Superplastic Research Articles

A mean field description of steady state isotropic structural superplastic deformation

A model developed previously to treat steady state isotropic superplastic deformation turned out to be of generic value and relevant to many classes of materials from metallic materials, ceramics, intermetallic compounds, composites, bulk metallic glasses, and geological materials. The present paper demonstrates the applicability of the concept of “oblate spheroidal ensembles of atoms containing quantified excess free volume present in a general grain boundary” to predict quantitatively the response of general, high-angle grain boundaries when subjected to external stimuli, e.g., an external stress, irrespective of the nature of the atomic bonds (metallic, ionic, or covalent) in preference to purely geometric descriptions of the grain boundary. The emergence of “oblate spheroids” as a response to an external stimulus is regarded in this analysis as self-organizing and a basic phenomenon that cuts across material classes and the nature of the chemical bonds.

The influence of rapid-diffusive β-stabilizers on the microstructure formation and superplasticity of titanium-based alloys

The superplasticity of Ti-based alloys is improved due to grain refinement, an increase in grain size stability, and an increase in the β-phase fraction up to ∼0.5. Alloying with β-stabilizers reduces the β-transus temperature and increases the β-phase fraction at low forming temperatures, thus improving the superplasticity and lowering its temperature. Both grain growth and superplastic deformation mechanisms are diffusion-controlled phenomena, and, therefore, the diffusivity of the alloying elements should have a significant effect on superplasticity. This work deals with the influence of the high-diffusive elements Fe, Co, and Ni on the grain structure and superplasticity of titanium alloys. For this purpose, the Ti-Al-Mo-V alloy, and alloys with proportional replacement of low-diffusive Mo by Fe, Co, or Ni, exhibiting an interstitial diffusion mechanism, were studied. The alloying elements content was selected to ensure the same β-phase fraction at a deformation temperature of ∼875 °C. The microstructure evolution after thermomechanical processing, annealing, and superplastic deformation, as well as post-deformation room-temperature mechanical properties of the studied alloys, were compared. The actual phase ratio was reconstructed by comparing scanning electron microscopy images in backscattered electrons and electron backscatter diffraction data for the same fragments. It was found that Mo replacement for highly diffusive elements accelerated dynamic grain growth during superplastic deformation at an elevated temperature of 875 °C but improved superplasticity at a lower temperature of 775 °C. The results confirmed that alloying with high-diffusive elements is a promising strategy for the design of low-temperature superplastic forming alloys.

Phenomenological Model for the Dynamic Superplastic Deformation Mechanism in a Zn-Al Eutectoid Alloy Modified with 2 wt% Cu

Phenomenological Model for the Dynamic Superplastic Deformation Mechanism in a Zn-Al Eutectoid Alloy Modified with 2 wt% Cu

INFLUENCE OF COOLING MEDIUM ON MICROSTRUCTURE AND MECHANICAL PROPERTIES IN FRICTION STIR PROCESSING OF MAGNESIUM ALLOY — A REVIEW

Friction stir processing (FSP) is used for changing the microstructure and material properties improvement. In modern years, special attention is exposed by governing the temperature level, and is applied by various coolants spraying on the top surface of the sample during FSP. This review paper explores the impact of several cooling mediums such as normal water, cold water, hot water, and cryogenic on the temperature distribution, grain refinement, mechanical characteristics, and superplastic deformation behavior of FSP using various grades of magnesium (Mg) alloys. It also includes the corrosion rate and wear behavior of FSP on Mg alloys. Through the systematic review, it has been observed that refined grains were formed and the generation of intermetallic compounds was suppressed after FSP in underwater and cryogenic conditions, leading to a notable increase in strength. The higher tensile strength and elongation are exhibited while using cryogenic compared to water medium. This is due to a rapid cooling process, where the high temperature was short for the newly-formed grains to fully develop. This review not only concludes the key findings of the preceding research but also suggests future recommendations.

