Superplasticity Effect Research Articles

Low-temperature superplastic behavior of nanostructured Al-Zn-Mg-Cu alloy

The evolution of Al-Zn-Mg-Cu alloy microstructure during high pressure torsion at room temperature and subsequent low-temperature superplastic deformation is studied. The formation of a nanostructured state in Al-Zn-Mg-Cu alloy made it possible to implement a superplasticity (SP) effect at 170 °C and a strain rate of 5 × 10−4 s−1. The deformation relief of the gauge part of an Al-Zn-Mg-Cu alloy sample at the stage of steady-state SP flow is analyzed. Low-temperature superplastic deformation is stated to take place due to grain boundary sliding. High formability of nanostructured alloy under biaxial tension at a temperature of 170 °C is recorded.

Study of titanium alloy Ti–Al–Zr–Nb–V during heating under deformation and its phase transformation features

An alloy based on Ti–Al–Zr–Nb–V was prepared and its deformation behavior at elevated temperatures was studied. The microstructure and phase of the alloys were characterized by optical microscopy, scanning electron microscopy, thermal analysis, and mechanical testing. The results showed that the Ti–Al–Zr–Nb–V alloy, when stretched, exhibits a superplasticity effect in the range of 975℃ to 1100℃, with an elongation of up to 400%. It was found that superplasticity develops in the temperature region of the α+β→β transition and is accompanied by a change in grain size and redistribution of alloying elements among phases.

EVOLUTION OF THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF AL-B COMPOSITE WITH THE ULTRAFINE-GRAINED ALUMINUM MATRIX

The paper examines the microstructural evolution of alloy 1565ch of the Al-Mg-Mn-Zn-Zr system during thermomechanical treatment, including severe plastic deformation by high-pressure torsion or equal channel angular pressing according to the conform scheme and subsequent isothermal rolling at 200°C. Formation of the nanostructured and ultrafine-grained states in alloy 1565ch with the controlled distribution of Al3Mg2, Al6Mn and Al3Zr phases both inside grains and at their boundaries allows for the superplastic effect at the temperatures 250 and 300°C and strain rates 5 × 10-2, 10-2, and 5 × 10-3 s-1. Microstructural analysis by transmission electron microscopy shows that superplastic deformation at the temperatures 250 and 300°C allows a homogeneous ultrafine-grained state to be preserved. The studied ultrafine-grained aluminum alloy 1565ch has a high strength and the ability to relieve stresses, and therefore it can be favorably used as the matrix material in composites reinforced with continuous boron fibers. In the paper, we use this alloy to study special features of production of a multilayer metal matrix composite according to the foil-fiber-foil scheme by isothermal pressing in the low-temperature superplastic mode. This method has a positive effect on the mechanical properties of the composite, such as ultimate strength at 200°C, impact strength at room temperature, and fracture toughness at room temperature.

Низкотемпературная сверхпластическая деформация никелевого сплава ЭК79 с ультрамелкозернистой структурой смешанного типа

One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

Overview: Using Severe Plastic Deformation in the Processing of Superplastic Materials

In tensile testing, polycrystalline materials generally fail at relatively low total elongations but under some limited conditions it is possible to achieve exceptionally high elongations of up to and exceeding 400%. This superplastic condition is important scientifically but also it has important uses through the industrial development of superplastic forming operations. This overview traces the historical development of this superplastic effect and it provides a summary of the main characteristics of the superplastic flow process. Conventional thermomechanical processing is not able to produce exceptionally small grain sizes within the submicrometer or nanometer range but this limitation was effectively overcome through processing using severe plastic deformation (SPD). The advantages of SPD processing are discussed and examples are presented. Finally it is demonstrated that the experimental data may be easily and effectively displayed through the construction of deformation mechanism maps based on combinations of stress, grain size and temperature.

Superplastic forming of EK61 nickel-based superalloy with ultrafine-grained structure

The formation of an ultrafine-grained structure in the heat-resistant nickel-based EK61 superalloy makes it possible to realize the effect of low-temperature superplasticity. This is important for the development of resource-saving technologies for forming hollow products of complex configuration. The study of mechanical properties of the nickel-based EK61 superalloy with ultrafine-grained structure under conditions of uniaxial tension and compression at temperatures of 650 – 850°C and strain rates of 10−3 – 10−4 s−1 was carried out. The process of superplastic forming (SPF) under conditions of low-temperature superplasticity of ultrafine-grained sheet blanks from the EK61 superalloy using cylindrical matrix has been studied. It was found that after SPF, a homogeneous equiaxed ultrafine-grained duplex structure is preserved in the samples.

