Crystal structure and magnetic properties of the binary uranium–nickel alloy U11Ni16

The crystal structure of the U–Ni binary compound previously designated U₅Ni₇ was studied by X-ray single crystal diffraction showing that the exact formula is U₁₁Ni₁₆. Uranium and nickel atoms are distributed respectively on 5 and 6 Wyckoff positions of the trigonal space group R (n° 148), and the unit-cell dimensions in the hexagonal setting are: a=11.7786(4) Å, c=20.7485(8) Å. Magnetisation measurements indicate itinerant ferromagnetism below T_c=33 K for U₁₁Ni₁₆.     

Formation of Al–Y oxide during processing of γ-TiAl

While processing Y₂O₃ dispersed γ-TiAl, Y₂O₃ particles which dissolved during hot isostatic pressing (HIP’ing) were found to precipitate during the heat treatment in the form of a mixed Al–Y oxide. To understand the chemical reaction that occurs between Y₂O₃ and γ-TiAl during the heat treatment cycle, a powder mixture comprising of γ-TiAl and 10 wt.% Y₂O₃ was mechanically alloyed (MA’d) for 8 h and the milled powder was subjected to differential thermal analysis (DTA) at 1150 °C prior to analyzing it using X-ray diffraction technique. The present study clearly demonstrates that aluminum in the combined form either as γ-TiAl or Al₂O₃ reacts in a similar manner with Y₂O₃ when milled and heat treated at 1150 °C. In either case there is formation of Al₂Y₄O₉ (2Y₂O₃.Al₂O₃).     

Structure and phase transformations in Fe–Ni–Mn alloys nanostructured by mechanical alloying

Ternary Fe₈₆Ni_xMn_14−x alloys, where x = 0, 2, 4, 6, 8, 10, 12, 14, 16 at.%, were prepared by the mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill. X-ray diffraction analysis and Mössbauer spectroscopy were used to investigate the structure and phase composition of samples. Thermo-magnetic measurements were used to study the phase transformation temperatures. The MA results in the formation of bcc α-Fe and fcc γ-Fe based solid solutions, the hcp phase was not observed after MA. As-milled alloys were annealed with further cooling to ambient or liquid nitrogen temperatures. A significant decrease in martensitic points for the MA alloys was observed that was attributed to the nanocrystalline structure formation.     

Experimental determination of phase equilibria in the Fe–Nb–V ternary system

The phase equilibria in the Fe–Nb–V ternary system were investigated by means of optical microscopy, electron probe microanalysis and X-ray diffraction. Four isothermal sections in the Fe–Nb–V ternary system at 1000 °C, 1100 °C, 1200 °C and 1300 °C were firstly experimentally established. Present experimental results indicate that: (1) there is a large (Nb, V) continuous bcc solid solution; (2) there are the larger solubilities of V in the FeNb and Fe₂Nb phases. The newly determined phase equilibria in this system will provide important support for the development of hydrogen storage materials and microalloyed steels.     

Interdiffusion in β-Ti–Zr binary alloys

The aim of this study is the determination of the interdiffusion characteristics in the β-solid solution of Ti–Zr alloys (from 830 to 1730 °C). The interdiffusion coefficients in this binary system are calculated by the den Broeder method. The interdiffusion coefficients are weakly dependent on the composition: their values lie between approximately 10⁻⁹ and 10⁻⁷ cm²/s. The Hall method is used to determine the diffusion coefficients at the Ti-rich and Zr-rich sides. These coefficients are compared with the impurity diffusion coefficients in the pure metals from the literature, and with coefficients calculated by the Vignes and Birchenhall relation. Whereas the impurity diffusion coefficients in Ti and Zr show the anomalous diffusion already observed in many body-centered-cubic metals and alloys, this behaviour is not observed for the interdiffusion in the Ti–Zr alloys. These results are compared with the results obtained in the binary systems Ti–Hf and Zr–Hf.     

Structural transformations in quenched Fe–Ga alloys

It has been speculated that the large increase in magnetostriction in Fe–Ga alloys results from local short-range ordering of the Ga atoms along specific crystallographic directions in the disordered Fe structure. The structural transitions associated with different cooling rates from the high temperature disordered state were investigated with X-ray diffraction of oriented single crystals of Fe–19 at% Ga. Results are presented for long-range ordering during slow cooling and indirect evidence of local short-range ordering of Ga atoms in the disordered state when the alloys are quenched is also presented. In the latter case, the short-range ordering of Ga atoms leads to a tetragonal distortion of the lattice. The dependence of the magnetostrictive response of Fe–Ga alloys on thermal history has been found to be directly related to these structural transformations in Fe–19 at% Ga alloys and experimental support for the proposed magnetostriction model based on Ga–Ga pairing along [100] crystallographic directions is presented.     

