electrochemical potentials _p of Cooper pairs and of quasiparticle excitations caused by a phase-slip center in several experimental situations. The results can only be understood by assuming that at a larger distance from the phase-slip center differs from the proposal of Skocpol, Beasley, and Tinkham by showing a swinging over or swinging below _p . We propose a modified slope of as a function of site. Possible explanations are discussed. The multiple-contact samples used also allow the study of the influence of phase-slip centers already present on the relaxation of nonequilibrium quasiparticles.     

The plastic behaviour of 〈100〉 and 〈111〉 textured polycrystalline metals during simultaneous torsion and extension

On the basis of computer-calculated yield functions, the work hardening of 100 textured Cu-0.64 at % Co-0.48 at % Si and 111 textured polycrystalline copper wires were studied by simultaneous torsion and extension and by pure extension. Representing the work hardening by resolved shear stress-resolved shear strain curves, the rate of hardening is significantly lower for torsion than for pure extension. This behaviour is explained by the operation of different slip systems activated in the two modes of deformation. In the 100 textured Cu-Co-Si wires, heterogeneous plastic deformation was observed beyond about 80% shear strain.     

Dislocations in extruded Co-49.3at% Al

Polycrystalline Co-49.3at% Al which had been extruded at 1505 K was examined using transmission electron microscopy. Diffraction contrast analysis showed that b = 100 as well as b = 111 dislocations contribute to elevated temperature deformation in CoAl. Therefore, it was concluded that sufficient slip systems exist in CoAl to allow for general plasticity in the absence of diffusional mechanisms. Since no examples of b = 110 dislocations were found, the importance of 110{1¯10} slip in CoAl at 1505 K is unclear. Dislocations of the type b = 001 were observed on both {110} and {100} planes while b = 111 dislocations were observed on {1¯10} planes.     

Multi-length scale modeling of CVD of diamond Part II A combined atomic-scale/grain-scale analysis

Chemical vapor deposition of polycrystalline diamond films is studied by combining an atomic-scale kinetic Monte Carlo model with two one three-dimensional and one two-dimensional grain-scale models. The atomic-scale model is used to determine the growth rates of 111- and 100-oriented surface facets, the surface morphology of the facets and the extent of incorporation of the crystal defects. Using the atomic-scale modeling predicted growth rates for the 111- and 100-oriented facets, grain-scale modelling is carried out to determine the evolution of grain structure, surface morphology and crystallographic texture in the polycrystalline diamond films. It is found that depending on the relative growth rates of the 111- and 100-oriented facets, which can be controlled by selecting the CVD processing conditions, one can obtain either 110-textured films with a relatively smooth faceted surface or 100-textured films with a highly pronounced deep facets. In both cases, however, the film surface is composed entirely of the 111 facets. This findings are found to be fully consistent with the available experimental results.     

Deformation of single crystals of gallium arsenide

Deformation of single crystals of gallium arsenide is reported in bend and tension up to 1000° C whilst maintaining stoichiometry in an arsenic atmosphere. Surface defects and impurity segregation are shown to be dislocation sources. The dislocation density is low enough, however, to show large yield drops which are analysed in detail. Strains of 39% are possible. The activation energy for dislocation movement is increased by heat-treatment owing to an increase in point defect population.Electron microscopy shows that the predominant slip systems are {111} 110 and the majority of dislocations have b=a/2 110, the axes lying along 110 and 112 directions. Sub-cell formation occurs with sub-boundaries lying along 110 directions.     

Photosensitive Centers in CdTe〈Ge〉, CdTe〈Sn〉, and CdTe〈Pb〉

The spectral and temperature dependences of photoconductivity in CdTePb crystals under band-gap and combined excitation were studied at photon energies in the range 0.53–1.7 eV and temperatures from 80 to 300 K. The high photosensitivity of the crystals and the observed IR and temperature quenching of photoconductivity indicate that, just as in CdTeGe and CdTeSn, the recombination processes in CdTePb are dominated by deep centers with drastically different capture cross sections for electrons and holes. Some parameters of the centers are determined. The results suggest that the likely defect species responsible for the high photosensitivity of CdTePb is an acceptor complex consisting of a Cd vacancy and a metal (Ge, Sn, Pb) ion on the Cd site: (V ^2– _CdM⁺)^–/0.     

On deformation twins and twin-related lamellae in TiAl

The crystal orientation relationships and atomic arrangements across deformation twin planes and twin-related lamellar interfaces in 1 1 0 projection directions in TiAl are examined crystallographically. Atomic arrangements across the true-twin plane and the true-twin-related lamellar interface are shown to be identical, while the atomic arrangements across the pseudo-twin plane and the pseudo-twin-related lamellar interface are quite different. Atom locations at the true-twin plane and the true-twin-related lamellar interface do not violate the atomic order in both crystals while those at the pseudo-twin plane or the pseudo-twin-related lamellar interface are shown to violate the atomic order. 1 1 0 zone diffraction pattern simulations show that the true-twins and the true-twin-related lamellae cannot be distinguished using the 1 1 0 zone diffraction patterns. Not every 1 1 0 zone diffraction pattern can be utilized to distinguish between any two different twin relationships. The true-twin and the pseudo-twin can only be distinguished using 1 0 1] zone diffraction patterns, while true-twin-related and pseudo-twin-related lamellae are distinguishable by only using 1 1 0] zone diffraction patterns.     

