Stress relaxation in zirconium carbide. Report 1. Test method and stress relaxation curves

A method of stress relaxation tests with use of four-point bending is described. Experimental data is given on pure stress relaxation in ZrC _1.00 with different grain sizes (d= 6–55m in the area of the ductile-to-brittle temperature (1600–2200C)Translated from Problemy Prochnosti, No. 1, pp. 76–83, January, 1994.     

Chebyshev polynomial approximation of the roots of the transcendental equation Μ tan Μ=b

A polynomial approximation of the roots of the equation tan=b are tabulated, valid uniformly on the interval b [0, ].Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 20, No. 2, pp. 347–348, February, 1971.     

Determination of the electric field gradient and relaxation time measurements in scandium metal at very low temperature

We present the results of measurements on a single crystal sample of scandium metal at temperatures down to 100 K using nuclear quadrupole resonance (NQR). We find two regimes in the relaxation curves: an initial fast relaxation, followed by a slower relaxation consistent with the three exponential recovery expected for an I = 7/2 system in zero external magnetic field. The Korringa constant for this longer time relaxation in our sample is 90 +- 9 msec K^–1. By observing deviations in the ratio of the intensities of adjacent nuclear spin transitions at the lowest attainable temperatures, we have been able to make a determination of the sign of the total electric field gradient present in the crystal. We find that the lowest energy state of the nuclear spin system corresponds to m _I = +-7/2. A combination of these deviations and pulse NQR allows us to use this system as an absolute thermometer in the Kelvin regime.     

A new process for atomization of metal alloys

A laboratory apparatus was constructed to atomize metal alloys by forcing them through sintered ceramic disc filters. The process combines filtration of oxides and/or undesirable second phase particles with atomization. Sintered Al₂O₃ and SiO₂ disc filters with average pore sizes in the range of 36 to 150 m were used. The effectiveness of various filters in removing synthetic inclusions from Al-Ti-B melts was studied. 2 to 10 m size TiB₂ particles were successfully filtered out. Atomization experiments were done with pure aluminium and 7075 aluminium alloy. Spherical powders, 150 to 2000 m in size, of 7075 aluminium alloy with secondary dendrite arm spacings between 4 to 8 m, were cold compacted and extruded into a billet. Room temperature longitudinal properties of the billet in T6 condition were: YS 80×10³ psi, UTS 94.3×10³ psi, elongation 15% and R.A. 42%.     

Mechanical relaxation of 4 wt% Y2O3-ZrO2 tetragonal single crystals

The mechanical relaxation was examined by a resonance piezoelectric method for a 3.5 wt % Y₂O₃-ZrO₂ polycrystal and 4 wt% Y₂O₃-ZrO₂ tetragonal single crystals with orientations in the 100 and 111 directions. The relaxation was observed for the 111-oriented crystal, but not for the 100-crystal. The results indicated that the relaxation was active only for the elastic compliance, S₄₄, and inactive for (s ₁₁–s ₁₂). The amplitude of the anelastic relaxation measured for the polycrystalline and the 111-crystal body was 4.2 × 10^–12 m²N^–1 and 6.7×10^–12 m² N^–1, respectively. An observed broad relaxation peak suggested that complex processes exist even in single crystals.     

Extended structural defects in α-Hgl2 single crystals

Extended structural defects in both -Hgl₂ crystals grown in solution or from the vapour-phase were studied by optical microscopy, light scattering, SEM operated in cathodoluminescence and in secondary electron mode, X-ray topography, neutron, - and X-ray rocking curves and oscillating crystal X-ray diffraction. The observed dislocations were compared with theoretically calculated dislocations. Dislocation loops, having diameters ranging from 2 m to 500 m, are observed on all low index faces. Hohlstellen (lens-shaped voids) having axes along the [0 0 1] direction, less than 1 m in thickness, and diameters lying in the (001) planes, ranging from 2 m to 10 m are characteristic defects. Observed plastic deformations like glide sheets and bands, tilt and twist boundaries, kink and fatigue bands, ridges and rumplings were characterized. Growth rings, spherical void inclusions 10–30 m in diameter, orthogonal walls of forest screw dislocations parallel to 1 00 planes, and streaks (planar void sheets crossing the (001) planes) were only observed in crystals grown from the vapour-phase. Cross-penetration twins having (1 1 4) twin planes are described. The possible formation of stacking faults was analysed. The mosaicity of solution-grown crystals ranges from 1 to 6. A characteristic cellular structure, having a cell size ranging from 2 um to 10 m, was observed in all the crystals examined and correlated to local deviations from the stoichiometric composition. Solid lens-shaped inclusions, having diameters ranging from 3 m to 500 m and thicknesses ranging from 0.3 m to 50 m, respectively, are entrapped in many crystals and correlated to spiral hillocks observed on 001 growing faces.     

