Low Temperature Superplasticity Research Articles

Excellent low temperature superplasticity and its deformation mechanism in nano/ultrafine grained Fe–17Cr–6Ni stainless steel

Superplastic deformation typically occurs in non-ferrous metals at high temperatures, which results in severe surface oxidation and high energy consumption. In this study, we designed and manufactured a nano/ultrafine-grained stainless steel with a dual-phase microstructure that exhibits excellent low-temperature superplastic deformation capability. A maximum tensile elongation of approximately 500% was achieved when the tensile test was conducted at 700 °C with an initial strain rate of 5 × 10⁻⁴ s⁻1. Even after a 500% tensile elongation, the austenite grains in the gauge section of the tensile specimen still maintained an equiaxed grain shape, and the texture also weakened significantly, indicating that grain boundary sliding and grain rotation dominated the deformation process during superplastic flow. The outstanding superplasticity is mainly attributed to the dual-phase microstructure composed of nano/ultrafine austenite grains and martensite.

Effect of Si content on low-temperature superplasticity in Fe–10Mn steel

We systematically investigated the effect of Si on the low-temperature superplasticity of 50% and 80% cold-rolled Fe–10Mn-(0.2–5.5)Si steels through tensile testing at 763 K with strain rates of 1 × 10−3 s−1 and 1 × 10−4 s−1. Superplasticity was achieved through interphase boundary sliding between fine recrystallized α grains and reverted γ grains in most specimens, except for the 50% and 80% cold-rolled 0.2Si specimens and the 50% cold-rolled 2.4Si specimen at the strain rate of 1 × 10−3 s−1. Notably, at the strain rate of 1 × 10−4 s−1, the 80% cold-rolled 3.5Si specimen exhibited the highest elongation of 948% even at the low temperature of 763 K. The increased cold reduction and Si content enhanced superplasticity by raising stored energy, a driving force of recrystallization of the α phase and dynamic α′-to-γ reverse transformation. Additionally, Si enhanced interphase boundary sliding by increasing the difference in hardness between the α and γ phases. However, the 50% cold-rolled 5.5Si specimen, which contained δ ferrite-(Fe,Mn)3Si compound constituents, exhibited similar elongation to the 50% cold-rolled 3.5Si specimen due to the dynamic α′-to-γ reverse transformation occurring rapidly only up to a strain of ∼100%. Therefore, it is believed that a Si content of 3.5 wt% is ideal for enhancing low-temperature superplasticity in Fe–10Mn steel.

Achieving low-temperature superplasticity of a coarse-grained BAZ531 magnesium alloy

An as-extruded Mg-5Bi-3Al-1Zn (wt%) alloy containing a coarse-grained structure and a large amount of nano-scale Mg3Bi2 precipitates showed 330 % tensile elongation-to-failure at 200 °C and 10-4 s-1. Superplasticity was mainly due to grain boundary sliding (GBS) and grain matrix slip deformation (GMD) at low and moderate strains, along with grain refinement at high strain making more GBS be activated.

Low-Temperature Superplasticity of Ultrafine-Grained Aluminum Alloys: Recent Discoveries and Innovative Potential.

The last two decades have witnessed significant progress in the development of severe plastic deformation techniques to produce ultrafine-grained materials with new and superior properties. This review examines works and achievements related to the low-temperature superplasticity of ultrafine-grained aluminum alloys. The examples are provided of the possibility to observe low-temperature superplasticity in aluminum alloys at temperatures less than 0.5 Tmelt and even at room temperature, and herein, we demonstrate the cases of achieving high ductility and high strength in aluminum alloys from processing utilizing severe plastic deformation. Special emphasis is placed on recent studies of the formation of segregations of alloying elements at grain boundaries in UFG Al alloys and their influence on the development of grain boundary sliding and manifestation of low-temperature superplasticity. In addition, the current status and innovative potential of low-temperature superplasticity in aluminum alloys are observed.

