Superplastic Deformation Behavior Research Articles

Superplastic Deformation Behavior of 2 mm Ti60 Rolled Sheet in Air Environment

The superplastic deformation behavior of 2 mm Ti60 sheet is studied, and the constitutive equation of superplastic deformation is established. The results show that when the strain rate is 5.00 × 10−3 s−1 and the temperature is 950 °C, the maximum superplastic elongation reaches 400%. Through the analysis of the true strain–true stress curve, it is found that the average apparent activation energy (Q) is 490.783 kJ mol−1 and the average strain rate sensitivity (m) is 0.49. Dynamic spheroidization (DG) promotes the transformation of lath α phase to equiaxed α phase. Dynamic recrystallization (DRX) promotes the generation of high‐angle grain boundaries (θ > 15°). After deformation, the strength of R‐type textures changes significantly. From the grip to the tip, the strength of R‐type texture gradually weakens, which is mainly caused by the rotation of grains during deformation. The deformation mechanism of Ti60 sheet is dominated by grain boundary sliding, and is coordinated by grain growth, DG, DRX, dislocation motion, and grain rotation.

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.

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.

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.

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.

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 temperature on superplastic deformation behavior of 2198 Al–Cu–Li alloy

Al–Li alloy possesses remarkable advantages such as low density, high specific strength and specific elastic modulus, making it an exceptional aerospace structural material with considerable application potential. However, Al–Li alloy suffers from poor formability, which restricts its broader engineering applications. Alternatively, superplastic forming at high temperatures is widely applied for producing such components. Temperature is a key factor affecting the thermal deformation properties of Al–Li alloy. In this study, tensile tests of 2198 Al–Cu–Li alloy were conducted at different temperatures, and dedicated characterizations were performed to reveal the underlying mechanisms responsible for the hot deformation behavior. Results reveal that three distinct stages are observed in the superplastic deformation process of this alloy. Specifically, in the initial low-temperature range (400 °C–450 °C), incomplete dynamic recrystallization (DRX), accompanied by grain rotation and elongation plays a dominant role in the hot deformation mechanism. In the middle temperature stage (450 °C–500 °C), both DRX and grain boundary sliding (GBS) occur. At the high-temperature stage (500 °C–550 °C), diffusion creep emerges as the prominent mechanism. Moreover, optimum superplasticity is achieved at 500 °C, which results from a synergistic combination of several factors, including grain refinement by DRX, an increased fraction of high-angle grain boundaries (HAGBs), reduced dislocation density and weak texture.

Effects of an Electric Current on the Superplastic Deformation Behavior of 3Y-TZP in an Oxygen-Lean Atmosphere.

The aim of this paper is to investigate the mechanism of an electric current-assisted superplastic deformation on 3Y-TZP in an oxygen-lean atmosphere. The experiments were performed with different electric currents in the range of 0~5 A. The results show that the flow stress of 3Y-TZP during the deformation was significantly decreased by the combination of Joule heating and the applied current effect. The microstructures of the deformed specimens were all equiaxed grains without an obvious preferential grain growth. The stress exponent n = 2.05~2.61 suggested that the dominant deformation of 3Y-YZP with/without the electric current was grain boundary sliding at 1400 °C. The activation energy of the deformation which decreased from 465 kJ mol-1 to 315 kJ mol-1 by the electric current indicated that the lattice diffusion of Zr cation during the deformation was enhanced. And the deformation rate of 3Y-TZP with the electric current may be controlled by the grain boundary diffusion of Zr cation.

Microstructure evolution characteristics of near-α TA32 titanium alloy during superplastic tensile deformation

The characteristics of superplastic microstructure evolution and deformation behavior of rolled near-α TA32 titanium alloy were investigated at different deformation temperatures (920 °C, 940 °C, and 960 °C) and initial strain rates (1 × 10−3 s−1 and 3 × 10−3 s−1). Results show that TA32 alloy exhibited exceptional superplastic deformability with maximum elongation near 900%, and flow stress sensitivity to temperature as well as strain rate. Continuous dynamic recrystallization (CDRX) and dynamic recovery (DRV) mechanisms mainly controlled the flow softening process of TA32 alloy, which transformed low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs). The main dislocation slip mode in αp phase was prismatic <a> slip, while basal <a> slip and pyramidal <c+a> slip gradually operated as the strain increased. The tensile deformation of rolled TA32 sheet was most ductile in the range of 40–55° from rolling direction (RD) to transverse direction (TD). Deformation and high temperatures caused the initial textures {112‾2}<11‾00> and {0001}<11‾00> to transform into multiple texture components with weak strength, such as (0001)[21‾1‾0], (011‾2)[45‾13], and (112‾4)[1‾3‾43]. The rotation of lattice/grain provided freedom for microstructure deformation. The superplastic deformation of TA32 alloy was controlled by a combination of deformation mechanisms. The main superplastic deformation mechanism was the relative sliding of grains along HAGBs, coordinated by dislocation motion, grain rotation, and dynamic recrystallization (DRX).

