Fatigue crack growth behaviour of tungsten carbide-cobalt hardmetals

Fatigue crack propagation studies have been carried out on a range of WC-Co hardmetals of varying cobalt content and grain size using a constant-stress intensity factor double torsion test specimen geometry. Results have confirmed the marked influence of mean stress (throughK _max), which is interpreted in terms of static modes of fracture occurring in conjunction with a true fatigue process, the existence of which can be rationalized through the absence of any frequency effect. Dramatic increases in fatigue crack growth rate are found asK _max approaches that value of stress intensity factor ( 0.9K_IC) for which static crack growth under monotonic load (or static fatigue) occurs in these materials. Lower crack growth rates, however, produce fractographic features indistinguishable from those resulting from fast fracture. These observations, and the important effect of increasing mean free path of the cobalt binder in reducing fatigue crack growth rate, can reasonably be explained through a consideration of the mechanism of fatigue crack advance through ligament rupture of the cobalt binder at the tip of a propagating crack.     

The stacked lamellar texture on the fracture surfaces of fibre composites

A fracture surface texture, which has been variously termed as lacerations, hackles or serrations, is often observed on the matrix surface of fibre composites, most often in resin-rich regions. This texture, referred to here as a stacked lamellar texture to emphasize its plate-like nature, was studied in an E-glass/epoxy composite. Scanning electron fractographs of these materials suggest that the stacked lamellar texture arises from crack fingers due to a meniscus instability mechanism interacting with a reorienting stress field.     

An extremely low noise photodetector based on the single electron transistor

We have demonstrated the use of the single electron transistor (SET) as an amplifier for a photodetector operated at 20 mK. The unparalleled low input noise of the SET permits the detection of very small numbers of charge carriers generated in a bulk p-type Si substrate. We present data showing the response of the detector when it is illuminated by extremely low levels of red light (=650 nm). Although we are not able to prove that individual charge carriers are being detected in our system, the magnitude of the detector response and the level of noise in the system are in good agreement with single charge, and therefore single photon, detection. From the dark current noise of 0.06 electron/s, we estimate a noise-equivalent power NEP=2×10^–21 W/Hz for infrared light with =30 µm, and from this calculate a detectivity D*=8×10¹⁷ cm-Hz/W.     

The Interplay of Electronic and Nuclear Magnetism in PtFe x at Milli-, Micro-, and Nanokelvin Temperatures

We have measured ac susceptibility, nuclear magnetic resonance, and nuclear heat capacity of two PtFe _x samples with concentrations of magnetic impurities x = 11 ppm and 41 ppm at magnetic fields (0 ± 0.05) mTB248 mT. The susceptibility data have been measured at temperatures of 0.3 KT100 mK, no hint for nuclear magnetic ordering could be detected to a temperature of 0.3 K. The nuclear heat capacity data taken at 1.4 KT10 mK show enhanced values which scale with x at low polarization. This effect is described by a model assuming an internal magnetic field caused by the impurities. No indication for nuclear magnetic ordering could be detected to 1.4 K. The nuclear magnetic resonance experiments have been performed on these samples at 0.8 KT0.5 mK and 2.5 mTB22.8 mT as well as on three other samples with x = 5, 10, 31 ppm in a different setup at 40 KT0.5 mK and at 5.4 mTB200 mT. Spin-lattice and effective spin-spin relaxation times ₁and ₂ ^* of ¹⁹⁵ Pt strongly depend on x and on the external magnetic field. No temperature dependence of ₁and ₂ ^* could be detected and the NMR data, too, give no hint for nuclear magnetic ordering to 0.8 K.     

