The second phases in a burn resistant stable beta titanium alloy—Ti40

The second phases in Ti40 (Ti25V-15Cr-0.2Si) burn resistant titanium alloy are studied. The higher solution temperature, the more second phases in Ti40 alloy. There are not second phases if the solution temperature is below 850°C, while there are rod-like and little Ti₅Si₃ phases if temperature is over 850°C. , Ti₅Si₃ and oblique phases emerge after Ti40 solution at 910°C followed by aging at 600°C, while only Ti₅Si₃ phases emerge after solution at 860°C followed by aging at 600°C. The effect of the second phases on properties at RT are not obvious. There are different shapes of and Ti₅Si₃ precipitates after Ti40 alloy exposure at 540°C for 100 h, which decreases the thermal stability.     

Phase decompositions of Fe-Si-Al ordered alloys

Stable structures of Fe-Si-Al ternary alloys and Fe-Si and Fe-Al binary alloys containing up to about 40 at% solute atoms were investigated by means of transmission electron microscopy. The following results were obtained. Two types of phase separation, B2+DO₃ and + DO₃ were observed in the alloys whose compositions lie in a narrow band connecting Fe-10 to 14 at% Si with Fe-20 to 25 at % Al and also in the neighbourhood of a Fe-30 at%Al-3 at% Si alloy. Such compositions of the alloys are located in the phase boundary of B2 and DO₃ single phases or and DO₃ single phases. The phase separation in the Fe-Si-Al and Fe-Si alloys produce the 100 modulated structure which differs from the morphology formed by the phase separation of the Fe-Al system.     

Thermal expansion of epoxy-fiberglass composite specimens

The thermal expansion behavior of three epoxy-fiberglass composite specimens was measured from 20 to 120°C (70 to 250°F) using a fused quartz push-rod dilatometer. Billets produced by vacuum-impregnating layers of two types of fiberglass cloth with an epoxy were core-drilled to produce cylindrical specimens. These were used to study expansion perpendicular and parallel to the fiberglass layers. This type of composite is used to separate the copper conductors that form a helical field coil in the Advanced Toroidal Facility, a plasma physics experiment operated by the Fusion Energy Division at Oak Ridge National Laboratory. The coil is operated in a pulsed mode and expansion data were needed to assess cracking and joint stresses due to expansion of the copper-composite system. The dilatometer is held at a preselected temperature until steady state is indicated by stable length and temperature data. Before testing the composite specimens, a reliability check of the dilatometer was performed using a copper secondary standard. This indicated thermal expansion coefficient () values within ±2% of expected values from 20 to 200°C. The percentage expansion of the composite specimen perpendicular to the fiberglass layers exceeded 0.8% at 120°C, whereas that parallel to the fiberglass layers was about 0.16%. The expansion in the perpendicular direction was linear to about 70°C, with an value of over 55×10^–6 °C^–1. Anomalous expansion behavior was noted above 70°C. The expansion in the direction parallel to the fiberglass layers corresponds to an value of about 15×10^–6 °C^–1. The lower values in the parallel direction are consistent with the restraining action of the fiberglass layers. The values decreased with the specimen density and this is consistent with literature data on composite contraction from 20 to –195°C.Nomenclature Thermal expansion coefficient, °C^–1 - L L(T ₂)–L(T ₁), cm - T T ₂–T ₁, °C - L ₀ Length at room temperature, cm - L(T _i ) Length at temperature T _i , cm - T _i Temperature, °C - T ₀ Room temperature, °C Paper presented at the Ninth International Thermal Expansion Symposium, December 8–10, 1986, Pittsburgh, Pennsylvania, U.S.A.     

The thermal diffusivity of ice and water between −40 and + 60° C

The thermal diffusivity _s of triply-distilled deionised water, and ^L of single-crystal ice along the c-axis, have been measured by Angström's method. The temperature range covered was –40 to +60° C. The results for water compare well with published data for the thermal conductivity, but for ice there are unexplained discrepancies. The linear relationships _s=(8.43–0.101 T) 10^–3 cm²/sec and _L=(1.35+0.002 T) 10^–3 cm²/sec where T° C is the temperature, fit the data obtained.     

