Presence Of Phase Transformations Research Articles

Effect of Bond Coating Surface Morphology on the TBC System Lifetime

AbstractA study on the effect of bond coating (BC) surface modifications prior to ceramic deposition is presented. Grit blasting and polishing were used to modify the BC surface finish. Thermal barrier coating (TBC) systems were made of a commercial yttria-stabilized zirconia (YSZ) deposited by electron beam physical vapor deposition on a β-(Ni,Pt)Al-coated Ni-based single crystal superalloy. Surface roughness measurements and scanning electron microscopy observations, before and after thermal cycling at 1100 °C, were performed to investigate the influence of the initial surface treatment on the YSZ/BC interface morphology and top coat spallation resistance. Surface states enhancing TBC spallation resistance have been found. In particular, it is shown that rumpling can be avoided even in the presence of phase transformations in the BC, by grinding samples with P600 SiC paper or by applying an “heavy” grit blasting leading to a thinner BC.

Percolation phase transition, self-organization processes and thermal conductivity in PbSe1-xTex semiconductor solid solutions at small Te concentration

ABSTRACT The isotherms of the lattice thermal conductivity λ L for the PbSe1-xTex semiconductor solid solutions (х = 0–0.045) were obtained in the temperature range T = (200–600) K. The λ L(x) dependences exhibit a general trend to a decrease in λ L with increasing x, but the peaks are observed near x = 0.007, 0.015 and 0.0025 indicating the presence of phase transformations. We associated the first peak with a percolation-type phase transition to the impurity continuum and estimated the critical index for λ L within the framework of dynamic scaling theory. The second and third peaks were attributed to the self-organization processes in the PbSe1-xTex after the percolation threshold reaching. The effective cross-sections σ s for phonon scattering by impurity (Te) atoms were determined experimentally and calculated theoretically using the Klemens theory. The data obtained are another confirmation of our assumption about the presence of such percolation-type phase transition in any solid solution.

On the pressure distribution in multi-phase pipelines

The results of investigations and measurements of actual pressure values carried out recently in technological-field pipelines show that the nature of pressure distribution in multi-phase pipelines differs from those in mono-phase ones. The paper analyzes the aspects affecting the pressure distribution in gas-saturated fluids in the presence of phase transformations. Considering the changes in compressibility of gas-saturated mixture, a mathematical model for pressure distribution through the length of pipeline has been developed. It was defined that depending on the compressibility ratio and flow regime, the pressure distribution in multi-phase pipeline decreases steadily at an exponential rate.

Acoustic waves in multifractional gas mixtures in the presence of phase transformations

Acoustic waves in multifractional gas mixtures in the presence of phase transformations

Acoustic Waves in Multifraction Gas Suspensions in the Presence of Phase Transformations

The propagation of acoustic waves in gas mixtures with vapor, monodisperse drops, and solid particles of various materials and sizes has been studied. A mathematical model is presented; the dispersion relation, the equilibrium and frozen speeds of sound, and low- and high-frequency asymptotes for the linear attenuation coefficient are deduced; the dispersion curves are calculated. The influence of particle size and disperse phase parameters on dissipation and dispersion of acoustic waves is analyzed for a mixture of air with vapor, water drops, and aluminum and carbon black particles. Fast Fourier transform is used to calculate the pulse perturbations in the studied media.

Surface morphology of PMMA/boehmite hybrid nanostructures prepared via facile one-pot process

In this study, we developed the novel aqueous-based PMMA/AlOOH hybrid by a one-pot process starting from their relevant precursors in a controlled manner. Starting chemical reactions directly from precursors and the sequence of adding reactants provide the possibility towards enhancing the homogeneity of the final product. Inorganic and organic segments were made compatible by means of oleic acid as a coupling agent. Boehmite to PMMA weight ratio as the main parameter was varied from 0 to 18% and the morphology, particle size, size distribution, and topography map of hybrids was shown to be composition dependent. Final PMMA/Bo nanohybrids were characterized using FTIR to confirm the chemical interactions between inorganic and organic segments. TEM analysis showed that nanohybrid particles with irregular shapes containing inorganic particles dispersed in the organic matrix are formed with an average diameter which depends on boehmite content. The presence of phase transformation of Bo makes PMMA/Bo hybrids significantly thermally stable. According to AFM topography map analysis and relevant Gaussian fit function, the roughness of nanocomposite, the size of hybrid nanoparticles and deviation from the mean value (size) were increased as Bo increases from 0 to 18.

