Superplasticity Effect Research Articles

The superplasticity of commercial aluminium alloy

In this work the superplasticity of cold-rolled sheet metal of LF6 aluminium alloy has been studied. An extremely significant superplastic effect has been attained in the cold-rolled condition without any special pre-treatment. A total elongation as high as 463% has been achieved under the following conditions: 490°C and 3.33 × 20 −1 s −1, where the corresponding strain rate sensitivity index m = 0.68 and the flow stress σ = 2.8 MPa. As compared with data available in the international literature, the above results are pre-eminent. The results of mechanical testing and metallographic examination indicate that the presence of particles of the second phases such as β (Mg 2Al 3), MnAl 6 and TiAl 3 leads to the formation of the fine and stable grains necessary for the achieving of superplasticity. The most probable deformation mechanism for the superplastic flow of LF6 aluminium alloy is grain boundary sliding accomodated by sliding within grains. The results presented in this paper may lead to the incorporation of the pre-treatment necessary for superplastic forming of certain alloys in the primary working process. As a result, superplastic forming processes would be simplified and the application of this new technology to industry could be expanded. The achievements of this study have been put into practice and the results are excellent. The authors have made some suggestions to the metallurgical industry in order that the present findings can be implemented as soon as possible.

変態超塑性による応力緩和 第１報 応力緩和におよぼす変態超塑性と変態膨張の割合

The effect of the transformation superplasticity (that is a martensite transformation) on the stress releasement has been examined. In the first study, using the new apparatus (a restraint thermal cycle test) by which the displacement of only the transformed part of the specimen can be measured, the proportion between transformation superplasticity and transformation expansion on the amount of the stress releasement was examined. The new composite specimen of which the test 9%Ni steel was joined by friction welding to SUS304 stainless steel on the both ends was also used.The results are shown as follows;1) The expansion by only transformation superplasticity was separated from whole expansion during transformation using the new apparatus and specimen.2) When the much amount of thermal stress is generated in spite of a small transformed area, the stress releasement during transformation chiefly occurs by transformation superplasticity.3) Regard as stress releasement in the midst of cooling just after transformation start, it mainly occurs by superplasticity because of its high thermal stress. But, in the latter half of the transformation, the stress releases mainly by transformation expansion.4) The proportion of the transformation expansion and superplasticity was measured.

Superplasticity of corrosion-resistant steels of the ferritic-austenitic class

1. Development of the superplasticity effect is typical for corrosion-resistant chromium-nickel steels of the ferritic-austenitic class type 08Kh22N6T in the hot-worked condition with deformation at rate of the order of 10\t-3 sec\t-1: at 850°C when dynamic polygonization is observed in ferritic grains; in the range 925–950°C when in austenitic grains there is dynamic recrystallization, i.e., dynamic polygonization, the start of which is controlled by the temperature for dissolution of chromium carbide in the steel; at 1050°C when the F→A-transformation provides a ratio A/F=1 and development of dynamic recrystallization promotes a significant refinement of the original grains to 1–10 μm. 2. After upsetting in a regime for development of superplasticity at 1050\dgC the impact strength of steel 08Kh22N6T is at a maximum.

Effect of prior working on the structure and deformation capacity of Mn−29.5% Al−0.5% C alloy

1. Alloy Mn−29.5%Al−0.5%C in the homogenized condition at temperatures below 650°C exhibits low working capacity, i.e., high flow stress and brittleness, which is due to presence in the alloy of lamellar τ-phase. Upsetting of the alloy is possible only in the temperature range 650–750°C and at deformation rates 5·10−3–10−2 sec−1. 2. As a result of extrusion at 700°C recrystallized fine τ-phase grains are formed with a size of 0.5–2 μm. With extrusion in the single-phase e-region (950°C) there is e-phase grain refinement, and then during subsequent cooling fine-grained τ-phase forms. Deformation by extrusion with e=80% promotes total transformation of lamellar τ-phase into granular phase which causes an improvement in the working capacity of alloy Mn−29.5%Al−0.5%C. 3. In alloy Mn−29.5%Al−0.5%C, containing τ-phase with a grain size of 0.5–2 μm the superplasticity effect is observed which is more clearly developed with t=650–750°C and vd=10−2–10−3 sec−1.

Zones of plastic deformation ? Main object of mechanics of real solids

The center of the model of modern mechanics of continuum contains the concept of determining relations: Hooke's law in the elasticity range, various equations of state of viscoelastoplastic bodies. These relations, supplementing Newton's mechanics equations, play the central role in all, or at least in the large majority of experimental investigations. They represent a central channel through which the theory is "saturated" with hypotheses; the hypotheses are not compulsory if instead of them we use direct experimental methods of closing the mechanics equations by direct experimental information. In this work, we discuss mainly the direct dynamic statistical observations of the application of experimental equations of state in situations in which the effects discovered in recent years operate, i.e., the superplasticity effect, the Spitsyn-Troitskii electroplastic effect, Kop'ev effect. Examination of the extreme effects of plasticity explains the principle of its normal effects. This type of examination makes it possible to formulate a new concept of the zonal plasticity mechanism, i.e., the zone of plastic deformation becomes the main object of the mechanics of condensed media. This concept represents the direct formulation of experimental observation; it contains no aprlori information and is equally suitable for any materials, composites or noncomposites.