Mechanical properties of thermosets

The tensile properties of a DGEBA (diglycidylether of bisphenol A)-norbornene anhydride network (T _g130±5 °C), were studied in the range (220 K-T _g); 4×10^–4 to 14×10^–3S^–1. The viscoelastic spectrum (1 Hz) reveals a low transition at 220 K. The bulk modulus is practically constant between 200 K andT _g — 20 K. The Poisson's ratio increases very slowly untilT _g — 30 K. Then it increases rapidly to reach its asymptotic value (0.5) near toT _g. The tensile (E) and shear (G) moduli display the classical behaviour linked to viscoelasticity. Plastic yielding occurs atT 80 °C, the elongation at yield is almost temperature and strain rate independent (G3_y = 0.035), whereas the yield stress obeys Kambour's relationship: _y = 1.1 (T _g —T) and Eyring's law (activation volume = 914cm³mol^–1). Physical ageing at 120 °C strongly affects the yield stress and the ductility. The maximum draw ratio, obtained atT T _g, is _RC = 1.35, which seems to be consistent with the network's crosslink density.     

The mechanisms of yield and plastic flow in HgTe and Cd x Hg1−x Te

Single crystals of HgTe and Cd _x Hg_1–x (0.18<x<0.30), oriented for single slip, have been deformed in four-point bending at strain rates 10^–4 sec^–1 and temperatures from –11 to +84° C for HgTe, and 20 to 195° C for Cd _x Hg_1–x Te. At the lowest temperatures, the stress-strain curve exhibits a sharp yield relaxation and subsequent zero work hardening regime, as commonly observed for other semiconductors. Experiments show that the yielding mechanism is that proposed by Johnston and Gilman for LiF. Possible explanations for the post-yield zero work hardening phenomenon are discussed. The influence of composition, temperature and strain rate on the stress-strain behaviour are reported. At 20° C, the upper and lower yield stresses ( _uy and _1y ) increase with increasingx in qualitative agreement with our earlier hardness results. For Cd_0.2Hg_0.8Te, _1y varies with temperature,T, at a strain rate of 10^–4 sec^–1, according to _1y exp (Q/kT) whereQ is 0.16 eV. For HgTe the comparable value is 0.11 eV. Atx=0.25 and constant temperature, _1y depends on strain rate as _1y ^1/n wheren is 4. The stress level for deformation of Cd_0.2Hg_0.8Te at 10^–4 sec^–1 and 20° C is 2–3 kg mm^–2, comparable with that for InSb at 300° C or Si at 1000° C. Strain rate cycling tests on Cd _x Hg_1–x Te give values of activation volumeV* around 10b³ at 20° C, independent of plastic strain (up to 2–3%), suggesting that deformation in these alloys is controlled by the Peierls mechanism, as observed in other II–VI compounds.     

The effects of quenching just after deposition for metastable compounds

It has been demonstrated that high rate d.c. magnetron sputtering can easily prepare materials such as Nb₃Ge and Nb₃Si in a metastable state. This sputtering-system was made in an effort to stabilize the metstable phases. Specimens were quenched just after sputtering from 1100° C to liquid N₂ temperature at the rate of 3500° C min^–1. The relation between quenching rate and superconducting onset temperture, T _c0, the transition width, T _c, and the lattice constant, a ₀ were examined. The results show that quenching just after sputtering is very useful in preparing metastable materials.     

Ordering of Fe-Si phases

The microstructure of Fe-Si alloys containing 8 and 15.5 at % Si and heat-treated between 550 and 1200°C is studied by transmission electron microscopy, and the phase composition of alloys containing 19 and 23 at % Si is determined by x-ray diffraction. The Fe-15.5 at % Si alloy heat-treated above 700°C is found to consist of a disordered solid solution and B2 phase. The B2 particles can be thought of as portions of {100} layers consisting entirely of Si atoms and sandwiched between {100} layers of Fe atoms, that is, as a two dimensional phase. At t 675°C, a compositionally modulated microstructure develops in which the Si-enriched zones have the Fe₃ Si stoichiometry and DO₃ structure. At high temperatures, the Fe-19 at % Si alloy consists of the and B2 phases, and the Fe-23 at % Si alloy consists of the and DO₃ phases. These findings are at variance with the generally accepted Fe-Si phase diagram.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 28–35.Original Russian Text Copyright © 2005 by Ustinovshchikov, Sapegina.     