Magnetic properties of highly dilutedPdFex andPtFex-alloys. Part II. Susceptibility at micro- and milli-kelvin temperatures

We have measured the 16 Hz susceptibility of the giant magnetic moments induced by Fe impurities in highly dilutedPdFe_x andPtFe_x samples with 2.5 ppm x 75 ppm in a wide temperature range, 30 K T 300 mK, and at static magnetic fields 0,01 mT B 25 mT. We find spin glass freezing at Tf(X)/X0,19mK/ppm Fe forPdFe_x and the larger value 0.26 mK/ppm Fe forPtFe_x. This is the first observation of spin glass freezing inPtFe_x. In the low-temperature range T 0.5T_f(x), the susceptibilities follow — ₀ T with small zero-temperature ₀ values forPdFe_X and vanishing ₀ values forPtFe_x. In the paramagnetic high-temperature range, we find (T — )^it-1 at T 10 mK independent of x forPdFe_x, and at T 2Tf(x) dependent of x forPtFe_x with vanishing values for both systems. The data compare well to the predictions of the Thouless-Anderson-Palmer TAP approach of the Sherrington-Kirkpatrick SK model for spin glasses.     

Evidence for collective excitations in superconducting tin whiskers

Based on the assumption that a phase-slip center in a clean quasi-one-dimensional superconductor excites a collective oscillation, the time-averaged value of the electrochemical potential of quasiparticles is calculated. At larger distances from the phase-slip center, swings below (or above) the electrochemical potential _p of the Cooper pairs. This makes it possible to understand the unexpected results of previous measurements.     

Phase decomposition of liquid-quenched β-type Ti-Cr alloys

Phase decomposition behaviour of liquid-quenched (bcc) type Ti-Cr alloys was investigated by means of transmission electron microscopy and hardness measurements. It was found that decomposition of to ₁ (Ti-rich, bcc) + ₂ (Ti-lean, bcc) takes place in the intermediate composition range of the Ti-Cr system. This experimental result proves the theoretical prediction made by Menon and Aaronson, but the observed ₁ + ₂ two-phase field expands towards higher temperatures than the predicted binodal line. The coherent ₁ + ₂ two-phase state exhibits the so-called 100 modulated structure and it was concluded that the formation of such a structure is a result of spinodal decomposition of the -phase. We obtained time-temperature-transformation (TTT) diagrams of -type Ti-30, 40 and 50 at % Cr alloys. A typical sequence of structural change is coherent ₁ + ₂ incoherent ₁ + ₂ incoherent ₁ + ₂ + grain boundary precipitates stable state of + TiCr₂ or + TiCr₂. Not all the states in the above sequence appear, depending on alloy composition, liquid-quenching rate and ageing temperature.     

Behaviour of amorphous poly(ethylene terephthalate) annealed at T<T g by thermally stimulated currents

Thermally stimulated current (TSC) discharges in open circuit of amorphous poly(ethylene terephthalate) (PET) corona-charged electrets show a heteropolar relaxation at 87 °C, ₁ between and peaks. This relaxation tends to become homopolar when the sample is annealed at temperatures below the glass transition temperature. This is due to the formation of a trapped charge density on the surface of the material that originates, during the TSC discharge, a current that counteracts the one that results in ₁ This trapping effect, which initially is null, increases with annealing due to the rise in resistivity. On the other hand, TSC discharges in short-circuited annealed samples result in a heteropolar peak, ^*, that corresponds to ₁ The area of ^* increases with the annealing time in a bounded way. This peak is related to the formation of thermal nuclei (embryos) in the bulk of the material that act as heterogeneities. This suggests that ₁ is associated with a barrier-type polarization. If the annealed sample is heated to temperatures above the glass transition temperature, the tendency to the inversion of ₁ vanishes and ^* disappears, whereas and are modified. This suggests that relaxation is related to a Maxwell-Wagner-Sillars effect.     

Distribution of α-AlFeSi and β-AlFeSi particles in surface layer of AA6063 alloy billets after heat treatment

We developed the EPMA mapping method of small -AlFeSi(Al_8.3Fe₂Si) and -AlFeSi(Al_8.9Fe₂Si₂) particles in the billets of Al-Mg-Si alloys such as AA6063 alloys. To discriminate between -AlFeSi and -AlFeSi particles we used the relative X-ray intensities of Fe/Si ratio, the I _Fe/I _Si ratio, instead of the Fe/Si mass ratio. To obtain the I _Fe/I _Si ratio, we used a Monte Carlo method. In this study, using this method the mapping of -AlFeSi and -AlFeSi particles in the surface layer of AA6063 billets after the heat treatment (for 2 h at 580°C) was done. Namely, the distribution of -AlFeSi and -AlFeSi particles of zones from the billet surface to a depth of 800 m was measured. Results showed the zone from the surface to a depth of 200 m was occupied mainly by -AlFeSi particles and the zone from a depth of 200 m toward the center was occupied mainly by -AlFeSi particles. From these results, it was found that if we remove zones from the surface to a depth of 200 m, we can remove the majority of the -AlFeSi particles, and thus improve the quality of anodizing performance of Al-Mg-Si alloys extrusions.     