Influence of alloy type, peak temperature and constraint on residual stress evolution in Satoh test

The evolution of residual stress in welds is affected by a variety of factors such as joint design, welding parameters, material properties and the possible presence of phase transformations. The Satoh test can be useful as a method to understand differences in welding residual stresses among various materials. This study compares the evolution of residual stress measured in the Satoh test for ferritic and stainless steels. For weld thermal cycles with a peak temperature above Ac3, the ferritic alloys exhibit lower residual stresses than the austenitic alloys due to the well known reduction in stress from the martensitic or bainitic transformation. However, the residual stress levels among these alloys are similar for peak temperatures below Ac3. The application of constraint during both the heating and cooling portions of the thermal cycle affects the final magnitude of residual stress in a way that is not often considered.

Model of Curvature of Crankshaft Blank During Heat Treatment, Accounting for Phase Transformations

The manufacturing process of forging of large crankshafts is affected by bending of the shaft during heat treatment, as well as at the forging step. For this reason, analysis of the curvature of the shaft at various stages of the technology is needed. This paper deals with the modeling of elastic–plastic bending of crankshafts during heat treatment after forging. Present work is dedicated to heat treatment after forging. The aim of the paper is to develop a model and finite element (FE) software to simulate the elastic–plastic deformation of the shaft due to thermal expansion and dilatometric effect caused by phase transformations. Shaft material model is developed and the elastic–plastic characteristics are implemented in the FE code. Heat exchange with the cooling medium, dependence of thermal properties on temperature, and heat of phase transformations are accounted for in a solution of the thermal problem. Dilatometric tests are performed to supply data for identification of the phase transformation model. The method of estimation of the curvature of the shaft with one design variable is proposed. This allows to perform optimization of heat treatment in order to reduce the curvature of the shaft. The calculations are performed for several modes of the heat treatment. It is shown that in the presence of phase transformations, cooling process is accompanied by a three‐time changing of stress sign and the direction of bending of the crankshaft, which is due to the nonlinearity of thermal deformation during the phase transformations.

Investigation into the properties of basalt of the Vasil’evskoe deposit in Yakutia as the raw material for obtaining continuous fibers

The results of investigations into the chemical and mineralogical composition of potentially suitable petrurgical raw materials of the Vasil’evka deposit for producing continuous basalt fibers and composite materials on its basis are presented. Electron probe microanalysis and petrographic analysis are used. The performed investigations proved the possibility of obtaining continuous basalt fibers based on basalt from the Vasil’evka deposit in Yakutia, since its composition and main characteristics correspond to requirements imposed on petrurgical raw materials by the viscosity modulus, the pyroxene composition, the presence of phase transformations, etc.

Coupled phase transformations and plasticity as a field theory of deformation incompatibility

The duality between terminating discontinuities of fields and the incompatibilities of their gradients is used to define a coupled dynamics of the discontinuities of the elastic displacement field and its gradient. The theory goes beyond standard translational and rotational Volterra defects (dislocations and disclinations) by introducing and physically grounding the concept of generalized disclinations in solids without a fundamental rotational kinematic degree of freedom (e.g. directors). All considered incompatibilities have the geometric meaning of a density of lines carrying appropriate topological charge, and a conservation argument provides for natural physical laws for their dynamics. Thermodynamic guidance provides the driving forces conjugate to the kinematic objects characterizing the defect motions, as well as admissible constitutive relations for stress and couple stress. We show that even though higher-order kinematic objects are involved in the specific free energy, couple stresses may not be required in the mechanical description in particular cases. The resulting models are capable of addressing the evolution of defect microstructures under stress with the intent of understanding dislocation plasticity in the presence of phase transformation and grain boundary dynamics.

