Presence Of Liquid Phase Research Articles

Special features of the structure of metastable “steel-copper” pseudoalloys

The structure and properties of concentration-inhomogeneous nickel-molybdenum TRIP steels and “steel-copper” pseudoalloys based on them are studied. A full statistical description (the distribution law and the coefficient of variation) of the distribution of concentrations in these materials is presented. Homogenization in the presence of liquid phase is studied. The causes of high parameters of mechanical properties are explained.

Sintering behaviour and microstructure of 3Y-TZP + 8 mol% CuO nano-powder composite

Nanocrystalline 3Y-TZP and copper-oxide powders were prepared by co-precipitation of metal chlorides and copper oxalate complexation–precipitation, respectively. A significant enhancement in sintering activity of 3Y-TZP nano-powders, without presence of liquid phase, was achieved by addition of 8 mol% CuO nano-powder, resulting in an extremely fast densification between 750 and 900 °C. This enhancement in sintering activity was explained by an increase in grain-boundary mobility as caused by dissolution of CuO in the 3Y-TZP matrix. The nano-powder composite was densified to 96% by pressureless sintering at 1130 °C for 1 h. Considerable tetragonal to monoclinic phase transformation of the zirconia phase was observed by high temperature XRD analysis. This zirconia phase transformation is discussed in terms of reactions between CuO and yttria as segregated to the 3Y-TZP grain boundaries.

Structuring on sintering in the presence of liquid phase in Cr-Cu-iron group metal systems. I. Cr-Cu system

Structuring has been examined for Cr-Cu composites under conditions of impregnation and subsequent liquid-phase sintering at 1200°C in a vacuum of (2–4) · 10−3 Pa with reduced and electrolytic chromium powders. The size distribution for the particles of the refractory component in the microstructure containing the reduced chromium on liquid-phase sintering for 60 min corresponds to a logarithmic normal distribution; the distribution parameters are sensitive to the volume fraction of refractory particles. The calculated values for the dihedral angle are close to one of the modes of the distribution for the dihedral angles in the microstructure for specimens made of electrolytic chromium (115°). At 1200°C, the equilibrium Crs-Cul system obeys the condition \(\frac{{\sigma _{sl} }}{{\sigma _{ss} }} \geqslant 0.5\). This indicates the probability of formation or preservation of framework structure elements during the liquid-phase sintering, which are observed by experiment in specimens containing reduced chromium.

Compressive Behavior of Extruded SiCw/AZ91 at Temperatures close to and above the Solidus of the Matrix Alloy

Compressive deformation behaviors of extruded SiCw/AZ91 were investigated in Gleeble-1500 thermal simulator at temperatures from 743 K to 783 K and strain rates from 6.4×10-2 s-1 to 1.0×101s-1. Results showed that high strain rate sensitivity (~0.5) occurred during compression; deformation activation energy normalized by threshold stress was higher than the lattice self-diffusion activation energy of magnesium. Dynamic recovery (DRV) and dynamic recrystallization (DRX) took place during compression, which refined the grains. The increase of deformation energy was attributed to non-basal planes slip and climbing of dislocations and also the presence of liquid phase.

Bi 2O 3 vaporization from ZnO-based varistors

Bi 2O 3-doped ZnO ceramic varistors are usually sintered at temperatures near to 1200 °C in the presence of a Bi-rich liquid phase, which is partially vaporized during the sintering process. Volatilization of bismuth oxide depends on the total surface area in direct contact to the reaction atmosphere and this in turn is related to the area/volume ratio of the ceramic compact. This loss of Bi 2O 3 has a significant role on the development of the varistor microstructure and more specifically ZnO grain growth, which is strongly enhanced by the presence of the liquid phase, should be particularly affected. In the present paper, X-ray fluorescence analysis is performed to describe the Bi 2O 3 vaporization profile as a function of distance to the outer surface, taking into account its influence on microstructural evolution.

Structural Variation and Microwave Dielectric Properties of ZrO2 Added Ba(Zn1/3Ta2/3)O3 Ceramics

Ba(Zn1/3Ta2/3)O3 (BZT) ceramic has 1:2 ordered hexagonal structure, but was destroyed with the addition of ZrO2. The 1:1 ordered cubic structure was developed when a large amount of ZrO2 was added. BZT has a porous and inhomogeneous microstructure with a Ba5Ta4O15 second phase. When ZrO2 was added, a new Ba0.5TaO3 second phase formed and grain growth occurred. Presence of liquid phase which is related to the Ba0.5TaO3 second phase could be responsible for the grain growth. Q value of BZT was greatly enhanced with the addition of ZrO2. The improvement of Q value can be explained by the increase of relative density and grain size. Especially, grain size is considered to be one of the crucial factors for the improvement of Q value of BZT ceramic.