Effect of equal channel angular pressing on strain deformation behavior of ultrafine grained during low temperature superplasticity of AA5083

AA5083 with ultrafine grain structure was produced through equal channel angular pressing using different levels of ECAP tensions, underwent a series of tensile tests. The superplasticity temperature 573 K at low temperatures. This study investigate how varying the ECAP strain influences the distinctive microstructure of the alloy and its impact on deformation mechanisms within the low-temperature superplasticity range. A fraction of the high angle borders increased when the equal channel angular pressing strain was increased from 1 to 2, while the sub-grain size stayed nearly same. This was the most applicable microstructural evolution. After double passes, the material showed superplastic elongations, but after single pass, it did not show low temperature superplasticity. Upon analyzing the mechanical data using typical deformation mechanisms, it was determined that dislocation climb controlled the samples deformation after the first pass, whereas grain boundary sliding was responsible for the sample's low temperature superplasticity after the second pass. In the present study, we explored the differences in deformation mechanisms by considering the microstructures formed under various ECAP strains. Equal channel angular pressing with a BC route and an effective strain of 1∼2, we created an ultrafine-grained AA5083. A significant increase was seen in the fraction of particles measuring 1.8–3.8 μm under the current ECAP conditions. The implementation of equal channel angular pressing, there was a significant increase in the occurrence of voids with sizes ranging from 0.8 to 1.8 μm. According to the current analysis and results, if moderate superplastic elongation is guaranteed, it may be preferable to have fewer equal channel angular pressing passes than those that result in the largest elongation while taking into account cavitation damage and the low temperature superplasticity of ultrafine grained AA5083 used in commercial applications.

Preparation of a Solid-Phase Compound from an Aluminum–Zinc Alloy under Conditions of Low-Temperature Superplasticity

Preparation of a Solid-Phase Compound from an Aluminum–Zinc Alloy under Conditions of Low-Temperature Superplasticity

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.

An Overview of the Principles of Low-Temperature Superplasticity in Metallic Materials Processed by Severe Plastic Deformation

Low-temperature superplasticity (LTS) is crucial to reduce manufacturing cost and to enhance the applications of superplastic forming. It is well known that grain refinement is the key point to decrease the temperature at which the superplasticity is attained. Therefore, ultrafine-grained (UFG) materials have become attractive for achieving LTS. Severe plastic deformation (SPD) techniques provide abnormal grain refinement, and thus they have been used to achieve LTS in metallic materials. This paper overviews and examines the reports of LTS in the severely-deformed metallic materials. It provides fundamentals of grain refinement via different SPD techniques in various classes of metallic materials including Al-, Mg-, and Ti-based alloys. It also gives a brief summary about the effect of microstructural requirements on LTS with an emphasis on grain size, type and chemical composition of grain boundaries and microstructural alteration during the superplastic deformation. In the last section of the manuscript, the main deformation mechanism of LTS were also explained.

Low-Temperature Superplasticity of the 1565ch Al–Mg Alloy in Ultrafine-Grained and Nanostructured States

—Homogeneous nanostructured and ultrafine grained (NS, UFG) states with mean grain sizes of 95 and 200 nm, respectively, have been formed in a 1565ch Al–Mg alloy (Al–5.66Mg–0.81Mn–0.67Zn–0.09Zr–0.07Cr–0.04Ti–0.001Be–0.3(Fe + Si) wt %). Microstructure of both states is represented by grain boundaries with predominantly high-angle misorientations. The alloy, produced both by high pressure torsion at room temperature and equal channel angular pressing at 200°C using the Conform approach, exhibits superplasticity at low temperatures in the range 250–300°C and strain rates in the range of 5 × 10–4–10–2 s–1. Elongation values range 170–560%, while the rate sensitivity coefficient (m) varies from 0.3 to 0.73 at low flow stress for both NS and UFG structures. The temperature range for the stability of strength properties of the 1565ch alloy in NS and UFG states after thermal and thermal mechanical treatments has been determined. The material in both structural states maintains a high level of strength after undergoing deformation under SP conditions. The deformation relief formed on the gage surface of the NS and UFG specimens of the 1565ch alloy during the established SP yield stage has been analyzed.

