Superplastic Tensile Deformation Research Articles

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).

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.

Superplastic deformation mechanical behavior and constitutive modelling of a near-α titanium alloy TNW700 sheet

TNW700 is a newly developed near-α high temperature titanium alloy and has great application potential in the aerospace industry owing to excellent creep strength and short-term service temperature up to 700 °C. The superplastic tensile deformation behavior and constitutive model of TNW700 alloy in the temperature range of 900–975 °C and strain rate range of 0.0005–0.01s−1 were investigated. Results indicated that TNW700 alloy exhibits significant work hardening behavior, which may be related to dynamic growth of β grains, dislocation evolution, and silicide precipitates. In addition, work hardening coefficient (n) as well as the critical strain between flow hardening and softening increases with decreasing strain rate, and first increases and then decreases with increasing deformation temperature. TNW700 alloy exhibits excellent superplasticity at 900 °C–950 °C corresponding to strain rate sensitivity exponent (m) greater than 0.3, and expresses poor superplasticity at 975 °C with lower m value. The m value decreases monotonously with strain owing to decrease of grain boundary sliding contribution caused by dynamic grain growth of β grains. The deformation activation energy increases with decreasing strain rate due to the change of deformation mechanism. A phenomenological constitutive model considering strain hardening, strain rate hardening and temperature softening was proposed and material constants were calibrated by true stress-strain data. The constitutive model was implemented into Abaqus code by UHARD subroutine to simulate the superplastic forming of cone parts, and thickness distribution and bulging heights under different forming time were used to verify the validity of constitutive model.

Superplastic Tensile Deformation Behavior and Microstructural Evolution of Al–Zn–Mg–Cu Alloy

The microstructural evolution of the Al–Zn–Mg–Cu alloy during the superplastic deformation process has been studied by high temperature tensile experiment. The superplastic deformation behaviors are investigated under different temperatures of 470 °C, 485 °C, 500 °C, 515 °C and 530 °C, and different strain rates of 3 × 10−4 s−1, 1 × 10−3 s−1, 3 × 10−2 s−1 and 1 × 10−2 s−1. The microstructure observation shows that uniform and equiaxed grains can be obtained by dynamic recrystallization in the initial stage of superplastic deformation. Once the recrystallization process has been finished, the variations of the fraction of high angle boundary, the grain aspect ratio and the Schmid factor are negligible during the superplastic deformation, which shows that the grain boundary sliding and grain rotation are the main deformation mechanisms. The maximum texture intensity decreases compared with the initial microstructure, indicating that grain boundary sliding and grain rotation can weaken the texture, however, the texture intensity increases in the final stage of superplastic deformation, which may be resulted from the stress concentration.

Superplastic behavior of a powder metallurgy superalloy during isothermal compression

In this work, the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated. Based on the strain rate sensitivity m determined by flow data, superplastic region is estimated at relatively low temperature and strain rate domains, specifically around 1000 °C/10−3 s−1. Thereafter, the cylinder specimens are isothermally compressed at 1000 °C/10−3 s−1 and 1025 °C/10−3 s−1 with different strains, to exam the superplasticity and related mechanisms. The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization (DRX), and the grain boundary sliding (GBS) contributes to the total strain during superplastic compression as well. In addition, the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected, which is different from superplastic tensile deformation.

Superplastic tensile characteristics of in situ TiBw/Ti6Al4V composites with novel network microstructure

In situ TiB whiskers reinforced Ti6Al4V (TiBw/Ti64) composites were fabricated by tailoring a novel network microstructure—which improved the strengthening and toughening effects of titanium matrix composites (TMCs). Superplastic tensile deformation of the composites was carried out at 900–1000°C and 0.0005–0.01s−1. The results showed that the tensile elongation of the novel composites is over 100%, even up to 214% at 940°C. The strain rate sensitivity (m) and the activation energy (Q) of the novel composites are 0.25 and 338kJ/mol, respectively. These phenomena indicate that the novel composites possess an improved deformability. The superplasticity of the TiBw/Ti64 composites can be attributed to the novel network microstructure, which can induce superior deformability by inhibiting local deformation, decreasing crack propagation rate and refining grain size.

Microstructure of TC21 Titanium Alloy after Superplastic Deformation and Heat Treatment

The isothermal constant strain rate tensile tests of the TC21 titanium alloy were conducted by SSAN-CMT4104 electronic tensile testing machine at different temperature. After superplastic deformation, the alloy was treated with double annealing heat treatment, and microstructure of the alloy was analyzed. The results show that dynamically recrystallization occurs during the superplastic tensile deformation. The primary α-grains aggregated and merged to form new crystal grains with irregular grain boundaries. The amount and morphology of primary α phase change gradually with the increasing of temperature. The alloy has duplex microstructure composed of primary α phase and different forms of β-transformed structure after superplastic deformation and double annealing. At deformation temperature of 930°C, the basket weave structure with equiaxed α phase appears.

