Superplastic Conditions Research Articles

Modeling and optimization of shape change in shell spatial cross-sections under superplastic moulding

The necessity to develop and optimize new technological processes of gas moulding of shells under the superplasticity conditions, which ensure large elongation and complexity of the shape of end items, makes the specialists in the field of mathematical simulation to pose and solve problems of constant improvement of the imitation models. Because of a large number of “embedded” nonlinearities (the physical properties of the material, friction, and unknown boundaries), the solution of such problems requires large computer resources, high qualification of designers, and large amount of labor.

Development of computer simulation of industrial superplastic sheet forming

A new technique estimating progressive shape changes for three-dimensional shells based on the generalized cross-sections method is introduced. The formulation of mathematical simulation of technological conditions of forming of three-dimensional shells in conditions of superplasticity is reviewed. An original algorithm of a solution finite element method with usage of orthogonal sections results. The veracity of a receivable solution is analyzed. Experimental tests are realized and a procedure to correlate the idealized forecasts with experimental data is constructed. The results and designed algorithms allow essentially to increase performance and operationability at mining new and retrofit of existing manufacturing processes of gaseous forming in conditions of superplasticity.

The New Approach to Produce Al Sheets with UFG Structure Using SPD Processing

Microstructure and mechanical properties of the ultrafine-grained (UFG) 1421 aluminum alloy processed by equal channel angular pressing (ECAP) have been studied. This UFG material was successfully rolled under the conditions of superplasticity. It was established that the rolled material exhibited not only the enhanced superplasticity, but also high strength retaining initial ductility at room temperature after additional short-term annealing and low-temperature aging.

The Features of Deformation Behavior of Ultra-Fine Grained Titanium and Aluminum Alloys under Conditions of High Strain Rate Superplasticity

The stress-strain curves at high strain rate superplasticity were analyzed for Ti-6Al-4V and aluminum 1420 industrial alloys in ultra-fine grained state produced by severe plastic deformation. For both alloys the observed strengthening effect can be caused by grain growth under the above mentioned conditions resulting to increase of grain boundary sliding resistance. In the case of aluminum alloy the grain recovery can be accompanied by significant change in phase composition which is also stimulates the recrystallization process.

Caracterización de tres aleaciones superplásticas utilizando análisis mecánico dinámico (DMA)

El Análisis Mecánico Dinámico (DMA) es un método que tradicionalmente se utiliza para el análisis de polímeros. Está técnica es muy sensible a cambios en las propiedades de los materiales, como la transición vítrea en polímeros. Se puede utilizar para evaluar el ángulo de desfasamiento (tan δ), el módulo de almacenamiento (E') el módulo de pérdida (E") y recientemente las temperaturas de transformación en aleaciones metálicas. Se utilizó DMA para estudiar tres diferentes aleaciones: Zn-21%Al-2%Cu; Cd-17%Zn y Sn-38%Pb, cada una en condición superplástica y no superplástica. Los resultados mostraron la presencia de un pico en la curva de módulo de pérdida el cual se puede relacionar con la temperatura superplástica para cada una de las aleaciones analizadas. Es posible que el incremento en el módulo de pérdida se relacione con procesos de reacomodamiento de bordes de grano desde un estado de no-deslizamiento hacia un estado de deslizamiento. La activación de un gran número de bordes de grano puede relacionarse con la disminución en el esfuerzo cortante requerido para vencer la energía de cohesión entre granos cuando el material se encuentra en la temperatura superplástica.

