Showing papers on "Superplasticity published in 1974"

Method for superplastic forming of metals with concurrent diffusion bonding

Abstract: A method for fabrication of metal structures, especially those with a complex variable thickness form, in which a metal such as a titanium alloy blank is superplastically formed and concurrently diffusion bonded to other metal workpieces to form a desired structure. The metal blank, at least one shaping member, and at least one metal workpiece to be bonded to the metal blank are located within an enclosure. The metal blank and metal workpieces are heated to a suitable forming and bonding temperature and the metal blank stretched substantially in excess of the original surface area under a fluid pressure loading causing it to deform against the shaping member and intimately contact the other metal workpieces for diffusion bonding. An inert gas and/or vacuum environment can be provided in the enclosed area to prevent contamination by air at the elevated temperatures employed.

Controlled environment superplastic forming of metals

Abstract: Metals such as titanium alloy blanks which are subject to contamination by air at elevated temperatures are precision formed into desired shapes in a controlled environment. The metal worksheet and a shaping member are located within an enclosure. An inert gas environment is provided in the enclosed area. The metal worksheet is heated to a suitable forming temperature and stretched substantially in excess of its original surface area under tensile stress from a fluid pressure loading and formed into the desired shape by interaction with the shaping member. Novel sealing arrangements for the enclosed area of the forming apparatus are provided.

On the possibility of transformational superplasticity in the Earth's mantle

Abstract: It is well known that metals and some ceramics deform superplastically during polymorphic phase transitions, but this phenomenon has not been considered as a possible deformation mechanism in the earth's mantle. Although phase transitions in the mantle can be expected to move significant distances in response to changing surface loads, the time scale of this motion (of the order of 105 yr) is too long to allow simple applications of laboratory results in the absence of a well understood mechanism. To examine possible mechanisms, an apparatus capable of applying a shear traction parallel to a polymorphic phase boundary has been developed. Preliminary results with the β-α transformation in CsCl show that macroscopic deformation was localized at the phase boundary and that microscopic deformation appears to be restricted to the high-temperature phase, in agreement with the mechanism proposed by Greenwood and Johnson. Seismic evidence suggesting that flow is localized at the 400- and 650-km discontinuities in the earth's mantle is reviewed.

Aluminium base alloys

Abstract: Aluminum-base wrought products containing the elements normally present in either non-heat treatable aluminium-base alloys of at least 5%Mg or at least 1%Zn or heat-treatable aluminium-base alloys of one or more of the elements Cu, Mg, Zn, Si, Li and Mn in known combinations, and at least one of the elements Zr, Nb, Ta and Ni in a total amount of at least 0.30% substantially all of which is present in solid solution, are superplastically deformable. The remainder of the superplastically deformable product may be the normal impurities and incidental elements known to be incorporated in heat-treatable and non-heat treatable aluminium-base alloys. Advantageously the alloy of the wrought product contains at least 0.3%Zr and preferably at least 0.40%Zr. The wrought product disclosed may in some cases be deformed superplastically under isothermal conditions but it has been found advantageous to heat the alloy quickly to the superplastic forming temperature and/or allow the temperature to rise whilst the deformaton is in progress.

Cavitation in alloy steels during superplastic deformation

Abstract: A study of cavitation during superplastic tensile straining of two microduplex steels has been made using density measurements and quantitative optical metallography. The steels were of basically similar composition with the exception of a trace addition of boron made to one alloy. During deformation cavities formedα/γ boundaries and matrix-carbide interfaces; the growth and coalescence of these cavities led to failure. Density measurements showed that the extent of cavitation increased with increasing strain and decreasing strain-rate, but the level of cavitation was reduced by the presence of boron. A time dependence of overall void volume of 1.4 to 2.0 was observed. Quantitative metallographic studies of the nucleation and growth contributions to the overall rate of void formation showed that boron inhibited each of these processeS. However, both the nucleation rate and the magnitude of the time exponent of void volume increase suggested that a substantial number of voids grew from pre-existing nuclei which were probably present as non-coherent carbide-matrix interfaces.

Blow molding process for container of superplastic alloy

Abstract: A container of a superplastic alloy material is manufactured by causing a fluid to blow into a bottomed cylinder. Prior to the blow molding, the cylinder has its surfaces finished smooth and is preheated in a temperature range of 200* - 300*C at least two minutes. Within a metal mold, the cylinder is subjected to an initial pressure of at least 8 atm., and is thereafter subjected to a molding pressure in the range of 7 - 20 atm. into the container blown out to the final dimensions. Since the molding pressure is lastly bestowed after somewhat inflating the cylinder by the initial pressure, the product is blowmolded finely, and a beautiful container having neither a flaw nor a crack on the surface is obtained.

Creep in the binary systems TiB2-TiC and ZrB2-ZrN

Abstract: It has been established that two-phase TiB2-TiC and ZrB2-ZrN alloys with approximately equal concentrations of their components exhibit the highest values of creep rate, which is linked with the manifestation of structural superplasticity. The maximum values of creep strain strongly depend on the inclusion size of the component phases.

