Superplastic Research Articles

METHODS OF ACCOUNTING FOR TEMPERATURE AND STRAIN RATE VARIATION IN MULTILEVEL CONSTITUTIVE MODELS OF METAL DEFORMATION (ANALYTICAL REVIEW)

Technological metal forming processes involving hot and superplastic deformation are sensitive to temperature and strain rate. This is because inelasticity mechanisms operate in different ways under different conditions, leading to the formation of different structures and therefore different effective physical and mechanical properties of the material. Optimal temperature and strain rate conditions for the forming process which provide improved performance characteristics of the resulting products with acceptable energy consumption (or, conversely, minimum energy consumption with acceptable performance characteristics) can be most effectively determined by mathematical modeling. The key elements of the latter are constitutive models for describing the behavior of the material (physical equations), which can account for the influence of temperature and strain rate on various mechanisms of inelastic deformation. Such constitutive models can be most effectively developed using a multilevel approach based on the introduction of internal variables, crystal plasticity, and an explicit description of the material structure and physical deformation mechanisms. There are many works that propose multilevel mathematical models of metals that somehow explicitly account for the temperature and strain rate effects on inelastic deformation. Based on physical considerations, this analytical review defines the most promising approach to constructing multilevel constitutive models with comprehensive consideration of the temperature and strain rate effects.

Friction stir processing of commercially pure aluminium in bare and reinforced conditions

Friction stir processing can imbibe super plasticity into the materials. Besides, it is also an established method for the fabrication of surface/bulk composites. With these advantages, the present investigation is devoted to friction stir processing of commercially pure aluminium in bare and copper-reinforced conditions. The copper is added in two steps 0.5 and 1 vol%. The base materials, processed bare, and composite materials were examined for microstructure, and tested for tensile and hardness properties. The process accounted for grain refinement. In processed bare aluminium A1 (45.8%) exhibited nearly 2.6 times higher ductility compared to BM Across (17.6%). Among processed composites, D1 with higher content of copper resulted in maximum strength (78.52 MPa) and retained considerable ductility (21.75%). The uniform distribution of self-hard copper particles in the aluminium matrix and the direct strengthening mechanism aided in improved hardness of composite materials.

Effect of static annealing on superplastic behavior of a friction stir welded Ti-6Al-4V alloy joint and microstructural evolution during deformation

• A new combination process of FSW + static annealing + superplastic deformation was proposed for eliminate strain localization and the welded structure • Similar superplastic abilities were obtained by the BM and NZ with totally different structures • An optimized view on the classical Langdon theory was put forward in the field of superplasticity • The mechanisms of the spheroidization in the NZ and the equiaxed structure fragmentation in the BM were discussed • This study provides a new way to fabricate large-scale complex Ti alloy components Structural integration is one of the most critical developing directions in the modern aerospace field, in which large-scale complex components of Ti alloys are proposed to be fabricated via the method of welding + superplastic forming. However, the undesired strain localization appeared during superplastic deformation of the entire joint has largely hindered the development of this method. In our study, a combination process of friction stir welding (FSW) + static annealing + superplastic deformation was first time proposed to eliminate severe local deformation. To achieve this result, a fully fine lamellar structure was obtained in the nugget zone (NZ) via FSW, which was totally different from the mill-annealed structure in the base material (BM). After annealing at 900 °C for 180 min, the BM and NZ then exhibited the similar elongation of >500% and similar flow stress at 900 °C, 3 × 10 −3 s −1 , which was the precondition for achieving uniform superplastic deformation in the entire joint. Moreover, the different microstructures in the BM and NZ tended to become the similar equiaxed structure after deformation, which was the result of different microstructural evolution mechanisms in the NZ and BM. For the NZ, there was a static and dynamic spheroidization of the fully lamellar structure during the process, which could largely reduce the flow softening of the fully lamellar structure. For the BM, a new view of “Langdon-CRSS theory” (CRSS, critical resolved shear stress) was proposed to describe the fragmentation of the coarse equiaxed structure, which established the relationship between grain boundary sliding and intragranular deformation during deformation.

Microstructural evolution during superplastic deformation of Al-Mg-Li alloy: Dynamic recrystallization or grain-boundary sliding?

