Activated slip systems during yielding of α-β brass two-phase bicrystals

- brass two-phase bicrystals, consisting of fcc () single crystals and bee () single crystals, which were made by the solid state diffusion couple technique, were tensile-tested at room temperature in order to clarify the role of phase-interface on the deformation. The two-phase bicrystals had small concentration gradients in the- and-phases and satisfied the Kurjumov-Sach's orientation relationships i.e. {1 1 1} {1 1 0} and [1 1 0] [1 1 1] at the interface. The slip traces observed in bicrystals deformed to about 3% plastic strain showed a striking contrast between the- and-phases; the slip traces in the-phase were clear and straight, while those in the-phase were fine and wavy. The slip systems in the bicrystals were attributed to those observed in and single crystals, and were explained by a plastic strain incompatibility mechanism. The slip systems, originating at the interface or propagating from another phase, were observed on matching planes.On leave from Mechanical Engineering Department, Faculty of Engineering, Al-Azhar University, Cairo, Egypt.     

Bone formation induced by calcium phosphate ceramics in soft tissue of dogs: a comparative study between porous α-TCP and β-TCP

Two kinds of tri-calcium phosphate ceramics (Ca/P = 1.50), -TCP and -TCP, which has the same macrostructure and microstructure, but different phase composition, were implanted in dorsal muscles of dogs. The samples were retrieved at 30, 45 and 150 days, respectively, after implantation, and were analyzed histologically. There were critically different tissue responses between -TCP ceramic and -TCP ceramic. Higher cell populations were observed inside the pores of -TCP than those of -TCP, bone tissue was found in -TCP at 45 and 150 days, but no bone formation could be detected in any -TCP implants in this study. On the other hand, the bone tissue in -TCP seemed to degenerate at 150 days. The results indicate that porous -TCP can induce bone formation in soft tissues of dogs; while the rapid dissolution of the ceramic and the higher local Ca²⁺, PO ₄ ^3- concentration due to the rapid dissolution of -TCP may resist bone formation in -TCP and the less rapid dissolution of -TCP may be detrimental to already formed bone in -TCP.     

Interface characterization of a β-SiC whisker-Al composite

The nature of the interface, the orientation relationship of -SiC whisker (-SiC_w)-Al combination, and the misfit dislocation structures at the -SiC_w-Al interfaces in a -SiC_w-Al composite have been observed by a high-resolution transmission electron microscopy (HRTEM). It was shown that quite a good bonding between the whisker and the aluminium was achieved due largely to the lattice match between SiC and aluminium at the interfaces. The orientation relationship between the whisker and the aluminium was {002}_SiC{111}_Al; 110_SiC110_Al. The interface was clean, faceted and semicoherent. The misfit dislocation cores were located in the whisker side away from the -SiC_w-Al interfaces.     

Stability of metastable phases and microstructures in the ageing process of Al–Mg–Si ternary alloys

Precipitation behaviour of Al–Mg–Si alloys, with balanced (Mg/Si=2), excess silicon (Mg/Si<2) and excess magnesium (Mg/Si>2) compositions, were studied by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and Vickers hardness tests. Four significant exothermic peaks were observed in DSC curves which were attributed to metastable clusters, , and stable phases. The peaks corresponding to and were formed closely in the DSC curves but showed different behaviour in isothermal annealing. The additional peak verifying the precipitation of phases, which has recently been proposed by some workers, was not detected. Transmission electron microscope observations and Vickers microhardness tests showed that precipitates played a major role in improving the hardness, but not precipitates. © 1998 Chapman & Hall     

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.     