Effect of strain rate on the microstructure evolution and superplastic deformation behavior of cold-rolled medium Mn lightweight steel

This work investigates the high-temperature tensile behavior of a Medium Mn lightweight steel (MMLS) with a chemical composition of Fe-0.3C-7.0Mn-3.5Al. The MMLS was prepared by hot-rolling followed by cold-rolling to produce a complete martensite microstructure with a high density of dislocations. The tensile tests were conducted at 800 °C within the strain rate range of 5 × 10−4 s−1-2.5 × 10−2 s−1 to explore the effect of microstructural evolution and deformation mechanism by strain rates during the tensile deformation. The results showed that the deformation behavior and mechanism of the MMLS depend not only on the initial grain size and morphology but also on the microstructure evolution during deformation. The MMLS exhibits high strain rate superplasticity (HSRS) behavior, and the deformation mechanisms are dependent on the strain rate. At lower strain rate (5 × 10−4 s−1), dislocation slip/creep is more pronounced in the γ-phase, and grain boundary sliding (GBS) is inhibited during the early deformation period, contributing to the significant texture enhancement. At moderate rate (5 × 10−3 s−1), GBS dominates deformation, while at high strain rate (2.5 × 10−2 s−1), dislocation activity and dynamic recrystallization (DRX) play a significant role. The HSRS behavior of MMLS is related to the dynamic reverse phase transition from cold-rolled ferrite to austenitic/ferrite fine-grained dual-phase structure. This work provides a theoretical basis for the development of superplastic MMLS with improved HSRS behavior and controlled the microstructure/mechanical property of component parts.

Superplastic deformation behavior of a β-rich α+β titanium alloy

Superplastic tensile test was performed on a β-rich α+β titanium alloy (SP700 alloy) sheet in the temperature range of 740–800 °C and strain rate range of 1 × 10−4-1 × 10−2 s−1. The effects of the deformation parameters on the flow curves, strain rate sensitivity (m-value), thermal activation energy (Q-value) and microstructural characteristics were investigated to elucidate the deformation mechanism. The results showed that the examined SP700 alloy exhibited excellent superplasticity with fracture elongation up to approximately 1800% deformed at 760 °C and 1 × 10−3 s−1, with the maximum m-value of 0.55. The shapes of the flow curves were dependent on the strain rate and showed a type of curves without an obvious steady-state flow at relatively high strain rates. For this β-rich α+β titanium alloy, when deformed at 740–780 °C and medium strain rates (approximately 5 × 10−3-5 × 10−4 s−1), the controlling deformation mechanism was the grain boundary sliding accommodated by dislocation slip. When deformed at 800 °C and a strain rate of 1 × 10−4 s−1, m-value decreased to 0.1 and the main deformation mechanism was dislocation slip with a high β volume fraction over 50% and average grain size over 5 μm. Meanwhile, the dominant texture changed from <0001> to <101¯0> or <21¯1¯0> because of the grain rotation caused by the grain boundary sliding.

The effect of Ti-Mo additions on microstructural evolution and superplastic deformation behavior of cold–rolled medium Mn steels

This study investigated the effect of Ti-Mo alloying on the microstructural evolution and superplastic deformation behavior of Fe–5.6Mn–1.1Al–0.2C steels. The steels were subjected to cold–rolling and intercritical deformation at a strain rate of 10−2 s−1 and temperatures between 655 and 775 °C. The results showed that Ti-Mo added steel exhibits a significant improvement in the strength due to the high density of nano–sized (Ti, Mo)C particles and optimized superplastic elongation of approximately 1000% at 745 °C. The superplastic flow behavior showed a strong temperature dependence under three typical temperature regions. This can be mainly attributed to the decreased interaction between precipitation and DRX with increasing deformation temperature. The grain boundary sliding (GBS) accommodation process varied with the deformation temperature due to the difference in precipitation nature of the (Ti, Mo)C particles.

