Magnetic field dependence of the density of states of YBa2Cu3O6.95: Implications for the vortex structure

The total specific heat of YBa₂Cu₃O_6.95 single crystals includes contributions from phonons and spin-1/2 particles, as well as electronic contributions. The electronic specific heat is described by a quadratic term T² in zero field and a linear term [(0)+(H)]T which is increased when a magnetic field H is applied perpendicular to the CuO₂ planes. In agreement with d-wave superconductivity, we find that _n/T_c and (H)_n(H/H_c2)^1/2, where _n is the coefficient of the normal-state linear term. The H^1/2 dependence of the density of states at the Fermi level was predicted by G. Volovik for lines of nodes in the gap: the quasiparticles which contribute to this density of states are close to the nodes in momentum space and are located outside the vortex core.     

Martensitic transformation of γ-Fe precipitates in a Cu 1.5 at % Fe Alloy

In the present work, the mechanism of martensitic transformation, the influence of -Fe particle size on the martensitic transformation induced by cold working, and the transformation of -Fe into -Fe by thermal treatment alone in a Cu-1.5 at% Fe alloy, was studied using field ion microscopy (FIM) and transmission electron microscopy (TEM). It has been found that -Fe precipitates smaller than about 10 nm did not transform martensitically to -Fe by cold working. Precipitates larger than 10 nm adopted a Kurdjumov-Sachs orientation relationship with the copper matrix; and the martensitically transformed -Fe precipitates were ellipsoidal in shape, with their major axes being oriented parallel to the 1 1 0 direction in the matrix. Dislocations were found in the matrix near the vicinity of transformed -Fe precipitates, giving support to the dislocation cutting mechanism proposed by other workers for the transformation. In thermally aged alloys, no transformation of -Fe to -Fe was observed during the coarsening of -Fe precipitates up to sizes as large as about 50 nm. These precipitates still remained coherent or semi-coherent with the copper matrix.     

First principles study of effect of lattice misfit on the bonding strength of Ni/Ni3Al interface

By using a discrete variational X (DV-X) method, the electronic structures and bonding strengths of Ni/Ni₃Al (or /) interface with different lattice misfits () were calculated in the framework of the nonrelativistic first-principles theory. In order to describe the effect of on the interfacial binding strength and the structural stability of coherent / interface, we calculated the interfacial binding covalent bond density (CBD) and the local environmental total bond overlap population (LTBOP). Very obvious effects of lattice misfits on the electronic structures of coherent / interface were found. On one hand, less than –0.6% negative lattice misfit can increase the binding strength of the /' interface. On the other hand, the local environmental total bonding strength of the /' interface decreases with increasing magnitude of . Therefore, the magnitude and sign of lattice misfit must be carefully controlled to balance the high-temperature creep strength of Ni-base single crystal superalloy and the structural stability of the /' interface when one designs new alloys.     

Mössbauer study on the magnetic state of iron particles in Fe-N and Fe-Zr-N soft magnetic thin films

The magnetic state of -Fe particles and the behaviour of nitrogen and zirconium during annealing in Fe₉₆N₄ and Fe_85.6Zr_7.6N_6.8 magnetic thin films have been studied by conversion electron Mössbauer spectroscopy for ⁵⁷Fe. The crystalline phases present in the Fe-N annealed films were -Fe and -Fe₄N, and those in the Fe-Zr-N annealed films were -Fe and ZrN. In the Fe-N films annealed below 300°C, about 60% nitrogen is incorporated interstitially into -Fe and the rest is used for the formation of -Fe₄N. In the Fe-N film annealed at 500°C, almost all nitrogen participates in the formation of -Fe₄N, leading to the grain growth of -Fe particles and an increase in coercive force. The values (291–325 kOe) of internal magnetic field of iron sites in -Fe in the Fe-Zr-N films are much smaller than that (333 kOe) of the iron site in pure -Fe. Even if the Fe-Zr-N films were annealed at 500–700°C, some zirconium and nitrogen is still incorporated substitutionally and interstitially into -Fe, respectively. In particular, the substitutional zirconium depresses the grain growth of -Fe particles, perhaps due to a chemical interaction between zirconium and iron.     

The Ni3Al-Ni3Cr-Ni3Mo section of the Ni-Cr-Al-Mo system

An investigation is reported of the constitution of the 75 at % nickel section of the Ni-Cr-Al-Mo system in the temperature range 1523 to 1073 K. Alloys in the region 10 to 20 at % Al were annealed at 1523, 1273, and 1073 K, respectively, and subjected to electron microprobe analysis, X-ray diffraction, and microscopical and hardness examination. Constitutional data are presented as partial isothermal sections and as vertical sections. At 1523 K the section consists only of fields containing ,+ and , the last mentioned phase being predominant. With decreasing temperature the and + fields increase in extent. Also, the NiMo and Ni₃Mo phases were encountered in the ternary Ni-Al-Mo alloy studied. The quaternary + alloys showed small lattice mismatch values, i.e. up to 0.25%. Raft like morphologies of were found in the quaternary alloys, resulting from directional coarsening. Observations of as-cast structures are also reported.     

