The athermal α → ω transformation in Zr-2 at% Nb alloy

The athermal transformation in Zr-2 at.% Nb alloy has been investigated by transmission electron microscopy. Analysis of the selected-area diffraction pattern has shown that the orientation relationships between the omega and the parent-phase in quenched Zr-2 at.% Nb alloy are the same as have been previously observed for the reaction in pure zirconium. Thus it was deduced that the direct transition has taken place in the alloy during cooling. The-originated -particles were visualized using the dark-field technique. The formation of the athermal omega in the-region of-stabilized Zr-Nb alloy is discussed in terms of the relative positions of the free energy equilibrium curvesT ₀ ,T ₀ ,T ₀ and the correspondingM _s ,M _s andT _s start curves. It is concluded that the omega phase can occur over a much wider range of alloy compositions than is usually recognized on the basis of transformation data.     

Interaction between a dislocation and an impurity in KCl: Mg2+ single crystals

The interaction between a dislocation and the impurity in KCl: Mg²⁺ (0.035 mol% in the melt) was investigated at 77–178 K with respect to the two models: one is the Fleischer's model and the other the Fleischer's model taking account of the Friedel relation. The latter is termed the F-F. The dependence of strain-rate sensitivity due to the impurities on temperature for the specimen was appropriate to the Fleischer's model than the F-F. Furthermore, the activation enthalpy, H, for the Fleischer's model appeared to be nearly proportional to the temperature in comparison with the F-F. The Friedel relation between effective stress and average length of the dislocation segments is exact for most weak obstacles to dislocation motion. However, above-mentioned results mean that the Friedel relation is not suitable for the interaction between a dislocation and the impurity in the specimen. Then, the value of H(T _c) at the Fleischer's model was found to be 0.61 eV. H(T _c) corresponds to the activation enthalpy for overcoming of the strain field around the impurity by a dislocation at 0 K. In addition, the Gibbs free energy, G ₀, concerning the dislocation motion was determined to be between 0.42 and 0.48 eV on the basis of the following equation ln / = G ₀/(kT_p0)1 – (T/T _c)^{1/2 –1}(T/T _c)^1/2 + ln ₀/where k is the Boltzmann's constant, T the temperature, T _c the critical temperature at which the effective stress due to the impurities is zero, _p0 the effective shear stress without thermal activation, and ₀ the frequency factor.     

TEM study of metastable β-phase decomposition in rapidly solidified Ti-6Al-4V alloy

A new rationale is presented for various decomposition products obtained from the metastable -phase found in Ti-6A1-4V alloy produced by hot isostatic pressing comminuted melt-spun fibres and cooled to room temperature by furnace cooling. This alloy has an -matrix with about 8 vol% retained -phase, which is supersaturated with -stabilizers to such an extent that the martensitic transformation has been suppressed. The metastable -phase decomposes by different modes during continuous cooling, depending on the actual composition of individual -grains. Less enrichment of vanadium and iron favours the direct formation of the equilibrium -phase from the -matrix, while greater enrichment of vanadium and iron leads to a spinodal decomposition of the metastable -phase, resulting in a + two-phase structure. During further continuous cooling, the -phase which is lean in -stabilizers will transform into isothermal -phase. In addition, an unknown phase has also been observed in the -phase, which is typified by the appearance of 1/2{112} reflections in the SAD patterns.     

Microstructure and mechanical properties of rapidly quenched L20 and L20+L12 alloys in Ni-Al-Fe and Ni-Al-Co systems