In this work, advanced capabilities of electron backscatter diffraction (EBSD) were applied to evaluate the role played dynamic recrystallization during superplastic deformation of a typical fine-grained material. It was found that the dynamic recrystallization occurred only locally and thus provided only minor contribution to microstructural evolution. Hence, the preservation of the nearly-equiaxed grain morphology, inherent to the superplasticity phenomenon, cannot be attributed to the dynamic recrystallization.

Theoretical Investigation of Forming Process of Aluminum Alloy Rail Vehicle Side Window

With the vigorous development of rail transit trains around the world and the emergence of global environmental pollution and energy shortages, the world has an urgent need for manufacturing technology for lightweight aluminum alloy rail transit train components. This paper mainly studied the superplastic forming law of 5083Al for rail transit. Through the high-temperature tensile test and blowing forming experiments, the superplastic properties of 5083Al were determined. Based on this, the die design, finite element simulation, and forming experiment of the rail vehicle side window were carried out. In order to study the superplastic deformation behavior of industrial 5083Al under complex stress conditions, the influence of the depth, area ratio, and friction coefficient of the pre-forming die on the part thickness distribution is simulated. The side window is made of a high-strength 5083Al sheet in the form of bending at both ends to ensure the strength of the connection between the overall side window and the side wall skeleton. The variation law of the side wall forming height of 5083Al box-shaped parts was studied. The efficient manufacture of parts that meet quality standards was made possible by the optimization of the pressure profile. The microstructure changes of the material after superplastic forming were studied by Energy Dispersive Spectrometer (EDS) and Electron Backscattered Diffraction (EBSD).

The influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr, 1420T, 1421, 1423

The article presents the results of research aimed at revealing the influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of several aluminum alloys. It was possible to form a homogeneous ultrafine-grained structure in samples of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr and 1423 due to dynamic recrystallization during their superplastic deformation. It is revealed that the initial microstructure of the 1420T alloy samples is bimodal. The average grain size is approximately 5 μm, in some areas of the working part of the samples there are large elongated grains, the average size of which is approximately equal to 25 μm. The initial structure of alloy 1421 samples is fine-grained, and the initial structure of alloy 1423 samples is multi-grained and coarse-grained. Metallographic studies showed that the grain structure of samples of alloys 1420T, 1421 and 1423 increases slightly during superplastic deformation at high homologous temperatures. Cavitation accumulates in the samples and structural changes occur, which are probably associated with local melting at grain boundaries and at interphase boundaries. It was established that the presence of zirconium and scandium additions in the composition of the samples ensures the formation of an ultrafine-grained structure in them and counteracts the grain growth during superplastic flow. Magnesium and lithium, which are included in the samples of the studied alloys 1420T, 1421 and 1423, form several intermetallic phases with aluminum. These phases are part of mixtures of crystals of peritectic origin, which are localized in the form of layers between some grains. The occurrence of peritectic reactions at high homologous temperatures can be one of the reasons for the partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation. Partial melting of samples of alloys 1420T, 1421 and 1423 can probably be carried out due to the presence of segregations of magnesium and lithium at the grain boundaries, which lower the melting temperature of the aluminum-based solid solution. Partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation, which is performed at high homologous temperatures, leads to the formation of cells of a metastable liquid-solid phase at the grain boundaries, the viscous flow of which leads to the formation of fibrous structures due to the development of grain boundary sliding.

Effect of Yb2O3 on superplastic behavior of laser welded joint of TC4 titanium alloy

The inhomogeneity of joints during superplastic deformation greatly limits the application of laser beam welding/superplastic forming (LBW/SPF). In order to adjust the deformation uniformity of the joint, Yb2O3 with different mass fractions was added to the laser welded joint of TC4 titanium alloy, and the effect of Yb2O3 on the superplastic deformation behavior of the laser welded joint of TC4 titanium alloy was studied. The results showed that the addition of Yb2O3 can effectively refine β grains. At Yb2O3 content of 6 wt%, the refinement effect of Yb2O3 on the weld grains is the most obvious. At this time, the peak flow stress of the longitudinal weld sample reaches a minimum value of 25.6 MPa, and the superplasticity of the joint is significantly improved. The elongation of the transverse welded sample reached 29% of that of the base metal and the joint deformation uniformity was significantly improved. The prior β grain of weld broke during superplastic deformation, and the acicular martensite structure in the weld was gradually transformed into a lamellar structure. After the addition of Yb2O3, the lamellar structure inside the weld becomes short and disordered, which promotes occurrence of superplastic deformation.