Increasing stable deformation by declining temperature during the process

AbstractRecently increasing amount of light metal sheets, especially based on magnesium, is being involved into various structural constructions and functional components. Such a rising trend can be observed, for instance, at automotive, aerospace and electronic industry. On the other hand there exist some processing difficulties, such as forming limits, caused by crystalline structure.To make processing of magnesium materials most reasonable with a maximum economical and material’s effect, detailed investigation of the material’s mechanical behavior is necessary to realize. Especially, an use of superplasticity is a point of the main interest. By optimum settings of the deformation process (especially temperature and strain rate) the superplastic conditions were determined optimally. Moreover, it was discovered that variable temperature very positively affects the superplasticity of magnesium materials. Actually by changing temperature conditions during the deformation, even higher level of superplastic deformation without rupture can be obtained. This very interesting fact was observed at the elevated temperatures that decrease almost constantly during the deformation process.Thus previously widely used constant temperature treatment opens door to the dynamic problems of searching for the optimal temperature gradient and its variation.

Rheological Models as the Basic Element of Metal Forming Processes Simulation

The variety of metal forming processes can be arranged according to some essential features such as structure, properties and structure evolution of the metal being deformed, deformation temperature and dynamics of its changing during deformation, interrelation between flow stress, strain and strain rate, temperature and structural parameters etc. These features in the aggregate compose rheological behavior of the metal being deformed and the rheological equation’s database for simulation of metal forming processes in cold, warm, hot and superplastic state. Taking these ideas into account, the authors would like to present some basic elements of these rheological models database i.e. classification of metallic materials as objects of deformation, classification of deformation modes in dependence on temperature regimes, thermal-kinetic map of metal processing and, as a result of this analysis, a set of rheological models related to certain modes of metal forming processes, which can be used as basic elements of computer software systems for simulation of these processes.

Macrokinetics Hierarchies of States at Dynamic Superplasticity

Dynamic superplasticity of aluminium alloys is considered from positions of the theory of nonequilibrium phase transitions. Evolution of the open nonequilibrium system by which temperature-rates process in materials is modelled, is investigated within the framework of worked out defining relations with attraction of thermodynamic functions of the response. It is shown, that to peak of superplasticity there corresponds a maximum of a specific thermal capacity. The entropy production in optimum thermomechanical conditions of superplasticity aspires to a minimum which corresponds to formation of qualitative ultrafine-grained structure. With use of the Focker-Plank equation mechanisms of deformation characteristic for superplasticity and boundary conditions are analyzed. It is shown, that at superplasticity the main is the mechanism grain-boundary sliding, and in metastable conditions are added diffusionary processes. Influence of the specified processes in conditions of superplasticity becomes prevailing.

Mathematical modeling of processes of pressure treatment of industrial titanium alloys in the superplasticity state

A variant statement is formulated for the boundary problem of mechanics of superplasticity (SP). The variant is aimed to the development of mathematical models of technological processes of SP formation of industrial titanium alloys. It involves determining relations of the theory of creep with internal variables responsible for the description of evolution of the material structure during the SP deformation. As examples, technological processes of superplastic shaping of commercial sheet titanium alloy VT6s (Ti-6% Al-4% V) in the SP state are considered. Identification of determining relations is carried out by the results of technological experiments. To solve the boundary problem, a packet of applied programs ANSYS is used; calculations are performed for various variants of the selection of a mesh of final elements and fastening conditions. The results of calculations are compared with the experimental data for the commercial titanium alloy VT6s and calculations by engineering procedures. In the course of the analysis of obtained solutions of the boundary problem of mechanics of SP, it is found that the previously suggested engineering approaches can be applied in practice under the conditions when the selected loading modes correspond to the realization of the optimal temperature and dynamic conditions of manifestation of the SP effect.

Use of simulation modeling to determine the process parameters for the production of large-diameter aluminum shells

This article describes a process for obtaining sized seamless shells with waffled internal finning. The process employs thermoelastic stamping in the superplastic state, and the sizing operation is performed while the product is being pneumatically separated from the die. The process is used to make 0.5–2-m-diam. shells of aluminum and aluminum-magnesium alloys for aircraft structural elements, engines, and a large number of domestic products that are made to above-normal standards. The technology is based on the use of the possibilities of simulation modeling.

