Microstructure and crystallographic texture of rolled polycrystalline Fe3Al

An imperfectly B₂ ordered Fe₃Al aggregate was cast, thermomechanically hot rolled and finally annealed at 870 K. Subsequently, the specimen was rolled at 800–830 K to a strain of 80%. The microstructure and the crystallographic texture of the rolled polycrystalline sample was investigated within the range =20–80%. The microstructure consisted of flat, elongated grains. In numerous grains straight slip lines were detected. Even after =80% recrystallization was not observed. The rolling texture of Fe₃Al considerably deviates from that of non-ordered body centered cubic (b.c.c.) alloys and pure b.c.c. metals. The {111}uvw texture fibre (7-fibre) was very pronounced, while the {hkl}110 fibre (-fibre) was very weak. The {112}110 orientation which represents the strongest texture component in non-ordered b.c.c. alloys did not occur at all. The textures are discussed in terms of the {110}111, {112}111, {112}111 and {123}111 slip systems. The contribution of crystallographic slip of the various types of potential slip systems was simulated by means of the Taylor theory.     

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.     

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.     

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.     

The mechanical behaviour of cuprous oxide

The stress-strain behaviour under compresion at constant strain rate of single crystals (051 and 122) compression axis) and polycrystalline samples of cuprous oxide have been examined at room temperature and hydrostatic pressure up to 12 kb and at atmospheric pressure and high temperature up to 600° C. At high environmental pressure, plastic flow occurs at 6 kb. At high temperatures and one atmosphere, extensive plastic deformation was observed after 500° C. The resultant slip planes were of the {110} and {100} types. Transmission electron microscopy of thin foils prepared from deformed specimens shows that the Burgers' vectors of the glide dislocations are of the 111, 110 and 100 types.     

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.     

Structural and magnetic characterization of nanocrystalline Ni-20%Fe permalloy films

Samples of nanocrystalline Ni-20%Fe permalloy, obtained by electrodeposition, were studied using an X-ray diffraction technique and magnetic force microscopy. After deposition, the alloy exhibited strong fiber texture with the major component being 1 0 0 and a lesser contribution from 1 1 1. An increase in deposition current density led to a reduction in the strength of the 1 0 0 texture. Despite the small magnitude of the magnetic interaction, images of magnetic domains were obtained using magnetic force microscopy. The images were, however, unstable and changed significantly with the scanning time. Annealing of the permalloy above 573 K caused rapid grain growth and a transformation of the 1 0 0 fiber to 1 1 1 fiber. Numerical analysis of the texture data was conducted to assess the atomic structure of grain boundaries in the as-deposited and annealed states.     

Agglomeration problems in the formation of FeSi2 from Fe-Si thin-film couples

The agglomeration process that occurs during annealing of thin Fe films (<200 nm) on Si substrates has been studied. Agglomeration occurred on uncapped films prior to silicide formation. Capping layers of SiO₂, or more appropriately Si-SiO₂, have been used to minimize agglomeration effects. Continuous thin films of -FeSi₂ have been grown on 11 1 and 100 oriented substrates. Preferred growth of (202) and (220) suicide planes on 111 Si has been obtained, while preferential growth was not observed on 100 Si.     

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.     

Cathodoluminescence of Cd4SiS6 , Cd4SiSe6 , and Si-Doped CdS, CdSe, and CdTe Crystals

CdS, CdSe, and CdTe single crystals were vapor-phase-doped with the corresponding silicon chalcogenides under nearly equilibrium conditions. Cathodoluminescence studies revealed that the Si dopant produced new luminescence centers in the crystals. The cathodoluminescence spectra of Cd₄SiS₆and Cd₄SiSe₆crystals were measured. Metastable, sphalerite CdSSi and CdSeSi films were grown under highly nonequilibrium conditions. The maximum of edge emission in their spectra was redshifted as compared to the stable materials. The CdSSi and CdSeSi crystals were shown to be photosensitive.     

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.     

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.     

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.     

The mechanism of continuous dissolution of the lamellar structure in aged Al 22 at% Zn alloy

The mechanism of continuous dissolution was studied using transmission electron microscopy, X-ray diffraction and hardness measurements. The metastable phase was identified in the first stage of dissolution nucleating at the - boundaries. Interface dislocations at the - boundaries forming a perpendicular net in the 110 directions were identified as of screw character and of Burgers vector b=1/2a 110. During dissolution a change of shape of precipitates occurs leading to their fragmentation and to a change of the direction of boundaries into 110 directions.     

Deformation behaviour of single crystals of titanium carbide

Single crystals of titanium carbide were deformed in compression over a wide range of temperature, and the operative slip systems were determined by etch-pitting and electron microscopy. Around the brittle-ductile transition temperature, the slip system undergoes a gradual change from {1 1 0} 1 ¯1 O to {1 1 1} 1 ¯1 0; this is interpreted to be the mechanism governing the brittle-ductile transition in titanium carbide.On leave from Defense Metallurgical Research Laboratories, Hyderabad 500258, India.     

Mechanical relaxation of 4 wt% Y2O3-ZrO2 tetragonal single crystals

The mechanical relaxation was examined by a resonance piezoelectric method for a 3.5 wt % Y₂O₃-ZrO₂ polycrystal and 4 wt% Y₂O₃-ZrO₂ tetragonal single crystals with orientations in the 100 and 111 directions. The relaxation was observed for the 111-oriented crystal, but not for the 100-crystal. The results indicated that the relaxation was active only for the elastic compliance, S₄₄, and inactive for (s ₁₁–s ₁₂). The amplitude of the anelastic relaxation measured for the polycrystalline and the 111-crystal body was 4.2 × 10^–12 m²N^–1 and 6.7×10^–12 m² N^–1, respectively. An observed broad relaxation peak suggested that complex processes exist even in single crystals.     

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.     

Transport Properties of TlInSe2〈Ln〉 (Ln = Eu, Sm, Yb)

The electrical conductivity and Hall coefficient of TlInSe₂Ln (Ln = Eu, Yb, Sm) were measured between 300 and 900 K. The results were used to determine the band gap, ionization energy of impurities, conductivity type, and Hall mobility of charge carriers in TlInSe₂Ln. The temperature at which the Hall coefficient changes sign is shown to increase with doping level.     

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.     

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.