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.

Evaluation of drug-eluting nanoparticle coating on magnesium alloy for development of next generation bioabsorbable cardiovascular stents.

Since the introduction of bioabsorbable magnesium alloys into cardiovascular stent technology, many researches have been conducted to improve these metallic scaffolds. Various coatings and different coating techniques, super plastic deformation techniques and synthesizing different Mg-based alloy are examples of such efforts. In this study, a magnesium based alloy (WE43) was coated with dexamethasone loaded polymeric nanoparticles via electrospraying method. Drug release behavior, drug inhibitory effects, surface properties and cell responses to the surface were evaluated. Drug release profile was investigated and compared to drug-loaded nanoparticle on stainless steel as a control. The inhibitory effects of the drug-loaded nanoparticle coatings on smooth muscle cells was evaluated via MTT assay. Endothelial cells response to the surface was investigated by SEM. The results showed that contact angle and roughness of the surface were 131° and 600-800nm, respectively. Drug release studies showed a burst release less than 30% after 24h which followed by nearly zero order release kinetic. MTT assay showed that SMCs viability decreased to 60% and 25% after 24 and 72h, respectively. SEM images indicated proper adhesion and proliferation of endothelial cells on the surface. The findings suggest that nanoparticle-coated surfaces could effectively inhibit SMC proliferation meanwhile provide desirable surface features for adhesion and proliferation of endothelial cell on magnesium alloy based stents.

Superplastic deformation behavior of cold-rolled Inconel 718 alloy at high strain rates

Cold-rolled Inconel 718 with a reduction of 84% exhibited excellent superplasticity at 950 °C with a high strain rate, which improves forming efficiency and reduces device dependency. The elongation to failure of 325% was obtained at a strain rate of 1 × 10−2 s−1. The ductility enhancement is attributed to the rapid atomic diffusion caused by dense dislocations and the grain refinement through recrystallization induced by cold rolling in the early deformation stage. Dislocation creep dominates the subsequent stretching process, accompanied by continuous dynamic recrystallization resulting from the transition of the accumulated dislocations into high-angle boundaries. The δ phase particles, which gradually coarsen and homogenize during deformation, promote recrystallization and hinder the dislocation motion. The cavities introduced by NbC particles primarily determine the material fracture. The present results provide a promising approach for developing superplastic superalloys adapted to high strain rates.

The mechanisms of the high-strain-rate superplastic deformation of Al-Mg-based alloy

High-performance aluminum-based alloys exhibiting a high-strain-rate superplasticity improve the formability of lightweight constructions with complex shapes. The microstructural evolution and contributions of the deformation mechanisms to the total strain during high-strain-rate superplastic deformation of Al-Mg-based alloy with minor Sc and Zr additions were analyzed. Strain-induced changes in the grain/subgrain structure confirmed the dynamic recrystallization even at large strains. The evolution of the surface structure with focus ion beam milled grids confirmed that grain boundary sliding provided up to 40% of the total strain. The role of dislocation slip/creep increased and diffusional creep decreased with an increase in the strain rate.

로봇 크로스 금속 조인트 경량화를 위한 소재 분석을 통한 슈퍼 엔지니어링 플라스틱 연구

Cross-joint super engineering plastics are commonly referred to as high-heat-resistant engineering plastics with a continuous usable temperature of over 150°C, but their types can be variously constructed depending on the constituents. However, the light weight of the material has a disadvantage that the development period is long, but it has been able to drastically reduce the production cost through the omission of the post-processing process utilizing the advantages of innovative injection material purchase cost and injection processing, and the range of application with the light weight effect of technology is advantage. It is a super engineering plastic material with reinforced thermal shock property degradation problem of polyphenylene sulfide(PPS), which is excellent in light weight and shape processability, and can replace metal.In this study, we applied engineering plastic materials to realize 40% light weight and verified the results that meet both the performance and strength required by cross joints.