Welding the Solid State of Zn–22% Al Alloy under Low-Temperature Superplasticity Conditions

Welding the Solid State of Zn–22% Al Alloy under Low-Temperature Superplasticity Conditions

High-strain rate and low-temperature superplasticity of Fe-Mn-Si-Ni steel

Superplastic steels with high elongation above 300% are expected to be used to manufacture complex-shaped mechanical parts without joining. However, their practical application is difficult due to high energy consumption and low productivity caused by high deformation temperature and low strain rate. In the present study, we newly developed an Fe-Mn-Si-Ni steel, which exhibited superplasticity at a low temperature of 1023 K and a high strain rate of 1 × 10−1 s−1. This steel also had remarkable room-temperature tensile strength (∼1.3 GPa) and total elongation (38%) after a simulation of superplastic forming. The mechanism of excellent superplasticity is grain boundary sliding occurring at the boundaries of fine γ grains, whose coarsening was suppressed by both Fe5(Mn,Ni)3Si2 and (Fe,Mn,Ni)3Si precipitates.

Achieving low-temperature superplasticity in a cold-rolled medium Mn steel with an equilibrium ultrafine equiaxed dual-phase microstructure

The present study reports an equilibrium ultrafine equiaxed dual-phase microstructure to regulate and achieved the low deformation temperature and high hot ductility balance in a novel 3.6 Al medium Mn steel. The cold-rolled specimens were subjected to high-temperature tensile tests and microstructure characterization with deformation temperature as a variable. The results showed that during the hot tensile process, the initial ultrafine martensite grains were transformed into ferrite + austenite equiaxed dual-phase grains, accompanied by dynamic recovery and recrystallization. At the deformation conditions of 625°C and 5 × 10-4 s-1, the accumulation of dislocations is obvious and the grain refinement is caused significantly. The reason for its failure is the development of the neck. The maximum elongation of 880% was obtained at 675°C and 5 × 10-4 s-1 due to the dynamic balance between ‘the grain refinement and strain hardening caused by dislocation creep and accumulation’ and ‘the grain coarsening and softening caused by dynamic recovery and recrystallization’. When the deformation temperature continues to increase to 775 °C, the elongation sharply decreases up to 491%. The stress concentration at the phase boundary induces cavity behavior, which is the main reason for the premature failure at 775 °C.

Effect of grain size on superplastic deformation behavior of Zn-0.033 Mg alloy

Zn alloys reveal excellent biological degradability and compatibility, suitable mechanical properties, and unique anti-atherosclerotic properties, which make them suited for miniaturized medical implants. Superplastic forming is a promising method to fabricate high-performance microparts with difficult-to-deform materials. However, the effect of grain size on superplasticity in Zn alloys and the underlying mechanisms still need to be determined. In this research, Zn-0.033 Mg (in wt.%) alloy with different grain sizes from 1.53 to 36.17 μm was obtained by equal-channel angular pressing and heat treatment, and its mechanical performance was evaluated by uniaxial tensile tests in the temperature range of 453–533 K and the strain rate range of 0.001–0.01 s−1. Experimental results indicated that the flow stress is significantly reduced with increasing deformation temperature, and the elongation is effectively improved with the reduction in strain rate. Furthermore, the Zn-0.033 Mg alloy with a grain size of 1.53 μm exhibited a superplastic deformation with an elongation of 376 ± 79% at 453 K and 0.001 s−1. Two distinguishing deformation stages were observed during the superplastic deformation. In the early stage, the ∼85 ± 5°/ <1‾1‾20> twins significantly emerged, leading to subsequent dynamic recrystallization by high-angle grain boundary migration. In the steady-state stage, the non-basal dislocation slip was significantly activated via changing the grain orientation from hard to soft orientation with the aid of continuous dynamic recrystallization. The fracture mechanisms were further discussed based on the fracture surface analysis, indicating that the ultrafine-grained structures can accommodate the nucleation and growth of cavities by grain boundary sliding, enabling low-temperature superplasticity. These findings can grant a new insight and understanding of the superplastic mechanism of Zn alloys and shed light on the manufacture of high-performance Zn alloys for medical implants.