CARS thermometry in high pressure rocket combustors

Coherent anti-Stokes Raman spectroscopy (CARS) has been used to investigate high pressure cryogenic liquid oxygen/gaseous hydrogen (LOX/GH 2) flames at pressures up to 6.5 MPa. The method employs two synchronized broadband CARS systems to probe simultaneously H 2 and H 2O. Temperature is deduced from the H 2 and H 2O CARS profiles while the H 2O concentration is deduced from the modulation from the resonant the H 2O resonant signal superimposed on the nonresonant background signal. Details of the modeling of the CARS spectra at high pressure and the data reduction are discussed. Problems issued from the presence of liquid phase are also investigated. The results demonstrate the applicability and usefulness of CARS for investigating cryogenic combustion under representative rocket model combustor regimes where the pressure range is above the supercritical condition ( P>5.04 MPa).

Effect of excess PbO on the structure and piezoelectric properties of Bi-modified PbTiO3 ceramics

Abstract Effect of 1–4 wt.% excess PbO, added to the calcined powder, on the structure and dielectric and piezoelectric properties of Bi-doped lead titanate ceramics was investigated. The ceramics containing 4, 6 and 8 mol% Bi were prepared by the usual ceramic technique, using high purity oxides. The calcined powder of each composition was next intimately mixed with 1, 2, 3 and 4 wt.% PbO and then sintered at 1200–1300 °C for 3 h. The dielectric piezoelectric and electromechanical properties were determined as a function of excess PbO. Addition of PbO up to 2 wt.% was found to improve the densification, by the presence of the PbO liquid phase during sintering. For all Bi doping levels, the dielectric constant and the thickness coupling factor reach maxima (representing an increase of 2.5–8% for dielectric constant and 7–8% for thickness coupling factor) at about 2 wt.% PbO addition. The planar coupling factor is very low, less than 0.01, regardless the PbO content. The disipation factor slightly decreases with increasing PbO content and the mechanical quality factor of the thickness mode was about 300. The experimental results were discussed in terms of the mechanisms of densification in the presence of the liquid phase and of lead vacancy concentration.

Comparative study of a high-strain-rate superplastic Al-4.4Cu-1.5Mg/21SiCW sheet under uniaxial and equibiaxial tension

In this paper, the strain rate sensitivity exponent and the cavitation behavior of a high-strain-rate superplastic Al-4.4Cu-1.5Mg/21SiCW sheet were examined under uniaxial and equibiaxial tension at the optimal temperature of 793 K. A maximum elongation of about 335% was obtained at the initial strain rate of 0.17 s−1. It was found that the strain rate sensitivity of the composite under uniaxial and equibiaxial tension was 0.34 and 0.36, respectively. The reasons for a large discrepancy between uniaxial and equibiaxial stress versus strain rate curves were analyzed. It was concluded that the flow stress–strain rate relationship determined from uniaxial tension could be used for forming processes subject to complex stress states after proper adjustment. The amount of cavity was found to increase with increasing strain and the amount of cavity obtained under equibiaxial tension was slightly larger than that under uniaxial tension at the same effective strain rate. A slightly higher cavity growth rate parameter was also observed under equibiaxial tension. The experimental results revealed that the cavity growth was essentially plastic-controlled. It was suggested that the presence of liquid phase was beneficial to nucleation at the interfaces and limited the cavity growth rate.

アルミニウム青銅の焼結に及ぼすＡｌ‐Ｃａ系フッ化物添加の効果

In order to accelerate sintering of Al-Bronze powder covered with passive oxide film, we focused on the way to add Al-Ca fluoride consisting of AlF3 and CaF2, examined effect of CaF2 mixing rate in Al-Ca fluoride, amount of added Al-Ca fluoride and sintering temperature on sintering properties of Al-Bronze powder and considered the mechanism of acceleration of sintering. Al-Bronze powder was sintered most effectively by adding Al-Ca fluoride with CaF2 mixing rate of 20 mass%. If amount of added fluoride was over 0.05 mass% and sintering temperature was over 1123K, the acceleration of sintering of Al-Bronze powder began to appear. On the mechanism of acceleration of sintering, it was presumed that Al2O3 film on the surface of Al-Bronze particles was removed in process of the formation of gaseous AlOF by, the reaction with AlF3, and the reaction was accelerated further by the presence of liquid phase appeared in Al-Ca fluoride.