Single‐crystalline indium selenide fibers by laser‐induced recrystallization and their tunable whispering‐gallery‐mode lasing by pressure‐modulating

AbstractIndium selenide (InSe) crystal, as an emerging Van der Waals semiconductor, showed great potential in optical and optoelectronic devices due to its remarkable electron mobility, flexible direct bandgap, and photoresponsivity. Especially, the bulk single‐crystalline InSe shows superplastic deformability with the aid of the interlayer gliding and cross‐layer dislocation slip. The extraordinary mechanical behavior brings significant opportunities and possibilities to pressure‐modulated optical devices, which, however, have not been explored sufficiently. Additionally, InSe crystals are challenged in the rapid large‐scale preparation and reproduction due to limitations, such as phase heterogeneity, dissociation risks, and chemical instability. Herein, we proposed a fiber drawing technique to create single‐crystalline InSe by the molten core drawing method combined with CO2 laser‐induced recrystallization. The fabricated InSe fiber, spanning several meters in length, shows a uniform and directional single‐crystalline InSe core encased within a 450 µm thick protective borosilicate glass cladding. The inherent core‐cladding configuration of the InSe fibers not only provides robust protection to the InSe crystals but also seamlessly creates a whispering‐gallery‐mode microcavity. Utilizing a 532 nm nanosecond pulsed laser as a pump, a tunable lasing from 1076.2 to 1111.8 nm was achieved, dictated by the controlled pressure within the InSe fiber. We present a simple and effective method for single‐crystalline InSe fabrication and first achieve a pressure‐modulated laser in a near‐infrared band based on InSe fiber, heralding an advancement for the scalable, efficient generation of tunable lasers.

A theoretical and experimental study of deformation mechanism dictated by disclination-dislocation coupling in Mg alloys at different temperatures

Dislocations and disclinations are fundamental topological defects within crystals, which determine the mechanical properties of metals and alloys. Despite their important roles in multiple physical mechanisms, e.g., dynamic recovery and grain boundary mediated plasticity, the intrinsic coupling and correlation between disclinations and dislocations, and their impacts on the deformation behavior of metallic materials still remain obscure, partially due to the lack of a theoretical tool to capture the rotational nature of disclinations. By using a Lie-algebra-based theoretical framework, we obtain a general equation to quantify the intrinsic coupling of disclinations and dislocations. Through quasi in-situ electron backscatter diffraction characterizations and disclination/dislocation density analyses in Mg alloys, the generation, coevolution and reactions of disclinations and dislocations during dynamic recovery and superplastic deformation have been quantitatively analyzed. It has been demonstrated that the obtained governing equation can capture multiple physical processes associated with mechanical deformation of metals, e.g., grain rotation and grain boundary migration, at both room temperature and high temperature. By establishing the disclination-dislocation coupling equation within a Lie algebra description, our work provides new insights for exploring the coevolution and reaction of disclinations/dislocations, with profound implications for elucidating the microstructure-property relationship and underlying deformation mechanisms in metallic materials.

Deformation mechanism and microstructure evolution during superplastic deformation of friction stir processed CoCrFeNiMn high entropy alloy

Since superplastic formation offers a significant advantage in preparing the complex structure parts of HEAs, the study of their superplastic behavior is extremely important. Using friction stir processing (FSP) with an improved convex hemispherical shape tool, this study reported for the first time an equiaxed ultrafine-grained CoCrFeNiMn HEA (489 nm) with a maximum elongation of 870% at 675 °C and 3 × 10−4 s−1. This superplastic property is much larger than ever reported in the CoCrFeNiMn HEA, which is even larger than that of the nano-sized CoCrFeNiMn HEA (10 nm) prepared by the high-pressure torsion. A high proportion of high angle grain boundaries and twin boundaries, a hard Cr-rich phase, and the sluggish diffusion effect of the CoCrFeNiMn HEA were primarily responsible for the exceptional superplasticity. Additionally, this study provides the first elucidation of the mechanism underlying Cr precipitation and Cr-rich phase growth, as well as the function of low-energy annealed twins during superplastic deformation. The diffusion of Cr along dislocations and grain boundaries facilitated grain boundary sliding as the predominant deformation mechanism. This study elucidates the superplastic deformation mechanism and microstructure evolution, thereby furnishing theoretical guidance for the practical implementation of superplastic forming of complex components of HEAs. Additionally, it presents an efficient method for fabricating such components.

