Decomposition studies of a liquisol quenched Al-33 at.% Mg alloy

X-ray and electron metallographic studies were undertaken on an aluminum-33 at.% magnesium alloy rapidly quenched from the melt by the “gun” technique. A small supersaturation of Mg in Al and two metastable intermediate phases were detected. These phases were found to display complex decomposition behavior on annealing at temperatures up to 300°C.     

Precipitation of Cr-rich phases in rapidly solidified Ni–20Al–8Cr (at.%) powders

The evolution of the microstructure in rapidly solidified Ni–20.9Al–8Cr–0.49B (at.%) powders after different continuous and isothermal heat treatments at temperatures up to 1100 °C has been studied by electron microscopy and microanalysis. Powders in the rapidly solidified condition have a dendritic microstructure consisting of Ni₃Al dendrites and a NiAl phase in the interdendritic regions. Chromium is in solid solution in both phases. This microstructure is stable when heating at 10 K min⁻¹ up to 750 °C. When the powders are heated up to 950 °C, partial dissolution of the NiAl phase and the precipitation of very small chromium-rich particles take place.The microstructure of the powders after annealing at temperatures between 750 and 1100 °C for different times is characterised by the dissolution of the β-NiAl phase and the simultaneous precipitation of various Cr-rich phases. α-Chromium, the metastable X-phase, and dark polygonal Cr₅B₃ precipitates have been identified.The segregation of chromium and boron in the form of borides removes these elements from the intermetallic matrix, so the content of both elements should be optimised to preserve their beneficial influence on the ductility of the γ′-Ni₃Al phase.     

X-ray diffraction studies of pristine and heavily-doped polyacenic materials

An X-ray diffraction study was performed for pristine and heavily-doped polyacenic materials prepared by pyrolytic treatment of phenolformaldehyde (PF) resin. Seven kinds of pristine samples prepared under different pyrolysis temperatures were studied, as well as the moulded PF resin itself. The result of the analyses shows that the structural change of the samples in the heavily-doped regime differs in a peculiar manner from what is expected in conventional intercalated graphite. An attempt is made to interpret the obtained results in terms of the amorphous structure of the present polyacenic materials.     

High-temperature brazing of molybdenum to 12Cr18Ni10Ti steel with the CTEMET 1301 rapidly quenched nickel brazing alloy

Extensive studies are being carried out to develop a divertor (Divertor: a device in a thermonuclear reactor, intended for receiving of particle flows and radiation from the periphery of the plasma column. It is the most heavily loaded part of the reactor chamber surfaces with energy fluxes.) for tokamaks with a container for supplying liquid metal to the reception surface, with the construction of actual structures with high reliability and long service life. In this case, it is necessary to develop methods for joining dissimilar materials. In the transition section, molybdenum and steel (12Cr18Ni10Ti) pipes are joined by brazing. In this work, the method of producing a strong, heat resisting and hermetic joint between molybdenum and 12Cr18Ni10Ti corrosion-resisting steel is developed. Brazing is carried out using a paste based on CTEMET-1301 brazing alloy. The method of assembling the components in order to produce optimum gaps in brazing resulting in the homogeneous brazed joint without the formation of a brittle eutectic interlayer is developed. The brazed specimens were tested for heat resistance, leak tightness and service life at the given load. All the specimens withstood the tests. The mechanical properties of the brazed joints were determined by measuring the microhardness of the region of the welded joint and by shear tests. The results show that the strength characteristics depend strongly on the size of the gap between the brazed components. For the specimens assembled with the optimum gap the ultimatum shear strength was 500 ± 50 MPa.     

Magnetic state and magnetocaloric properties of rapidly quenched Gd75 M 25 alloys (M = Co, Ni)

Effect of rapid quenching on the magnetic state and magnetocaloric properties of the Gd₃Co and Gd₃Ni intermetallic compounds has been studied. The rapidly quenched Gd₇₅Co₂₅ and Gd₇₅Ni₂₅ alloys were found to exhibit a ferromagnetic behavior below the Curie temperature T _C = 172 and 117 K, respectively, whereas their crystalline counterparts Gd₃Co and Gd₃Ni are characterized by an antiferromagnetic order and Néel temperatures T _N = 130 and 99 K, respectively. Data have been obtained which indicate that the amorphization of Gd₃Co leads to the appearance of a magnetic moment at cobalt atoms. The rapid quenching is shown to lead to a significant increase in the low-field magnetocaloric effect.     