Structure and properties of low-carbon steels and iron after deformation under superplasticity conditions

1. The superplasticity effect during upsetting of low-carbon steels develops in the temperature range Ac1S-Ac3S, to a greater extent close to Ac3S with deformation rates\(\dot \varepsilon\)≅ sec−1, and it is characterized by a simultaneous reduction in deformation resistance, absence of residual hardening for ferrite, and deformation predominantly by a grain boundary sliding mechanism. 2. After superplastic deformation in the temperature range Ac1S-Ac3S the microstructure of low-carbon steels is characterized by retention of the original grain size or refinement, presence of a developed subgrain structure, low dislocation density within the body of grains, and absence of pore type defects, which gives a high impact strength compared with that obtained after deformation at higher temperatures. 3. With an increase in carbon content in low-carbon steels (up to 0.3% C) the superplasticity effect develops to a lesser degree, and there is a reduction in the difference in impact strength after deformation in a superplasticity regime and at higher temperatures.

Development of the superplasticity effect in aluminum alloys with lithium

Development of the superplasticity effect in aluminum alloys with lithium

Superplasticity of transition and martensitic-class stainless steels

1. In the Md-Ms temperature range, Kh17N5M3, Kh15N4AM3, 08Kh15N5D2T, and 06Kh14N6D2MVT steels possess the effect of superplasticity. 2. The temperature of superplasticity tsp, the same as the Md-Ms range, depends upon the austenitizing temperature. 3. The structure formed at tsp does not have a significant influence on the strength and ductile properties of unnotched samples and the strength of samples with a notch tested with misalignment, but the fatigue life increases and the tendency toward corrosion cracking under stress decreases sharply.

Conditions for superplasticity of aluminum alloy 1201

1. Under certain temperature-rate conditions alloy 1201 is converted to the superplastic condition. For hot extruded strips (λ=23.4) the superplastic effect is evident at 500° with a deformation rate of (2.2–4.4)×10−3 sec−1. In this case, σ20 = 15−20 MPa, δ = 160–170%, and m=0.45. 2. The optimal structure ensuring the superplastic effect is a polygonized structure formed before superplastic deformation begins. 3. To achieve the superplastic effect in alloy 1201 the temperature and rate of deformation must ensure dynamic recrystallization processes with formation of a fine-grained structure.

Effect of deformation under conditions of superplasticity on the structure and properties of high-speed steels

1. With different arrangements of straining high-speed steels as supplied, the effect of superplasticity manifests itself steadily. 2. Blanks of high-speed steels, strained under conditions of superplasticity, have minimum hardness, and this makes it possible to machine them without previous annealing. 3. Volumetric strain under conditions of superplasticity in combination with heat treatment is an efficient method of improving the structure and the mechanical properties of high-speed steels. As a result of strain under conditions of superplasticity, the initial structural inhomogeneity is eliminated, and a finely disperse homogeneous structure forms; this ensures a considerable increase in bending strength and hardness of these steels.

A possible mantle instability due to superplastic deformation associated with phase transitions

Laboratory deformation studies of metals and some oxides indicate that these solids are easily deformed while undergoing a phase transformation. This superplastic effect, if it occurs for mantle silicates, may result in an instability of mantle flow. The instability is illustrated by considering a sheared layer of viscous fluid containing a phase transition. With a simple idealization of the phase transition weakening effect, an oscillatory fluid motion which cycles material through the phase transition is shown to reduce the rate of viscous dissipation associated with shearing the fluid layer. Some possible consequences for mantle flow include the partial decoupling of mantle layers at phase transitions and short wavelength free air gravity anomalies due to induced normal stress variations at the base of the lithosphere.

超塑性Zn-Al合金の開放型盛り上げ加工

The open-die extrusion experiment of both the water quenched superplastic Zn-Al alloy (the water quenched material) and the annealed non-superplastic alloy of the same composition (the annealed material) was carried out under various working conditions to investigate the effect of superplasticity on deformation phenomenon of the material. The results obtained were as follows.(1) The reduction in height (αs) at which the water quenched material began true reverse extrusion decreased with increasing working temperature, while it increased with increasing working speed.(2) The height of workpiece (H0βs) at which the water quenched material began true reverse extrusion increased with increasing working temperature, but decreased with increasing working speed.(3) When the water quenched material was extruded at 250°C with lubricant, the value of αs was large and the value of H0βs was smaller than those obtained under the same conditions but with no lubricant.(4) The reduction in height at which the material began true reverse extrusion nearly coincided with the one at which the diameter of neutral position of workepiece became equal to the diameter of the punch hole.(5) At 250°C, the value of αs for the both materials decreased while the value of H0βs increased with increasing diameter or decreasing height of the unworked workpiece.(6) The adaptability of the annealed material for open-die extrusion was greater than that of the water-quenched material.

The deformation mechanisms of superplasticity

Under various conditions of stress and temperature various deformation mechanisms could be rate-controlling for superplastic deformation. In general at low stresses diffusion creep should be rate-controlling. At temperatures between approximately 40 and 65 pct of the absolute melting point grain boundary diffusion should be the dominant diffusion path while at higher temperatures volume diffusion should dominate. At intermediate stresses, grain boundary sliding should be the major deformation mode, but the sliding rate should be governed by the lesser rate of dislocation creep within the grains. At temperatures between 40 and 65 pct of the melting point, the rate of dislocation creep should be controlled by dislocation pipe diffusion, while at higher temperatures volume diffusion should be ratecontrolling. At high stresses the superplastic effect of unusually large tensile extensibility should diminish due to the greater possibility of work-hardening processes such as dislocation cell, tangle, and pile-up formation.