Size-strength effects in sapphire and silicon nitride whiskers at 20° C

Tensile tests at 20° C have been carried out on seventy-three sapphire whiskers and on seventeen silicon nitride whiskers. The sapphire whiskers were of 0001, 1¯120, 10¯10, and 10¯11 orientations, while the silicon nitride whiskers were 0001, 11¯20, and 10¯13. Tensile strengths were in the range 45 to 1500 kg/mm², and deformation was found to be purely elastic. The tensile strength data have been analysed and fitted to empirical equations describing the effect of size on strength for different orientations. These empirical equations have been used to deduce possible fracture nucleation mechanisms. It is concluded that, in the case of 0001 sapphire whiskers, fracture nucleation may be due to dislocation pile-ups or interactions, while in the other cases a Griffith flaw mechanism is probably applicable.     

Texture instability in Ni electrodeposits applied in optical disk technology

An x-ray diffraction technique was used to assess the thermal transformation of the crystallographic texture in 300 m thick Ni electrodeposits applied in optical disks technology. The initially strong 100 fiber texture was transformed during annealing to 211 fiber and the temperature range for rapid changes was between 300 and 350°C. A numerical analysis of texture data indicates that the grain boundaries with a low and high misorientation angle (<30° and >45°) had mobility advantage and their migration contributed to the growth of the 211 texture.     

A transmission-electron-microscopy study of a face-centred-cubic phase in an Al-Li-Cu-Mg-Zr alloy

Icosahedral T₂ phases can form either by solid-state precipitation or during solidification in Al-Li-Cu-Mg alloys. The T₂ phase forming during solidification can transform to an R phase at high annealing temperatures. The T₂ phase forming by solid-state precipitation coexists with the Y phase, which has a face-centred cubic (f.c.c.) structure with lattice parameter a2.0 nm and can form microtwins with the twin plane of (111). The orientation relationships between the C phase and the T₂ phase are: i¯5Y0 1 1, Y1 1 3; i¯3Y1 1 1, Y1 2 3, Y1 1 5; Y2 3 5; i2Y0 1 1, Y1 1 1, Y1 1 2, Y1 1 3, Y1 1 5.     

Electron diffraction study of superlattices and orientation variants in Ca3SrAl6SO16

Samples having the nominal composition of Ca₃SrAl₆SO₁₆ were sintered at 1380 °C and analysed by electron diffraction. The frequent appearances of forbidden and satellite reflections in this compound imply the presence of a number of basal and nonbasal superlattices so that the microstructure of this cement clinker was characterized by various superstructures including one-, two- and even three-dimensional superstructures along the 0 0 1, 1 1 0, 1 1 2, 1 1 4 or 2 2 1, 0 1 3 and 1 2 3 directions with repeat periods of two or three times of that of basic one, respectively, and intergrowth of these. Various domain structures with 90°, 120° and 48.2°, etc., orientation relationships were also detected in these superstructures and the total number of these orientation variants related to the symmetry elements lost in the process of phase transformation, can be predicted according to the conclusions of Van Tendeloo and Amerlinckx, or they are equal to the number of those unique planes in the matrix.     

Atom positions in the R-phase unit cell in TiNi shape memory alloy

A crystallographic analysis of the atom positions in the unit cell of the R-phase of the TiNi shape memory alloy has been performed. In addition to a homogeneous shape change the atoms are found to shuffle in the [111]_B2 and –211_B2 directions during the B2 to R-phase transformation. The origin of these shuffles is found to be a complex interaction between 1101–10 transverse acoustic and 111 longitudinal acoustic soft phonon modes.     

Deformation in spinel

Stoichiometric MgAl₂O₄ spinel was deformed in compression at temperatures from 1790 to 1895 C and the dislocation structures analysed by transmission electron microscopy. {1 1 1}1 1 0 slip was observed on both the primary and cross-slip systems, and there was much secondary slip as well; all six 1 1 0 Burgers vectors were present in electron micrographs. This secondary slip leads to very high work-hardening rates, approximately/70 at 1790 C, where is the shear modulus. Since it is known that deformation in nonstoichiometric (alumina-rich) spinel crystals occurs by {1 1 0}1 1 0 slip, the electrostatic and geometric aspects of 1/4 110 dislocations moving on {1 1 1} and {1 1 0} planes are considered in some detail. It is porposed that the octahedral cation vacancies present in non-stoichiometric spinel diffuse to dislocations during deformation and thus favour {1 1 0} slip.     

Dislocation structures in Zr3Al-based alloys

Transmission electron microscopy has been used to investigate dislocation structures in deformed binary and ternary Zr₃Al-based alloys. In the binary alloy deformed at temperatures between 293 and 673 K the dislocations in the Zr₃Al phase consisted of a/31 1 2-type partial dislocations bounding superlattice intrinsic stacking fault on {1 1 1} planes. The {111} a/31 1 ¯2 stacking fault energy was approximately 2mJ m^–2 at 673 K. In binary specimens deformed between 873 and 1073 K cube slip predominated. Dislocations consisted mainly of a/2 1 1 0 pairs separated by antiphase boundary. For this temperature range the {1 0 0} a/201 1 antiphase boundary energy was between 30 and 45 mJ m^–2. Alloying with niobium or titanium was found to increase the {111} a/31 1¯2 stacking fault energy and thus increase the propensity for antiphase boundary-type dissociation.