Mössbauer study of Fe magnetic state at the interface between Fe-Al-Si thin films and crystallized glass substrate

The magnetic state of Fe atoms at or near the interface between Fe_74.3Al_9.8Si_15.9 sendust magnetic thin films and SiO₂-based crystallized glass substrate (Fotoceram, Corning Co.) has been examined using conversion electron Mössbauer spectroscopy. The thicknesses of sputtered films are 0.05–2.0 m, and annealing conditions are at 500 C for 1 H. The excellent soft magnetic properties are not obtained for films with a thickness of less than 0.5 m. The presence of ferromagnetic Fe atoms with internal magnetic fields of 24.3–24.9 MAm^–1 is confirmed at or near the interface, indicating the formation of an Fe-rich phase such as Fe₉₀Si₁₀. The fraction of Fe atoms forming the Fe-rich phase at or near the interface is estimated to be around 20.... The formation of the Fe-rich phase is one of the main reasons for the degradation of the soft magnetic properties of sendust films deposited on SiO₂-based crystallized glass substrate, even though the DO₃-type ordered structure has also been formed.     

Josephson effect in indium bridges with large dimensions

We report experiments searching for Josephson behavior in indium bridges with dimensions in the following range : thickness 2–3 m ; length 3–15 m ; width 10–100 m. Josephson behavior has been observed in bridges up to 20 m wide prepared by a single-step evaporation procedure and photolithography. In this case the V-I characteristics, including the rf-induced step structure, can be well described by the RSJ model if the amplitude of the applied rf current exceeds a distinct value. These results and in particular the magnitude and temperature dependence of the normal resistance of the Josephson element can be explained by the formation of an extended, two-dimensional phase slip center. Indium bridges prepared by a multiple-step evaporation method often show complicated behavior, the Josephson effect being localized somewhere within a contamination layer separating the underlay films from the overlay film representing the bridge. Such multiple-step evaporation procedures should therefore be avoided.Supported by a grant of the Deutsche Forschungsgemeinschaft.     

Stress relaxation in hot-drawn low density polyethylene

The tensile stress relaxation behaviour of hot-drawn low density polyethylene, (LDPE), has been investigated at room temperature at various draw ratios. The drawing was performed at 85° C. The main result was an increase in relaxation rate in the draw direction, especially at low draw ratios when compared to the relaxation behaviour of the isotropic material. This is attributed to a lowering of the internal stress. The position of the relaxation curves along the log time axis was also changed as a result of the drawing, corresponding to a shift to shorter times. The activation volume, , varied with the initial effective stress ₀ ^* according to ₀ ^* 10kT, where ₀ ^* =₀ — _i, is the difference between the applied initial stress, ₀, and the internal stress _i. This result supports earlier findings relating to similarities in the stress relaxation behaviour of different solids.     

Specific heat near the lambda point in 4He and 3He-4He mixtures: Test of universality of the critical exponent and the amplitude ratio,and observation of the critical-tricritical crossover effect

The specific heat under saturated vapor pressure of pure ⁴He and of six ³He-⁴He mixtures up to X = 0.545 was measured in the temperature range 3 × 10^–6 <¦T-T ¦ <10^–2 K. The critical exponents and along the path = are independent of X up to X = 0.545, where (= ₃ – ₄) is the difference between chemical potentials. If we take account of higher order terms, the exponent (= ) and the amplitude ratio A /A are independent of X up to X = 0.545. The values of and A /A are –0.023 and 1.090, respectively. The critical-tricritical crossover effect was observed for X = 0.545 and the boundary of crossover region closest to the critical region was at /T = (1–2) × 10^–4, where is the distance ¦T – T ¦ along the path = . This value is in good agreement with the estimated value by Riedel et al. But, remarkably, in the case of X = 0.439 this effect was not observed.     