Superplastic Bonding of Electrodeposited Nanocrystalline Ni Alloys

Superplastic bonding was performed using electrodeposited Ni and electrodeposited Ni-B to apply to low-temperature diffusion bonding of carbon steel. Electrodeposited Ni and Ni-B were bonded at 450℃ in air and at a strain rate of 1 × 10−4 s−1. The shear test measured the bond strength, and the maximum bond strength of 69 MPa was obtained. Since the obtained bonding strength at 450℃ is comparable to that obtained by diffusion bonding of carbon steel at 0.5Tm, it is possible to decrease the bonding temperature to 0.4Tm by applying this boning process. The bonding strength depended on the amount of strain and increased as the strain increased in the range of strain 0.2 to 0.4. The voids at the interface shrink by superplastic deformation with grain boundary sliding, and the bonded area increases. In the superplastic bonding of electrodeposited Ni alloys, superplastic deformation effectively shrinks voids with a radius of 1-2 µm.

Low-Temperature Superplastic Deformation of Cold-Rolled Fe–5.6Mn–1.1Al–0.2C Steel

Low-Temperature Superplastic Deformation of Cold-Rolled Fe–5.6Mn–1.1Al–0.2C Steel

Influence of minor Zn additions on grain boundary anelasticity, grain boundary sliding, and superplasticity of Al-Mg-based alloys

Al-Mg alloys (AA5083-type) are widely used for superplastic forming. Limited grain boundary sliding as compared to other superplastic alloys limits the formability of Al-Mg based alloys. Grain boundary sliding intensity depends on the grain size, grain boundaries structure, and chemical composition of alloys. To improve superplastic properties of Al-Mg based alloys, we investigated the influence of a minor addition of Zn on the grain boundary relaxation effect and grain boundary sliding ability. The temperature dependence internal friction, superplastic deformation behavior, and microstructural changes during superplastic deformation for the AA5083 alloy and Zn modified alloy were compared. A minor Zn addition of 0.7 wt% does not influence the mean grain size but decreases the relaxation strength and the activation energy of grain boundary relaxation. The mechanisms of superplastic deformation and their contributions to the total strain were analyzed using FIB-milled grids evolution on the samples’ surface. Grain boundary sliding, grain rotations, and intragranular strain included both dislocation slip/creep and diffusional creep were involved in the deformation process. The contribution of grain boundary sliding increased from 10% to 25% for the Zn-free AA5083 alloy to 30–50% for the Zn-modified alloy. In result, a minor Zn addition proved to stimulate grain boundary sliding that decreases stress and increases strain rate sensitivity and elongation-to-failure of the studied alloy.

High strain rate superplasticity and secondary strain hardening of Al-Mg-Sc-Zr alloy produced by friction stir processing

There have been many studies on superplasticity of Al-Mg-Sc-Zr alloy with middle magnesium content in friction stir processing (FSP), while few studies on superplasticity of FSPed Al-Mg-Sc-Zr alloy with low-magnesium were researched. In this work, the microstructure of Al-3Mg-0.1Sc-0.1Zr alloy with the grain size of ~1.6 µm and high-angle grain boundaries dominated was obtained by FSP. The high-temperature tensile test was carried out, which showed that Al-3Mg-0.1Sc-0.1Zr alloy had good superplasticity in the range of 400 ℃ ~ 500 ℃ and 3 × 10−3 s−1 ~ 3 × 10−1 s−1, and the optimal elongation reached 1850% at 475 ℃ and 10−2 s−1, showing a high strain rate superplasticity. The FSPed alloy had a significant secondary strain hardening ability with increasing flow stress in the failure fracture stage at higher temperature or relatively low strain rate, showing “H” type (continuous hardening) and “C” type + secondary hardening type (initial hardening then softening + secondary hardening) curves, which was mainly attributed to the concurrent grain growth at higher strain during high-temperature tension. By studying the microstructure evolution and constitutive equation, it was found that the main mechanism of superplastic deformation was grain boundary sliding accommodated by grain boundary diffusion, the coordination mechanism was lattice diffusion. Al3(Sc, Zr) particles hindered the coarsening of grains obviously with good thermal stability, which were conducive to the realization of excellent superplastic properties.

High-performance flash joining of MgAl2O4 transparent ceramics

The MgAl2O4 transparent ceramic was firstly flash joined in 3 min at 1500 °C by applying direct current (DC) electric field. Three-point flexural strength of the joints reached approximately 256.0 MPa, which was even 114.7% of that of the parent material. Compared with parent transparent ceramics, transmittance loss of the MgAl2O4/MgAl2O4 joints in band of visual light and mid-infrared was only 1.5% and 4.5%, respectively. A possible mechanism of flash joining was proposed. The applied DC electric field induces numerous charged defects in the sample and superplastic deformation of the ceramic. The defects generated at the pores of the joining interface migrate directionally under the action of the DC electric field, which accelerates the diffusion rate of substances and enables the samples to be quickly jointed at a lower temperature.