Ductile L2₀-type wires and+L1₂-type duplex wires with high strengths and large elongation in the Ni-Al-Fe and Ni-Al-Co ternary systems have been manufactured directly from the liquid state by an in-rotating-water spinning method. The wire diameter was in the range 80 to 180m and the average grain size was 2 to 4m for the wires and 0.2 to 1.0m for the+ wires. _y, _f and _p of the wires were found to be about 360 to 760 MPa, 560 to 960 MPa, and 0.2 to 5.5%, respectively, for the Ni-Al-Fe system, those of the+ wires were about 395 to 660 MPa, 670 to 1285 MPa, and 3.5 to 17%, respectively, for the Ni-Al-Fe system, and about 260 to 365 MPa, 600 to 870 MPa, and 4.0 to 7.0%, respectively, for the Ni-Al-Co system. Cold-drawing caused a significant increase in _y and _f and the values attained were about 1850 and 2500 MPa, respectively, for Ni-20Al-30Fe and Ni-25Al-30Co wires drawn to about 90% reduction in area. The high strengths, large elongation and good cold-workability of the melt-quenched and+ compound wires have been inferred to be due to the structural change into a low-degree ordered state containing a high density of phase boundaries, suppression of grain-boundary segregation and refinement of grain size.     

The constitution of the Ni-Al-Ru system

The constitution of the Ni-Al-Ru system has been investigated in the range 0 to 50 at% Al. Isothermal sections at 1523 and 1273 K have been determined using microstructural observations, electron probe microanalysis and X-ray diffraction. The phases present were: nickel-based solid solution (); (based on Ni₃Al); solid solutions based on NiAl and RuAl, respectively (designated ₁ and ₂), and ruthenium-based solid solution (Ru). The maximum solubility of Ru in was 5 at%. ₁, and ₂ show extensive range of solubilities, namely up to 20at% Ru in ₁ and up to 25 to 35 at% Ni in ₂. Three-phase equilibrium between , ₂ and (Ru) existed at 1523 and 1273 K. Also at 1523 K, three-phase equilibria existed between , and ₁ and ,₁ and ₂, while at 1273 K, the equilibria were between , ₁,₂ and , , ₂ indicating the occurrence of a reaction +₁, +₂ at a temperature between 1523 and 1273 K. Liquidus features have been deduced from data on as-solidified structures. Lattice parameter data and hardnesses are also reported.     

Knudsen molecular flow in a channel with a small temperature difference at its ends

The thermomolecular pressure difference (TPD) of helium, argon, and krypton is measured in a packet of glass capillaries for temperatures 273 and 293 K at their ends in a 10–100 range of Knudsen numbers.Notation exponent of the thermomolecular pressure difference effect - Kn Knudsen number - rarefaction parameter - Q_T reduced thermal creep flux - Q_P reduced Poiseuille flux - C(_t) Cercignani-Lampis scattering kernel - R specular scattering kernel - (1 – ) fraction of specular reflection - _t accommodation coefficient of the tangential momentum - P_c, P_h gas pressure in the cold and hot volumes, respectively - coefficient of dynamic viscosity - m mass of gas molecules - k Boltzmann constant - D, L the capillary diameter and length, respectively Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 54, No. 5, pp. 719–724, May, 1988.     

Liquid phase sintering of RE2O3: YSZ ceramics Part I Grain growth and expelling of the grain boundary glass phase

Experiments on silicate liquid phase sintering of YSZ ceramics with addition of 0.5 mol% of rare earth ions have been done in order to study the effect of these ions on the kinetics of grain growth and the expulsion of glass through the grain boundaries. Kinetics follow a third power law in the following order YPr>YPrEr>YY>YEr. The expelled glass does not spread over the ceramic grains and its mass is inversely related to grain size. Glass phase separation inside the grain boundaries is found to be a necessary condition for glass expulsion.     

Numerical simulation of an explosive plasma generator in the gasdynamic approximation

A two-dimensional gasdynamic model of a plasma generator is proposed. A numerical solution of the problem is obtained, and peculiarities of the gasdynamic flow are considered. Results are compared with experiment.Notation T temperature - p pressure - N number of gas particles per unit volume - w gas mass velocity vector with components w_z=u and w_r=v - z axial coordinate - r radial coordinate - t time - E total specific energy of gas - specific internal energy - density - V plate velocity - E_in initial plate energy - M plate mass - S plate area - p pressure difference between left and right sides of plate - t, z, r time and space steps - k<1 Courant number - c velocity of sound in the gas Indices 0 initial value - * characteristic dimensional quantities - i, j grid cell indices along z and r - n number of time step - () symbol denoting intermediate values of gasdynamic variables in a time layer Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 5, pp. 859–867, November, 1979.     