The formation of single-phase Si-Al-O-N ceramics

Si-Al-O-N ceramics have been prepared by hot-pressing mixtures of Si₃N₄, AIN and SiO₂ (with an addition of 1% MgO) having varying ratios of AIN/SiO₂. Microstructural analysis by transmission electron microscopy and Auger electron spectroscopy has demonstrated the progressive increase in grain-boundary silicate glass in pressings prepared from compositions with excess SiO₂ to compositions given by the formula Si_6–zAl_zO_zN_8–z. This formula represents the simple substitution of Al for Si atoms and O for N atoms in the hexagonalSi₃N₄ crystal. Microstructures for this balanced composition are essentially single phase, consiting of non-faceted, sub-micron, grains with a grain-boundary segregate layer of glass-forming silicate composition, containing impurity and additive metal ions, which may be detected only by Auger spectroscopy. This microstructure is in contrast with unbalanced compositions which contain faceted grains joined by a glassy silicate phase which is easily detected by electron microscopy. Final microstructural analysis combined with observations of density and phase content with progress of hot-pressing has confirmed the important role of liquid silicate formation and a solution-reprecipitation mechanism for densification. The presence of a 1% MgO additive is shown to accelerate this process, forming a low melting point silicate by reaction with SiO₂, assisting the early solution of AIN and the reprecipitation of substituted crystals.     

Formulas for evaluating the stabilization time of sluggish measuring instruments

Conclusions In this article formulas are suggested for calculating the stabilization time in ranges of 0<1 and 1.04<. These formulas are universal, they have a higher precision than has been hitherto obtained and they reflect the actual nature of the relationship between t_s and .Translated from Izmeritel'naya Tekhnika, No. 11, pp. 58–60, November, 1966.     

Mechanical properties and microstructure of β-SiAION-β-SiC composites by pressureless sintering

-SiAION--SiC composites containing up to 12 wt% -SiC were prepared by pressureless sintering. The strength of composites at room temperature remained relatively unchanged, whereas strength at 1200 °C increased for composites. The fracture toughness (K _IC) for composites was higher than that for -SiAION ceramics. The maximum value was 5.4 MPa m^1/2 for 6 wt% -SiC, and this was an improvement of 15% in comparison with -SiAION ceramics. From SEM observations, an improvement inK _IC values was attributed to crack deflections and branching-off of cracks. Intra-granular fractures were frequently observed in -SiAION. From TEM observations, -SiAION crystals were nanocomposites, within which existed the fine crystals in -SiAION crystal. For composite, -SiAION and -SiC crystals were directly in contact. The mismatching zone was observed in -SiC.     

Deformation behaviour of retained β phase inβ-eutectoid Ti-Cr alloys

Plastic deformation mode and its relation to tensile properties were investigated in retained phase of-eutectoid type Ti-Cr alloys. A plate-like single variant phase is induced during deformation of the most unstable phase having a minimum chromium content required to suppress martensitic transformation. A selected area electron diffraction pattern taken from a boundary region of the stress-induced phase plate can be explained by the idea that a single variant of phase is induced in a {3 3 2} 1 1 3 twin produced during deformation. Anisotropy in population of four phase variants decreases with increasing chromium content. On further increasing chromium content, deformation occurs by slip. Enhanced ductility is obtained in as-quenched Ti-Cr alloys accompanied by phase transformation or {332} 1 1 3 twinning during deformation, phase of as-quenched Ti-Cr alloys changes continuously from commensurate structure with sharp reflections to incommensurate structure with diffuse reflections with increasing chromium content. The obtained results in-eutectoid type Ti-Cr alloys are quite similar to those in-isomorphous type Ti-V alloys.     

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.     

The reaction hot-pressing of compositions in the system Al-Si-N-O corresponding to β′-sialon

The reaction hot-pressing at 1700 and 1750° C of a number of compositions in the system Al-Si-N-O corresponding to points spanning the-sialon phase line in the region of z=0.8 has been studied. Measurements have been made of densification rate and of the rate of conversion of-Si₃N₄ to-sialon. The densification process for these compositions may be described in terms of a liquid-phase assisted fast particle rearrangement process succeeded by Coble creep. The rates of these processes are sensitive to the volume of grain-boundary liquid phase present, which in turn is determined by the position of the compositional point in relation to the-sialon line. For systems containing very little grain-boundary phase, the vapour-phase transport of material may become important.     

o′-β′ sialon ceramics

Powders of Si₃N₄, Al₂O₃ and SiO₂ were mixed with Y₂O₃ as sintering aid and hot-pressed to form o- sialon. During sintering, the o phase preferentially precipitated in the temperature region of 1550 to 1600 °C, and the phase precipitated at temperatures of 1700 °C and above. The resultant microstructure consisted of dual phases of o and . The mechanical properties of o- sialon were improved with increasing amount of the phase. When SiO₂ required for the formation of the o phase was all included in the grain boundary phase, o- sialon exhibited a three-point bending strength as much as 1400 MPa. The oxidation resistance of o- sialon is expected to improve due to the presence of the o phase, but actually was not so good due to the presence of the grain-boundary glassy phase and impurities.     