Dynamic Recrystallization and Its Effect on Superior Plasticity of Cold-Rolled Bioabsorbable Zinc-Copper Alloys.

High plasticity of bioabsorbable stents, either cardiac or ureteral, is of great importance in terms of implants’ fabrication and positioning. Zn-Cu constitutes a promising group of materials in terms of feasible deformation since the superplastic effect has been observed in them, yet its origin remains poorly understood. Therefore, it is crucial to inspect the microstructural evolution of processed material to gain an insight into the mechanisms leading to such an extraordinary property. Within the present study, cold-rolled Zn-Cu alloys, i.e., Zn with addition of 1 wt.% and 5 wt.% of Cu, have been extensively investigated using scanning electron microscopy as well as transmission electron microscopy, so as to find out the possible explanation of superior plasticity of the Zn-Cu alloys. It has been stated that the continuous dynamic recrystallization has a tremendous impact on superior plasticity reported for Zn-1Cu alloy processed by rolling to 90% of reduction rate. The effect might be supported by static recrystallization, provoking grain growth and thereby yielding non-homogeneous microstructures. Such heterogeneous microstructure enables better formability since it increases the mean free path for dislocation movement.

Selection of interference-fit tolerance when rolling thin-wall bushings

Roller burnishing tools are widely used in various sectors of the economy. When rolling thin-walled bushings, plastic deformation takes place. Therefore, to calculate stresses and interference fits, complex 3D models based on the finite element method are often used. The model proposed by the author is simpler in terms of taking into account the plastic component of deformations. Based on this model, numerical calculations were carried out and the dependence of arising interference fits on the number of roller burnishing tools was obtained. The importance of this manuscript is to identify the causes of superplastic effect material. The proposed mathematical model makes it possible to determine the required number of roller burnishing tools when processing thin-walled bushings. The results obtained can be used for cold bending of pipes or hardening the surface of cylindrical parts by rolling.

Studies of Kinetic Plasticity Effect in High-Speed Steels under Martensite Transformation

In the paper the authors study how the kinetic plasticity effects the temporary and residual stresses formed in instrumental steels when cooling. They also present the results of temporary stresses relaxation. This phenomenon was applied within the temperature range of the martensite transformation to reduce the cold cracking of the surfaced metal. The paper shows that the superplasticity effect emerging at the moment of martensite transformation plays the crucial role in temporary stresses relaxation.

Peculiarities of Alloying Effect on the Eutectic Cementite Behavior Under Hot Rolling

Abstract Currently, cast iron remains one of the major modern casting materials in metallurgy and machine-building industry and is sure to take the lead in the future. Chilled cast iron has high hardness and wear resistance due to a large number of carbide phases in its structure. However, low ductility and impact hardness essentially limit its applicability in terms of processing. Hot plastic working, under which the eutectic net crushing is observed, appears to be one of the most effective means of the eutectic alloy products shape and microstructure transformation. Chilled cast iron properties fundamentally improve after hot plastic working: ductility, strength and impact hardness increase by 2-3 times on retention of the high hardness factor. Chilled cast iron ductility increase can be attained when using phase transformations in eutectic cementite under lean alloying with carbide forming elements. The purpose of the paper is to study alloying effect on the chilled cast iron ductility as well as eutectic cementite behavior under hot rolling. In the paper hardening and softening of the structural components in chilled cast iron under hot working have been studied. The deformation texture forming in eutectic cementite under hot rolling has been revealed, which is connected with the dynamic softening and depends on the degree and the nature of its alloying. The mechanism and regularities of the phase transformation effect in cementite on its behavior under plastic deformation and on the alloys ductility in general have been studied. In cementite chromium alloying initiates processes, that can be characterized as the pre-precipitation stage of the new phases, and this way it contributes to the cast iron ductility reduction and embrittles cementite. Carbide transformation, that occurs in eutectic cementite under alloying with vanadium, stimulates softening of the alloy and increases its ductility level. Moreover, the multiple glide planes {130},{011},{112} in cementite have been determined. It has been found out, that in supersaturated cementite vanadium carbides precipitation stimulates the extra glide plane {111} occurrence under hot rolling. The essence of the carbide transformation phenomenon is that under hot working there occurs the lubricating effect at the transition of the metastable iron carbide condition, which is strengthened with vanadium supersaturation and mechanical hardening, to a more stable condition due to precipitation of the proeutectoid constituents on the one hand, and because of the dynamic softening processes on the other hand. At that, the autocatalyticity effect is observed: there is precipitation of carbides with hardening and softening, similar to the processes that arise as a result of the superplastic effect induced by phase transformations.

