Superplastic Forming Research Articles

Investigating the effect of hot preforming combined with superplastic forming on thickness distribution and forming time of Ti-6Al-4V alloy using finite element analysis

The present work focuses on the development of a new superplastic forming (SPF) that utilizes hot preforming to improve thickness distribution and decrease forming time. For this purpose, finite element analysis (FEA) was employed as an efficient tool to indicate feasibility of the new method by designing the appropriate die geometry. The experimental tests were performed to find the tensile properties of Ti-6Al-4V alloy at different temperatures and angles. Detailed FEA technique was employed to model the SPF process by a constitutive model that considers both microstructural features and geometrical instabilities. The variations of the forming time and distribution of thickness due to the variation of the forming parameters such as strain rate and friction coefficient were studied to compare the results with the results of hot preforming combined with SPF process. The obtained results from FEA showed that this new method can provide a good thickness distribution, so that the thickness variation reduced from 44% to about 21% and the forming time considerably reduced from 1100 to 610 s.

Superplastic behavior of a metastable β-type Ti alloy governed by grain size: Microstructure evolution and underlying deformation mechanism

The superplastic forming (SPF) technology has gained widespread adoption in the manufacturing of intricately shaped components made from Ti alloys with high dimensional accuracy due to its near net forming capabilities. It is crucial to systematically investigate the superplastic behavior in metastable β-type Ti alloys. However, the microstructure evolution and underlying superplastic deformation mechanism governed by grain size in these alloys remain unclear. In this study, three types of fine-grained (<10 μm) Ti-15V-3Cr-3Sn-3Al (Ti-15-3) alloys were obtained using friction stir processing (FSP), and tensile tests were conducted at temperature of 650 °C with strain rates ranging from 1 × 10−4 s−1 to 3 × 10−3 s−1. The deformation behavior of the coarse-grained (>3 μm) Ti-15-3 alloy can be described as quasi-superplastic rather than strictly superplastic. In this microstructure, plasticity is synergistically contributed by grain boundary sliding (GBS), continuous dynamic recrystallization (CDRX), and dynamic phase transformation (DPT). For the fine-grained (<3 μm) Ti-15-3 alloy, deformation enters into the superplastic region with GBS becoming the predominant deformation mechanism accompanied by DPT. Additionally, strain/stress promotes α phase precipitation from the β matrix, which inhibits grain growth and serves as a supplementary stress accommodation mechanism facilitating continuous operation of GBS and ultimately achieving exceptional superplasticity.

EVALUATION OF SUPERPLASTIC PROPERTIES OF AA7075 ALUMINUM ALLOY SHEET FABRICATED BY THERMOMECHANICAL PROCESSING

The superplastic forming (SPF) process is the large plastic deformation ability of metals and alloys. However, SPF ability can only be achieved under certain conditions including ultrafine grain (UFG) microstructure, high temperature, and very small strain rate. In this work, the high-strength aluminum alloy AA7075 was selected for the experimental process due to its outstanding industrial application. First, thermomechanical processing (TMP) is performed to create a fine stable grain size for the studied alloy. The UFG microstructure was obtained after TMP with an average grain size of about 10 μm. Subsequently, the tensile test method and the bulging free-forming (BFF) method were used to evaluate the superplastic properties of the AA7075 aluminum alloy sheet fabricated by TMP. These two methods are performed at temperatures of 500ºC and 530ºC with strain rates from 10-4 (s-1) to 10-3 (s-1). The relative elongation and the strain rate sensitivity are the evaluation criteria. At the temperature of 530ºC and strain rate of 10-3 (s-1), the maximum relative elongation and flow stress were achieved at 280% and 7.6 MPa, respectively. The value of the coefficient m ranges from 0.3 to 0.6. The obtained results confirm the SPF properties of the aluminum alloy sheet AA7075.

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.

In vivo validation of highly customized cranial Ti-6AL-4V ELI prostheses fabricated through incremental forming and superplastic forming: an ovine model study

Cranial reconstructions are essential for restoring both function and aesthetics in patients with craniofacial deformities or traumatic injuries. Titanium prostheses have gained popularity due to their biocompatibility, strength, and corrosion resistance. The use of Superplastic Forming (SPF) and Single Point Incremental Forming (SPIF) techniques to create titanium prostheses, specifically designed for cranial reconstructions was investigated in an ovine model through microtomographic and histomorphometric analyses. The results obtained from the explanted specimens revealed significant variations in bone volume, trabecular thickness, spacing, and number across different regions of interest (VOIs or ROIs). Those regions next to the center of the cranial defect exhibited the most immature bone, characterized by higher porosity, decreased trabecular thickness, and wider trabecular spacing. Dynamic histomorphometry demonstrated differences in the mineralizing surface to bone surface ratio (MS/BS) and mineral apposition rate (MAR) depending on the timing of fluorochrome administration. A layer of connective tissue separated the prosthesis and the bone tissue. Overall, the study provided validation for the use of cranial prostheses made using SPF and SPIF techniques, offering insights into the processes of bone formation and remodeling in the implanted ovine model.