Low-temperature superplastic deformation mechanism of ultra-fine grain Ti–6Al–4V alloy by friction stir processing

The ultra-fine grain Ti–6Al–4V alloy sheet was successfully achieved by friction stir processing (FSP). The low-temperature superplastic deformation mechanism of Ti–6Al–4V alloy under the strain rate of 3 × 10−4 s−1 at 600 °C was studied by scanning electron microscope, electron backscatter diffraction and superplastic tensile test. It is found that the grain size of Ti–6Al–4V alloy by FSP is refined from 7.48 μm to 0.82 μm, and there is no preferential crystallographic orientation of the uniform grain. After FSP, the β phase of the base material (BM) in the grain boundary is refined and homogenized. During the superplastic tensile processing, with the increase of strain, the grain is refined continuously, and the α→β phase transition is induced by the dislocations pile-up at the β grain boundary, and the content of β phase increases. The grain near the fracture was refined to 0.35 μm, and the stress concentration led to the formation of cavities near the β phase, which eventually caused the fracture. The dynamic recrystallization in superplastic tensile processing is mainly geometric dynamic recrystallization and discontinuous dynamic recrystallization. The elongation of superplastic tensile (1033%) is 19.7 times higher than that of BM (50%). The order of superplastic deformation mechanism in the low-temperature superplastic deformation of the ultra-fine grain Ti–6Al–4V alloy sheet is as follows: intragranular dislocation slip and diffusion, grain boundary sliding, and phase boundary sliding. Phase boundary sliding is the main deformation mechanism for low-temperature superplastic deformation.

Superplastic deformation behavior of low Al–added medium Mn steels with and without Ti and Mo elements

Fe-Mn-Al-C medium Mn steels were found to reveal extraordinary superplasticity and have significant potential for forming the complex structural parts due to high strength, excellent ductility and material cost. In present study, the effect of tensile deformation temperature on the superplastic deformation behavior of a cold-rolled low Al-added medium Mn steel was studied. A maximum tensile elongation of approximately 1170% was obtained at 745 °C and 10−2 s−1, which is to our best knowledge the highest low-temperature-high-strain-rate superplasticity in medium Mn steels. Also, the role mechanism of microalloying elements such as Ti and Mo was revealed to further enhance the strength level of superplastic medium Mn steels. In view of the representative microstructural features, such as equiaxed grains, random texture, and sluggish grain growth, grain boundary sliding is thought to be the dominative mechanism during the high-strain-rate superplastic deformation.

Fluorescence behaviors of perylene-dispersed super engineering plastic films

We attempted to manufacture films in which fluorescent dye is dispersed using engineering plastic as a matrix which has high heat and chemical resistance as well as excellent mechanical performance. In this study, films containing highly dispersed perylene in colorless and transparent aromatic polyamide (PA) and polyimide (PI) were manufactured. The perylene-dispersed PA film emitted strong blue light with a maximum fluorescence at 457 nm. On the other hand, the perylene-dispersed PI film showed significant fluorescence quenching with its maximum fluorescence wavelength significantly red-shifted to 546 nm. The perylene-dispersed PI film treated with ethylene diamine at 80 °C showed strong blue fluorescence, and when the film was further heated at 200 °C, the fluorescence was quenched. These films are expected to be applied as back light unit or color conversion layer for OLED and Micro LED due to their excellent physical properties.

Superplastic behavior of fine-grained Ti-10V-2Fe-3Al alloy fabricated by friction stir processing

Ti-10V-2Fe-3Al alloy with fine-grained β phases was fabricated by friction stir processing with optimized processing parameters. The superplastic behavior of the specimens was investigated by tensile deformation at different strain rates and temperatures, and an optimal superplastic elongation of 634 % was achieved at 700 °C and 3 × 10–4/s. An annealing treatment at 650 °C for 60 min showed a microstructure with α precipitates distributed in the β matrix in the friction stir specimen. Such pre-heat treatment improves the superplasticity of the specimen, achieving an elongation of up to 807 % at 750 °C and 3 × 10–4/s. The influences of tensile temperatures and strain rates on the microstructural evolution, such as grain size variation, grain morphology, and phase transformations, were discussed. The superplastic deformation behavior of fine-grained Ti-10V-2Fe-3Al alloy is controlled by grain boundary sliding and accompanied by dynamic phase transformation and recrystallization.

