0Cr25Ni7Mo4N双相不锈钢高温热塑性及组织演变

采用热拉伸实验研究了两种不同元素(O、N)含量的双相不锈钢0Cr25Ni7Mo4N在1 000~1 200℃范围内、1s-1应变速率条件下的热变形行为。利用光学显微镜(OM)、扫描电镜(SEM)和透射电镜(TEM)观察并分析了实验钢的组织和夹杂物。结果表明,经铝和硅铁脱氧后的实验钢热塑性良好,而未经脱氧的高O、N含量的实验钢在1 150℃以上才具有良好塑性,故双相不锈钢0Cr25Ni7Mo4N的热加工过程中应该控制温度在1 150℃以上;热加工过程中实验钢以铁素体的动态回复和奥氏体的动态再结晶为主要软化机制;高O、N含量钢中,在相界析出的含铬的氧化物夹杂引起的相界结合强度降低,及高温加工中不恰当的两相比例,是其热塑性较低的主要原因。     

Percolation effect and thermoplasticity of conducting [poly(acrylic acid)/C16TAB-modified graphene oxide]n multilayer films

The feasibility and effectiveness of the electrostatic self-assembly technique are demonstrated for the fabrication of thermoplastically conducting multilayer films. The layer-by-layer self-assembly process is based on the alternating adsorption of low molecular weight (M _n) poly(acrylic acid) (PAA) and cetyltrimethyl-ammonium bromide-modified graphene oxide (GO) with three carbon layers. A unique conductivity percolation effect is observed at a percolation threshold (percolation bilayer number) because the carbon–carbon interlayer can be expanded by the diffusion of PAA molecular chains. The resultant multilayer films show typical positive/negative temperature coefficient effects because of the thermoplasticity of the PAA with low M _n. After being reduced from GO to graphene (G), the electrical conductivity of the resulting (PAA/G)_n multilayer film is dramatically enhanced, and the percolation threshold occurs at a high bilayer number. The reasonable conductivities and the percolation effect make these films inherently interesting and potentially useful as components of advanced electronic devices.     

Fracture Parameter for Thermoplasticity in the Case of Dilatation Symmetry

An extension of the M integral to thermoplasticity related to the dilatational or scaling symmetry is presented. Based on a discrete Lagrangian describing the thermoinelastic system andon Noether's theorem defining the conservation law, the null Lagrangian theorem is applied in order to introduce thermoplasticity. By the use of the divergence theorem, the modified M integral is obtained.     

Path-independent integral for the dilatation symmetry group in thermoplasticity

The aim of this study is to establish a fatigue criteria based on an energy threshold corresponding to crack initiation in the case of dilatational symmetry of a structure under thermomechanical loading. An extension of the M integral to thermoplasticity relating to the scaling symmetry is presented. Based on a discrete Lagrangian describing the thermo-inelastic system and Noether's theorem defining the conservation law, the null Lagrangian theorem is applied in order to introduce thermoplasticity. By the use of the divergence theorem, the modified M integral is obtained. Path-domain independence is discussed illustrated by a numerical example.     

Modelling,simulation, and graphical user interface for industrial gas carburising process

Abstract

A mathematical model has been developed for the gas carburising (diffusion) process using finite volume method. The computer simulation has been carried out for an industrial gas carburising process. The model's predictions are in good agreement with industrial experimental data and with data collected from the literature. A study of various mass transfer and diffusion coefficients has been carried out in order to suggest which correlations should be used for the gas carburising process. The model has been interfaced in a Windows environment using a graphical user interface. In this way, the model is extremely user friendly. The sensitivity analysis of various parameters such as initial carbon concentration in the specimen, carbon potential of the atmosphere, temperature of the process, etc. has been carried out using the model.     

Analysis of boundary-value problems describing the non-isothermal processes of elastoplastic deformation taking into account the loading history

We discuss the theory and approximate methods for solving boundary-value problems of thermoplasticity in a quasi-static formulation when the process of non-isothermal elastoplastic deformation of a body is a sequence of equilibrium states. In this case, the stress-strain state depends on the loading history, and the process of inelastic deformation is to be observed over the whole time interval being studied. The boundary-value problem is stated as a non-linear operator equation in the Hilbertian space. The conditions that provide the existence, uniqueness and continuous dependence of the generalized solution on the applied loads and initial strains are defined. A convergence of the methods of elastic solutions and variable elastic parameters is studied to solve the boundary-value problems describing the non-isothermal processes of active loading taking into account the initial strains dependent on the deformation history and heating. __________ Translated from Problemy Prochnosti, No. 1, pp. 69–99, January–February, 2006.     