Acoustic disturbances in a mixture of liquid with vapor-gas bubbles

Results are given of theoretical study into the propagation of acoustic disturbances in mixtures of liquid with vapor-gas bubbles in view of interphase diffusion mass transfer. A unified general dispersion relation is obtained, which defines the propagation of harmonic disturbances in two-phase mixtures of liquid with bubbles of vapor and gas in the plane, spherical, and cylindrical cases. Numerical calculations are performed of the evolution of weak pulse disturbances of pressure of different geometries in liquids with vapor-gas bubbles at different values of parameters of the medium. It is demonstrated that the velocity of propagation of waves significantly decreases with increasing initial concentration of vapor in vapor-gas bubbles, and the wave damping significantly increases. In so doing, the effect of vapor content on the dynamics of acoustic disturbances significantly increases with the initial volume content of bubbles. The nonmonotonic dependence of damping of pulse disturbance of pressure on the initial radius of bubbles in liquid with vapor-gas bubbles in the presence of phase transformations is demonstrated.

The effect of phase transformations at the inner core boundary on the Slichter modes

We analyze the effect of phase transformations at the inner core boundary on the period of Slichter modes. We show that the presence of phase transformations can lead to qualitatively new phenomena. In particular, the frequency is inversely proportional to the density contrast at the inner core boundary. We offer a thought experiment that demonstrates this effect. The complete analysis combines an instantaneous kinetics model for phase transformations with a simple planetary model: a rigid inner core, an inviscid, incompressible, constant density outer core, a stationary mantle. The reciprocal dependence on the density contrast leads to periods that are an order of magnitude shorter than those predicted by models that disallow phase transformations.

The influence of phase transformations on residual stresses induced by the welding process—3D and 2D numerical models

In this work, a numerical study of laser beam welding of steel was performed. In particular, phase transformation effects were considered, which consist mainly of volume change and transformation plasticity. Thanks to the possibilities of numerical modelling, additional analyses were performed (a) without taking into account phase transformations and (b) considering only the transformation plasticity phenomenon.The aim of this study was to examine the influence of phase transformation on the residual stress induced by the welding process, by comparing the results obtained with the described differences in the analyses. Finally, the residual stress field computed by the three-dimensional (3D) model was compared with the one computed by a two-dimensional (2D) model in order to estimate the grade of reliability of the more efficient 2D analyses, also in the presence of phase transformations. It was found that both volume changes due to phase transformations and transformation plasticity have a great influence on the residual stress induced by the welding process. 2D numerical models can be used with good accuracy instead of 3D models, if the in-plane stresses are of primary interest. All analyses in this investigation were performed with the finite element code SYSWELD®.

The Dynamics and Heat Transfer of a Droplet in a Dusty Gas in the Presence of Phase Transformations and Dust Catching

The dynamics and heat transfer of a droplet in a mixture of gas with fine particles (dusty gas) are investigated in the presence of deposition of fine particles on the droplet (dust catching) and of phase transformations (evaporation, condensation). Separately treated is a case in which only phase transformations occur. Analytical solutions of the problem are found in the limiting cases of Stokes and Newtonian flow past a droplet (corresponding to low and high values of the Reynolds number). The combined effect of dust catching and phase transformations on the droplet motion is investigated numerically.