Numerical calculation of a generalized thermal model of radio-electronic apparatus

A method is proposed for numerical calculation of the temperature field of a generalized model of electronic equipment with high component density.Notation x,y,z,x,y spatial coordinates, m - time, sec - L_x, L_v, L_z dimensions of heated zone, m - _x, _y, _z effective thermal-conductivity coefficients of heated zone, W/m·deg - ₂ thermal conductivity of chassis, W/m·deg - a _z thermal diffusivity of heated zone along z axis, m²/sec - c₁ effective specific heat of heated zone, J/kg·deg - ₁ effective density of heated zone, kg/m³ - c₃, ₃, c₂, ₂ thermophysical characteristics of cooling agent and chassis, J/kg·deg·kg/m³ - q_v(x, ), q(x, y) volume heat-source distribution, W/m³ - q_s (x) surface heat-source distribution, W/m² - p number of cooling agent channels - Fo Fourier number - Bi Biot number - Uⁱ coolant velocity in i-th channel, m/sec - T₁(x, ), T₂(x, ), T₃(x, ) temperature distribution of heated zone, chassis, and coolant, °K - T₃₀, T₁₀(x), T₂₀(x) initial temperatures, °K - T_3in coolant temperature at input to channel, °K - T_T(x) effective temperature distribution of heat loss elements, °K - T_C temperature of external medium, °K - dimensionless heated zone temperature - _v(x) local volume heat exchange coefficient, W/m³·deg - ₁₂(x), _1C(x), _1T(x) heat liberation coefficients - W/m²·sec; ₂₁(x, y), _2c(x, y), _2T(x, y) volume heat-exchange coefficients of chassis with heated zone, medium, and cooling elements, W/m³·deg Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 40, No. 5, pp. 876–882, May, 1981.     

Nonequilibrium solidification of poly(ethylene oxide)-sodium thiocyanate mixtures

Mixtures of polyethylene oxide (PEO) and sodium thiocyanate (NaSCN) were isothermally crystallized at temperatures between 7 and 37° C, below the eutectic temperature T _e=63° C. The stable phases are semicrystalline polyethylene oxide, SPEO, and a crystalline complex, CC, with the formula PEO₃ NaSCN; these two solids grow by different mechanisms. Salt mole fraction was varied between 0.067X0.143 for studies by optical microscopy and differential scanning calorimetry. Solidification was observed to proceed by primary growth followed by coupled growth at a nonequilibrium composition X_e much greater than the equilibrium eutectic composition X _e=0.026. The boundaries of this skewed coupled zone could not be determined because of a dependence of X_e on the nature of the primary phase.     

Steady-state creep of an alloy based on the intermetallic compound Ni3Al(γ′)

An investigation of the steady-state creep of a Ni₃Al.10 at% Fe alloy () has shown that two creep mechanisms were operative over the temperature range 530 to 930° C. The experimental data at low temperatures (below 680° C) were not consistent with any of the established creep theories. However, the experimental data were in good agreement with a proposed model for cross-slip from octahedral {111} planes on to cube {100} planes in Li₂ crystals. Above 680° C, the rate-controlling mechanism, which had an activation energy of 3.27eV atom^–1, is considered to be the removal/production of APBs during climb.     

Thermal shock resistance of alumina-sialon composites

The thermal shock behaviour of pure alumina and an alumina-sialon composite was examined. The critical temperature difference of the thermal shock, T _c , had a good relationship with the calculated thermal shock resistance parameter,R. The thermal shock resistance of the composite was remarkably improved by simple modification, such as oxidation at 1400 °C for 100 h. The oxide layer, with porous microstructure, consisted mainly of mullite and a small amount of alumina. The T _c of pure alumina, the composite and the oxidized composite was 210, 225 and 360 °C, respectively. This improvement was considered to be due to the characteristics of the oxide layer, which had high strength as well as a low elastic constant and a low thermal expansion coefficient.     