Rational Methods of Plastic Deformation Providing Formation of Ultrafine-Grained Structure in Large-Sized Products

Based on the peculiarities of plastic deformation mechanics and physical mesomechanics, the processes are considered and technological schemes for their realization are proposed to ensure the formation of ultrafine-grained structure in axisymmetric products of large sizes. Deformation of coarse-grained materials in temperature-velocity conditions of superplastic deformation and methods of severe plastic deformation are taken as methods of preparation of such a structure. All of these deformations include large strain, and they are carried out at low hydraulic press speeds, but at different temperatures: in the mode of superplasticity at hot temperatures, and in the mode of severe plastic deformation at warm or cold temperature deformation. The first mode allows grains to be refined to microcrystalline sizes of 1–10 microns, and such a material acquires the ability to deform in a state of superplasticity, i.e., in tension with low resistance to deformation and high elongation. The second mode (severe plastic deformation) refines grains to submicro- (1÷0.1 µm) and nanosizes (less than 0.1 µm), thus giving metal materials record structural strength, as well as the possibility to use processing in extended temperature-velocity conditions of superplastic deformation in comparison with microcrystalline structure.

Superplastic Deformation of Cold-Rolled Ni-Graphene Oxide Nanocomposites Foils

Superplastic Deformation of Cold-Rolled Ni-Graphene Oxide Nanocomposites Foils

Effect of Sc/Zr ratio on superplastic behavior of ultrafine-grained Al–6%Mg alloys

Al–6%Mg-Sc-Zr alloys with a combined Sc and Zr ratio of 0.32 wt% make up the focus of this research. The content of Sc and Zr varied with an increment of 0.02%. Their ultrafine-grained (UFG) microstructure was formed with Equal Channel Angular Pressing (ECAP). Superplasticity tests were performed at temperatures ranging from 300 to 500 °C and at a strain rate varying between 3.3·10−3 and 3.3·10−1 s−1. The values of strain hardening factor (n), strain rate sensitivity factor (m), and superplastic deformation threshold stress (σp) were determined. The microstructure and failure patterns of the alloys post superplasticity tests were studied. The effect of the Sc/Zr ratio on the superplastic behavior, cavitation fracture and dynamic grain growth of UFG Al–6%Mg alloys was investigated. The satisfiability of Hart's criterion for calculating uniform deformation value under superplastic conditions was verified. Grain boundary sliding and intragranular deformation make comparable contributions to superplastic flow in the UFG aluminum alloys under study. Al–6%Mg-0.20%Sc-0.12%Zr (Sc/Zr = 3.3 at.%) and Al–6%Mg-0.18%Sc-0.14%Zr (Sc/Zr = 2.8 at.%) alloys exhibit the highest superplasticity. Shown that changes in the Sc/Zr ratio affect the precipitating mechanism, spatial distribution and composition of the precipitating particles Al3(ScxZr1-x). The optimal Sc/Zr ∼2.6–3.3 (at.%) ratio for the Al–6%Mg alloy corresponds to an Al3(Sc0.5Zr0.5) and Al3Sc precipitated particles. The large Al3Zr particles formed through the discontinuous precipitation mechanism was detected at Sc/Zr < 1 (at.%).

Superplastic deformation behavior of 5 vol% (TiBw+TiCp)/Ti matrix composite sheets with lamellar microstructure

Superplastic forming is considered a highly efficient technique for shaping intricate components from titanium matrix composites (TMCs). In this work, high-temperature TMCs with 5 vol% (TiBw + TiCp) reinforcements underwent superplastic tensile tests at various temperatures and strain rates. The results demonstrated that at all deformation temperatures (900 °C–1050 °C) and strain rates (5 × 10−3 s−1 to 10−4 s−1), the elongation of composite sheets surpassed 100%. The strain rate of 10−3 s−1 and a temperature of 1000 °C were found to yield the maximum elongation of 328.1%. At 900 °C, the matrix grains maintain a lamellar morphology during the main stage of deformation, and dynamic recovery (DRV) is the primary mechanism of matrix softening. At 1000 °C, wide-range dynamic recrystallization (DRX) takes place, and grain boundary slip coordinated by grain rotation is the main mechanism of deformation. At 1050 °C, the matrix grains undergo DRX and grow rapidly by migration, and the number of grain boundaries decreases dramatically, resulting in poor superplastic qualities. In the early stages of superplastic deformation, micropores sprout at the triple grain boundaries and at the interfaces between the reinforcements and the matrix. As the deformation proceeds, the micropores extend along the tensile direction and connect with each other to form cavity stringers (CS). The distance between the CS rapidly narrows as the stretching process continues, and eventually the CS links horizontally to form cavity coalescence (CC). Micropore dilatation around the reinforcements causes debonding and cavitation, leading to material failure.