Preparation of W–Al–Mo ternary alloys by mechanical alloying

Single phase W_XAl₅₀Mo_50−X (X = 40, 30, 20 and 10) powders have been synthesized directly by mechanical alloying (MA). The structural evolutions during MA and subsequent as-milled powders by annealing at 1400 °C have been analyzed using X-ray diffraction (XRD). Different from the Mo₅₀Al₅₀ alloy, W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys were stable at 1400 °C under vacuum. The results of high-pressure sintering indicated that the microhardnesses of two compositions, namely W₄₀Al₅₀Mo₁₀ and W₃₀Al₅₀Mo₂₀ alloys have higher values compared with W₅₀Al₅₀ alloy.     

A new type of FCT martensite phase in single-crystalline Fe3Pt Invar alloy

Martensitic transformation in a highly ordered Fe₃Pt has been investigated by magnetization and X-ray diffraction measurements. We confirmed that a new type of face-centered tetragonal (FCT) martensite phase appears below 60 K in Fe₃Pt with a degree of order S = 0.88. The tetragonality c/a gradually increases with decreasing temperature, and is approximately 1.005 at 10 K. This is in contrast to the tetragonality c/a < 1 generally observed in the FCT martensite with a degree of order less than 0.8. The spontaneous magnetization increases in association with the transformation.     

Preparation of Ti–Al–Si alloys by reactive sintering

The isothermal section of the Dy–Co–Ti system at 500 °C has been investigated in the whole composition range by means of X-ray diffraction, thermal analysis, scanning electron microscopy and energy dispersive X-ray spectroscopy. The only ternary phase DyTi_xCo_12−x is of ThMn₁₂-type structure, space group I4/mmm, and shows a small homogeneity range of 1 ≤ x ≤ 1.6. The lattice parameters for DyTi_xCo_12−x with 1 ≤ x ≤ 1.56 are a = 0.8336(4)–0.8402(1) nm and c = 0.4691(3)–0.4727(1) nm. Along a constant Dy concentration, the solid solubilities of Ti in the compounds Dy₂Co₁₇, DyCo₃, DyCo₂ and Dy₃Co are about 2.0, 2.0, 3.0 and 4.0 at.%, respectively. The TiCo phase has a homogeneity range of 50–54 at.% Co at 500 °C and dissolves up to 2.0 at.% Dy.     

Thermal stability and primary phase of Al–Ni(Cu)–La amorphous alloys

Thermal stability and primary phase of Al_85+xNi_9−xLa₆ (x = 0–6) and Al₈₅Ni_9−xCu_xLa₆ (x = 0–9) amorphous alloys were investigated by X-ray diffraction and differential scanning calorimeter. It is revealed that replacing Ni in the Al₈₅Ni₉La₆ alloy by Cu decreases the thermal stability and makes the primary phase change from intermetallic compounds to single fcc-Al as the Cu content reaches and exceeds 4 at.%. When the Ni and La contents are fixed, replacing Al by Cu increases the thermal stability but also promotes the precipitation of single fcc-Al as the primary phase.     

Annealing temperature dependance of magnetic properties and magneto-impedance effect in CoZrB alloys

The influence of conventional annealing on the magnetic properties and the magneto-impedance (MI) effect of Co₇₂Zr₈B₂₀ alloys has been intensively studied in this paper. The as-quenched Co₇₂Zr₈B₂₀ ribbon is identified to be amorphous alloy. After Co₇₂Zr₈B₂₀ being annealed at 495 °C for 10 min, there is almost no change in the XRD pattern. When the annealing temperature (T_a) reaches 540 °C, a diffraction peak representing some crystalline phase appears. After the sample being annealed at 630 °C, Co, Zr and B₁₂Zr crystalline phase are formed in the alloy. Magnetic measurements reveal that the as-quenched Co₇₂Zr₈B₂₀ possesses smaller coercivity, higher permeability and larger saturation magnetization. With the increasing annealing temperature, the soft magnetic properties of the sample greatly deteriorate. The study on the MI ratio (ΔZ/Z(%)) versus external magnetic field curves indicates that the MI behavior changes from single-peak to double-peak shape when T_a increases from 495 to 540 °C. The most drastic MI ratio about 90% is obtained in the as-quenched Co₇₂Zr₈B₂₀ at 1110 kHz. The mechanism of thermal treatment affecting the magnetic properties and the MI effect in Co₇₂Zr₈B₂₀ alloys will be discussed in this paper.     

Influence of fluxing in the preparation of bulk Fe-based glassy alloys

Fe-based master ingots, with composition [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄, have been prepared by arc-melting and subsequently purified using the fluxing technique. Rods, with diameters from 1 to 2.5 mm, ribbons and wires with a maximal diameter of 200 μm have been produced from these purified master ingots. The amorphous structure, thermal stability, hardness and magnetic properties of the specimens were studied. In particular, we show by high-energy synchrotron X-ray diffraction that the rods are fully amorphous up to a maximal diameter of 2 mm. Moreover, the [(Fe₅₀Co₅₀)₇₅B₂₀Si₅]₉₆Nb₄ glassy alloy exhibits high hardness (HV = 1050) combined with good soft-magnetic properties (H_c = 63 A/m).     