The role of silicon in the formation of the (Al5Cu6Mg2) σ phase in Al-Cu-Mg alloys

The role of silicon in the precipitation of the phase (Al₅Cu₆Mg₂) has been investigated through comparative studies on Al-3.63Cu-1.67Mg (wt%) and Al-3.63Cu-1.67Mg-0.5Si alloys. Both alloys were extensively examined after solution treating at 525°C for 2.5 h followed by ageing at 265°C for times up to 650 h. Limited studies were also undertaken on both alloys after ageing at 200 and 305°C. Precipitation of was observed in Al-3.62%Cu-1.66%Mg-0.5%Si for all ageing conditions studied but was absent in Si-free Al-3.62%Cu-1.66%Mg. In addition, S and phases were observed in both alloys. The volume fraction of phase in the Si containing alloy was substantially reduced by a pre-age stretch followed by ageing for 24 h at 265°C with S being the dominant precipitate type. The volume fraction of phase in the Si containing alloy was lower after ageing 24 h at 200°C than after 24 h at 265 and 305°C. Peak hardness was higher for the Si free alloy on ageing at 200 and 265°C, but the Si free alloy softened more rapidly, reflecting the more rapid coarsening kinetics of S compared with .     

Flow and fracture behaviour of Ni3(Al·Ti) single crystals tested in tension

The deformation and the fracture behaviour of the [0 0 1] orientated Ni₃(Al.Ti) single crystals were investigated to determine the relation between the positive temperature dependence of the flow stress in the -phase and the malleability of nickel-base superalloys. The positive temperature dependence of the flow stress is observed in the [0 0 1] orientation below about 1000 K (T _p) and the failure occurs in a catastrophic and brittle manner after considerable plastic deformation. The room temperature fracture stress increases with increase in the angle between the [0 0 1] orientation and the tensile axis at 290 K, and it is well expressed by a crack propagation criterion only by considering the effect of the normal stress on the {1 0 0} cleavage plane. The cleavage fracture stress for the [0 0 1] orientation is nearly independent of temperature below T _p, while the elongation decreases with temperature in contrast to the yield stress. The cleavage fracture of Ni₃(Al.Ti) single crystals is explained by the rapid decrease of the mobile dislocation density due to a dislocation pinning mechanism based on the cube cross-slipping of the screw superdislocations which causes the positive temperature dependence of the flow stress. The insufficiency of the malleability of nickel-base superalloys seems to be attributed to that of the -Ni₃ (Al.Ti) phase, and the hot working of nickel-base superalloys near T _p in the -phase should be avoided.     

Reactivity of Coal Activated by Mechanochemical Treatment

The paper presents new information on the transformation changes in the chemical structure of coal caused by mechanical activation using the GACL procedure. In the case of chemical treatment of Pittsburgh bituminous coal, the CAPTO method has confirmed a temperature T _max shift for identification of carbonaceous and sulfur compounds (T _max/S_organic) – 50°C; T _max/C_organic – 50°C). The temperature reduction of the thermal destruction maximum of carbonaceous and sulfur aromatic compounds is a result of activation of the coal structure of bituminous coals. The environmental effect of desulfurization (approx. 70%), detoxication, e.g., removal of arsenic (approx. 95%) and increase in the content of humic acids in the treated coal batch, have been proved by mechanical activation of Nováky brown coal using the GACL procedure. It is possible to improve the technological parameters of chemical treatment by optimization of the GACL procedure.     

Spin-lattice relaxation in gadolinium-doped calcium tungstate

The spin-lattice relaxation of the S-state ion Gd³⁺ in a calcium tungstate host lattice has been examined at 37.5 GHz over the temperature range 1.5 to 30 K. The gadolinium concentrations in the doped single crystals used were about 50 ppm. Single exponential recovery was observed and the spin-lattice relaxation time (T ₁) varied from about 14 msec at 1.5 K to 0.03 msec at 30 K, measured with =90° and =8°. It was found that T ₁ varied with temperature (T) as T ₁ T ^–1 below 8 K and as T ₁ T ^–3 between 8 and 30 K. The experimental data was fitted by the expressions T ₁ ^–1 =35 T+0.5 T ³ and T ₁ ^–1 =35T+0.1 T ^3.6 for crystals of nominal gadolinium concentrations 0.005 wt % and 0.05 wt % respectively. The difference between the observed dependence and the T ^–5 variation predicted in the Raman region for an S-state ion in a perfect lattice is attributed to defects. Measurements in the -plane at 4.2 K showed that T ₁ was anisotropic with a maximum value at =25° about three times greater than the minimum value obtained at =55°. The angular positions at which these features occur show a remarkable coincidence with the acoustic axes of symmetry of the crystal, which have recently been determined by ultrasonic methods.     