Formation and characteristics of lead lanthanum zirconium titanate thin films formed by using the r.f. sputtering method

PLZT (lead lanthanum zirconium titanate) thin films were prepared by using the r.f. magnetron sputtering method and post-annealing for crystallization at 650 C. The films which were annealed at 650 C for 10 min consisted of a metastable phase and a stable phase. However, another film which was annealed at 650 C for 20 min had only stable perfect perovskite phase. The stability of the post-annealed thin film and substrate interfaces was observed by using scanning electron microscopy. The longer the annealing time, the more unstable were the interfaces. By analysing the EDX data, the composition difference between the sputtering target and thin films, and the composition variation between as-deposited and post-annealed PLZT were studied. The films annealed at 650 C for 20 min showed good ferroelectric and electrical properties with a remanent polarization (P _r) of 11.5 C cm^–2, and a coercive field (E _c) of 164 kV cm^–1.     

Barium titanate fabricated from fur-fibres

Long-fibrous barium titanate (BaTiO₃) particles were prepared by a hydrothermal reaction of potassium titanate hydrate (2K₂O·11TiO₂·3H₂O) and barium hydroxide (Ba(OH)₂). Effects of preparation conditions on crystal structure and powder morphology were examined. Fur-fibres of K₂O·4TiO₂, 1–10 mm long and 1–100 m in diameter, were obtained by heating a mixture of K₂CO₃ and TiO₂ powders at 1000 C for 100 h. Keeping the fur-fibres in ion-exchanged water for 4 days gave fur-fibres of 2K₂O·11TiO₂·3H₂O). Long-fibrous BaTiO₃, with fibres 100m–1mm long and 1–10 m in diameter, was obtained by a hydrothermal reaction of the hydrate and Ba(OH)₂ (Ba/Ti ratio of 1) at 150 C for 24 h. As-prepared long-fibrous BaTiO₃ was composed of fine crystallites (average size about 270 nm) of cubic phase. The cubic phase and morphology of fur-fibres were maintained up to 1250 C, but heat treatment at 1300 C brought about a growth of crystallites to a few micrometers and a phase transformation to tetragonal phase. It was found that the hydrothermal reaction was effective in producing crystalline BaTiO₃ powder at a low temperature of 150 C.     

Hot-roll bonding of aluminium matrix composites with different volume fractions of alumina

Metal matrix composites (MMC) with volume fractions of 0.08, 0.11 and 0.14 alumina (Al₂O₃) were fabricated by roll bonding. This low-cost approach to MMC manufacture has the flexibility of controlling the volume fraction of the MMCs by varying the oxide thickness on the anodized aluminium foil, and the number of layers of these foils to be sandwiched between plain aluminium sheet as the matrix metal. The fragmentation of the laminate alumina is achieved by a series of hot- and cold-rolling operations. The resulting reinforcing alumina particles have platelet shape measuring approximately 20 m×11m×5 m instead of a stringer shape as expected. It is found that the improvement in modulus and strength did follow very closely with the rule of mixtures. A small scatter of measured data, especially the resistivity of the MMCs, was observed. This can be explained by the inefficient bonding between the reinforcing alumina and the matrix metal as demonstrated later in this study.     

Two-stage nuclear demagnetization refrigerator

Two-stage nuclear demagnetization has been performed using PrCu₆ and Cu as coolants. The Cu nuclear stage reached temperatures as low as 10 K with a rate of temperature rise of less than a few K/h. The corresponding conduction electron temperature is estimated to be less than 50 K. A nuclear orientation thermometer of Al ⁵⁴Mn has been successfully used to measure temperatures down to 10 K.Supported by the Japan Society for the Promotion of Science.     

Transport property and battery discharge characteristic studies on 1−x(0.75Agl∶0.25AgCl)∶ xAl2O3 composite electrolyte system

Various experimental studies on a new fast Ag⁺ ion-conducting composite electrolyte system: (1–x) (0.75Agl0.25AgCl)xAl₂O₃ are reported. Undried Al₂O₃ particles of size <10 m were used. The conventional matrix material Agl has been replaced by a new mixed 0.75Agl0.25AgCl quenched and/or annealed host compound. Conductivity enhancements 10 from the annealed host and 3 times from the quenched host obtained for the composition 0.7(0.75Agl0.25AgCl)0.3Al₂O₃, can be explained on the basis of the space charge interface mechanism. Direct measurements of ionic mobility as function of temperature together with the conductivity were carried out for the best composition. Subsequently, the mobile ion concentration n values were calculated from and a data. The value of heat of ion transport q* obtained from the plot of thermoelectric power versus 1/T supports Rice and Roth's free ion theory for superionic conductors. Using the best composition as an electrolyte various solid state batteries were fabricated and studied at room temperature with different cathode preparations and load conditions.     