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.

Functionalized magnesium alloys obtained by superplastic forming process retain osteoinductive and antibacterial properties: An in-vitro study

ObjectivesThis study aimed to investigate the biocompatibility, osteogenic and antibacterial activity of biomedical devices based on Magnesium (Mg) Alloys manufactured by Superplastic Forming process (SPF) and subjected to Hydrothermal (HT) and Sol-Gel Treatment (Sol-Gel). MethodsMg-SPF devices subjected to Hydrothermal (Mg-SPF+HT) and Sol-Gel Treatment (Mg-SPF+Sol-Gel) were investigated. The biocompatibility of Mg-SPF+Sol-Gel and Mg-SPF+HT devices was observed by indirect and direct cytotoxicity assays, whereas the colonization of sample surfaces was assessed by confocal microscopy. qRT-PCR analysis and microbial growth curve analyses were employed to evaluate the osteogenic and antibacterial activity of both SPF-Mg treated devices, respectively. ResultsMg-SPF+HT and Mg-SPF+Sol-Gel showed a high degree of biocompatibility. Analysis of mRNA expression of osteogenic genes in cells cultured on Mg-treated devices revealed a significant upregulation of the expression levels of BMP2 and Runx-2. Furthermore, the bacterial growth in strains developed in contact with both the Mg-SPF+HT and Mg-SPF+Sol-Gel devices was lower than that observed in the control. SignificanceHydrothermal and Sol-Gel Treatments of Mg alloys obtained through the SPF process demonstrated bioactive, osteogenic and antibacterial activity, offering a promising alternative to conventional Mg-based devices. The obtained Mg-based materials may have the potential to enhance the tunability of temporary devices in maxillary reconstruction, eliminating the need for second surgeries, and ensuring a good bone reconstruction and a reduced implant failure rate due to bacterial infections.

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.

Research of Superplastic Forming, Mechanical Properties, and Thermal Insulation Performance of Titanium Alloy 3D Lattice Structure

A physically constitutive model based on microstructure evolution was constructed to describe the coupling relationship between various macro and micro variations of TA32 titanium alloy in superplastic deformation. Then, a finite element analysis model was established to simulate and analyse the superplastic forming process of titanium alloy based on the physically constitutive model. The deformation characteristics, mechanical properties and thermal insulation performance of the three dimensional lattice structure were analysed and tested. The results show that the three-dimensional lattice structure of titanium alloy has good formability, excellent mechanical properties, and good thermal insulation performance, indicating that it is a promising load-bearing functional integrated structure.

Microstructural evolution during superplastic deformation of commercial Al5083 alloy

The aluminum alloy SPF process has found extensive application in the aviation and rail transportation industries. The commercial Al5083 alloy presents the advantages of low density, high specific strength, a simplified manufacturing technique, and low cost, thus making it an appealing option for producing components with minor strain and complex configurations. This study focused on examining the mechanical properties of the commercially available Al5083 alloy. Different temperatures (450 °C, 480 °C, 510 °C) and strain rates (0.01 s−1, 0.005 s−1, 0.001 s−1, 0.0005 s−1) were employed to investigate the behavior of the material. Furthermore, a constitutive equation was developed to describe the alloy's response under superplastic conditions. The utilization of EBSD allowed for the investigation of the evolution of grain and dislocation density, while XRD was employed to determine the development of macroscopic texture strength and texture type. The dominant mechanism of superplastic deformation in the commercial Al5083 alloy was identified as dynamic recrystallization and intra-crystalline slip, which distinguishes it from conventional fine-grained aluminum alloys. SEM was used to establish the exponential relationship between void volume fraction and true strain. The results provide valuable insights into the evolution of the macro-mechanical properties and microstructure of commercial Al5083 alloy during superplastic forming.