The crystallization of the amorphous alloy Fe40Ni40P14B6

The isothermal transformation behaviour of the metallic glass Fe₄₀Ni₄₀P₁₄B₆ between 320 and 400° C is described. Crystallization occurs by a eutectic mechanism to form Fe-Ni austenite and a body-centred tetragonal phase which is isomorphous with Fe₃P and Ni₃P. The eutectic crystals have a barrel shape such that the c-axis of the tetragonal phase is parallel to the barrel axis. The orientation relationship between the two phases is 1 1 0T 1 1 0 and 0 0 1T 1 1 2. The austenite phase contains (1 1 1) twins.     

Mapping co-word structures: A comparison of multidimensional scaling and leximappe

The LEXIMAPPE method and Multidimensional Scaling (MDS) are discussed as methods to visualize (map) characteristics of structures of word-occurrence (co-word) relations. Utilization of MDS is proposed as an alternative mapping method able to circumvent problematic features of LEXIMAPPE maps of the total co-word structure. A comparison of both methods on the same real-life co-word matrix demonstrates topological advantages of an extended MDS-mapping.     

The variation of the index of refraction in a vortex tube

Three models of a vortex tube (isentropic, isothermal, and isochoric) are considered as optical inhomogeneities. Expressions relating the index of refraction to the coordinate are obtained. The possibility of obtaining Schlieren pictures of such flows is discussed.Notation a speed of sound - n index of refraction - p pressure - r radius - T absolute temperature - v linear velocity - angular deflection of the beam - x adiabatic exponent - density - angular velocity - ¯v, ¯p etc. dimensionless parameters - v₀, ₀ values at the core bounboundary - p, etc. stagnation values - n_c index of refraction at center of vortex     

Microstructural development in cast and aged Ni–Al–Cr-based alloys derived from the B2 type β-NiAl structure

The formation of intermetallic compounds consisting of nickel-rich B2-type NiAl (-phase) ductilized by two-phase A1 ()/L12 () regions provides the possibility of combining ductility and high-temperature performance. Similar microstructures can also form the basis of high-temperature shape memory alloys, due to martensitic transformation of the -phase to an L10-type product. One route by which –/ microstructures can be produced involves the use of chromium as a -stabilizer. However, microstructural development in such a case is complicated by the formation of -Cr precipitates.This paper examines microstructural development and stability in cast Ni-25 at % Al-14 at % Cr, Ni-29 at % Al-22 at % Cr and Ni-27 at % Al-8 at % Cr alloys, together with a more complex material, namely, Ni-20 at % Al-13 at % Co-9 at % Cr-4 at % Ti-1 at % Mo-1 at % V. Both the as-cast condition and samples aged at 850 and 1100 °C for 140 h are examined using transmission electron microscopy. The paper discusses the formation of L10 martensite, intradendritic ', interdendritic /' and -Cr precipitation.     

The α- to β-Si3N4 transformation in the presence of liquid silicon

The compacts consisted of , -Si₃N₄ and free silicon are heat treated in the range 1650° C to 1750° C in an argon atmosphere in order to observe the following behaviours; the to phase transformation and variations of the microstructure during heat treatment in silicon nitride. For the microstructural observation of the heat treated specimens, the same grains in the polished surface were investigated before and after eliminating the retained silicon by etching. The to phase transformation, in this case, occurs via silicon melts irrespective of added -Si₃N₄. Both and phases are soluted and precipitated into molten silicon and their morphology are changed from an equiaxed shape to prismatic one. Although elongated grains are precipitated at low temperature or in the early stage of heat treatment, fine precipitated grains are mainly observed with increasing heat treating temperature.     

Ageing characteristics of cast Zn-Al based alloy (ZnAl7Cu3)

Microstructure and ageing characteristics of a cast Zn-Al based alloy (ZnAl7Cu3) were studied using X-ray diffraction, electron scanning microscopy and back-scattered diffraction techniques. Two stages of phase transformation, i.e., decomposition of zinc rich phase and four phase transformation, + T + , were detected during ageing at 150°C. Electron back-scattered diffraction technique was applied in distinguishing both zinc rich and phases.     