The β ⇄ α transformation in dilute Ti-Mo alloys

An investigation has been made of the various phase transformations which occur when dilute Ti-Mo (0.5 and 1.0 wt% Mo) alloys are cooled from the phase field and are subsequently tempered in the + phase field. The morphology of the decomposition products varied with cooling rate and can be correlated with the competition between the formation of by martensitic and by diffusional processes. On isothermal transformation below theM _s, or upon tempering, phase precipitates grow heterogeneously from the supersaturated plates formed by shear. The precipitate habit plane is irrational and corresponds to the {334} plane.Formerly at Imperial College.     

Structure of martensite formed in Cu-Al-Fe single crystals duringin situ HVEM pseudoelastic tensile experiment

Single crystals of the CuAlFe alloy, containing 14.5 wt% Al and 2.2 wt% Fe were subjected toin situ tensile experiment using straining attachment in a 1 MV electron microscope. Loadelongation curves were obtained for three foil plane/tensile direction orientations: (001) [0 1 0], (0 0 1) [1 1 0] and (1 1 0) [¯1 1 2]. Each crystal was subjected to two cycles of pseudoelastic deformation up to maximum 2% strain, showing almost complete shape recovery. Structure observations and electron diffraction pattern indicated that during deformation of samples of (0 0 1) [1 1 0] and (1 1 0) [1 1 2] orientations, formation of ₁ martensite was observed and only at later stages narrow needles of ₁ nucleate in front of ₁. During pseudoelastic deformation in the (0 0 1) [1 0 0] direction, martensite forms as a mixture of narrow plates possessing either 2H or 18R structures. The following crystallographic relationship between the parent phase and both types of martensite was observed: [1 00] ₁ [101] ₁ and (0 0 1) ₁ (0 1 0)₁;(0 0 1) ₁ (0 1 0) ₁ and [1 1 0] ₁ [0 0 1] ₁. From the character of sidebands reflections presence of 1 0 1 1 0¯1 static displacement waves was inferred.     

An unusual behavior in the melting region of isotactic polypropylene crystals revealed by temperature-modulated DSC

We present a new method to analyze irreversible transformation kinetics of melting in polymer crystals with temperature modulated differential scanning calorimetry (TMDSC). In the melting region of several polymers, the apparent heat capacity obtained with TMDSC can be expressed as C _s + (|F _melt|/)/(1 + i ()), with the true heat capacity,C _s, the endothermic heat flow of melting,F _melt, the angular frequency of temperature modulation, , and the mean time of melting of each crystallite, , depending on the underlying linear heating rate, . In the case of isotactic polypropylene, the frequency dependence cannot be approximated by this formula. The dependence suggests the possibility of the retardation in the melting kinetics to follow temperature modulation.     

Structural transformation during sintering and annealing of beta alumina

Changes in the phase content, microstructure and lattice parameter are observed in stabilized/ alumina specimens following extended sintering and annealing treatments. The resulting state is dependent on composition of the starting powder and on temperature and duration of heat treatment; the kinetics of transformation between and alumina are generally slow and certain/ ceramics remain in a metastable state even after a prolonged high temperature anneal. Following post-sinter heat treatment, splitting of X-ray diffraction peaks reveals a segregation of the phase into two components of differing lattice parameter. With sintering schedules of a long duration the splitting may even be present in the as-fired condition as recently reported by Harbach [1]. The splitting is attributed to a structural change resulting from the expulsion of Na₂O from supersaturated grains.     