Superplastic Forming of Zr-Based Bulk Metallic Glasses

In this paper, the partially crystallized Zr70Cu13.5Ni8.5Al8 bulk metallic glasses (BMGs) were prepared, and their superplastic deformation ability in the supercooled liquid region was studied via compression over a wide range of strain rates from 5 × 10−4 s−1 to 1 × 10−2 s−1. It has been found that the superplastic deformation behavior of the BMGs is strongly dependent on the strain rate and temperature. The flow behavior of the BMGs transformed from Newtonian fluid to non-Newtonian fluid with the increase in the strain rate and the decrease in temperature. Based on the high-temperature compression results, a thermalplastic forming map was constructed, and the optimal superplastic forming parameters were obtained. Then, gears were successfully extruded using part of the optimal thermal processing parameters. Further studies showed that high-temperature extrusion induced the crystallization of the BMGs, which increased the microhardness of the gears.

Effect of misorientation evolution on the fracture mechanism

This communication identifies the fracture mechanism for Ti-6Al-4V alloy during superplastic forming, which is established based on the grain size evolutions. Particularly, the dominant fracture mechanism is identified by misorientation evolutions. In total, the grain-growth-dependent fracture mechanism is proposed, potentially useful for forming limit determination.

Finite Element Formulation and Computation of Superplastic Metal Forming Processes with Optimized Rate of Deformation Control

Superplastic forming (SPF) is a material forming technique that uses superplastic exceptional elongations and deformation characteristics to form superplastic materials into certain shapes. The combination of superplastic forming with diffusion bonding (SPF/DB) gives rise to an almost unlimited extension of superplastic forming since more integral lightweight cellular structural components can be manufactured. This paper discusses numerical modelling of the mechanism of superplasticity in metallic materials. The SPF computational method based on the finite element technique augmented with the controlling rate of deformations is developed to examine a range of design or operating conditions leading to more economical forming processes. The non-Newtonian ‘viscous flow’ material is used to model the constitutive of superplastic material during the forming period. The contact mechanics between the sheet material and the mold surface and the intersheet material contact mechanics are imposed using the penalty control method, in which the sticking contact boundary conditions are employed. The space discretization is carried out using the membrane element under plane strain and axisymmetric flow stress conditions, while the implicit time integration technique is utilized to follow the shape changes of the formed sheet material. The validation of the SPF finite element formulation was performed by comparing it with the available analytical solution of Hydraulic Free Bulging of Thin strips. The SPF of a hemispherical dome made of 7475 aluminum sheet alloy was performed to demonstrate the forming process as well as to validate the results obtained between the SPF finite element numerical simulation and the experimental results. The SPF/DB of the multicell component section is considered in the final part.

A constitutive model based on internal variable method and its application to the superplastic forming of four-layer structure

A constitutive model based on internal variable method and its application to the superplastic forming of four-layer structure

Manufacture of Multilayer Cellular Structures Using Superplastic Forming and Diffusion Bonding for Aerospace Applications

Manufacture of Multilayer Cellular Structures Using Superplastic Forming and Diffusion Bonding for Aerospace Applications

Finite element simulations and experimental investigations on formability of magnesium alloys in superplastic forming

The paper presents the formability aspects of magnesium alloy (AZ31B) sheets into regular and intricate shapes during Super Plastic Forming (SPF). Finite Element (FE) simulations are performed at specific strain rates within the superplastic temperature range. The formability of 1 mm sheet into conical, cylindrical, box and groove shaped dies are simulated. The simulated Pressure-Time (P-T) curve is given as pressure control algorithm to form the shapes experimentally. Thickness strains of the experimentally formed components validated with simulation results are found to be in close agreement with each other. It is demonstrated by the analysis that regular shapes posses uniform thickness distribution throughout the profile. The components with complex intricate shapes recorded unevenness in thinning behavior. The unevenness in thinning is influenced by the Grain Boundary Sliding (GBS) and diffusion kinetics. GBS is well controlled by optimum P-T algorithm to produce sharp intricate shapes with uniform thickness.

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.

Technological properties of sheet titanium alloys VT6

This paper presents a comprehensive study of the microstructure, mechanical and technological properties (formability and weldability in solid state) of sheet blanks made of titanium alloy VT6, developed specifically for superplastic forming and diffusion bonding (SPF / DB) in PJSC VSMPO-AVISMA Corporation using various technologies. The conducted studies have made it possible to establish that sheets of titanium alloy VT6 with different microstructure in the temperature range of 850 – 920°C exhibit good superplastic properties. Studies of the technological properties of experimental sheets show their good weldability and high formability under superplasticity conditions. The relative length of the pores in the zone of the solid-phase joints is from 5.3 to 1.8 %, the equivalent deformation during SPF is from 1500 to 2700 %. The technological properties of the VT6 alloy in different states are very similar. The results obtained allow us to recommend this experimental sheet alloy for the manufacture of hollow structures by the SPF / DB process under superplasticity.

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.