Dielectric properties of thin solid films formed on silicon

We report on the measurement of the frequency-dependent complex permittivity, ()=()-i(), over the frequency range, 30 MHz to 6 GHz, of silicon wafers and of thin dielectric films formed on silicon. Measurements, as a function of temperature and time treatments, were obtained by means of an HP Network Analyzer and dielectric probe and the resulting ()and()plots for the silicon wafers are shown to have a Debye-type [1] profile, thereby indicating that the associated polarization mechanism is of the orientational variety.     

Martensitic transformations in Ti-Mo alloys

A detailed investigation has been made of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from the-phase region. With increase in molybdenum content, the martensite structure changes from hexagonal () to orthorhombic () at 4 wt% Mo, and at 10 wt% Mo, the structure is completely retained . For alloy compositions <4 wt% Mo, there is a diffusional component in the transformation of the -phase at the quench rates employed. There is a transition, with increase in molybdenum content, in morphology (from massive to acicular) and in substructure (from dislocations to twins). However, the transitions in crystallography, morphology and sub-structure are not directly related to one another except for an abrupt loss of dislocation substructure at the/ transition. The to crystallographic transition has the characteristics of a second order transformation, and evidence has been obtained of the existence of a spinodal within the metastable orthorhombic system. The orthorhombic martensites of Ti-6 and 8 wt% Mo decompose during quenching producing a fine modulated structure within the martensite plates, consistent with a proposed spinodal mode of decomposition.     

Grain boundary sensitization and desensitization during the ageing of 316L(N) austenitic stainless steels

Two casts of type 316L(N) austenitic stainless steel have been solution treated for 1 h at 1070 C, air-cooled, then aged for up to 20 000 h at temperatures between 550 C and 750 C. Grain boundary precipitation of the M₂₃C₆ phase occurs, and the Cr composition profile normal to the grain boundaries has been determined at high resolution by an analytical electron microscope. The data have been fitted firstly to collector plate models, which indicated that some of the material was in the process of desensitization, or healing, indicated by a rise in the boundary Cr content. The data were then fitted to a model of the Cr profile as a function of ageing treatment in the healing regime, and a good correlation was obtained.     

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.     

IN-713C characteristic properties optimized through different heat treatments

The strength of a nickel-based superalloy hardened through precipitation is related to the volume fraction, particle size and distribution of the precipitated phase, . These parameters may vary as a result of heat treatment, or high-temperatures service. The information obtained, describing the influence of time and temperature on the precipitated phase, , is of special importance owing to its technological application at high temperatures. Dissolution or precipitation kinetics are such that the volume-fraction balance of the phase is quickly established at an ageing temperature given by successive changes due only to the particle growth. The results of the present study describe heat-treatment effects on size and distribution of the phase, and precipitated carbides ageing of a nickel-based superalloy (IN-713C). These on ageing studies at a certain temperature show that the kinetic growth of particles by controlled diffusion follows that r t ^1/3 law.     

Rheological properties of aqueous silicon nitride suspensions

The effect of surface modification of Si₃N₄ particle on the colloidal behavior and the rheological properties of aqueous Si₃N₄ suspensions under steady and oscillatory conditions are investigated in detail. Due to the decrease of the oxidizing level, the isoelectric point (IEP) of the modified particle shifts to basic region gently. Attempts have been made to apply rheological models to the suspensions with various solid volume fraction (). For the as-received suspensions, the Sisco model provides the best fit in the range of 0.30 while the Casson model in 0.35 0.45. The shear behavior of modified suspensions fits to Sisco model in the range of 0.40 and Casson model in 0.45 0.54. The rheological behavior of modified suspensions is improved efficiently. The critical strain decreases and the linear viscoelastic regime narrows continuously with increasing solid concentration. For the modified suspensions, the linear viscoelastic regime broadens and the corresponding elastic modulus decreases sharply. With increasing solid concentration, the characteristic frequency shifts toward lower frequencies and the suspension transforms from more viscous to more elastic.