A high-resolution-electron-microscopy study of a γ/γ′-α directionally solidified eutectic alloy

The microstructure of a /- directionally solidified (DS) eutectic alloy with a nominal composition of Ni-30.26Mo-6.08Al-1.43V (wt%) was investigated by means of high-resolution electron microscopy (HREM) and analytical electron microscopy. The -fibres exhibited a typical morphology with a rectangular cross-section and they displayed the Bain orientation relationship (OR) with the / matrix; that is, [001][001] and (110)(010). Misfit dislocations and lattice strain fields existed at the / interface for different habit planes; that is, (110)(010) and (100)(110) were analysed. EDAX (Energy dispersive X-ray) analysis showed that the composition of the -phase was approximately Ni₄(Mo, Al, V); it contained 90° rotational domains of Ni₃(Mo, Al, V) with a DO₂₂ structure and Ni₂(Mo, Al, V) with a Pt₂Mo structure.     

High temperature oxidation behavior of Ti-Al-Nb ternary alloys

The oxidation behavior of four Ti-Al-Nb ternary alloys with different microstructures were investigated at 1000°C using interrupted oxidation test in air. Alloys with single-phase -TiAl, two-phase -TiAl + ₂-Ti₃Al, multi-phase -TiAl + ₂-Ti₃Al + Nb₂Al and two-phase ₂-Ti₃Al + Nb₂Al were prepared. The oxidation resistance of the Ti-Al-Nb ternary alloy at high temperature was found to be better than that of the binary Ti-Al alloy. Among the four Ti-Al-Nb ternary alloys, the + ₂ two-phase alloy has the best oxidation resistance. The presence of Nb-enriched phase such as Nb₂Al and Nb₃Al decrease the oxidation resistance at elevated temperature presumably due to the formation of Nb₂O₅, which would accelerate the exfoliation of oxide.     

Stress-induced phase transformations in a hot-deformed two-phase (α2+γ) TiAl alloy

Stress-induced 2, 2 and 9R phase transformations in a hot-deformed Ti–45 at% Al–10 at% Nb alloy have been investigated using high-resolution transmission electron microscopy. The 2 phase transformation is an interface-related process. The interfacial superdislocations emitted from the misoriented semicoherent 2– interface react with each other or with the moving dislocations in the phase, resulting in the formation of the 2 phase. The nucleation of the 2 phase transformation takes place either at the 2– interfaces or at the stacking faults on the basal plane of 2 phase, and the growth of plate is accomplished by the moving of a/61 0 1 0 Shockley partials on alternate basal plane (0 0 0 1)2. The 9R structure was usually found to form at incoherent twin or pseudotwin boundaries. During deformation the interfacial Shockley partial dislocations of these incoherent twin and pseudotwin boundaries may glide on (1 1 1) planes into the matrix, resulting in the formation of 9R structure. The interfaces (including 2– and – interfaces) as well as the crystallographic orientation relationship between the as-received or stress-induced 2, and 9R phase have been analysed. The mechanisms for the stress-induced 2, 2 and 9R phase transformations were also discussed. © 1998 Chapman & Hall     

Deformation behaviour of recrystallized Ni3Al

Deformation behaviour of the recrystallized Ni₃AI with non-stoichiometric and stoichiometric compositions have been investigated. Recrystallization microstructures in non-stoichiometric Ni₃AI are composed of the Ll₂ ordered and a small amount of the f c c disordered . It is shown that the large elongation of non-stoichiometric Ni₃AI is due to -phase existing at recrystallized t'- grain boundaries. Recrystallization microstructures in stoichiometric Ni₃AI are confirmed to be a single phase of . Coarse-grained stoichiometric Ni₃AI shows considerable ductility, although the fine-grained compound is brittle. The ductility may be related to the low yield strength in the coarse-grained samples.     

The influence of ageing on the stability of β-γ/γ′ derived microstructures in Ni-Al-Cr-(Co) alloys

Multiphase Ni-Al-(Fe)-(Cr)-(Co)-based intermetallics with (B2)- (A1)/(L1₂), - or - microstructures can exhibit significant room-temperature tensile ductility. In the case of Ni-Al-Cr-based alloys, microstructural development is complicated by the precipitation of -Cr, which can supplant the -phase during ageing of three-phase -/ microstructures. An investigation of the stability, during ageing, of cast Ni-Al-Cr-(Co) alloys with microstructures derived from -/ is reported. In the as-cast condition, the materials investigated consisted of a dendritic matrix containing L1₀ type martensite and interdendritic /. Extensive intra- and interdendritic -Cr precipitation was also observed. The stability during ageing of the interdendritic / microstructure is also considered and transformation of the L1₀ martensite is examined.     