A multi-phase media formulation for biomechanical analysis of periodontal ligament

A numerical analysis of the biomechanical response of the periodontal ligament is presented. A multi-phase media formulation is developed for representing soft tissue constitutive models, and implemented in a specific finite element code. It is possible to simulate the presence of liquid phase permeating the extra-cellular material and to interpret the consequent time-dependent behaviour due to the fluid flux through periodontal ligament. The analysis of the mobility of human upper incisor, under the application of short time transversal forces, is reported. The numerical results are compared with in vivo experimental data. The agreement of different approaches confirms the effectiveness of the proposed model for investigation of the biomechanical behaviour of periodontal ligament under application of low magnitude forces, and represents the basis for the definition of a general multi-phase constitutive model.

Nonstoichiometry and sintering of bismuth-germanium binary oxides in the presence of liquid phase

Results of a study of the effect of deviation from stoichiometry of the compositions of binary bismuth-germanium oxides with structures of sillenite and eulitine on the sinterability in the presence of liquid phase are presented. It is established that the change in the degree of nonstoichiometry of the substances determines the substantial contribution to the driving force of the sintering process and increases considerably the efficiency of the latter.

Critical reinforcement size for cavity nucleation during superplastic deformation of metal matrix composites

A high strain rate superplastic composite Al–Cu–Mg/Si3N4p has been investigated to estimate the critical particle size for cavity nucleation. Specimens superplastically deformed to a strain of 0.2 at 773 K contained no liquid phase whereas those deformed at 783 K contained liquid phase. The critical particle size, i.e. the smallest size to nucleate a cavity, obtained experimentally was 0.5 µm dia. for deformation at 773 K and 0.4 µm for deformation at 783 K. The critical particle size for deformation at 773 K can be estimated accurately using Stowell's equation for critical strain rate. However, for deformation at 783 K when liquid phase was present, the predicted critical strain rate was much lower than the experimental strain rate for critical particle size for cavity nucleation. It is suggested that the actual critical strain rate was increased by an increase in diffusivity at the interfaces and grain boundaries due to the presence of liquid phase.

Diffusion of oxygen out of AlN polytypoid grains

The phase change from 27R AlN polytypoid to AlN in the presence of oxide has been investigated in order to determine the qualitative behavior of oxygen release from AlN grains. The 27R polytypoid (Al 9O 3N 7) powders were mixed with a stoichiometric amount of Y 2O 3 and, then hot-pressed at 20 MPa. X-ray diffraction analysis revealed that the phase change from 27R to AlN started at about 1350°C in the absence of a liquid phase, since the lowest liquidus temperature in the system AlN–Al 2O 3–Y 2O 3 is reported to be about 1690°C. The result revealed that the diffusion of oxygen out of 27R grains can progress in part through solid-state reaction at low temperatures. However, the reaction was complete at temperatures exceeding 1700°C in the presence of liquid phase. Thermal conductivity of the hot-pressed samples was also measured and discussed in terms of the phase change as well as microstructural evolution.

High-strain-rate superplasticity of an Al–4.4Cu–1.5Mg/21SiC W composite sheet

High-strain-rate superplasticity (HSRS) of an Al–4.4Cu–1.5Mg/21SiC W composite sheet was evaluated by tensile tests and microstructural characterization over a range of initial strain rates from 1.67×10 −3 to 1.67×10 0 s −1 and temperatures from 723 to 818 K. The strain rate sensitivity exponent of the composite was found to be approximately 0.34 at a strain rate of 10 −2–10 0 s −1 and at temperatures between 723 and 818 K. From the experimental findings, the strain rate sensitivity exponent is almost constant during deformation. A maximum elongation of ≈446% was obtained at 3.33×10 −1 s −1 and at 793 K, which is near the partial melting temperature of the composite. The threshold stress is strongly temperature dependent. The cavitation behavior of the composite during deformation was also examined and compared with that of a typical superplastic aluminum alloy (Al7475). The experimental results revealed that the cavity growth was essentially plastic-controlled. It was suggested that the presence of liquid phase was beneficial to nucleation at the interfaces and limited the rate of cavitation growth.

