Showing papers on "Superplasticity published in 1976"
TL;DR: In this paper, the roles of grain-boundary sliding (GBS) and of other creep mechanisms in creep and fine-grain superplasticity are presented in relation to a model based on the division of grains into their central cores and peripheral “mantles.
Abstract: The roles of grain-boundary sliding (GBS) and of other creep mechanisms in creep and fine-grain superplasticity are presented in relation to a model based on the division of grains into their central “cores“ and peripheral “mantles”; GBS and its accommodation is limited to the latter, which changes with the mode of accommodation,viz by fold formation, dislocation motion in the mantle or pure diffusion. This description is used to adapt from the literature or develop equations for creep rate based on dislocation or vacancy mechanisms, which are then combined to give plots of the various regimes of superplastic (or creep) behavior, all of which involve GBS in a quantitatively defined manner. The predictions of these equations are compared with a number of results in the literature and with those of a lead-thallium alloy of grain sizes intermediate between superplastic behavior and normal creep. Some preliminary comparisons of measured GBS are also made with the predictions of the model. Agreement is good.
570 citations
TL;DR: In this paper, sufficient experimental results are available for the construction of deformation maps for two superplastic materials, Zn-22% Al and Pb-62% Sn, and when plotted in the form of grain size versus stress, the maps for these two alloys provide strong evidence that super-plasticity only occurs at grain sizes sufficiently small that a stable subgrain structure is not formed during deformation.
100 citations
TL;DR: In this paper, the grain-boundary sliding during superplastic flow of the Pb-Sn eutectic was observed and a threshold stress of 1.3×106N m−2 was observed for the onset of super-plastic deformation.
Abstract: Dynamic observations of grain-boundary sliding during superplastic flow of the Pb-Sn eutectic are reported. These observations confirm the postulate that the dominant deformation mode during superplastic flow is grain-boundary sliding with localized deformation necessary to maintain grain coherency. Extensive grain-boundary sliding is also observed when the strain-rate and/or grain size is outside the superplastic flow regime. Stress relaxation tests were also carried out on the Pb-Sn eutectic. These tests provide data on the activation energy (45±5 kJ mol−1), grain-size dependence (d−3), and stress dependence of superplastic flow in this alloy. A threshold stress of 1.3×106N m−2 for the onset of superplastic deformation is also observed.
92 citations
TL;DR: In this article, the instability of plastic flow is analyzed in terms of the development of internal bifurcations (analogous to diffuse, multiple, external necks for non-cavitating superplastic alloys) and the linking of cavities by internal necking.
65 citations
TL;DR: An Al-6 wt.-%Mg alloy containing Zr, Cr, and Mn was found to deform highly superplastically when produced in a heavily cold-rolled and recrystallized condition.
Abstract: An Al-6 wt.-%Mg alloy containing Zr, Cr, and Mn was found to deform highly superplastically when produced in a heavily cold-rolled and recrystallized condition. Grain-boundary sliding was detected during superplastic flow of this alloy and dislocations were observed to interact with precipitate particles within grains. The alloy specimens, obtained at 0°, 45°, and 90° to the rolling direction, exhibited anisotropy with respect to their flow stresses and textures. The superplastic deformation process in this alloy can be well explained in terms of grain-boundary sliding accommodated by dislocation motion within grains.
60 citations
TL;DR: The role of alloying additions in modifying the recrystallization behavior of aluminium alloys is discussed in this article, and possible deformation mechanisms in the newer alloys are discussed to demonstrate their relative importance.
Abstract: Although the phenomenon of super plasticity in metals was recognized for many years, the majority of alloys that were shown to be super plastic consisted of two phases present in approximately equal volumes. The only aluminium alloys known to be superplastic were of eutectic composition and did not, in general, possess other properties that would make them commercially attractive. More recently, superplasticity has been obtained in relatively dilute aluminium alloys with more useful user properties. A brief summary is given of the aluminium alloys of eutectic composition that have been shown to exhibit superplasticity, but the authors are mainly concerned with the newer, relatively dilute alloys. The roles of alloying additions in modifying the recrystallization behaviour, because of both their presence in precipitate particles and their influence in solid solution, are considered. Additionally, possible deformation mechanisms in the newer alloys are discussed to demonstrate the relative importanc...
57 citations
TL;DR: In this paper, the rheology of dry polycrystalline olivine is examined by adopting a hyperbolic sine flow law (which reduces to a power law below 3 kbars) for high stress behavior, and a model for diffusion accommodated, coherent, grain boundary sliding (structural superplastic creep) for low stress behavior.
52 citations
TL;DR: In this article, the superplastic deformation characteristics of a microduplex stainless steel were examined over the temperature range 700 −1020°C and the strain rate sensitivity index, m, was observed to increase with the temperature.
Abstract: The superplastic deformation characteristics of a microduplex stainless steel were examined over the temperature range 700–1020°C. The strain rate sensitivity index, m, was observed to increase wit...
51 citations
TL;DR: In this paper, a transmission electron microscope study of the Al-rich phase of a deformed Zn-40wt% Al alloy, the dislocation structures were determined as a function of strain and strain rate.
42 citations
TL;DR: In this article, the properties and microstructure of superplastic materials are summarized, together with the principles involved in obtaining material in a super-plastic condition, and examples of development of super plasticity in existing commercial Ni, Ti, and Cu alloys are given.
Abstract: The mechanical properties and microstructure of superplastic materials are summarized, together with the principles involved in obtaining material in a superplastic condition. Examples of development of superplasticity in existing commercial Ni, Ti, and Cu alloys are given, and it is demonstrated how superplastic steels may be designed. Typicalformed components in IN 100 and IMI 318 alloys are shown and the advantages of superplastic forming are discussed briefly.
