Superplastic Deformation Behavior Research Articles

Experimental studies on the superplastic forming of square shaped components from sheets of Ti-6Al-4V alloy

Superplasticity is the ability of a polycrystalline material to exhibit, in a relatively isotropic manner, large elongations when deformed in tension. This property is exploited during superplastic forming in the fabrication of complex shaped components which are otherwise technically difficult or economically costly to form by conventional methods. The ability of some titanium alloys to undergo superplastic deformation coupled with their diffusion bonding capability (SPF/DB) provides excellent opportunities to fabricate intricate parts in a single operation resulting in significant cost and weight savings, particularly in the manufacture of aerospace structures. In the present work, experimental studies to characterize the superplastic behaviour of an as-received titanium Ti-6Al-4V alloy sheet commonly used in aerospace structural applications are reported. Tensile test coupons prepared from the alloy sheet were subjected to high temperature tensile tests in the temperature range of 1123 K (850°C) to 1223 K (950°C) and strain rate range of 10−4 s−1 to 10−2 s−1 in order to characterize the superplastic deformation behaviour. Suitable dies, for superplastic forming of 80 mm × 80 mm square components to depths of 43 and 50 mm, were designed and fabricated. Components were superplastically formed at a temperature of 1200 K (927°C) and 0.7 MPa constant argon pressure. The components were characterized for their thickness distribution, mechanical and metallurgical properties and the results are presented.

Microstructure and Elevated Temperature Tensile Behavior of Directionally Solidified Ni-rich NiAl-Mo(Hf) Alloy

The microstructure, high strain rate superplasticity and tensile creep behavior of directionally solidified (DS) NiAl-Mo(Hf) alloy have been investigated. The alloy exhibits dendritic structure, where dendritic arm is NiAl phase, interdendritic region is Ni(3)Al phase, and Mo-rich phase distributes in the NiAl and Ni(3)Al phases. The alloy exhibits high strain rate superplastic deformation behavior, and the maximum elongation is 104.2% at 1373 K and strain rate of 1.04x10(-2) s(-1). The balance between strain hardening (by dislocation glide) and strain softening (by dynamic recovery and recrystallization) is responsible for the superplastic deformation. All the creep curves of the DS NiAl-Mo(Hf) alloy have similar shape of a short primary creep and dominant steady creep stages, and the creep strain is great. The possible creep deformation mechanism was also discussed. The creep fracture data follow the Monkman-Grant relationship.

Enhanced superplasticity in equal-channel angularly pressed Sn–5Sb alloy

The superplasticity of a fine-grained Sn–5 wt.% Sb alloy, processed by equal-channel angular pressing (ECAP), was investigated by impression testing in the temperature range of 298–370 K. The deformation response of the ECAPed material with a grain size of 2.5 μm conforms to regions I, II and III, typical of superplastic behavior. In region II, the strain rate sensitivity indices of 0.42–0.60 and activation energy of 42 kJ mol−1 are indicative of a superplastic deformation behavior dominated by grain boundary sliding.

Superplastic deformation behavior and mechanism of 1420 Al-Li alloy sheets with elongated grains

True stress-true strain curve, microstructure and texture information were obtained to investigate the superplastic deformation behavior of 1420 Al-Li alloy sheets with initial elongated grains. From the true stress-true curve, the stress increases with the increase of strain to 0.15, then dramatically decreases with the increase of strain to 0.80, and finally keeps almost a horizontal line. Meanwhile, initial elongated grains are gradually changed into equiaxed grains and the initial strong Brass {0 1 1} 〈2 1 1〉 and S {1 2 3} 〈6 3 4〉 orientations are turned into nearly random orientation with increasing strain. All these results suggest that dislocation activity is the dominant mechanism during the first stage, then dynamic recrystallization occurs, and grain rotation is expected as an accommodation for grain boundary sliding (GBS). At larger strains, grain boundary migration (GBM) becomes necessary to accommodate GBS.