Particle weakening in superplastic SiC/2124 Al composites at high temperature

High-strain-rate superplastic behavior of powder-metallurgy-processed 2124 Al matrix alloy and 10%, 20% and 30% SiC particulate reinforced 2124 Al composites were investigated over the temperature range from 370°C to 565°C, and the strain rate range from 10 −4/s to 1/s. The true activation energy for the plastic flow after threshold stress compensation was close to that for lattice diffusion in aluminum for the 2124 Al alloy, while the activation energies for the 2124 composites were considerably higher than those for the unreinforced alloy, increasing with an increase in the volume fraction of SiC. The strength of the 2124 Al composites is lower than the strength of the 2124 Al alloy at high temperatures. The strength differential between the unreinforced and reinforced 2124 Al alloys is a function of temperature and is seen to decrease systematically with decrease in temperature and virtually vanishes at 460°C. Particle weakening is discussed in the light of load transfer effect, interphase diffusion, dissolution of second phase particles into matrix and the presence of liquid phase. It is proposed that interphase weakening, possibly with some liquid formation, is the principal factor contributing to the results obtained. Interphase and boundary sliding is believed to be the rate-controlling process in plastic flow of the SiC/2124 Al composites.

X-ray and dielectric studies of liquid-phase sintered PBB1/2 3+B1/2 5+O3 ceramics with differing degree of compositional ordering

Ceramics of several PbB1/2 3+ B1/2 5+O3 perovskites (B3+-In, Sc, Yb, Lu, Er, Tm; B5+-Nb, Ta) with differing degree of compositional ordering were obtained using Li2CO3 additions. Ordering process in Li-doped ceramics is greatly enhanced due to recrystallization of grains in the presence of liquid phase. The properties of Li—doped ceramics are similar to those of crystals grown from the flux at the same temperatures. In some of the perovskites studied compositional order-disorder phase transitions and the transformation of antiferroelectric phase transition into ferroelectric one were observed.

Superplastic Deformation of Aluminum Systems at 500-650 °C with or without Presence of Liquid Phase

Three aluminum base materials were studied over the high temperature range of 500-650 °C, in an attempt to examine the role of liquid phase on controlling deformation mechanisms based the observed m- and Q-values. For the two near-pure At systems, the 1050 At and AO, no solute-induced incipient partial melting was expected, and the solidus and liquidus temperatures should merge to near 655±5 °C. The m-values of these materials were consistently scattered with 0.1-0.25 up to the extrahigh temperature of 650 °C. The high activation energy in the A0 material at T>600 °C is postulated to be related to the load transfer effect or bubble-induced stress reduction, but not the liquid phase role in explaining the deformation mechanism. In the 6061A1, an appreciable amount of liquid should have been present at 590 and 610 °C. The low activation energy of 20 kJ/mole over the temperature range of 570-610 °C might reflect the transition of deformation mechanisms, though no pronounced increase in m-values was observed even at 610 °C. This result was controversial and needs future studies.

Computational Modeling of Grain Growth in Self-Reinforced Silicon Nitride.

A model is proposed for studying grain growth in silicon nitride by computer simulation. The simulation is based on the Monte Carlo method and uses the Potts model with additional features peculiar to silicon nitride ceramics, such as anisotropy of grain boundary energies and the presence of liquid phase. The simulation successfully produced self-reinforced microstructures. It was found that the self-reinforcement phenomenon occurred only within a particular range of liquid phase fractions. The influence of anisotropy in interface energy on inhomogeneous grain growth was also examined. When interface energies are isotropic, the microstructure was essentially homogeneous. The results of these simulations suggest that anisotropy in interface energy and the presence of an appropriate amount of liquid phase are two important factors controlling the self-reinforcement process in silicon nitride materials.

Electrical properties of donor defects at the surface of InSb after laser irradiation

An investigation of the laser induced p-n junction in p-InSb has been completed using the magnetoconcentration effect (MCE). A theoretical calculation of the distribution of Sb vacancies (V Sb ) in a nonuniform temperature field in InSb was performed in terms of the model of redistribution of V Sb under laser exposure. Comparison of the theoretical and experimental data has shown that the depth of the p-n junction increases with temperature and that the relatively large value of the localisation depth of the p-n junction is connected with the presence of liquid phase at the laser modification process. InSb samples were used in the temperature range 180–290 K. The temperature gradient was provided by YAG : Nd laser irradiation (λ = 0.53 μm, t p = 15 ns). Two kinds of laser-induced donor centres (LDC) were found : unstable, which were annealed at room temperature with a relaxation constant of 5 s and stable ones, which could be annealed