The effects of diffusion coefficient on the etching process of sacrificial oxide layers

The etching rate in hydrofluoric acid (HF) of a sacrificial oxide layer decreases during the extended etching process, as indicated by experiments with temperature from 298 to 308 K at different HF concentration. Existing models indicate that the etching solution's concentration at the etching front decreases during extended etching since the diffusion distance of HF from the source of the solution increases, resulting in the decrease of the etching rate. However, it is found that the measured etching rates do not decrease as seriously as predicted by the models. The difference of etching rate between the experiments and the model can reach as high as 30% for extended etching process. A modified model is proposed to explain this phenomenon by considering the diffusion coefficient of HF as a function of concentration in the solution. In the modified model, the decrease of the HF concentration causes the increase of the HF diffusion coefficient, which will partly compensate the decrease of the concentration caused by the long diffusion distance. In addition, the diffusion coefficient as a function of temperature is also included in the modified model. It is found that the modified model matches well the experimental data.     

Mixing and separation characteristics of isobutane with refrigeration oil

This paper discusses the transient mixing and separation characteristics of isobutane with/from refrigeration oil. The mixing/separation processes are observed and investigated experimentally in a glass cylindrical vessel. Since liquid isobutane is less dense than refrigeration oil, the mixing process proceeds one dimensionally by diffusion from the interface between isobutane gas and refrigeration oil. The progress of mixing, therefore, is very slow compared with a combination of halocarbon refrigerant and refrigeration oil having convection flow during the mixing process. The diffusion process can be analyzed using a one-dimensional diffusion model with an appropriate diffusion coefficient, which increases linearly with temperature. The separation of isobutane from the oil–refrigerant mixture occurs at the interface and the denser oil from which isobutane is separated causes a convective flow. Bubble generation under the depressurized conditions is unstable, but in the most cases, it tends to start when a high super saturation degree is reached. The temperature change during the separation process is estimated using latent heat as the separation heat of refrigerant.     

Wetting kinetics of liquid aluminium on an Al2O3 surface

The wetting process of a liquid aluminium drop on a solid Al₂O₃ surface has been investigated. Two different models have been proposed: a hydrodynamic model based on the effect of viscosity as well as a diffusion model which considers diffusional effects. The prediction from the models was compared with experiments. It was found that the wetting process of a liquid aluminium drop on an Al₂O₃ surface can be represented by the diffusion model rather than by the hydrodynamic model. In contrast, the hydrodynamic model could be employed to describe the wetting process of a liquid polymer drop on a solid.     

Computer Simulation of Physical and Mechanical Processes Running in the Reaction Cells of High-Pressure Installations in the Course of Synthesis of Diamonds

We study the problem of finite-element simulation of coupled nonlinear nonstationary processes of electric conductivity, heat conduction, and thermoplasticity taking into account the phase transitions in the materials. As a practical application, we develop a procedure of computer simulation of the process of spontaneous crystallization of diamonds. We solve the problem of determination of the fields of temperature, stresses, and concentrations of phases in the reaction volume of a high-pressure installation and in the local diamond–melt–graphite system in the course of crystallization of diamonds. It is discovered that these fields are strongly coupled, the solutions obtained for the reaction mixture and local system are characterized by a pronounced mutual influence, and the effect of self-regulation of pressure in the reaction zone exists and takes the form of oscillations of pressure about the line of the graphite–diamond phase transition.     

Detailed study of silver metallic film diffusion in a soda-lime glass substrate for optical waveguide fabrication

We present the study of multimode glass waveguides fabricated by a silver-ion electromigration process followed by a diffusion process. The study is concerned mainly with the diffusion process, which occurs by variation of the diffusion time. The obtained guides are analyzed by the prism-coupling technique, which determines their effective refractive indices that are treated by the inverse WKB method,assumed to be proportional to the silver ions' concentration profiles, for which a Gaussian model is attributed. Diffusion coefficients then are determined from these Gaussian profiles experimentally by both methods. These diffusion coefficients show a concentration dependence related to the variation of the diffusion time. A mathematical model representing the best fit to this dependence is also presented. Finally, our results are compared with other research results, with which we find good agreement.     

Thermoplastic films from cyanoethylated chicken feathers

This paper demonstrates that etherification can be used to develop thermoplastic films from chicken feathers. Feathers are inexpensive, abundantly available and renewable resources but have limited applications mainly due to their non-thermoplasticity. However, it has been shown that chemical modifications such as grafting can make feathers thermoplastic. Etherification provides better thermoplasticity to biopolymers compared to chemical modifications such as acetylation. In this research, chicken feathers were etherified using acrylonitrile and various concentrations of catalyst. Even at low weight gain (3.6%), cyanoethylated feathers were thermoplastic and showed a melting peak at 167 °C. Films compression molded from the cyanoethylated feathers had strength ranging from 1.6 to 4.2 MPa and elongation ranging from 5.8 to 14% depending on the extent of cyanoethylation. Feathers modified by cyanoethylation had good thermoplasticity and could be useful to develop various thermoplastics.     

