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SUPERPLASTICITY

SUPERPLASTICITY

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SUPERPLASTICITY

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  1. Permanent deformation of materials on the application of a load can be either plastic deformation or creep. • The permanent deformation at temperature below 0.4 Tm is called PLASTIC DEFORMATION. • Amount of deformation occurring after the application of load is negligible. Rate at which material deformed determines deformation characteristics • At temp above 0.4 Tm permanent deformation is a function of time too. This behaviour is CREEP.

  2. SUPERPLASTICITY The unusual ability of some metals and alloys to elongate uniformly thousands of percent at elevated temperatures, much like hot polymers or glasses. Under normal creep conditions, conventional alloys do not stretch uniformly, but form a necked-down region and then fracture after elongations of only 100% or less. The most important requirements for obtaining superplastic behaviour include a very small metal grain size, a well-rounded (equiaxed) grain shape, a deformation temperature greater than one-half the melting point, and a slow deformation rate

  3. In materials science, superplasticity is a state in which solid crystalline material is deformed well beyond its usual breaking point, usually over about 200% during tensile deformation. Such a state is usually achieved at high temperature, typically half the absolute melting point. Examples:some fine-grained metals and ceramics. Superplastically deformed material gets thinner in a very uniform manner, rather than forming a 'neck' (a local narrowing) which leads to fracture. Also, the formation of internal cavities, which is another cause of early fracture, is inhibited Other non-crystalline materials (amorphous) such as silica glass ("molten glass") and polymers also deform similarly, but are not called superplastic, because they are not crystalline; rather, their deformation is often described as Newtonian flow

  4. Interest in the phenomenon of superplasticity has been increasing steadily over the past thirty-four years, both from the viewpoint of fundamental scientific understanding as well as of industrial application. • The scope of superplasticity has also broadened materials-wise, and now includes, in addition to metals: intermetallics, ceramics, bulk metallic glasses, nanostructured materials and composites

  5. STRAIN RATE SENSITIVITY Relationship to express true strain εas a function of true stress is σ = K εn K is the strength coefficient, n the work hardening exponent (Copper, brass n = 0.5; Heat treated steel n= 0.15) Another power relationship to express σ at a given strain in terms of the strain rateﻍ σ = A ﻍm A is a constant, m is index of strain rate sensitivity. m = 0.4 to 0.9, material exhibits superplastic behaviour High strain rate sensitivity allows inhibition of necking: no “ localized” failure of material at a reduced cross sectional area

  6. SUPER PLASTICITY & FORMING OF ADVANCED MATERIALS • Capability to deform crystalline solids in tension to unusually large plastic strains, often in excess of 1000%. • Results from the ability of the material to resist the localized deformation in the same way as hot glass. • High elongations possible, and complex contoured parts can be formed in a single press cycle often eliminating the need for multipart fabrications. • Enables designer to capture several detailed parts into a one piece complex formed structure and to very near dimensions. • Enhances design freedom, minimizes amount of scrap, reduces the need for machining. Also reduces the amount of material used thus lowering overall material costs.

  7. Mg - 3 Al -1Zn

  8. Initially superplastic (SP) deformation was considered as unique phenomenon inherent only to several alloys. However, systematic studies displayed its more general character as compared to conventional deformation. • In reality, this effect can be observed not only in metals but in intermetallides and ceramics as well which, as known, are characterized by brittle failure under common conditions and display no features of plastic flow.

  9. The physical nature of this phenomenon is very complex. • Just recently it seemed that SP deformation could be explained by the operation of usual mechanisms of deformation, namely, grain boundary sliding (GBS), intragranular dislocation slip and diffusion creep. • However, the latest data have shown that this phenomenon is conditioned by the operation of a specific mechanism of deformation - cooperative grain boundary sliding (CGBS) • The operation of this deformation mechanism does not depend on the crystal lattice type and dislocations present. It depends on the long-range area and structure of grain boundaries in a polycrystal.

  10. Scheme of cutting and types of zinc bicrystals for investigation of "pure" GBS (1) and "stimulated" GBS

  11. Formation of deformation bands on sample surface (a) and their development during tension

  12. Cooperative grain boundary sliding in Al tricrystals: a) formation of a fold, b) fine adjustment of a grain boundary via migration, c) migration of a grain boundary.

  13. Scheme of strain rate-stress dependence within a wide stress interval

  14. 1155%

  15. Laser Induced superplasticity technology Since 1997, scientists working in the Aerospace Manufacturing Research Centre (AMRC) at University of the West of England (UWE) have been investigating novel ways of developing the phenomena of Superplastic Forming and Diffusion Bonding (SPF/DB). Their motto: We have a vision, we know it will work Laser Induced Superplasticity is a technique enabling the manufacture of exceptionally light, strong, corrosion resistant and complex structures from metal alloys, using superplastic forming (SPF) and diffusion bonding (DB). SPF provides extraordinary ductility to many metals, allowing complex shapes to be produced. DB joins components, without using fasteners, welding or adhesives, but with strengths similar to the parent material. Investigating Laser Transparent Ceramics for use as moulds in the Superplastic Form

  16. The work has led to the vision of an integrated cell in which laser(s) will be used to perform, not only the SPF/DB operations, but most of the pre and post forming work as well. Central to fulfilling the vision is the use of ceramic moulds in which the components will be directly heated by a laser beam(s) and subsequently formed. • A new company, LISTech, has been formed to exploit UWE's expertise in laser induced superplasticity. UWE is based in an area of strategic importance for aerospace. Their researchers collaborate on a wide variety of projects with many major manufacturers including Airbus UK, British Aerospace and the Ministry of Defense

  17. Result: The manufacture of some remarkable structures from alloys of titanium, aluminium and nickel, primarily for use in aircraft. In place of the conventional equipment, such as hot platen presses or furnaces, use of a combination of lasers and ceramic moulds, which is a particularly fast, cost effective and energy-efficient process and which is far superior to methods currently used. • The collaboration between LISTechnology Ltd & Horizon Ceramics Ltd and the two Universities (University of the West of England & the University of Bristol) investigates detailed questions relating to the creation of the proposed new manufacturing process,- whether certain ceramics possess an ability to withstand the rigors of the Superplastic Forming process, and whether those ceramics have the desired optical transparency. • If successful, the research will have long-term benefits for the collaborating companies and for the aerospace industry.

  18. SPF International, Inc. was formed to address the need for technology-focused suppliers that can reliably and affordably apply advanced processing technology. The company was founded in March, 2001 In April, 2005 the company moved their manufacturing facility to co-locate with their new strategic partner, AMSI of Gardena, CA. The capabilities of each company compliment each other exceptionally well. SPF International, Inc. possesses the specialized equipment and expertise needed for SPF and hot sizing whereas AMSI has extensive experience and capabilities with more conventional forming methods

  19. SPF International, Inc. uses advanced manufacturing technology to produce complex sheet metal products Superplastic forming (SPF) and hot sizing to produce aerospace parts such as leading edges for the F-15 and ducting for the new Joint Strike Fighter aircraft (F-35). The forming of intricate metal sculptures, the production of architectural panels, the fabrication of short-run automotive parts and even the development a prototype titanium kayak. The equipment and expertise among the best in the world for this niche technology. Hot presses capable to produce sizes of 48” x 96” weighing 600-tons. The longest is 112-inches.