Superplastic Properties of Al 2O 3/Ni-Mn Nanocomposite Fabricated by Electrodeposition

Ni-Mn nanocomposite reinforced by Al 2 O 3 particles was fabricated by pulse electrodeposition. The average grain size is 60 nm and the content of Mn and Al 2 O 3 particles is 0.3 and 0.6 wt pct, respectively. The superplastic deformation behavior was further studied at the temperatures ranging from 673 to 873 K. A maximum elongation of 530% is obtained in the tension test at a temperature of 773 K and at a strain rate of 1.67×10 −3 s −1 . The curves of the flow stress vs strain rate have features similar to the trend of conventional superplastic materials. The test temperature (773 K) equals to 0.35 T m , which means the material obtains low temperature superplasticity. The microstructures of the composite were examined and grain growth was observed during deformation.

Superplastic deformation of hydrogenated Ti–6Al–4V alloys

Superplastic deformation behavior of hydrogenated Ti–6Al–4V alloys was investigated at an extensive hydrogen concentration. The superplastic elongation was studied in detail. The microstructures before and after deformation were both observed. Hydrogen enhances superplastic elongation at some certain deformation temperatures, strain rates, and hydrogen concentrations. Hydrogen decreases optimum superplastic temperatures and increases optimum superplastic strain rate. The calculated result of activation energies indicates that hydrogen did not change the superpalstic deformation mechanism. The variation of elongation is attributed to the microstructures of hydrogenated alloys, which are more sensitive to strain rate and temperature in the process of superplastic deformation.

High Strain Rate Superplastic Deformation Behavior of TiN<sub>P</sub>/2014Al Composite

TiNP/2014Al composite was prepared by powder metallurgy method with a reinforcement volume fraction of 15%. High strain rate superplastic deformation behavior of the TiNP/2014Al composite was investigated by tensile tests conducted at 818 K with different strain rates range from 1.7×100 to 1.7×10-3 s-1, DSC, OM, TEM and SEM. It is shown that a maximum elongation of 351% is achieved at 818 K and 3.3×10-1 s-1. The curve of value can be divided into two stages with the variation of strain rate and the critical strain rate is 10-1 s-1. Plastic deformation of the TiNP/2014Al composite at 818 K and 3.3×10-1 s-1 is conducted at an almost constant maximum value of flow stress. High strain rate superplastic deformation mechanism of the TiNP/2014Al composite deformed at 818 K with the strain rate of 3.3×10-1 s-1 is grain boundary sliding accommodation mechanism plus liquid phase helper accommodation mechanism.

ECAP 가공한 Zn-0.3Wt%Al 합금의 초소성 변형 특성

Superplastic deformation behavior and texture evolution after equal channel angular pressing (ECAP) of Zn-0.3Wt%Al alloy were investigated in this study. ECAP was conducted at temperatures from to on the plate type specimens of 5 mm thickness and 20 mm width. The specimens obtained by ECAP showed typical texture with basal poles tilted away from the ND toward ED, which is called shear texture. Tensile tests were carried out at for ECAPed specimens under the strain rate of 0.0002/s. After ECAP of the Zn-0.3Wt%Al alloy, elongation was dramatically increased up to 500% at . The effect of ECAP on the anisotropy in the superplastic deformation behavior was negligible.

Superplastic behavior of a fine-grained ZK60 magnesium alloy processed by high-ratio differential speed rolling

Grain size of the ZK60 alloy was effectively reduced to 1∼2 μm through high-ratio differential speed rolling (HRDSR) for a thickness reduction of 70% in a single pass. Due to the strengthening effects of grain boundaries and particles, the HRDSR processed ZK60 exhibited a high tensile strength of 340 MPa. Low temperature superplasticity was attained at 473–493 K at low strain rates (5 × 10 −4 s −1) and high strain rate superplasticity was attained at 523–553 K at high strain rates (10 −2 s −1). The optimum superplastic temperature was found to be 553 K where a maximum tensile elongation of ∼1000% was obtained at 1 × 10 −3 s −1. The deformation behavior of the HRDSR processed ZK60 at elevated temperatures could be depicted by considering contribution of grain boundary sliding and slip creep to total plastic flow. Difference in superplastic deformation behavior between the HRDSR processed and equal channel angular press processed ZK60 alloys was examined and discussed.