Improvements in the transverse properties of composites

Fracture surface energies of initiation ( _I ^c) for a transverse fracture process in glass-reinforced epoxy composites have been measured and the results calculated by three different treatments and are compared with the average fracture surface energies ( _F ^c) for the complete fracture process.Changes in these two fracture properties are studied as a function of the volume fraction of the fibres, and the relation between the surface energies is established as a factor which determines the nature of the fracture process. When _I{sic}– _F ^c>0 a catastrophic failure is expected, whereas a controlled fracture is observed for _I ^c– _F ^c<0.     

Electronic specific heat of La2−xSrxCu1−yMyO4(M=Ga,Zn): Impurity effects on a D-wave superconductor

The electronic specific heat C_el was studied in Ga- and Zn-doped La_2–xSr_xCuO₄ (0.16x0.22) at T10K. Partial substitution of Ga or Zn for Cu suppresses T_c and revives the T-linear electronic specific heat, T, markedly. The (y)/n vs T_c/T_c0 relation for Zn-doped samples with x0.2 is in good agreement with the theoretical one for resonant impurity scattering in a d-wave superconductor, while those for Ga-doped samples and for Zn-doped samples with x 0.2 deviate slightly from the theoretical curve. The deviation will be discussed in relation to changes in the magnetic properties of 3d electrons.     

The fracture energy of a glass fibre composite

The fracture energy of a glass fibre-polyester composite has been measured by work of fracture ( _f) measurements on bending beams, and by linear elastic fracture mechanics analyses ( _i) of the bending beams and edge-notched tensile plates. It was found that for the bend specimens _i< _f. The work of fracture, _f, displayed a strain rate dependence, but there was no such dependence of _i. It is postulated that _i is determined by a debonding mechanism while _f is the sum of a debonding mechanism plus a pull-out contribution. The edge-notched tensile plate experiments showed that _i obtained from thick plates was less than that obtained from side-grooved plates, and that in each case there was a dependence of _i on crack size.     

A transmission electron microscopic study of the Bethany iron meteorite

The Bethany iron meteorite which is a part of the Gibeon shower is a fine octahedrite with zoned plessite fields of various sizes. The optically irresolvable microstructural details inside the plessitic fields have been studied by transmission electron microscopy, and the crystallographic relationships between the primary kamacite () and the parent taenite (), and between the and particles in the coarse plessite, have been examined using electron diffraction. In the case of primary kamacite the orientation-relationship with was close to the Nishiyama-Wasserman relationship, whereas, for the plessitic , the orientation-relationship with was close to Kurdjumov-Sachs. It was also found that the (111) and (110) planes were not strictly parallel. Additionally, measurements of the composition profile through the zoned plessite have been made using STEM microanalysis technique, and related to microstructure.     

Microstructures of titanium-aluminides produced by laser surface alloying

The microstructures of Ti-Al layers (from 43–80 at %Al) produced by laser surface alloying of titanium substrate with a powder feed technique have been investigated. The laser processing parameters were; 1.8 kW laser power, 3 mm beam diameter, 7 mm s^–1 traverse speed, and values of powder flow rates of aluminium ranging from 0.07–0.11 g s^–1. The microstructures were dendrites of ₂ and interdendritic regions of ₂+ in the Ti-43 at %Al alloy; dendrites of either ₂ or ₂+ with interdendritic in the Ti-50 at %Al alloy; dendrites of ₂+ with interdendritic in the Ti-55 at %Al alloy; single phase in the Ti-60 at %Al alloy and TiAl₃ dendrites and Al solid solution in the interdendritic regions in the Ti-80 at %Al alloy. The microstructures were fine and comparable to those produced by other methods of rapid solidification processing. The microstructures of the Ti-50 and Ti-55 at %Al alloys were in agreement with the existence of the peritectic reactions:L + andL + , in the Ti-Al system.     

Dielectric Properties of Pb(Ti,Zr)O3–∑n=14 (PbB"1-αB""αO3)nSolid Solutions

Dielectric permittivity measurements in Pb(Ti,Zr)O₃–_n=1 ⁴ (PbB^" _{1 -} B^" O₃) _n solid-solution systems demonstrate that the permittivity ^T ₃₃/₀of the solid solutions correlates with the molar ratio of the more soft-electric to the less soft-electric component of PbB^" _{1 -} B^" O₃(). With increasing , ^T ₃₃/₀rises because of the decrease in the uniform cell distortion parameter. The permittivity is also sensitive to structural disordering at > 1 and reduction in the density of the materials at 1.     