Modelling precipitation of niobium carbide in austenite: multicomponent diffusion,capillarity, and coarsening

Abstract

The growth of niobium carbide in austenite involves the diffusion of both niobium and carbon. These elements diffuse at very different rates. A model is presented for the overall transformation kinetics of niobium carbide precipitation in austenite that takes into account the multicomponent nature of the diffusion process while at the same time allows for the curvature of the transformation front. The inclusion of the curvature (capillarity) effect has, in a numerical scheme, permitted the precipitation and coarsening reactions to be treated in a single model. The model is compared with published experimental data.     

Constitutive relations of micromorphic thermoplasticity

The constitutive theory of micromorphic thermoplasticity has been formulated in Lagrangian form. The generalized Lagrangian strains, strain rates, temperature, temperature rate and temperature gradients are considered as the independent constitutive variables. Internal variables, including generalized Lagrangian plastic strains, are incorporated. The axioms of objectivity and equipresence are strictly followed. The entropy inequality has been fully utilized to guide the derivations of the constitutive relations. No restrictive assumption has been made to the magnitude of any independent constitutive variables. Finite element formulations for micromorphic thermoplasticity are developed based on the balance laws and the constitutive theory.     

Spin drift and spin diffusion currents in semiconductors

Abstract

On the basis of a spin drift-diffusion model, we show how the spin current is composed and find that spin drift and spin diffusion contribute additively to the spin current, where the spin diffusion current decreases with electric field while the spin drift current increases, demonstrating that the extension of the spin diffusion length by a strong field does not result in a significant increase in spin current in semiconductors owing to the competing effect of the electric field on diffusion. We also find that there is a spin drift-diffusion crossover field for a process in which the drift and diffusion contribute equally to the spin current, which suggests a possible method of identifying whether the process for a given electric field is in the spin drift or spin diffusion regime. Spin drift-diffusion crossover fields for GaAs are calculated and are found to be quite small. We derive the relations between intrinsic spin diffusion length and the spin drift-diffusion crossover field of a semiconductor for different electron statistical regimes. The findings resulting from this investigation might be important for semiconductor spintronics.     

Numerical solution of the problem of thermoplasticity for welded shell structures heated by a moving heat source

A numerical solution is suggested for the thermoplasticity problem for flattened shells heated by moving heat sources distributed over areas. Plastic flow theory associated with the Mises flow condition is used. As an example numerical calculations are provided for estimating the efficiency of reducing the level of residual stresses by moving heat sources over a welded plate.Translated from Problemy Prochnosti, No. 4, pp. 65–72, April, 1996.     

A New Analysis of Hydrogen Diffusion in Metals with Trapping

A new model of hydrogen diffusion in metalshas been developed,it is more efficient todescribe the hydrogen diffusion with trappingin metals.In the model newly developed an impli-cit dependence on time of hydrogen diffusioncoefficient in metals with trapping was firstlybuilt and it is shown that hydrogen diffusioncoefficient will be different at different posi-tions in a dynamic process of hydrogen diffusionin a metal.Numerical solutions of the present modelwere obtained by finite difference method.Bychanging the parameters in the model the diffusionof hydrogen in a metal and the effect of trappingwere described and discussed.And the comparisonbetween the well known McNabb and Foster's modeland the present model was also made.     

Unsteady diffusion in a multi‐layer medium with immobilization reaction at the interfaces

Abstract

A mathematical model is developed to describe the unsteady diffusion in a multi‐layer medium with interfaces that have non‐zero thickness. A general interface condition is used to account for the secondary phenomena that may take place in the interfaces. Analytical solution is obtained by the use of the linear operator method. An example is given to show the effects of the secondary phenomena on the diffusion behavior in the diffusion process with membrane as the interfaces.     

Modeling effects of particle size in LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material on peak current level in lithium-ion batteries

Mathematical simulation of the current transfer characteristics of submicron and nanodimensional objects has been used to predict some properties of a structured electrode material in lithium-ion batteries. A diffusion model of the intercalation-deintercalation (ID) process is presented. Using this model, the current density in cathode material particles (nanocrystals) has been numerically simulated and an equation for the current density in the absence of diffusion polarization is derived. The proposed model can be used to optimize the ID process for improving the functional properties of cathode materials and increasing the working life of cathodes. Results are illustrated by examples for LiMn₂O₄ cathode material.     

On the theory of formation of gas hydrate in partially water-saturated porous medium when injecting methane

We present a planar one-dimensional theoretical model and numerical solutions for the process of the formation of methane gas hydrate by injecting gas into a porous reservoir partially saturated with water. The case where the intensity of formation of the gas hydrate is limited by the diffusion of gas through a hydrate layer formed between water and gas in the pore channel core is considered. Within this process, the kinetics of hydrate formation is determined by empirical parameter D, having the dimension of a diffusion coefficient (m²/s). The effect of the value of this parameter on the characteristics of the hydrate formation process is studied depending on the parameters that determine the initial state of the porous reservoir and its porosity and permeability characteristics. The equilibrium mechanism of hydrate formation is considered, which is a limit adopted by the diffusion pattern that corresponds to the case of D → ∞.