Alloys-by-design: Application to titanium alloys for optimal superplasticity

An alloy design approach for titanium alloys is presented. New alloys are isolated, manufactured and tested with an emphasis on the superplastic response. The superplastic effect is found to be optimal between 650 to 750∘C at strain rates between 8.3×10−2 and 8.3×10−3/s – this is a substantial improvement in terms of temperature and deformation rates over traditional titanium alloys such as Ti–6Al–4V. Elongations approaching ∼2000% are demonstrated. Electron backscatter diffraction studies confirm a randomisation of texture and absence of significant intragranular dislocation density, confirming superplasticity and thus grain-boundary sliding as the overarching deformation mechanism. At strain rates faster than 0.01/s, the alloys exhibit large elongations (∼200–500%) but softening is evident and lower ductility results. Our results reveal that the physical factors controlling the alloy composition/property/manufacturing interrelationship are understood and quantified. Physically-based constitutive equations are presented and used to demonstrate the practical advantages of the designed alloys.

Superplasticity induced by the competitive DRX between BCC beta and HCP alpha in Ti-4Al-3V-2Mo-2Fe alloy

With the purpose of identifying underlying insights into deformation mechanism (DM) of superplastic effect, a constitutive equation was developed on the basis of the experimental data. Superplastic tensile tests were conducted in the temperature range of 760–840 °C and strain rate range of 0.03–0.3 s−1. The results show that the superplastic behavior can be interpreted by grain boundary sliding (GBS) under most deformation conditions in addition to the high strain rate. To fully understand the DM of superplasticity in this exceptional condition, the corresponding microtexture and microstructure were discussed. These demonstrate that the subgrain size λ is of profound significance for accommodation mechanism responses. α grains-group migrates along the boundaries coordinated by the softer β, synchronously, inducing the accumulated stress being spreaded by dislocations traveling through β to the opposite boundaries. In the meantime, the rearranged dislocations are converted into high-angle sub-boundaries in α grains, characterizing continuous dynamic recrystallization (CDRX) mode, while the recrystallized β grains are dominantly provoked by discontinuous dynamic recrystallization (DDRX), aided by CDRX. A competitive DRX mechanism between HCP and BCC crystallographic structures is first proposed. Both grain boundaries expand towards the counterpart side and absorb surrounding dislocations until they contact each other, weakening the driving force of DRX and suppressing grain coarsening. As a result, the superplasticity of Ti-4Al-3V-2Mo-2Fe alloy is achieved by GBS associated with the refined grains caused by DRX.

Use of the superplasticity effect of materials in engineering technology

Annotation. Technological aspects of using the effect of superplasticity in the manufacture of many mechanical engineering products by pressure treatment methods are considered. Superplasticity, which manifests itself under special conditions, allows the formation of complex forms of specific materials with heat and deformation resistance, hardness and brittleness, and atypical physical and technical properties at low costs. The conditions and factors of the manifestation of superplasticity effect for traditional and innovative materials, such as metallic glass and nanoceramics, are revealed. New mold forming technologies that do not require press equipment are considered, and the areas of optimal use of the capabilities of the superplastic state of materials are specified.

The Influence of Warm abc-Pressing on the Structure and Mechanical Properties of Stable Chromium-Nickel-Molybdenum Steel

The structure and properties of the 17Cr13Ni3Mo0.01C stable austenitic steel subjected to high-temperature plastic deformation by the abc-pressing (multiaxial forging) are investigated in the temperature range from 800 to 600°С. The results of investigations demonstrate that after the abc-pressing the steel has a single-phase austenitic ultrafine-grained structure with the size of its elements (grains and subgrains) of (200 ± 140) nm. The formation of the ultrafine-grained state increases the strength properties (0.2 proof stress increases threefold) and decreases the elongation value of the steel at room temperature compared to the coarse-grained specimens. An analysis of the contributions from hardening during abc-pressing evidences in favor of the strength improvement being primarily due to the grain refinement; it is well described by the Hall–Petch relationship. In this case steel with ultrafine-grained austenitic structure exhibits an effect of structural superplasticity at the temperatures T > 750°С: the elongation value at Т = 800°С is found to be 180%.

Change in elastic properties of eutectic alloys under conditions of superplastic deformation

In this study, experimental data have been obtained which reveal taking place of complex physical processes under conditions of the structural superplasticity not only in the grain boundary, as it is commonly believed, but also in the grain body. It was established for the first time that superplastic deformation of the eutectic alloys is accompanied by significant changes in their Young’s moduli. It was demonstrated that under superplastic deformation the observed changes of the elastic properties of the eutectic Sn–38wt%Pb alloy under study are caused mainly by the decomposition of supersaturated solid solutions on the basis of the alloy components and the relaxation of internal stresses. It was also found that the viscous dislocation–diffusion non-conservative flow is actively developing in the eutectic alloys under conditions of superplasticity, in contrast to the existing ideas about grain boundary sliding as the main mechanism of the matter transport. The experimental results obtained are important for the deeper understanding of the physical nature of the structural superplasticity effect.