Low-temperature superplasticity of Al 2O 3(p)/Ni–Co nanocomposites

Nanocomposites of Al 2O 3/Ni–Co prepared using Al 2O 3 of various particle sizes were fabricated by pulse current electrodeposition. Their superplastic tensile deformation was investigated at strain rates of 8.33 × 10 −4 s −1 and 1.67 × 10 −3 s −1 and temperatures of 723–823 K. The Al 2O 3 particle sizes and the deformation temperature had significant influence on the elongation of the deposited materials. The optimal superplastic condition and the maximum elongation were determined. A low temperature superplasticity with elongation of 632% was achieved at a strain rate of 1.67 × 10 −3 s −1 and 823 K. Scanning electron microscopy and transmission electron microscopy were used to examine the microstructures of the deposited and deformed samples. The grains grew to a micrometer dimensions and were elongated along the tensile direction after superplastic deformation. Superplasticity in electrodeposited nanocomposites is related to the presence of S at grain boundaries and to deformation twinning.

Texture evolution with superplastic deformation of a AlCu4Mg/Si 3N 4/20p composite

The deformation mechanisms which operate during superplastic tensile deformation at 783 K in a AlCu4Mg/Si 3N 4/20p composite have been investigated by means of the crystallographic texture evolution with strain. Three stages of texture evolution have been observed: in stage I, little texture variation occurs up to a true strain of 0.4. In stage II, a progressive decrease of texture intensity up to a true strain of 0.8 is noted. This suggests that a mechanism of grain boundary sliding, GBS, typical of superplastic deformation of monolithic fine grained polycrystalline materials, prevails in this stage. At higher deformations, in stage III, the intensity of the main texture components tends to increase, indicating that the dominant deformation mechanism becomes crystallographic slip, CS.

The Research on Superplasticity of Two New Ti Alloys

The superplastic tensile deformation behavior and structural evolution of two kinds of α+β titanium alloys were investigated in this paper, one is a new high strength high toughness Ti alloy with damage tolerance called TC21, and the other is a new superplastic Ti alloy so called Ti-SP2500. The results indicated that TC21 alloy has good superplasticity at the temperature from 720 to 960 and with the strain rate of 5.510-5s-1∼1.110-2s-1. On the optimal superplastic condition, the maximum elongation is over 1300%. During the superplastic tensile deformation, the dynamic recrystallization occurs in deformation zone of the specimens and the superplasticity is improved. Ti-SP2500 alloy has good superplasticity at the temperature from 720°C to 800°C and with the strain rate of 6.67 10-4s-1∼1.1110-2s-1. The maximum elongation for Ti-SP2500 alloy will exceed 2200% at 780°C with the strain rate of 5.5610-3s-1. Its superplastic deformation mechanism is controlled by grain boundary sliding, and the grain deformation and dislocation creep has the coordinating action.

Superplasticity of Nanostructured Nickel Alloy and Composite Fabricated by Electrodeposition

In the present paper, a nanostructured nickel alloy and a Ni/Si 3 N 4 (w) composite were fabricated by pulse current electrodeposition, and their superplastic tensile deformation behaviors were investigated at strain rates ranging from 1×10 -3 s -1 to 2×10 -2 s -1 and temperatures ranging from 673K to 823K. Optimal superplastic condition and the maximum elongation were determined. Scanning electron microscopy and transmission electron microscopy were employed to examine the microstructures of the as-deposited and deformed samples. The superplastic behavior of the alloy and composite were compared and discussed in terms of their grain growth behavior and accommodation mechanisms.

Mechanical analysis of temperature impact on stability during superplastic tensile deformation

Based on state equation that stress is the function of strain, strain-rate and temperature, the paper establishes the differential constitutive equation used for analyzing load-stability and the variational constitutive equation used for analyzing geometry-stability during superplastic tensile deformation, which contain strain hardening index, strain-rate sensitivity index, temperature sensitivity index introducted for the first time and tempera-ture undulation index introducted for the first time in the paper. And then, based on the universal condition of plastic elementary theory, the paper analyzes load-stability and geometry-stability under continuously rising temperature and under the non-uniform tem-perature along the axes of specimen respectively. The results prove the impact of con-tinuously rising speed and non-uniform value of temperature on deformation stability is that the faster temperature rises and the more non-uniform temperature is, the smaller the corresponding uniform strain of load-stability and geometry-stability are; strain hardening index is the necessary condition of stability during superplastic tensile deformation, and geometry-instability will not happen when load-instability occurs, but happen when uniform deformation has lasted after load-instability; in the superplastic temperature field, constant temperature is not necessary condition of superplasticitiy, but during the deformation, the slower temperature rises and the more uniform temperature is, the more stable deforma-tion is.