In situ ESTM and ESTS studies of the nanostructure and energetic properties of Fe-20% Cr-40% Ni and Fe-20% Cr-70% Ni alloy surfaces

Fe-20% Cr-40% Ni and Fe-20% Cr-70% Ni alloys are studied in air and in 0.01 N HCl and 0.1 N H₂SO₄ solutions at the controlled potentials of the specimen and needle using in situ techniques of electrochemical scanning tunneling microscopy (ESTM) and electrochemical scanning tunneling spectroscopy (ESTS). The changes in the potential of Fe-20% Cr-40% Ni alloy specimen fall in ranges of −0.3 to 1.1 V and 0–0.3 V (N.H.E.) in 0.01 N HCl and 0.1 N H₂SO₄, respectively, and the changes in the potential of Fe-20% Cr-70% Ni specimen, in ranges of 0.09–0.94 V and −0.1 to 0.5 V in 0.01 N HCl and 0.1 N H₂SO₄, respectively. Local spectral dependences of the tunnel current on the tunnel voltage are obtained and processed and the coefficients that characterize the local electrophysical properties of the surfaces are calculated on their basis. It is found that, in the studied acid solutions at the controlled potential, the surfaces are more energetically homogeneous than in air, where a substantially larger dispersion of the properties is observed. It is concluded that the energetic characteristics of separate surface sites of these alloys are determined on the atomic scale by the mutual effects of the neighboring atoms involved in its composition, i.e., by the matrix effect, which was discovered previously in the case of Kh18N10T stainless steel [1].     

Detailed of X-ray diffraction and photoluminescence studies of Ce doped ZnO nanocrystals

Pristine and Ce doped ZnO nanopowders were synthesized by simple refluxing technique. A detailed X-ray diffraction analysis was carried out to evaluate the contribution of dopant ion concentration on strain and lattice parameters. A particle size of 20 nm was obtained via TEM studies. Spherical morphology was obtained for Ce doped ZnO nanocrystals. Multiple emission bands were observed for pristine and doped ZnO samples where, 401 nm emission band corresponds to a contribution due to free excitons recombination through an exciton-exciton collisions. With the Ce addition, the surface defects increases and the emission intensity decreases.     

Dielectric,Raman, calorimetric and X-ray diffraction studies of a polycarbazolyldiacetylene

We report the temperature dependence of the dielectric properties of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) from 30 to 400 K. The data obtained from these measurements are confirmed, in selected temperature ranges, by FT-Raman spectroscopy, differential scanning calorimetry and X-ray diffraction. The transition from the blue to the red form in polyDCHD-S is detected in correspondence to the monomer melting point (about 340 K). Other transitions, above and below this feature, are reported and discussed.     

Computed depth profile method of X-ray diffraction and its application to Ni/Pd films

This paper develops a method that uses parallel beam X-ray diffraction (XRD) for profiling structure and phase distributions along with the depth. This method was used to characterize the Ni/Pd thin film sample and to obtain the phase depth profile. In the data analysis procession, the non-negative least square (NNLS) algorithm was introduced to resolve the ill-posed inverse problem that emerged in the solving procession. The grains with same crystallographic orientation were measured when the incident angles varied in the designed diffraction manner and the influence of the texture in the films was avoided properly. It should be noticed that this method is employed for the first time to analyze a system containing more than two phases.     

The microstructure and properties of rapidly quenched Ti-rich Ti-Ni binary alloys with shape memory effects

The structure, phase composition, and martensitic transformations in binary titanium-rich Ti-Ni alloys with shape memory effects, produced by ultrarapid quenching using melt jet spinning, have been studied using electron microscopy, X-ray diffraction, and measurements of some physicomechanical properties in a wide temperature range. The alloys with a Ti content that exceeded the stoichiometric composition by 5% and more can be produced in an amorphous state. The alloys with a smaller deviation from the stoichiometry, as well as the Ti₅₀Ni₅₀ alloy, are crystallized in a submicrocrystalline state and undergo a B2 → B19’ martensitic transformation at temperatures above room temperature. They have high strength and plastic properties and demonstrate narrow-hysteresis shape-memory effects.     