37 citations
TL;DR: In this paper, the peculiarities of dislocation slip, grain-boundary slip and boundary migration are studied at superplastic deformation of the Zn-0.4% Al alloy.
Abstract: The peculiarities of dislocation slip, grain-boundary slip and boundary migration are studied at superplastic deformation of the Zn—0.4% Al alloy. The nature, interconnection, and role of these processes are investigated. Dislocation slip at the deformation of the alloy which is the primary deformation mechanism is found to be of great importance. At the same time the importance of grain boundary sliding (GBS) consists in the fact that it is not only a deformation mechanism but a recovery mechanism as well. Grain-boundary migration is a process concurrent to sliding.
[Russian Text Ignored]
TL;DR: The superplasticity of Ti-6Al-4V was measured in tensile specimens by calculating the true stress and true strain rates at various points along the load displacement curve (randomly selected i.e. a, b, c, d, e, etc) as discussed by the authors.
Metz1
TL;DR: One hypereutectic (10% P) and two hypoeutectical (7 and 5%) alloys were investigated in this article, with α β ratios of 0.35:2.
TL;DR: In this article, high-temperature mechanical properties were studied in Zr--2.5 percent Nb alloy, in which the cap alpha....-->....beta.. transformation range covers 880 to 1160/sup 0/K.
TL;DR: A detailed experimental study of the development of plastic flow has been made in a non-cavitating superplastic alloy (wrought Pb-Cd eutectic) as discussed by the authors.
Abstract: A detailed experimental study of the development of plastic flow has been made in a non-cavitating superplastic alloy (wrought Pb-Cd eutectic). The behaviour has been analysed in terms of two instabilities, the first corresponding to the development of measurable external necks and the second to the rapid growth of one neck to cause plastic rupture.
Patent•
10 May 1976
TL;DR: In this article, metal powders are hot isostatically pressed in a can or container produced from superplastic metal sheet, and they are hot-isostatically sealed.
Abstract: Metal powders are hot isostatically pressed in a can or container produced from superplastic metal sheet
TL;DR: In this paper, a sigmoidal log σ versus log ge curve was observed for the deformation of Zircaloy-4 in the α, α + β and β modifications.
TL;DR: The fine grain size required for superplasticity is produced by dynamic recrystallization and is lost above 360°C and activation energy suggests grain boundary diffusion as the controlling mechanism for super-plastic deformation as mentioned in this paper.
Abstract: 1)
It is feasible to develop superplasticity in a standard commercial aluminum alloy BA 708 following a simple thermomechanical processing route and yielding elongations > 200 pct over a range of temperatures and strain rates.
2)
The fine grain size required for superplasticity is produced by dynamic recrystallization and is lost above 360°C.
3)
The activation energy suggests grain boundary diffusion as the controlling mechanism for superplastic deformation.
TL;DR: In this paper, the influence of test temperatures and sample anisotropy upon the yield stress, the strain rate sensitivity and the ductility of Zry-4 sheet-type tensile specimens was examined.
TL;DR: In this paper, superplasticity has been investigated in three carbon-manganese steels with small additions of Nb, V, Al and Ti and the results showed that the strain rate sensitivity did not vary with strain although it was very dependent on strain rate and temperature.
Abstract: Superplasticity has been investigated in three carbon-manganese steels with small additions of Nb, V, Al and Ti. Superplasticity was observed from 800 to 1000°C at strain rates from 0.002 to 0.01 min-1. Strain rate sensitivities above 0.7 have been observed; however elongations to fracture are quite low with a maximum value observed of 184 pct. The strain rate sensitivity did not vary with strain although it was very dependent on strain rate and temperature. Cold work prior to hot tensile testing enhanced the superplasticity in the vanadium steel. The premature failure of these steels with large strain rate sensitivities has been attributed to crack nucleation due to the fine particle network from the Nb and V precipitation.
Journal Article•
Patent•
28 Oct 1976TL;DR: In this article, a metal preform having superplastic characteristics is positioned relative to a shaping member, which substantially defines the final configuration of the preform, and then a preform is superplastically expanded and forged against the shaping member to produce the final structure.
Abstract: A method for making metallic structures especially those having a complex variable thickness, utilizing superplastic forming and forging. A metal preform having superplastic characteristics is positioned relative to a shaping member which substantially defines the final configuration of the preform. The preform is superplastically expanded and forged against the shaping member to produce the final structure.
TL;DR: In this article, the response of powder metallurgy In-738 in stress relaxation was studied and the results confirmed the superplastic forming potential of high strength superalloys in the powder form.
Abstract: The response of powder metallurgy In-738 in stress relaxation was studied. Results confirm the superplastic forming potential of high strength superalloys in the powder form. The load relaxation test as described is particularly suitable for identifying in a short period the precise strain-rate/temperature regime where superplasticity should occur. A master curve may be used to construct a curve for any temperature within the range tested by simple interpolation based on an Arrhenius relationship between strain rate and temperature. Moreover, in many cases, several tests may be made on one specimen if desired rather than using separate specimens. (JRD)
TL;DR: Stress-strain curves obtained at constant cross-head velocity tensile tests of Ti-6Al-4V sheets at different temperatures show different behavior as discussed by the authors, suggesting that necking occurs at various locations along the gauge length.
TL;DR: In this article, an investigation into the creep of Al2O3-AlN and Y 2O3AlN ceramics has been conducted and it has been shown that the addition of 20-80% AlN reduces the creep rate.
Abstract: An investigation into the creep of Al2O3-AlN and Y2O3-AlN ceramics has demostrated that the addition of 20–80% AlN reduces the creep rate of Al2O3. In the system Y2O3-AlN the existence of a creep rate maximum has been discovered, which may be a manifestation of structural superplasticity.