The influence of oxygen and nitrogen on the growth of intermediate phases during the bonding of iron to aluminium

The reaction between aluminium, and iron containing a range of oxygen and nitrogen up to 0.08% and 0.009% respectively, has been investigated. The kinetics of the early stages of intermediate phase formation have been determined using quantitative metallography, and the results are presented as T-T-T curves. The rate of reaction to form intermediate phases is shown to decrease with increasing oxygen and nitrogen content. In the later stages of intermediate phase growth, the nature and identity of the phases have been established using X-ray diffraction, optical and electron metallography. In the low oxygen and nitrogen specimens a multiphase layer of (FeAl₃),(Fe₂Al₅) and (FeAl₂) phases develops. In the high oxygen and nitrogen specimens no(Fe₂Al₅) or (FeAl₂) is present, but a thin layer of (FeAl₃) forms at all temperatures up to 640° C together with the spinel FeAl₂O₄ and possibly the oxy-nitride Al₂O₃/AlN. Simple bend tests indicate that when the layer at the interface consists solely of iron-aluminium intermediate phases the bonding is poor. When the layer is(FeAl₃) together with ceramic phases as in the high oxygen and nitrogen specimens, bonding is good and the aluminium is still adherent even after 1000 h at 640° C. It is also shown that the accelerating effect of cold work on intermediate phase formation is suppressed by increased oxygen and nitrogen content.     

Sintering mechanisms of 0.99 SnO2-0.01 CuO mixtures

The densification kinetics of 0.99 SnO₂-0.01 CuO molar mixtures have been studied between 850 and 1150 °C. Both experimental analyses and theoretical modelling show the role of a liquid phase for sintering temperatures T _s 940 °C: sintering is controlled by a liquid phase after a fast shrinkage due to grain rearrangement. The analytical formulation of the shrinkage behaviour suggests that dissolution at the solid-liquid interface is the limiting process when T _s 1000 °C and diffusion is the limiting step at higher temperatures.     

Dielectric and pyroelectric properties of PZFNT/PZT bimorph thin films

Pyroelectric Pb_1,1(Zr_0.58Fe_0.2Nb_0.2Ti_0.02)O₃/Pb_1.1(Zr_0.9Ti_0.1)O₃ (PZFNT/PZT) bimorph thin films are processed via a modified sol-gel method on highly textured (1 1 1)Pt/Ti/SiO₂/Si substrates. XRD and SEM investigations show full pyrochlore to perovskite phase transformation after annealing at 750 °C. XPS depth profiling reveals diffusion of Fe leading to a broad transition layer. The PZT 90/10 bottom layer was shown to be effective for dielectric permittivity control of the bimorph structure. The small signal dielectric constant, , was determined as 580 at 10 kHz. The temperature dependence of is shown to exhibit a single maximum at approximately 195 °C. The C–V characteristics of the bimorph structure show the typical behavior of ferroelectric perovskites. These results are attributed to microstructural effects, particularly the presence of a broad transition layer. The pyroelectric properties are reported in the temperature range from 20 to 60 °C and compared to monomorph PZT and PZFNT films. It is shown that the bimorph thin film has higher pyroelectric coefficient and detectivity than the constituent monomorph films.     

An apparatus for measuring the thermal conductivity and diffusivity of solid materials

An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation thermal conductivity at the mean temperature of specimens, W/m· °C - Q power of the central heater, W - F cross section area of a specimen, m² - t_1,2 temperature drop across the specimens, °C - ₁, ₂ difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m - t temperature, °C - time coordinate, min - d₁= (d_1u+d_1l )/2 mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m - d₂= (d_2u+d_2l )/2 mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m - dt(d₁,)/d rate of temperature rise at section d₁ of the specimen at time, °C/h - t=t₁+t₂ sum of temperature drops in the specimens at time, °C - m heating rate, h^–1 - a thermal diffusivity of specimens, referred to their mean temperature, m²/h - =m/a, m^–1 b=¦(t_u–t_l)/t_u¦ heating nonuniformity factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972.