The oxidation properties of U-16.6 at.% Nb-5.6 at.% Zr and U-21 at.% Nb

The fundamental oxidation characteristics of two U-base alloys, U-16.6 at.% Nb-5.6 at.% Zr and U-21at.% Nb, in the temperature range 500–1000° C in oxygen at 0.05 Torr are described. Both alloys undergo large dimensional changes during oxidation at temperatures above 650° C due to stresses generated in the oxide during oxidation. Oxidation rate curves for both alloys were determined at 100° C intervals between 500 and 1000° C; the activation energy for the process is shown to be small. The morphology of the oxide scale formed on the two alloys is complex and is described in detail. Stresses estimated at 10⁶ psi are shown to develop in oxidizing specimens, and a mechanism for the generation of these stresses is proposed.Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation.     

Selective dry oxidation of the ordered Pt-11.1 at.% V alloy surface evidenced by in situ temperature-controlled X-ray diffraction

A temperature-controlled X-ray diffraction study of the cold-rolled Pt-11.1 at.% V alloy was undertaken to gain better insight into the incomplete transformation of the metastable cubic disordered phase into the tetragonal ordered Pt₈V phase, earlier reported by Nxumalo and Lang [11]. This study has revealed a complex behaviour of the alloy when is annealed in primary vacuum. Upon heating above 450 °C, an ordering of vanadium atoms in the Pt-11.1 at.% V alloy leads to the appearance of a tetragonal Pt₈V phase. Concomitantly, vanadium atoms at the surface of the ordered alloy are slowly oxidized into V₂O₃ Corundum type phase by the low oxygen partial pressure existing in primary vacuum. This segregation of vanadium oxide onto the surface depleting the subsurface region in vanadium, an almost pure Pt cubic phase grows at the V₂O₃-ordered Pt₈V alloy interface with increasing the temperature. This investigation also shows that an external selective oxidation of the cold-rolled Pt-11.1 at.% V alloy takes place when is annealed in flowing argon atmosphere.     

Solid state amorphization and nanocrystallization of a Ti−50.0 Ni(at.%) alloy

Amorphization and crystallization behavior of an equiatomic Ti−Ni alloy have been investigated by means of differential scanning calorimetry, X-ray diffraction, optical microscopy and transmission electron microscopy. Amorphous phases were induced by cold working, and their morphologies changed from domain like shape to band shape with increasing the amount of cold working. Volume fraction of amorphous phase increased from 17 to 43% with increasing working ratio from 30 to 70%. With increasing the amount of cold rolling from 30 to 70%, the crystallization temperature increased from 552 to 539 K and enthalpy changes associated with crystallization increased from 170 to 447 J/mol. The average grain size of the 40% cold rolled alloy increased from 27 to 80 nm with increasing annealing temperature from 573 to 673 K.     

Cold rolling and recrystallization textures of a Ni–5 at.% W alloy

The formation of recrystallization texture has been studied in a sintered Ni–5 at.% W alloy after heavy cold rolling (～95%) and annealing. Although the cold-rolled texture is a typical pure metal or Cu-type deformation texture on a global scale, variations in microstructure and microtexture are found in the deformed material between locally sheared regions and away those from these regions. The primary recrystallization texture consists of the cube ({1 0 0}〈0 0 1〉), a RD-rotated cube ({0 1 3}〈1 0 0〉) and twin-related orientations of these two components. The presence of both cube and the RD-rotated orientations are identified in thin bands of materials in the deformed matrix. However, predominantly cube-oriented grains nucleate and grow in regions away from the locally sheared regions. In contrast, the nucleation and growth of non-cube grains are observed in the vicinity of locally sheared regions. The formation of cube texture in Ni–5 at.% W alloy appears to occur primarily via the oriented nucleation of cube grains owing to the special properties of the cube bands.     