Influence of Microstructure Change on the Superplastic Properties of Ti<sub>3</sub>Al Base Alloy

The superplastic properties of Ti3Al base alloy have been investigated in the range of 900~1020°C and strain rate range of 3.3×10-4~3.3×10-2s-1 .The largest elongation of 1570% was obtained under the optimal superplastic deformation condition of 980°C and 3.3×10-4 s-1. The m-value varied from 0.46 to 0.59, its maximum value was obtained at 980°C.The microstructure of the alloy after heat treatment was composed of two phases of small spherical α2 phase particles distributing in βtransus matrix. Microstructure change has an obvious effect on the superplastic properties of Ti3Al-based alloy. At 980°C,when theα2 phase grain size changed from large to small then large and the cavitations in the fracture surface were larger and deeper with decreasing strain rate, the alloy showed the larger elongation and the lower flow stress.

Superplastic deformation of Ti3Al based alloy

Superplastic deformation behaviours of Ti3Al based alloy at high temperature have been investigated by using the non-constant strain rate electronic tensile testing apparatus. The results show that the effect of strain rate on the deformation ability of the alloy at high temperature is more significant than that of the temperature. When the alloy is deformed at lower temperature and higher strain rate, the large grain occurs necking and the small grain occurs sliding along grain boundary. Under the optimal superplastic deformation condition, the main superplastic deformation mechanism is the grain boundary sliding accompanying the dynamic recrystallisation process, which can supply the sliding and deformation sources for the deformed alloy. At higher temperature (1020°C), the superplastic deformation of the alloy consists of grain boundary sliding and the homogeneous extensions of the soft phase as well as the hard phase during the superplastic deformation.

Formation of textural inhomogeneity in a Zn-1.1% Al alloy during superplastic deformation

The Zn-1.1% Al alloy with a strong rolling texture has been tested under the conditions of superplasticity. The samples were cut from a sheet 5 mm thick at an angle of 20° with the sheet plane. The material in the initial state was characterized by the absence of a texture gradient over the sample thickness. Deformation led to a substantial weakening of texture maxima inside the sheet and their retention at the surface. Estimate of intragrain slip revealed that the contribution from slip was greater in deeper layers and smaller at the sheet surface. The effect was explained by different conditions of accommodation of grain-boundary sliding at the surface and inside the sheet.

Modelling the process of gas casting for the production of housing parts from tubular semifinished products

An example is given of the use of a technology developed by the Moscow State Institute of Steel and Alloys to make parts of housings from tubes (alloy Zn-22% Al) of rectangular cross section under superplastic conditions. The technology employs gasostatic casting.

Superplasticity of hydrogen-containing VT6 titanium alloy with a submicrocrystalline structure

Concentration and temperature regimes of hydrogen treatment have been found, which in combination with severe plastic deformation allow one to obtain a microstructure with a size of constituents of about 0.1 μm in the VT6 titanium alloy. It has been shown that the alloy with such a structure has superplastic properties in a temperature range from 500 to 650°C. Characteristics of superplasticity of a hydrogenated submicrocrystalline VT6 alloy and a basic alloy, in which the submicrocrystalline structure was obtained without hydrogen alloying, have been compared. Particular features of a hydrogenated submicrocrystalline VT6 alloy in a superplastic state are considered.

Analysis of Different Specimen Geometries for Tensile Tests in Superplastic Conditions for an Aluminium Alloy

Different geometries of tensile test specimens have been analyzed to get information about the variability of the measured physical quantities during tensile tests in superplastic conditions. A commercial aluminium alloy (AA5083) sheet has been used for the experimentation. The influences of main geometrical parameters on the elongation to failure, the measured stress and other test responses have been investigated using a universal testing machine and a split furnace. A numerical model has been used to better understand deformation phenomena involved in tensile tests.