The relationship between intergranular cavitation and superplastic flow in an industrial copper base alloy

Abstract: Intergranular cavitation has been observed during the superplastic deformation of a fine grain sized (1 μm) Cu-2.8% Al-1.8% Si-0.4% Co alloy when tested at temperatures ≥500° C. High voltage electron microscopy revealed that the cavities could be nucleated at twin boundary/grain boundary intersections. The maximum elongation occurs at a higher temperature than that of the maximum strain-rate sensitivity and this is explained in terms of grain-boundary migration, at the higher temperature, which restricts the cavitation process. This explanation was put forward on the basis of texture analysis which was used to study the deformation characteristics at the temperatures of maximum elongation and strain-rate sensitivity. The final fracture mode is shown to change with test temperature: (i) at 400° C no cavitation occurs and fracture is by ductile rupture, (ii) at 500 to 550° C cavitation occurs and fracture is by the interlinkage of voids by an intergranular void sheet (IVS) mechanism and (iii) at 800° C grain growth occurs and fracture occurs by the propagation and interlinkage of grain-boundary cracks along the grain boundaries.

Design of a superplastic alloy steel

Abstract: An iron alloy, containing a relatively low concentration of alloying elements, which shows good superplastic behaviour in the temperature range 900°–960°C, has been designed from first principles. The alloy, of composition Fe–4%Ni–3%Mo–1·6%Ti, was developed so that at high temperatures it would have a duplex α-γ structure containing approximately equal proportions of the two phases. Grain refinement was achieved by hot rolling in the two-phase field or by cold working and recrystallizing in the two-phase field. At elevated temperatures values of strain-rate sensitivity for the microduplex structure lay in the range 0·5–0·6, and under optimum conditions tensile elongations of >BOO % were obtained. Cavitation occurred during superplastic straining and failure was associated with the growth and interlinkage of cavities. In the air-cooled condition the alloy was fully ferritic and showed good room-temperature tensile properties. A similar alloy which had a lower titanium content and, as a consequence...

Mechanical Properties of Cast Tin-Lead Solder

Abstract: The tensile behavior of a near eutectic tin-lead solder has been determined as a function of various solidification parameters. The results indicate that at solidification rates observed in solder joints the solder alloy possesses superplastic properties similar to those previously observed in deformed and aged alloys.

Superplastic testing conditions and grain growth

Abstract: The strain-rate sensitivity indexm of the Cu-9.5 wt % Al-4 wt % Fe alloy has been determined by two different procedures: (1) from a rate-change test and (2) from the slopes of the maximum engineering stress/initial strain-rate curve. The discrepancies between the results obtained according to the two different procedures are outlined and discussed. Besides the necking behaviour during deformation, factors such as (1) changes in the primitive defect structure, (2) large variations ofm over the strain-rate interval covered and (3) grain growth during deformation, are to be considered in explaining the origin of the discrepancies. Dunlop and Taplin's method is considered to be the better of the two procedures used for determiningm, since it introduces fewer errors. In this alloy, graincoarsening is caused by thermal activation as well as by the deformation process itself.

Superplastic alloy of tin and zinc

Abstract: A superplastic alloy of tin and zinc is disclosed of nominally eutectic composition (91 percent by weight of tin and 9 percent by weight of zinc) with an actual analysis of 9.8 percent zinc in tin, the alloy having an average grain size ranging between 1-2 microns (0.001-0.002 mm) and exhibiting superplastic behavior at temperatures of approximately 250*F. and higher with a maximum index of strain rate sensitivity of 0.4 to 0.5. The alloy shows elongations under tension of 570 percent at temperatures between 300*F.-350*F.

Method for forming superplastic and super ductile metal alloys

Abstract: In forming a structural member from a sheet of superplastic or super ductile metal alloy material, the strain pattern to which the material is subjected in isothermal forming is modified by holding different portions of the sheet being formed to different temperatures, thus controlling the ultimate tensile strength and therefore the material thickness of such portions in the finished product.

Lamp cap connections using superplastic alloy

Abstract: Electric lamps are disclosed having lead-in wires which extend out of the lamp envelopes and are connected to external electrical terminals, the terminals including hollow metal sleeves receiving the wires and the wires being joined thereto using alloys which exhibit superplastic behaviour, the alloys being heated, without melting, and caused to flow or creep superplastically into the sleeves and around the wires.

Rheological analysis of superplasticity in metallic materials

Abstract: By making use of the empirical relations between stress and strain rate useful expressions concerning the variation of viscosity and activation energies for superplastic deformation are derived. The analyses of superplasticity, based on conventional continuum mechanics, neglect grain size effects. A new technique has been developed where the grain-size effect is incorporated into the rheological analysis. The analysis is subsequently made use of in understanding die-less drawing of superplastic bars. It is shown that the analysis is able to predict stress-strain rate relations, viscosity variation and so forth satisfactorily. It is concluded that the present analysis could be useful in practical situations where the constitutive equations are of great importance.

Interdependent processes in high temperature deformation

Abstract: Relationships between stress and strain-rate are examined where two processes significantly influence high temperature deformation. The case when the two processes are interdependent is examined in detail and a gradual transition from one process to the other is predicted. Processes that show an interdependent transition are illustrated by data for the creep of polycrystalline Fe2O3 and for superplastic deformation.

The deformation behaviour of a dispersion strengthened superplastic zinc alloy

Abstract: The deformation behaviour of a new dispersion strengthened superplastic zinc alloy was investigated. A significant long range internal stress was observed at all strain-rates. The activation volume of deformation decreased very rapidly with a decrease in the true effective stress. The maximum strain-rate sensitivity corresponds to a region of change from this high stress dependence of the activation volume to a much lower stress dependence. The observation of a metallographic halo effect shows that apart from dislocation movement, diffusive creep plays a role during superplastic deformation. It is stipulated that both these processes aid boundary sliding which accounts for the largest part of the strain.