A Study of the Superplastic Deformation Behavior of Low-Cost Ti-2Fe-0.1B Alloys.

Titanium alloys have high specific strength and corrosion resistance, which have promising applications in industry. However, the machinability of titanium alloys is limited due to their crystal lattice and physical properties. Thus, in recent years, the superplastic forming of titanium alloys has been intensively developing, in particular, forming at low temperatures and/or high strain rates. In this work, a tensile test of low-cost Ti-2Fe-0.1B alloys was carried out at a temperature of 550~750 °C and a strain rate of 1 × 10-3 s-1~1 × 10-2 s-1. The results showed that the alloy exhibited good superplasticity even at a high strain rate (1 × 10-2 s-1) and a low deformation temperature of 550 °C; the elongation of the alloy in this state reached 137.5%. The high strain rate sensitivity coefficient m (0.3) and the maximum elongation (452%) were obtained at a strain rate of 1 × 10-3 s-1 and a temperature of 750 °C. Characteristics of the microstructure showed that during superplastic deformation, the recrystallization and grain boundary sliding of the alloy phases were accelerated, which could be ascribed to the effect of the element Fe. At the same time, the TiB phase located around the primary elongated α grains could also induce dynamic recrystallization and dynamic globularization during deformation.

Enhanced superplasticity of ultrafine-grained WEQ612 magnesium alloy via the coupling effect of grain boundary segregation and dense precipitation

Achieving low-temperature, high-strain-rate (LTHSR) superplasticity is important for preparing rare-earth (RE)–Mg alloy products with complex shapes. Herein, an ultrafine-grained Mg–6.22Y–0.98Er–2.11Ag (wt%, WEQ612) alloy was prepared via equal-channel angular pressing (ECAP). After 16 passes of ECAP and aging at 473 K for 58 h, an average grain size of 600 nm was achieved, and there was a high density of intergranular precipitates with an average size of approximately 180 nm. The WEQ612 alloy exhibited excellent superplasticity during superplastic deformation, with elongations of 451% at 523 K and 1 × 10−4 s−1, and 834% at 573 K and 1 × 10−2 s−1. The high density of intergranular precipitates, which were uniformly distributed at the grain boundaries, promoted dynamic recrystallization (DRX) during superplastic deformation and inhibited grain growth. The grain boundary co-segregation of Y and Ag further improved the grain boundary stability of the alloy. Despite the general consensus that grain boundary sliding (GBS) is the main mechanism of superplasticity, a more complex role of GBS and DRX was identified in this study. The identified mechanism provides a reference for GBS and grain boundary rotation as well as dislocation motion during superplastic deformation, and helps to describe the intermediate processes that occur during superplastic deformation. Thus, this study provides insights into the development of LTHSR superplastic RE–Mg alloys.

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

Revealing the Void Formation Mechanism during Superplastic Deformation of a Fine-Grained Ni–Co-Base Superalloy

The Constitutive Equation-Based Recrystallization Mechanism of Ti-6Al-4V Alloy during Superplastic Forming

The present paper is concerned with the dynamic recrystallization of the Ti-6Al-4V alloy. Electron Backscatter Diffraction (EBSD) observations are performed after high-temperatures tensile tests, with the temperature ranging from 700 to ~950 °C, and the strain rates varying between 10−4 and 10−2/s. Based on the analysis of flow behavior, the dominant mechanism is identified, and a mechanism map is proposed. In particular, the conditions of 890 °C and strain rates ranging from 10−3 to ~10−2/s serve as the delineating boundary of dynamic recovery (DRV) and dynamic recrystallization (DRX). For superplastic deformation, the dominant softening mechanism is DRV. Consequently, the occurrence of continuous dynamic recrystallization (CDRX) can naturally be ascribed to the process of grain refinement. Then, a multi-scales physical-based constitutive model of CDRX is developed, demonstrating a good agreement is obtained between the experimental and calculated grain sizes, so the above model could be used to describe the grain growth for superplastic deformation. In conclusion, DRV and DRX in the superplastic forming of Ti-6Al-4V are studied in this study, the condition boundaries of their occurrence are distinguished, and a constitutive equation-based CDRX recrystallization mechanism is given, which might be employed in the fracture mechanism research.

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.