동적재료모델을 이용한 Zn-Al 합금의 초소성 변형거동 연구

Abstract Superplastic deformation behavior of a Zn-0.3 wt.% Al was investigated. Grain sizes of 1 ㎛ and 10 ㎛ were obtained by a thermomechanical treatment. A series of load relaxation and tensile tests were conducted at various temperatures ranging from RT (24℃) to 200℃. A large elongation of 1400% was obtained at room temperature in the specimens with the grain size of 1 ㎛. In the case of specimens with the grain size of 10 ㎛, relatively lower elongation at room temperature was obtained and, as the temperature increases above 100℃, a high elongation of about 400 % has been obtained at 200℃ under the strain rate of 2×10 -4 /s. Dynamic materials model (DMM) has been employed to explain the contribution from GBS of Zn-Al alloy. Power dissipation efficiency for GBS was evaluated as above 0.4 and found to be very close to the unity as strain rate decreased and temperature increased, suggesting that GBS could be regarded as Newtonian viscous flow. Key Words

Microstructure and superplasticity of laser welded Ti–6Al–4V alloy

In this paper laser beam welding (LBW) was used to join Ti–6Al–4V alloy as a pre-forming operation before superplastic deformation (SPF) process. Superplastic deformation behavior of laser welded Ti–6Al–4V alloy was investigated. The results indicated that the welded Ti–6Al–4V alloy had good superplasticity when deformed at temperature range of 870–920 °C and strain rate range of 10 −3–10 −2 s −1, and the elongation was 233–397%. The microstructure observation indicated that dynamic recrystallization happened in the weld bead, and the acicular structure of weld bead was transforming into equiaxed grains during tensile process.

Superplastic deformation behavior of twin-roll cast Mg–6Zn–1Mn–1Al alloy

The high-temperature deformation behavior of twin-roll cast (TRC) Mg–6Zn–1Mn–1Al (ZMA611) alloy has been investigated and compared with that of ingot cast (IC) Mg–3Al–1Zn (AZ31) alloy. At 543–603 K and at 10−4–10−2 s−1, TRC ZMA611 alloy shows much larger tensile elongation at a faster strain rate than IC AZ31 alloy. The superplastic properties of TRC ZMA611 alloy are mainly due to the presence of thermally stable fine particles, which stabilize grain size and hence promote grain boundary sliding.

Superplastic behaviors of a Mg–Zn–Y–Zr alloy processed by extrusion and equal channel angular extrusion

Superplastic deformation (SPD) behaviors of a Mg–5.8%Zn–1.0%Y–0.48%Zr alloys produced by conventional extrusion and equal channel angular extrusion (ECAE) methods, respectively, have been comparatively studied in this paper. It is found that the optimum superplastic condition in as-extruded alloy was obtained at 450 °C and 3.3 × 10 −4 s −1 with the largest elongation to failure about 450%; while in as-ECAEed alloy it was at 350 °C and 1.7 × 10 −3 s −1 with about 800% elongation. Microstructural observations showed that structure evolution and cavity formation behaviors were different in these two materials during SPD. The probable mechanisms for superplasticity such as grain boundary sliding (GBS) and dynamic recrystallization (DRX) under different deformation conditions were discussed in terms of strain rate sensitivity, activation energy, as well as microstructural evolution.

Stretching behavior of a carbon nanowire encapsulated in a carbon nanotube

Molecular dynamic simulations are performed to study the deformation behavior of nanocomposite structures formed by the insertion of a carbon nanowire (CNW) into a carbon nanotube (CNW@CNT) under tension. The simulation results indicate that insertion of the CNW into CNT makes the plastic elongation increase. A superplastic deformation behavior is observed and finally, CNW@CNT is drawn to be a very long elongated nanobridge. During the tensile deformation, pentagon–heptagon defects, octagonal defects, and higher-order rings are observed. A large hole caused by some defects accelerates the fracturing of the CNT.

SUPERPLASTIC INDENTATION CREEP OF FINE-GRAINED Sn-1% Bi ALLOY

Creep and superplasticity of the fine-grained Sn -1wt.% Bi alloy, processed by conventional rolling (CNR), cryorolling (CRR) and equal channel angular pressing (ECAP) routes, were investigated by indentation testing at room temperature (T > 0.6T m ). Based on the steady-state power law creep relationship, the stress exponents of 4.1, 2.8 and 2.5 were obtained for the CNR, CRR and ECAP routes, respectively. The corresponding strain rate sensitivity (SRS) indices of 0.24, 0.36 and 0.40, corresponding respectively to the grain sizes of 2.8, 2.1 and 1.2 μm, indicate that the materials processed by ECAP and CRR exhibit superplastic deformation behavior for which, grain boundary sliding is the possible creep mechanism.