Dielectric properties of chemically treated wood

Dielectric properties along the grain for absolutely dried untreated and seven kinds of chemically treated Sitka spruce (Picea sitchensis Carr.) woods were measured. Cole-Cole's circular arc law was applied to the results of the relaxation due to the motions of methylol groups. The following changes were caused by chemical treatments. In polyethylene glycol (PEG) impregnation, the distribution of relaxation times became very narrow, the generalized relaxation time (_m) was considerably decreased, and the relaxation magnitude (₀ – ) was slightly increased. In acetylation, the distribution of relaxation times became very broad, _m was considerably increased, and (₀ – ) was remarkably decreased. In propylene oxide treatment, the distribution of relaxation times became slightly narrow and _m was decreased. _m was slightly decreased in formalization, phenol-formaldehyde (PF) resin treatment and wood methyl methacrylate (MMA) composite. (₀ – ) was decreased in formalization and PF-resin treatment and was hardly changed in wood-MMA composite and heat treatment. The distribution of relaxation times was almost unchanged in formalization, PF-resin treatment, wood-MMA composite and heat treatment.     

The crystallization kinetics of a glass based on the cordierite composition studied by DTA and DSC

The crystallization kinetics of a glass based on the cordierite composition have been studied by DTA and DSC. Crystallization has been observed to be very dependent on the particle size of the glass employed, indicating a strong dependence on surface crystallization. For coarse particle sizes (eg. 600–1000 m) a single crystallization exotherm is obtained, corresponding to the formation of -cordierite. For smaller particle sizes (eg 212m) two distinct crystallization exotherms are resolved corresponding to the initial formation of metastable -cordierite, followed by its transformation at higher temperatures to the -cordierite phase. Activation energies for crystallization have been determined for different particle sizes of glass using a number of isothermal and non-isothermal methods, and the results compared. In general, agreement between DTA and DSC, and the various methods employed, is good, although the isothermal methods appear to reflect more strongly theearly crystallization processes, i.e. they relate more closely to the activation energy for the formation of the -cordierite phase. A value for the activation energy corresponding to structural relaxation at temperatures around the glass transition has also been determined for this cordierite glass.     

Excess carrier lifetime measurements in indium antimonide using a contactless laser technique

In this paper we offer a new method and technique for the separate measuring of both excess electron and excess hole lifetimes at temperatures from 77 K to 300 K. The contactless non-destructive method is based on simultaneous irradiation of the sample by CO₂-laser probe beam (_z = 10.6 m) and by the beam of a wavelength-tunable (5.3–6.3 m) CO-laser which is generating electron-hole pairs. The influence of the processing technology on charge carrier lifetimes in InSb is studied by this method.     

Fast adiabatic heating and temperature relaxation in near-critical fluids under zero gravity

Heat transport in supercritical CO₂ is studied under microgravity conditions. A large temperature and density region around the critical point is explored (CO₂ cells were filled at critical density= _c and off-critical densities= _c±0.18 _c). Local heating is obtained by using a small thermistor located in the bulk fluid. Through interferometric observations, a new mechanism of thermalization has been evidenced. Thermal expansion of a warm diffusing boundary layer around the heating thermistor is responsible for rapid adiabatic heating of the bulk fluid through the emission of pressure waves at the border. The scaled thickness of the thermal boundary layer follows a power law. When the heat flow stops, the bulk adiabatic heating instantaneously vanishes and the temperature relaxation inside the thermal boundary layer follows locally a diffusive process.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

On the measurement and physical meaning of the cleavage fracture stress in steel

Elastic-plastic two-dimensional (2D) and three-dimensional (3D) finite element models (FEM) are used to analyze the stress distributions ahead of notches of four-point bending (4PB) and three-point bending (3PB) specimens with various sizes of a C-Mn steel. By accurately measuring the location of the cleavage initiation sites, the local cleavage fracture stress _f and the macroscopic cleavage fracture stress _F is accurately measured. The _f and _F measured by 2D FEM are higher than that by 3D FEM. _f values are lower than the _F, and the _f values could be predicted by _f=(0.8––1.0)_F. With increasing specimen sizes (W,B and a) and specimen widths (B) and changing loading methods (4PB and 3PB), the fracture load P _f changes considerably, but the _F and _f remain nearly constant. The stable lower boundary _F and _f values could be obtained by using notched specimens with sizes larger than the Griffiths–Owen specimen. The local cleavage fracture stress _f could be accurately used in the analysis of fracture micromechanism, and to characterize intrinsic toughness of steel. The macroscopic cleavage fracture stress _F is suggested to be a potential engineering parameter which can be used to assess fracture toughness of steel and to design engineering structure.