Processing routes leading to superplastic behaviour of magnesium alloy ZK60

There has recently been discussion on processing of magnesium alloys by equal channel angular extrusion (ECAE) to achieve a high elongation-to-failure under superplastic tensile deformation. A two-step processing route was suggested to improve superplastic capabilities of such alloys. In this work, superplastic behaviour of ZK60 processed by ECAE alone was compared with that for the material that was rolled prior to the ECAE processing. It was shown that deformation preceding the ECAE step does not bring any benefit with regard to superplastic behaviour in the low temperature range around 200 °C. An important finding is that ECAE processing by itself leads to a record elongation of 1400 and 2040% at the strain rates of 3 × 10 −3 and 3 × 10 −4 s −1, respectively.

Superplasticity and Deformation Mechanism of LD10 Aluminium Alloy

The commercial hot-rolled bars of LD10 alloy (grain size 25~75µm) are pretreated via proper recrystallization annealing (temperature 380°C, 420°C and 460°C) and solution annealing (temperature 500°C). The average elongation is increased from 158% to 270%, 223%, 219% and 233% respectively and the maximum elongation is 321% (500°C, 3.3×10-4s-1). The test results show that the alloy can present certain superplasticity owing to structural effect of dynamic recrystallization refining during superplastic deformation of coarse-grained LD10 alloy. Large and deep cavities form in grain boundaries and result in intergranular fracture after larger superplastic tensile deformation. And a large amount of metal filaments appear on grain surfaces. The formation of filaments is attributed to viscous flow of solid-liquid mixture in grain boundaries caused by grain-boundary sliding. The appearance of solid-liquid mixture makes grain-boundary sliding easier.

Quantitative determination of homogeneous strain value in superplastic tension

After load instability, a passage of homogeneous strain e can be still continued in superplastic tensile deformation. But untill now, no one has given the precise value of e corresponding to actual materials, neither in experimental measurements nor in theoretical calculations. Using the elaborate experimental measuring methods of m value and its function expressions, the note first gives the method to determine homogeneous e, and the homogeneous e value of typical superplastic alloy Zn-5% Al under 18°C and 340°C respectively.

406 ジルコニア-アルミナ複合セラミックスの超塑性引張変形による機械的性質の変化 : 破壊靭性に及ぼす粒界キャビティーの影響(オーガナイズドセッション : 超塑性と材料および造形法)

Relationship between some mechanical properties and cavitation behavior has been investigated on zirconia-alumina composites (3Y-20A) after the superplastic tensile deformation. Hardness and bending strength of the material have degraded gradually, as quantity of the cavity in the material inside has increased, and fracture toughness has changed complicatedly. The fracture toughness, especially, has been improved most with about 1% cavity volume fraction specimen. The fracture toughness must be affected in not only the quantity of cavity but also size of it.

Superplastic Tensile Behavior of Silicon Nitride

Microstructural development, stress sensitivity and activation energy for superplastic tensile deformation of silicon nitride consisting of rod-shaped grains were investigated. Rod-shaped grains, which oriented randomly before deformation, aligned along tensile direction. Both the stress sensitivity and the activation energy increased during the deformation. The principle deformation mechanism is considered to be the Non-Newtonian viscous flow of grain boundary glassy phase at the former and middle stages. At the last stage (more than 200 % elongation), however, superplastic behavior is considered to be mainly controlled by the solution - precipitation with 2-D nucleation.

Indentation cracks in superplastically deformed silicon nitride consisting of strongly aligned rod-shaped grains

Vickers indentation in silicon nitride, which was produced by superplastic tensile deformation of 150%, was conducted. The specimen had a highly anisotropic microstructure, where rod-like grains aligned along the tensile direction, and showed unusual crack systems. In the case of the indentation whose diagonals point to 0°/90° (0° direction is the tensile direction), two V-shaped surface cracks were propagated from each 90° edge and one crack from each 0° edge. In the case of the 45°/45° indentation, surface cracks emanated from the edges of the indent and deflected towards the tensile direction. Subsurface crack systems also showed unique shapes, differing from a cross-shaped crack system in isotropic brittle materials. Three-dimensional crack systems were estimated on the basis of the observation, and the crack evolution process was considered. Furthermore, the mechanical properties of the anisotropic silicon nitride were measured, and showed superior bending strength and fracture toughness in specific directions, compared to the undeformed material.

Common features of intragranular dislocation slip and intergranular sliding

Abstract An analogy between the occurrence of intragranular dislocation slip and intergranular (grain-boundary) sliding at different structural levels is discussed. Observation of in-situ superplastic tensile deformation in a scanning electron microscope on a Pb-62wt.%Sn eutectic alloy showed that the phenomenon of intergranular sliding on the scale of the entire deformed volume and on the scale of grain groups is similar to the occurrence of intragranular dislocation slip deformation at these microstructural levels.

An evaluation of the densification characteristics of nanocrystalline materials

The possibility of superplastic tensile deformation in nanocrystalline materials has not yet been realized, largely due to the difficulty in maintaining a fine grain size during the densification of nanocrystalline powders. In this preliminary study, it is demonstrated that it may be possible to retain a nanocrystalline grain size in a 3 mol% yttria stabilized zirconia by sinterforging, which enhances densification without significantly affecting grain growth. In addition, other published data are examined to identify conditions favorable for enhancing densification and limiting grain growth.