Critical Autoignition Conditions for Heterogeneous Condensed Systems in the Presence of Phase Transformations

The critical ignition conditions for a single particle which interacts with a melting medium to form an intermetallic compound on its surface were investigated using the model of a quasistationary melting front. For linear and parabolic drag laws, three characteristic regions, which transform with change of Biot's criterion, are distinguished on the diagram of critical parameters. It is shown that for small values of this criterion, the conditions of self‐heating of the particle are identical to the ignition conditions in a medium with constant temperature. For values of Biot's criterion greater than unity, the critical conditions are substantially affected by the parameters determining the melting kinetics. The characteristic features of self‐heating of a single particle can determine the qualitative pattern of self‐heating of the heterogeneous system as a whole.

Texture of primary recrystallization on nonoriented electrical steel sheet with phase transformation

The magnetic properties of nonoriented (NO) electrical steel sheet are commonly improved if the texture of their products possesses “cube texture” (e.g., {100 〈0vw〉, “goss texture”) (i.e., ¹10〈011〉, and less ²22 texture). Industrially “cube type” has not been obtained, but “goss texture” has been. In a greater or lesser degree, {222} texture exists. To improve “goss texture” and reduce ²22 texture, the grain size of the material prior to cold rolling should be larger. When the grain size before cold rolling is larger, during primary recrystallization, “goss texture” is enriched, ²22 texture is decreased, and the grain grows so easily that higher induction and lower core loss can be obtained. This does not depend on the presence of phase transformation. In case of NO steel with phase transformation, heat treatment before cold rolling has been done below the austenite transition temperature (Acin1) in order to prevent the fine grain size caused by α → γ(+α) → α transformation. By using material that was heated over Acin1 and cooled with changing cooling rates, this study describes (a) the relationship between textures before cold rolling and the texture of the final product, and (b) the development of the magnetic properties.

Investigation of transonic unsteady-state flow in the presence of phase transformations

Investigation of transonic unsteady-state flow in the presence of phase transformations

Thermal stresses in the plane problem of the theory of elasticity caused by phase transformations: PMM vol. 38, n≗5, 1974, pp. 847–850

We study the state of stress in an elastic half-plane in the presence of phase transformations caused by temperature variations at the points of the half-plane. Separately we consider the states of stress caused by the lack of homogeneity in the temperature field and the consequent volume changes taking place in the regions of phase transformations. Under the term “phase transformation” we understand the structural change in the crystal lattice which occurs when the body is heated above a certain critical temperature [1, 2], Here the purely thermal stresses are accompanied by the stresses associated with the volume change in the region undergoing phase transformations. Similar problems arise during the investigation of the stress states in the case of elastic tension and in the problems on inclusions. Such problems were studied by D.I.Sherman, Iu.A. Amen-Zade, and others. However in all the problems studied the region occupied by an inclusion was always completely contained within some external region. The present paper deals with the case in which the boundary separating the media has common points with the outer boundary of the region containing the inclusion. The stresses and strains are assumed to satisfy the conditions of the linear theory of elasticity, with the external region and the inclusion possessing the same elastic properties.

Composition and structure of plasma-sprayed high-carbon steels

1. The structure of plasma-sprayed steel coatings and their strength of adhesion to a substrate are governed to a large extent by the technological parameters of the spraying process. Under the optimum conditions, the resistance to stripping of such coatings equals 325 kg/cm2. 2. During plasma spraying with U8A and PK-2 steel wires, the carbon content changes from 0.79% in the initial condition to 0.63%. 3. During the plasma spraying process, phase transformations take place in the steel, resulting in the formation of quench sorbite. 4. A characteristic feature of the structure of plasma-sprayed steel coatings is its nonuniformity, the carbon content of local volumes of material varying from 0.16 to 0.7%. 5. The presence of phase transformations in high-carbon steels during plasma deposition provides a means of controlling the structure and properties of plasma-sprayed steel coatings.

Kinetics of temperature field in a three-layered colloidal body

The net method is used to obtain the numerical solution of the problem of the kinetics of the temperature field in a three-layered colloidal body in the presence of phase transformations. The obtained results are compared with experimental data.