Relation of phase fraction to superplastic behavior of multi-principal element alloy with a multi-phase structure

An Al0.3CoCrNi medium-entropy alloy was annealed in two conditions to differentiate the phase fraction of nano-scaled B2 and sigma precipitates in FCC microstructure, processed by high-pressure torsion, and subjected to a superplasticity test. The Al0.3CoCrNi with different microstructure exhibited distinct superplastic performance, with maximum elongation of 1900% and 1735% from tensile deformation at 1073 K at the strain rate at 5 × 10−3 s−1 and 10−2 s−1, respectively. The microstructural analysis revealed that the superplasticity is dominantly governed by the grain boundary sliding mechanism with the accommodation of intragranular dislocations. The Al0.3CoCrNi alloy, after superplastic deformation, consists of the mixture of FCC, B2, and sigma phases with different phase fractions. The comparison of this multi-phase structured alloy at two conditions and the sister alloy, Al0.5CoCrFeMnNi high-entropy alloy, suggests that increment of B2 and sigma phase fraction is beneficial to promote high-strain rate superplasticity by limiting the grain growth.

Experimental Analysis of Superplastic Deformation of Titanium Alloy Based on Sports Equipment

At present, titanium alloy is widely used in the field of materials. Because of its high specific strength and good corrosion resistance, it is also widely used in sports equipment. To overcome the shortcomings of traditional sports equipment, such as low yield and weak strength, the superplastic deformation effect of titanium alloy was tested and analyzed in this paper. The superplastic strength of titanium alloy was adjusted by adjusting the structure of the material. In this paper, by adjusting the proportion of Ti, Mo, alloy, CD, and Fe, the inductively coupled parameters of sports equipment were improved by vacuum consumable melting. The macro high temperature tensile test of sports equipment was carried out, and the temperature and strain rate under different states were recorded. Finally, the mechanism of superplastic deformation of titanium alloy for sports equipment is analyzed. The results show that the superplastic titanium alloy has higher elongation after fracture at high temperature and lower strain rate. The elongation ratio is more than 90% between 500 °C and 800 °C. At high temperature, the corrosion resistance of titanium alloy is high α, The number of phases decreases, and the alloy particles change from short rod to equiaxed. When the strain rate is reduced, the mechanical properties of titanium alloy are improved α, phase increases, the β the number of phases decreased. From its mechanism, the elongation of titanium alloy is caused by the dislocation movement caused by its structure. Therefore, titanium alloy in sports equipment can generally increase the short axis shape to improve the superplasticity of titanium alloy.

Superplastic deformation mechanisms of a fine-grained Al–Cu–Li alloy

The superplastic flow behavior and microstructural evolution of a fine-grained Al–Cu–Li alloy deformed at a temperature of 490 °C and an initial strain rate of 2 × 10−4 s−1 were studied by electron backscatter diffraction, scanning electron microscope and focused ion beam techniques. Based on the obtained data, the contributions of grain boundary sliding and intragranular dislocation slip to superplastic deformation of the Al–Cu–Li are carefully calculated. The results show that the whole superplastic deformation process can be divided into three stages. Strain from 0 to 0.1 can be identified as the strain hardening stage, in which dislocation movement is the main deformation mechanism and grain boundary sliding is the accommodation mechanism, multiplication of dislocation leads to strain hardening. Strain from 0.1 to 1.2 can be identified as the nearly steady flow stage, in which the grains are nearly equiaxed, the average grain size increases slowly and the proportion of high angle grain boundaries increases. Moreover, with the increase of the strain, the contribution of grain boundary sliding on deformation decreases gradually. The strain softening caused by dynamic recrystallization was observed at the end of this stage. The third stage is another strain hardening stage, in which rapidly dynamic grain growth and dislocation slip result in the strain hardening. The current research results emphasize that the diffusion creep is mainly responsible for the superplastic deformation, and the grain boundary sliding and intragranular dislocation slip play an accommodating role.