Studies on the Superplasticity Effect in UFA: History and Development (In Memory of Prof. O.A. Kaibyshev)

Abstract Prof. O.A. Kaibyshev initiated studies on superplasticity of metals and alloys in Ufa in the 70s-80s of the last century. These studies gave momentum to the development of fundamental and applied studies on superplasticity not only in Russia but in numerous laboratories around the world. This paper highlights the major results of this early work and considers their state-of-the-art and development perspectives for the science and practice of materials superplasticity.

Investigation of Structural-Phase States and Features of Plastic Deformation of the Austenitic Precipitation-Hardening Co-Ni-Nb Alloy

This article presents the results of investigation of the influence of holding temperature during the quenching process on the microstructure and superplasticity of the Co-Ni-Nb alloy. Temperature-strain rate intervals of the deformation of the superplasticity effects are stated. The optimal regimes of the preliminary treatment by quenching and rolling as well as the routine of the superplastic deformation of the Co-Ni-Nb alloy are defined. The interval of the temperatures of the precipitation, morphology, composition, type and parameters of the lattice of the secondary phase, which appears after the annealing + rolling (to 90%) Co-Ni-Nb alloy, are determined.

Structural Characterization of FeAl28Cr5 Alloy Deformed in the Hot Torsion Process

Current research in the field of iron aluminides are directed towards to understand the structural phenomena occurring during plastic deformation of these alloys. The obtained results of the study and collected informations will be used to determine the description of the structural changes taking place during hot deformation of Fe ̶Al alloys. The article presents the results of the study of the alloy FeAl28Cr5 deformed by hot torsion in temperature range of 800÷1100°C and a strain rate of 0.1 s-1. The analysis of the structure of the alloy FeAl28Cr5 allowed to reveal changes caused by dynamic processes of deformation. The results of torsion tests show the possibility to obtain a fine-grained structure with of parameters of the processes (T=1000°C, 1100°C) and strain of ε=40. After deformation at strain of (ε=40) the structure consists of fine grains with a misorientation angle higher than 15°, and the average grain size diameter D=28.5 micrometers. Deformation at a temperature of T=1000°C and 1100°C is accompanied by superplastic flow effect.

On the mechanisms of superplasticity in Ti–6Al–4V

Surface observations are used to elucidate the deformation mechanisms responsible for the superplastic effect in Ti–6Al–4V. High-temperature in-situ tests for tensile and shear deformation modes are performed in the scanning electron microscope at temperatures in excess of 700∘ C. Grain boundary sliding is predominant; the micro-mechanics of accommodation are consistent with the dislocation-based Rachinger theory. The volume fraction of β plays a crucial role. For temperatures greater than 850 °C, the α grains remain unaffected; cavitation is minimal and slip bands needed for dislocation-based accommodation are detected in the β phase but are absent in α. At this temperature, grain neighbour switching is observed directly under shear deformation. At a temperature lower than 850∘ C, the β volume fraction is lower and a different mechanism is observed: slip bands in α and cavitation are found to accommodate grain boundary sliding. In addition, an increase in the α phase intragranular dislocation activity triggers the formation of subgrains and dynamic recrystallisation, consistent with the Rachinger dislocation creep effect. For temperatures lower than 700∘ C, superplasticity is absent; classical creep behaviour controlled by dislocation climb persists. A numerical treatment is presented which accounts for the Rachinger effect. The computational results are used to deconvolute the contributions of each of the competing mechanisms to the total strain accumulated.

Superplasticity Effect Demonstrated by Gas Forming Hot Bent AA5XXX Sheets into V-Shaped Trough Containing Uneven Concavities

Using low gas pressure as a tool to form metal sheets is certainly feasible. However, the intrinsic flow properties of metal sheet are often a key factor in determining degree of formability, which has not been emphasized or explained well. Most metals, for examples aluminum alloys, can be either superplastic or non-superplastic depending on their original processing history or route (consequently, yielding suitable microstructure) and forming conditions, i.e. mostly temperature and strain rate. This superplasticity effect is clearly demonstrated by gas forming superplastic AA5083 and non-superplastic AA5052 into a V-shaped deep trough containing uneven concavities. The results show the superiority of superplastic material when harsh product standard is required.