Ultrasonic crack characterization via a constrained inversion algorithm

The Kirchhoff approximation is used to show that the time domain impulse response of an isolated flat crack can be given a simple geometrical interpretation in terms of the derivative of a projected length function. For an elliptical crack, this derivative can be obtained explicitly to yield the two edge-diffracted waves which originate from the flashpoints of the crack. An explicit coordinate invariant expression is obtained from this elliptical crack solution which relates the time difference, t, between the arrival of these edge-diffracted waves and the crack size and orientation. Previously, we have proposed that this expression, together with t measurements in different scattering directions, could be used in a regression analysis as the basis for performing a constrained inversion of crack scattering data (i.e., where we attempt to obtain the best equivalent flat elliptical crack that fits the scattering measurements). Here we will demonstrate some results of applying the proposed algorithm using noisy synthetic data. The sensitivity of the results to both, number of measurements and transducer orientation, will be discussed.     

The effect of Si,Zr, Al and Mo on the structure and strength of Ti martensite

The structure and strength of martensite in near titanium alloys have been studied in the composition range (wt %) up to 10% Zr, 6%, Al, 1/2% Mo, 2.4% Si. [0001], 1/3 11¯20 dislocations, 1/3 10¯10 stacking faults and approximately {10¯11} twin related martensite plates are found to be common features of the martensite. Martensite midribs consist either of finely transformed material between martensite plates, or regions of low dislocation density within martensite plates.The martensite morphology is related to the alloy composition, changing from massive to plate-like with increasing solute content. The strength of the martensite is controlled largely by solid solution strengthening.     

Simulation of the Process of Water Freezing in a Round Pipe

The problem of freezing of pure water in a round pipe is treated with due regard for convection under asymmetric thermal boundary conditions in the absence of motion along the pipe. The problem is solved numerically using the control volume approach, SIMPLER algorithm, and the enthalpy method. Results are obtained for three Grashof (Gr) and six Biot (Bi) numbers: Gr = 1.55 × 10⁶, Bi = 0.305 (0 < ), Bi = 0.044 ( < 2); Gr = 1.24 × 10⁷, Bi = 0.610 (0 < ), Bi = 0.087 ( < 2); Gr = 9.89 × 10⁷, Bi = 1.220 (0 < ), Bi = 0.174 ( < 2). The correctness of calculation of the problem disregarding free-convection flows is analyzed.     

Spin hydrodynamic equations with external disturbances and suitable Green's functions for superfluid3He-B. New onsager relations

The spin hydrodynamic equations for superfluid³He-B have been obtained for the case of external, time-dependent fields. On the basis of a microscopic approach, expressions are found for additional terms in equations containing these fields. Considering the linear response of the system to the switching on of external fields, formulas are found for suitable Green's functions (magnetization-magnetization, rotation-rotation, magnetization-rotation, rotation-magnetization). The rotation-rotation Green's function has the 1/q ² singularity characteristic of superfluid systems. Connections between Green's functions lead to relations among kinetic coefficients v, ₁, and ₂. It is also shown that there is a conserved quantityQ ^(B) = div v _s ^(B) that describes sources or magnetic type charges (monopoles) of the superfluid velocity v _s ^(B) . Comparison with the phenomenological approach suggests thatQ ^(B) is proportional to a pseudoscalar giving the projection of the spin density onto the vector describing the axis of rotation.     