Enhanced superplastic deformation behavior of ultrafine‐grained Ti‐6Al‐4V alloy

AbstractThe mechanical behavior of the Ti‐6Al‐4V ELI alloy in both conventional grain size (CG) and ultrafine‐grained (UFG) conditions under tension and compression at elevated temperatures (500–800 °C) is considered. Grain refinement by equal‐channel angular pressing (ECAP) followed by multicycle extrusion was observed to result in a considerable improvement of superplastic characteristics of Ti‐6Al‐4V ELI alloy. The alloy exhibits a superplastic deformation behavior already at 600 °C. The enhanced regime of superplasticity allows more efficient forming of parts and components. In addition, the UFG microstructure and, consequently, enhanced mechanical properties are kept after superplastic forming.

The anisotropy of deformation for friction stir processed Mg alloy due to the existence of onion rings

Abstract In the present study, it is found that one-pass friction stir processed AZ61 alloy exhibits inferior deformation ability along the longitudinal direction compared with the transverse direction at high temperatures. Based on observation of microstructure and fracture surface, premature onion ring splitting is suggested to be mainly responsible for this anisotropy of deformation behavior. Furthermore, the homogeneous microstructure from multi-pass friction stir processing can cure the premature onion ring splitting and then exhibit isotropic high-temperature superplastic deformation behavior.

Integrated molding of nanocrystalline tungsten carbide powder with stainless steel

Nanopowder of tungsten carbide ( d < 100 nm) was prepared by the planetary ball milling of the commercial powder with the particle size of the submicron order. The WC powder was densified by the spark plasma sintering. The milled powder was possible to be densified at a temperature which was 500 °C lower than densification temperature for the commercial powder. The tungsten carbide body sintered at 1100 °C for 3 min under 50 MPa mainly consisted of nanograins with the grain size of <100 nm. It exhibited superplastic deformation behavior under compression at 1200 °C to a strain of >2 without brittle fracture. Applying such superplastic property, we successfully covered the inwall of the cylindrical metal mold made of stainless steel with tungsten carbide layer of the 2 mm in thickness by using spark plasma sintering method.

Superplastic Deformation Behavior of Spray Formed High Speed Tool Steel at 820°C

Being examined by tensile tests at 820°C with initial strain rates of 2.5×10-4 s-1, 5.0×10-3 s-1and 1.0×10-1 s-1, the hot-rolled spay formed high speed steel (SF-HSS) had superplastic properties. With έ=2.5×10-4 s-1and 5.0×10-3 s-1, the σ-ε curves indicate that there has occurred dynamic recrystallization at the later stage of deformation.The tensile elongation decreases monotonously with strain rate increasing. The strain rate sensitivity m =dlogσ/dlog έ is about 0.23. In the sub-surface of fractured SF-HSS samples with έ=2.5×10-4 s-1,, most of holes on the subsurface are observed to distribute near the carbides and arranged along the tensile axis direction. The interface between coarse carbides and matrix is very weak sites where the holes are easy to nucleate and connect to cracks during deformation. In the necked region, fine carbide particles on the grain boundary have pinned the slip of dislocations and formed dislocation wall inside the grain. Dynamic recrystallization and some climb of dislocations has occurred. The superplastic deformation mechanism with έ=2.5×10-4 s-1 was dislocation creep mechanism controlled by dynamic recrystallization. During deformation, the role of some carbide in the materials was to retard the grain growth and keep SF-HSS having fine equiaxed grain size and remain stable.

Low Temperature Superplasticity of Titanium Alloy Processed by Thermohydrogen Treatment

Effects of hydrogen on superplastic deformation behavior were investigated through high temperature tensile experiment in this paper. It is found that reasonable hydrogen contents can improve the superplastic behavior such as lowering flow stress and temperature and increasing m value. While addition of 0.1wt% hydrogen in Ti-6Al-4V alloy, peak flow stress decrease to 53%, deformation temperature decrease 60°C. The influence of hydrogen on microstructure transition by means of optic microscope, SEM, TEM and XRD was also researched. The results show that β phase amounts in the hydrogenated alloy increase with hydrogen contents, while hydrogen contents reach to 0.2wt%, martensite becoming coarser with the increase of hydrogen contents. Moreover, dislocations density of hydrogenated alloy after deformation is lower than that of unhydrogenated alloy because of hydrogen action.