Transformation behavior and mechanical properties of a nanostructured Ti−50.0Ni(at.%) alloy

Transformation behavior, the shape memory effect and the superelasticity of an equiatomic 40% cold worked Ti−Ni alloy followed by annealing at various temperatures have been investigated by means of differential scanning calorimetry (DSC), transmission electron microscopy, thermal cycling tests under constant load and tensile tests. The B2-R-B19 transformation occurred in all samples, and the R-B19’ transformation occurred in a wide temperature range. The B2-R transformation start temperature kept constant with raising annealing temperature. The average grain size increased from 23 to 80 nm with raising annealing temperature from 523 to 673 K. Transformation hysteresis increased rapidly with raising annealing temperature up to 623 K, above which they almost keep constant, which was ascribed to the small grain size and large constraints of grain boundaries.     

Effect of ageing treatment on the deformation behaviour of Ti–50.9 at.% Ni

This study investigated the effect of ageing on mechanical behaviour of a Ti–50.9 at.% Ni alloy. The findings enable the construction of a deformation diagram of stress-induced martensitic transformations, depicting the regions and limitations of pseudoelasticity and the shape memory effect of this alloy. It was found that the alloy exhibits pseudoelasticity within a certain temperature and stress window. This window narrows with increasing ageing temperature between 673 and 833 K, with the sample aged at 673 K for 3.6 ks exhibiting the maximum temperature window of 40 K for pseudoelasticity. This diagram enables the design of ageing treatment for different thermomechanical behaviour of the alloy. The experimental evidence also indicates that the mechanically induced transformation sequence is different from the thermally induced transformation sequence, implying that the mechanical behaviour of the alloy cannot be predicted from the knowledge of the thermally induced transformations based on the Clausius–Clapeyron correlation between stress and temperature. This study is a sequel to a previous work published in Acta Materialia (2008;56:736). The experimental evidence and the discussions presented in this work are complex. Reading the two articles together is strongly recommended.     

Analysis of local composition gradients in the hard-phase grains of cermets using a combination of X-ray diffraction and electron microscopy

Combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) was used for investigation of local composition gradients in the hard-phases of cermets. XRD revealed distribution of lattice parameters in hard-phase grains, from which the composition gradients in the hard-phases were estimated using an appropriate microstructure model. This microstructure model was build with the aid of SEM micrographs, which were taken with back-scattered electrons (BSE) and completed by the registration of the electron back-scatter diffraction (EBSD) patterns and characteristic X-ray spectra. SEM/BSE yielded the first information about the spatial distribution of elements in individual hard-phase grains, SEM/EBSD about the morphology, the size and the size distribution of these grains. The final interpretation of the distribution of lattice parameters, which was obtained from the X-ray line profile analysis, was done with the aid of the local elemental analysis that was performed using SEM with the energy dispersive analysis of the characteristic X-ray spectra (EDX) and the known dependence of the lattice parameters on concentration.     

Local atomic structure of Pd–Ni–P bulk metallic glass examined by high-resolution electron microscopy and electron diffraction

Structural fluctuation in a Pd₄₀Ni₄₀P₂₀ bulk metallic glass is investigated by transmission electron microscopy and electron diffraction. Local atomic ordered regions with a fcc-(Pd,Ni) type structure was sharply imaged by a high-resolution electron microscopy (HREM) attached with a Cs-corrector. Interference function for the glassy state was obtained from electron-diffraction intensity profiles using energy-filter and imaging-plate techniques. We used a reverse Monte Carlo (RMC) simulation method to develop a realistic structure model. The model consists of a dense-random-packing structure, in which an fcc ordered region with Pd, Ni, and P atoms was embedded. The structure model is consistent with the diffraction and HREM results. In Voronoi polyhedral analysis of the RMC simulated structure, P-centered (Pd,Ni)-P trigonal prisms are found primarily in the matrix structure embedding the fcc-cluster. Around Pd and Ni atoms deformed-fcc type polyhedra were frequently observed. From these local structural features, nanoscale phase separation was revealed to occur during the glass formation.