Low-temperature superplastic deformation of EK61 and EP975 wrought nickel-based superalloys with an ultrafine-grained structure

It is shown that thermomechanical treatment (TMT) of the EK61 superalloy with a strain rate (ε∙) of 10−3 s−1 and a gradual decrease in the treatment temperature from (0.92 – 0.65)Tδ leads to the transformation of the initial coarse-grained structure into an ultrafine-grained (UFG) mixed type structure. Such a mixed UFG microstructure consists of γ-phase grains and δ-phase particles 0.3 μm in size and relatively large particles of the δ-phase up to 2 μm in size. The EK61 superalloy having such a microstructure exhibits low-temperature superplasticity in the temperature range of 700 – 900°C, the maximum characteristics of which are achieved at 850°C and ε∙ =10−3 s−1. Low-temperature TMT in the temperature range of (0.84 – 0.8)Тγ' also leads to the formation of an UFG structure in the EP975 superalloy. The UFG microstructure of the EP975 superalloy consists of γ-phase grains and γ'-phase particles 0.5 μm in size. And there are relatively large particles of the γ'-phase up to 3.5 μm in size of a globular-shaped form. The EP975 superalloy with such a structure exhibits low-temperature superplasticity in the temperature range of 900 –1000°C, the maximum characteristics of which are achieved at 1000°C and ε∙ =10−3 s−1.

Low-Temperature Superplasticity and High Strength in the Al 2024 Alloy with Ultrafine Grains.

This study aims to achieve an ultrafine-grained (UFG) Al 2024 alloy superplasticity at temperatures lower than the traditional ones for commercial Al alloys (400-500 °C). The UFG structure with a mean grain size of 100 nm produced in the alloy by high-pressure torsion at room temperature provided a very high strength-microhardness (HV0.1) of 286 ± 4, offset yield strength (σ0.2) of 828 ± 9 MPa, and ultimate tensile strength (σUTS) of 871 ± 6 MPa at elongation to failure (δ) of 7 ± 0.2%. Complex tensile tests were performed at temperatures from 190 to 270 °C and strain rates from 10-2 to 5 × 10-5 s-1, and the values of flow stress, total elongation and strain rate-sensitivity coefficient were determined. The UFG alloy was shown to exhibit superplastic behavior at test temperatures of 240 and 270 °C. For the first time, 400% elongation was achieved in the alloy at an unusually low temperature of 270 °C (0.56 Tm) and strain rate of 10-3 s-1. The UFG 2024 alloy after superplastic deformation was found to have higher strength (150-160 HV) than that after the standard strengthening heat treatment T6.

Obtaining of a solid-phase compound from an aluminum-zinc alloy under conditions of low-temperature superplasticity

A method is developed for pressure welding of cylindrical workpieces in the solid state of an aluminum-zinc alloy in a vacuum at a temperature of 250 °C under conditions of low-temperature superplasticity. Tensile tests showed that the strength of the welded joints is 90÷95 % of the tensile strength of the base material. Keywords ultrafine-grained structure, aluminum-zinc alloy, low-temperature superplasticity, solid-phase compound, welding using pressure, mechanical properties

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.

The Microstructure and Strength of UFG 6060 Alloy after Superplastic Deformation at a Lower Homologous Temperature.

The paper reports on the features of low-temperature superplasticity of the heat-treatable aluminum Al-Mg-Si alloy in the ultrafine-grained state at temperatures below 0.5 times the melting point as well as on its post-deformation microstructure and tensile strength. We show that the refined microstructure is retained after superplastic deformation in the range of deformation temperatures of 120–180 °C and strain rates of 5 × 10–3 s–1–10–4 s–1. In the absence of noticeable grain growth, the ultrafine-grained alloy maintains the strength up to 380 MPa after SP deformation, which considerably exceeds the value (250 MPa) for the alloy in the peak-aged coarse-grain state. This finding opens pathways to form high-strength articles of Al-Mg-Si alloys after superplastic forming.

The Limits of Low Temperature Superplasticity in AA 5083 Produced By Accumulative Roll Bonding (ARB)

The Limits of Low Temperature Superplasticity in AA 5083 Produced By Accumulative Roll Bonding (ARB)

Biaxial Low-Temperature Superplasticity of AA 5083 Produced by Accumulative Roll Bonding

Biaxial Low-Temperature Superplasticity of AA 5083 Produced by Accumulative Roll Bonding