The age hardening effect in Ti-6 Al-4 V due to ω and α precipitation in the β grains

The structure at room temperature of a quenched TA6V titanium alloy has been investigated. This structure is + or + according to the treatment temperature; it is always metastable. During ageing the grains decomposed by the reaction + + +; this decomposition was accompanied by a large increase of the 0.2% yield stress. No structural modification was observed in. The and phase of TA6V were separately investigated in the form of single-phase alloys. The hardness of was insensitive to ageing, while was considerably hardened by and; we deduced that the strengthening of the minor phase during ageing is mainly responsible for the hardening of TA6V.     

The structure of the γ′ extended solid solution in a splat-cooled Ag-50 at.% Cu alloy

The structure of the extended solid solution in electron transparent areas of a splatcooled Ag-50 at.% Cu alloys was examined by transmission electron microscopy. This phase was usually found to be spinodally decomposed at large grain sizes (–1m in diameter), in contrast to X-ray diffraction data indicating that the solid solution was undecomposed. A solidification model for rapidly quenched eutectic alloys is proposed to account for the observed structure of the splat-cooled alloy. A transformation curve for the spinodal decomposition of is also calculated and related to predictions derived from the solidification model.     

Influence of Multiple‐Scattering Processes on the Laser Probing of Biological Tissues

Theoretical aspects of multiplescattering processes in laser probing of biological tissues have been considered. The method of digital dynamic specklephotography has been described. The results of experimental studies of the nearsurface blood flow and stressedstrained states in a pinstructure–toothroot model are presented.     

Fatigue striation in a wide range of crack propagation rates up to 70 μm/cycle in a ductile structural steel

The relationship between striation spacing and fatigue crack propagation rate up to 70 m/cycle was investigated for a ductile structural steel, qualified as JIS SM58Q. A modified compact-type specimen 400 mm wide and a centre-cracked specimen 200 mm wide were tested at a stress ratio, R, of 0 and 0.8. The fracture surface of the specimen was examined in detail under a scanning electron microscope. The crack propagation rate was expressed by a power function of the range of stress intensity factor from 0.1 to 70 m/cycle for R=0 and to 0.5 m/cycle for R=0.8. The striation spacing coincided with the fatigue crack propagation rate over the range 0.1 to 70 m/cycle. The profile of striation was found to be a ridge and valley type, and the ridges on one fracture surface coincided with those on the matching surface. It is suggested that the striation is formed by a plastic blunting mechanism.     

Modern Problems of Intensification of Heat Exchange in Channels

The current achievements in the field of intensification of heat exchange in tube heatexchange apparatus are considered. Requirements for highefficiency heattransfer surfaces have been formulated. Problems of intensification of heat exchange in bundles of finned tubes and in heatexchange apparatus under conditions of condensation and boiling of heattransfer agents and under scaling conditions have been investigated. Highefficiency designs of heatexchange apparatus are presented.     

Theoretical estimation of the effect of interfacial energy on the mechanical strength of spinodally decomposed alloys

New interfaces are produced on the slip plane when a crystal with continuous composition fluctuation arising from spinodal decomposition is deformed by slip. In this work, the energy of such interfaces is evaluated for both modulated and mottled structures, and their effects on slip behaviour are discussed. It is concluded that the contribution of this interfacial energy is large enough to account for the age-hardening concomitant with spinodal decomposition.     

Texture study of two molybdenum shaped charge liners by neutron diffraction

The textures of two different conical shaped liners, fabricated by the same forging processes from arc-cast and powder-sintered ingots, were investigated by using neutron-diffraction measurements and three-dimensional orientation-distribution-function (ODF) analysis. The major textures of both liners could be described by the (1 1 1) uv w and (1 0 0) u v w type. The two liners had essentially identical texture at the 8 cm position (measured from the base of the cone) with strong sheet-type texture components, i.e. (1 1 1) ¯1 0 1, (1 1 1) ¯1 1 0 and (1 0 0) 0 1 1. However, the dominant textures at the 3 cm positions were 1 1 1 and 1 0 0 fibre textures with the fibre axes oriented parallel to the normal direction in both liners. A strong cube texture was observed at the 3 cm position of the arc-cast liner but it was not observed for the powder-sintered liner. The arc-cast liner had a generally higher degree of texture than the powder-sintered liner.