Recent studies of uranium and plutonium chemistry in alkaline radioactive waste solutions

Solubility studies of uranium and plutonium in a caustic, radioactive Savannah River Site tank waste solution revealed the existence of uranium supersaturation in the as-received sample. Comparison of the results to predictions generated from previously published models for solubility in these waste types revealed that the U model poorly predicts solubility while Pu model predictions are quite consistent with experimental observations. Separate studies using simulated Savannah River Site evaporator feed solution revealed that the known formation of sodium aluminosilicate solids in waste evaporators can promote rapid precipitation of uranium from supersaturated solutions.     

Structures and superparamagnetic properties of overaged Fe–Al–Mn–C alloys

Microstructures and superparamagnetic properties in aged-hardened Fe–9%Al–30%Mn– (x)C,Si alloys, resulting from overaging at a temperature of 823 K for 48 h to 313 days, have been investigated by transmission electron microscopy (TEM), X-ray diffraction patterns, and vibrating sample magnetometry (VSM). The results reveal that the precipitate κ-phase [(Fe,Mn)₃AlC] decomposition in this alloy, overaged at 823 K for one week, resulted from two separate mechanisms: (1) wetting of the antiphase boundary segment (APBs) of D0₃ [(Fe/Mn)₃Al] domains by the B2 [(Fe/Mn)Al] phase; and (2) precipitation of the B2 [(Fe/Mn)Al] phase within the domain. A superparamagnetic behaviour was discovered when the alloy was overaged at 823 K for ≈120–313 days. The super-soft magnetic property was mainly attributable to the ferromagnetic spinel-ordered (B2 [(Fe/Mn)Al]+D0₃ [(Fe/Mn)₃Al]) phases and ordered B2 with monoclinic ′Mn structures.     

Deformation and texture of copper–manganese alloys

Manganese is the only element that can be dissolved in copper up to 12% without markedly changing the stacking fault energy (SFE). Hence, investigation of the deformation behaviour of Cu–Mn alloys may yield insight into the influence of alloying elements apart from the (usual) decrease in SFE. The development of the crystallographic texture is analysed in various Cu–Mn alloys that were deformed either in compression or by cold rolling. The texture development is simulated by means of a novel materials-dependent Taylor-deformation model. The spatial arrangement of the rolling texture orientations in the as-deformed microstructure is studied by an orientation-sensitive etching technique. Despite the constant SFE, with increasing Mn content the rolling textures change from the pure metal (copper) type towards the alloys (brass) type. This effect is attributed to the altered deformation behaviour as well as the increased tendency to form shear bands due to the large increase in strength of the Cu–Mn alloys.     

Crystallization processes and phase evolution in amorphous Fe–Pt–Nb–B alloys

Fe–Pt system is nowadays widely studied due to its potential applications as magnetic recording media. The hard magnetic FePt L1₀ phase has extremely promising potential as permanent magnet with high magnetocrystalline anisotropy. Of recent interest is also the developing of the hard magnetic phase from an amorphous precursor by appropriate crystallization processes. The melt-spun amorphous Fe₆₈Pt₁₃Nb₂B₁₇ alloy has been submitted to dynamical annealing and its phase transformation during the process has been monitored by differential scanning calorimetry and in situ energy-dispersive X-ray diffraction of the synchrotron radiation. In the first stage of crystallization, -Fe and cubic FePt phases are formed from the amorphous precursor. At around 600 °C superlattice Bragg reflections corresponding to tetragonal FePt are indexed in the XRD spectra and -Fe phase diminishes drastically. Finally, between 900 °C and 975 °C the tetragonal superlattice peaks disappear and cubic FePt phase is formed again. This reversible order–disorder transformation is accompanied by a strong uniaxial lattice expansion of the cubic FePt unit cell. The system show promising features for the co-existence of hard and soft exchange coupled magnetic phases crystallized from FePt-based amorphous precursors.     

Crystal structure of the R3Ag1−δSiS7 (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23) compounds

The crystal structure of the R₃Ag_1−δSiS₇ (R = La, Ce, Pr, Nd, Sm, δ = 0.10–0.23, space group P6₃, Pearson symbol hP23.80 − 23.54) compounds were determined by means of X-ray single crystal diffraction (a = 1.04168(8) nm, c = 0.57825(4) nm, R1 = 0.0116 for La₃Ag_0.90SiS₇; a = 1.0312(1) nm, c = 0.57395(7) nm, R1 = 0.0152 for Ce₃Ag_0.82SiS₇; a = 1.0248(1) nm, c = 0.57223(5) nm, R1 = 0.0105 for Pr₃Ag_0.85SiS₇; a = 1.0192(1) nm, c = 0.57020(6) nm, R1 = 0.0292 for Nd₃Ag_0.81SiS₇, a = 1.0100(1) nm, c = 0.56643(6) nm, R1 = 0.0208 for Sm₃Ag_0.77SiS₇. Gradual decrease of the silver amount in the series of chalcogenides was found.