Effect of Superplastic Deformation on the Properties of Zirconia Dispersed Alumina Nanocomposite

In this paper constrained extrusion of the zirconia dispersed alumina nanocomposite under superplastic conditions was conducted. The mechanical properties of deformed material were studied and its results were compared with those of the initial materials. The microstructure evolution during superplastic deformation was also analyzed. The results demonstrated that after superplastic extrusion the flexural strength, relative density, Vickers hardness as well as fracture toughness of the material increased noticeably. The flexural strength of the deformed composite even retained at a high value of 310MPa at 800°C. The fracture toughness of the material increased from 6.92 MPa·m1/2 to 8.87 MPa·m1/2 after deformation. After superplastic extrusion due to grain boundary sliding and the compressive stress state, the internal porosities in as-sintered materials were eliminated. During extrusion with grain coarsening the effect of t-ZrO2 to m-ZrO2 transformation toughening increased because more zirconia grains reached the critical dimension. Although grain coarsening may cause the decrease of the fracture toughness in some extent, the phase transformation toughening and strengthening dominated. As a result, the mechanical properties of the deformed material were improved.

Tool Thermal Behavior in SPF Environment

During a superplastic cycle and part loading/unloading operations, a superplastic tool withstands thermal cycles which affect its life-time, the superplastic cycle time and hence the productivity of the press. A thermal simulation of the tool behavior in superplastic conditions helps to understand which actions could reduce the effects of heat-shields opening/closing and of part loading/unloading on the cooling of the tool and on the heating of the part. Temperature measurements in transitory conditions and in steady-state have been collected on a tool of large dimensions in superplastic conditions of production. The paper will present the correlation between actual measures and simulation in steady state, in slow transitory conditions and in fast transitory conditions.

Isothermal Compressive Superplastic Deformation and its Constitute Equation of Structural Steel and Tool Steel

The microstructure of structural steel (40Cr) and tool steel (T10A) samples and its surface are respectively fined through salt-bath cyclic quenching (SCQ) and high frequency hardening (HFH), then the superplasticity is studied under isothermal compressive superplastic deformation condition. The experimental results indicate that the true stress-strain curves of 40Cr and T10A steel are separately shown to take place obvious superplastic flow characteristic at the temperature of 730-770 °C 710-770°C and at the initial strain rate of 1.7-50×10 -4 s -1 2.5-8.3×10 -4 s -1 , its strain rate sensitivity are respectively 0.30-0.38 and 0.32-0.50, the steady superplastic flow stress are respectively 60-70 MPa and 35-45 MPa, the superplastic flow activation energy are respectively 198-217 KJ/mol and 182-195 KJ/mol, and they are close to α-Fe grain boundary self-diffusion activation energy. The compressive superplastic constitute equations of both steels are correspondingly set up. Due to the finer microstructure of HFH, it appears higher strain rate sensitivity value, smaller the steady superplastic flow stress and the superplastic flow activation energy, so it has better capability of superplastic deformation.

Cavity of Al-Cu-Mg Alloy during Superplastic Deformation

According to the characteristic of appearing cavitation in the metals during superplastic deformation, the influence of strain rate on cavity evolvement, the influence of cavity on superplastic deformation capability, and the formation, development process of cavity were investigated for Al-Cu-Mg alloy (i.e. coarse–grained LY12). The results show that: ①The pore nucleation occurs not only at triangle grain boundaries, but also along nearby the second phase particles, and even within grains. The cavities at the triangle grain boundaries are present in V-shape, others near the second phase particles and within grains are present in O-shape. These cavities may result from disharmony slippage of grain boundaries. ②The tendency of cavity development decreases with increasing of strain-rate. In lower strain-rate condition, though Al-Cu-Mg alloy has better superplasticity, many big cavities in the specimen may reduce the room temperature properties of the alloy. In higher strain-rate condition, Al-Cu-Mg alloy has certain superplasticity and room temperature properties as well as few cavities forming. By analyzing, viscous layer on grain boundaries is very thin and grain sizes can be refined during their extruding and rotating each other in higher strain-rate superplastic deformation condition. ③Growth and coalescence of cavity are the main reason of the superplastic fracture of Al-Cu-Mg alloy. And small and a certain amount of cavities with dispersion and independence state are very useful to crystal boundary slippage.