A method of joint determination of the effective coefficients of horizontal mixing of large particles and of external heat exchange in an organized fluidized bed

A method is proposed for the joint determination of the coefficients of horizontal particle diffusion and external heat exchange in a stagnant fluidized bed.Notation c_f, c_s, c_n specific heat capacities of gas, particles, and nozzle material, respectively, at constant pressure - D effective coefficient of particle diffusion horizontally (coefficient of horizontal thermal diffusivity of the bed) - d equivalent particle diameter - d_t tube diameter - H₀, H heights of bed at gas filtration velocities u₀ and u, respectively - H_a height of active section - l width of bed - L tube length - l _o width of heating chamber - N number of partition intervals - p=H/H₀ expansion of bed - s_n surface area of nozzle per unit volume of bed - S_h, S_v horizontal and vertical spacings between tubes - t_c, t₀, t_s, t_n, t_w initial temperature of heating chamber, entrance temperature of gas, particle temperature, nozzle temperature, and temperature of apparatus walls, respectively - u₀, u velocity of start of fluidization and gas filtration velocity - y horizontal coordinate - ^*, coefficient of external heat exchange between bed and walls of apparatus and nozzle - ₁, ₁, ₂, ... coefficients in (4) - thickness of tube wall - _b bubble concentration in bed - ₀ porosity of emulsion phase of bed - _n porosity of nozzle - =(t_s – t₀)/(t_c – t₀) dimensionless relative temperature of particles - _n coefficient of thermal conductivity of nozzle material - f, _s, _n densities of gas, particles, and nozzle material, respectively - _be=_s(1 – ₀) (1 – _b) average density of bed - time - _max time of onset of temperature maximum at a selected point of the bed - R =l _o/l Fourier number - Pe = ₁ l ²/D Péclet number - Bi = /_n Biot number Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 457–464, September, 1981.     

On the dispersion of gases under the action of the medium

Some general regularities of dispersion of a gas emerging from a nozzle submerged in a liquid are considered. A condition for establishment of the so-called maximum dispersion state is formulated.Notation ₀ coefficient of surface tension at the liquidgas boundary - contact angle of wetting of the nozzle material surface by the liquid - p_at atmospheric pressure - p air pressure - density of the liquid - g gravitational acceleration - h height of the liquid column - ₁, and _g dynamic viscosity coefficients of the liquid and gas, respectively - R and r radii of the bubble and nozzle, respectively - Q and F dimensionless criteria - , , , , and undetermined coefficients - ratio of the circumference of a circle to its diameter     

A nonlinear composite shell element with continuous interlaminar shear stresses

A numerical model for layered composite structures based on a geometrical nonlinear shell theory is presented. The kinematic is based on a multi-director theory, thus the in-plane displacements of each layer are described by independent director vectors. Using the isoparametric apporach a finite element formulation for quadrilaterals is developed. Continuity of the interlaminar shear stresses is obtained within the nonlinear solution process. Several examples are presented to illustrate the performance of the developed numerical model.List of symbols reference surface - convected coordinates of the shell middle surface - ⁱ coordinate in thickness direction - ⁱ h thickness of layer i - X_o position vector of the reference surface - ⁱX_o position vector of midsurface of layer i - t _k orthonormal basis system in the reference configuration - ⁱ a _k orthonormal basis system of layer i - ⁱW axial vector - R_o orthonormal tensor in the reference configuration - ⁱ R orthonormal tensor of layer i - ⁱ Cauchy stress tensor - ⁱ P First Piola-Kirchhoff stress tensor - ⁱ q vector of interlaminar stresses - ⁱ n, ⁱ m vector of stress resultants and stress couple resultants - v _x components of the normal vector of boundary - ⁱ N, ⁱ Q, ⁱ M stress resultants and stress couple resultants of First Piola-Kirchhoff tensor - stress resultants and stress couple resultants of Second Piola-Kirchhoff tensor - ⁱ , ⁱ , ⁱ strains of layer i - _K transformation matrix - u_o displacement vector of layer 1 - ⁱ local rotational degrees of freedom of layer i     

Hydrodynamic reaction to accelerated onedimensional motion of gas bubbles of variable volume in an unbounded liquid

A solution is given for the problem of the hydrodynamic reaction of an ellipsoidal gas bubble of variable volume to accelerated motion and the relation between the value of the apparent mass and the eccentricity of the bubble.Notation (,) velocity potential - V velocity of motion of the bubble with respect to the liquid - (, ) velocity potential of the near field - T₂ kinetic energy of the liquid due to the variation in bubble volume - F_r reaction force of the liquid - B₁ momentum of the liquid - _e apparent mass of the ellipsoid - density of the liquid - V_e volume of the ellipsoidal bubble Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 1, pp. 47–50, July, 1980.