Effect of Mo content on the microstructure, superplastic behavior, and mechanical properties of Ni and Fe-modified titanium alloys

Novel titanium-based alloys are required to increase the efficiency of superplastic forming technology and decrease energy consumption. For this purpose, the superplastic deformation behavior, strain-induced microstructure evolution in a temperature range of 625–775 °C, and post-deformation mechanical properties of Ti–4Al–1V–1Fe–1Ni-0.1B-xMo alloys (x = 1, 2.5, or 5 wt%) were investigated. The studied alloys demonstrated a stable flow with a high strain rate sensitivity coefficient m of 0.50–0.65 and an elongation-to-failure δ of 700–1000% at temperatures of 700–775 °C. Molybdenum insignificantly influenced superplastic deformation behavior at high temperatures due to a high fraction of the β phase of 22–62%. The Mo effect was significant at a low deformation temperature of 625 °C. At this temperature, an increase in Mo content from 1 to 5% provided the β-phase fraction above the critical value of ∼20% and increased the m-value from 0.4 to 0.5 and δ from ∼200 to ∼700%. Increasing Mo from 1 to 5% enhanced the post-deformation yield strength at room temperature by 180 MPa, the ultimate tensile strength by 170 MPa, and the ductility by 2.5%. Consequently, alloying Ti–4Al–1V–1Fe–1Ni-0.1B with 5% Mo provided an excellent combination of superplasticity at a low temperature of 625 °C and post-forming tensile mechanical properties.

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.

Microstructure Evolution, Constitutive Modelling, and Superplastic Forming of Experimental 6XXX-Type Alloys Processed with Different Thermomechanical Treatments.

This study focused on the microstructural analysis, superplasticity, modeling of superplastic deformation behavior, and superplastic forming tests of the Al-Mg-Si-Cu-based alloy modified with Fe, Ni, Sc, and Zr. The effect of the thermomechanical treatment with various proportions of hot/cold rolling degrees on the secondary particle distribution and deformation behavior was studied. The increase in hot rolling degree increased the homogeneity of the particle distribution in the aluminum-based solid solution that improved superplastic properties, providing an elongation of ~470-500% at increased strain rates of (0.5-1) × 10-2 s-1. A constitutive model based on Arrhenius and Beckofen equations was used to describe and predict the superplastic flow behavior of the alloy studied. Model complex-shaped parts were processed by superplastic forming at two strain rates. The proposed strain rate of 1 × 10-2 s-1 provided a low thickness variation and a high quality of the experimental parts. The residual cavitation after superplastic forming was also large at the low strain rate of 2 × 10-3 s-1 and significantly smaller at 1 × 10-2 s-1. Coarse Al9FeNi particles did not stimulate the cavitation process and were effective to provide the superplasticity of alloys studied at high strain rates, whereas cavities were predominately observed near coarse Mg2Si particles, which act as nucleation places for cavities during superplastic deformation and forming.

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).

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.

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.

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.

Superior superplasticity and multiple accommodation mechanisms in TiB reinforced near-α titanium matrix composites

Superplastic forming is a promising technique for producing complex-shaped components of hard-to-deform titanium matrix composites (TMCs). Superplastic tensile tests were performed on hot-rolled TiB/near-α Ti matrix composites with different reductions to investigate the effects of matrix microstructural characteristics and whisker orientation on superplastic deformation behavior. The results showed that the composite with initial BT-type texture and finer matrix grains at a rolling reduction of 80% exhibited lower flow stress and larger elongation than the composite with initial T-type texture at a rolling reduction of 40%, and superior elongation of 682% was achieved in the former. Significant randomization of crystal orientation and dynamic grain growth phenomenon occurred in the matrix alloys during deformation. The originally misaligned TiB whiskers gradually rotated to the tensile direction and simultaneously rotated circularly around the [010] axis during superplastic tensile deformation, which would accommodate the matrix deformation and share more load transferred from the matrix. Another important accommodation mechanism of TiB whiskers was to accelerate the dynamic recrystallization of the surrounding matrix by particle-stimulated nucleation. TEM and EBSD observations together with GND-distribution analysis confirmed that the primary superplastic deformation mechanism of TiB/Ti composites is grain/phase boundary sliding accommodated by dislocation slip and dynamic recrystallization.