Microstructural and dimensional stabilities of a potential γ/γ′-α(Mo) directionally solidified eutectic superalloy under cyclic thermal exposure to 1000° C

A potential heat-resistant ductile eutectic composite,/-, in the Ni-Al-Mo ternary system has been thermally cycled in the temperature range 200 to 1000° C for up to 1000 cycles in an attempt to examine dimensional as well as microstructural stability of the composite under thermal fatigue conditions. The composite examined has two types of initial microstructure; in one, blocky -Ni₃Al encircles individual-Mo fibres (as-grown condition) whereas in the other, is in the form of fine cuboidal particles uniformly distributed in an Ni-rich fcc matrix (heat-treated condition). Dilatometric measurements upon temperature cycling show that the composite is stable against thermal ratchetting irrespective of initial microstructural conditions. However, the cycling induces microstructural change, which is characterized by segmentation of-Mo fibres or formation of a detrimental brittle phase identified as an intermetallic-NiMo that consumes-Mo fibres whether the fibres are encircled by or not. Post-cycling tensile tests at room temperature show that the fibre damage in the former has no fatal effect on tensile strength and ductility. A beneficial effect of the-encircling configuration is discussed on the basis of the recognition of a peritecto-eutectoid reaction:++ that has been disregarded.     

Investigation of the effect of substrata on the surface free energy components of silica gel determined by thin layer wicking method

The components of surface free energy of silica gel deposited on glass plates, aluminium or plastic sheets (commercial Merck's plates for TLC) were determined by applying two theoretical approaches: the Lifshitz-van der Waals acid-base approach (LWAB), the geometric mean of apolar and polar interactions approach (GM). The thin layer wicking method was applied. Besides, from the measured contact angles of probe liquid (diiodomethane, -bromonaphthalene, water, formamide, glycerol and ethylene glycol) surface free energy components were calculated for the substrata on which the silica gel was deposited. In this case the equation of state (ES) was additional by applied. The study has shown that both the kind of substratum and that of the chambers used for measuring the penetration rate of the liquid do not influence the calculated values of the surface free energy components of silica gel. The components calculated from the two models of interfacial interactions: ^LW _s and ^AB _s or ^d _s and ^p _s appeared to be practically the same if diiodomethane and -bromonaphthalene were considered as weakly polar liquids, i.e. donor-acceptor interactions in the surface tension were taken into account. However, when _l ⁺ and _l ^– of these liquids are neglected, considerable differences occur, particularly in the determined value of Lifshitz-van der Waals component. The values of the total surface free energy of substrata calculated by applying three thermodynamic approaches are very similar, but if diiodomethane and -bromonaphthalene are considered as weakly polar liquids this similarity is more distinct.     

Preparation of Fe-N films by r.f. sputtering

Fe-N films over a wide compositional range have been prepared by the reactive sputtering method. Fe-N sputtered films were composed of a single or two phases such as-Fe₂N,-Fe_3.02N,-Fe_3.82N,-Fe₄N and-Fe; however, an unknown phase was observed at a higher nitrogen pressure. A remarkable preferred orientation of the-Fe_3.02N (110) plane parallel to the film surface was observed. The Curie temperature of the sputtered -Fe_3.82N sample was 490° C, which was almost the same as that of-Fe₄N prepared by metal nitriding. The saturation magnetization, _s, of the sputtered Fe-N samples decreased from 151.8 to 42.4 e.m.u.g^–1 with increasing nitrogen content from 7.94 to 24.87 at%, and its coercive force,₁ H _c was found to lie in the range 150 to 600 Oe in the powder form at room temperature.     

Study of interaction effects inAu-V alloys through susceptibility and specific heat measurements

We measured the magnetizationM of diluteAu-V alloys of concentration varying between 0.2 and 10 at.% at 4.2 K in fields up to 60 kOe.M is proportional to the field for all fields. The specific heat, measured between 0.4 and 3 K, shows a term linear in temperature T, with =3.3 and 4.6 mJ · mole^–1 · K^–2 for the 5 and 10% V alloys, respectively. x and increase less rapidly than the vanadium concentration. In terms of different magnetic character between isolated impurities and nearest neighbors, the analysis of the specific heat results is consistent with a drastic reduction in thed spin susceptibility of V nearest neighbors by interaction effects, contrary to the case ofAu-Co,Cu-Co,Cu-Ni, andCu-Fe where interaction effects produce an enhancement of x. The fluctuation temperature of these two types of impurities is very different;T _f 270 K for isolated V atoms andT _f 2500 K for V nearest neighbors. The V atoms in group tend to have the same character as vanadium metal. The observed increase of the ratio =(xd/dc)/(dx/dc) from 0.2 for isolated atoms to 0.8 for V in group is consistent with the decrease of Hund's coupling.