Superplastic properties

Abstract Superplastic properties of an advanced Al-Li-Mg-Cu-Sc alloy with fine-... 

Warm rolling of preform with a submicrocrystalline structure can be produced at much lower temperatures than generally used. Submicrongrained sheets demonstrate mechanical isotropy and high superplastic properties at reduced temperature range of 650-750°C. The Ti-64 sheets with SMC structure can be successfully used for SPF and SPF/DB applications with significantly decrease in operations temperature (by 200°C). 

L.B. Johannes, I. Charit, and R.S. Mishra, High Strain Rate Superplastic Properties of 7075 Aluminum via Friction Stir Processing, Friction Stir Welding and Processing III, 2005 TMS Annual Meeting, Feb 13-17, 2005 (San Francisco, CA), p123-130... 

Superplastic Forming. The alloy displays superplastic properties between 725 and 775 C (1340 and 1430 F) 1000% ductility can be reached at strain rates as high as 8 x 10 s. Diffusion bonding is being studied. 

As shown in Fig. 9 and 10, the ratio of the volume fi actions of a and P in many titanium alloys is strongly reflected in the superplastic properties of strain-rate sensitivity and elongation. For these alloys, the highest ductihties are observed with the P concentration in the range of 15 to 50 vol%. The maximum in m value also occurs at a significant concentration of the P phase, but there is no clear correspondence between this and the total elongation, because the maxima of each are indicated at different p volume fractions. 

Table 5.4 Properties of Selected Alloys Exhibiting Superplasticity...

My own criticism on the theories proposed for superplasticity can be summarized in one word, electrons , or more accurately the lack of electronic consideration. This is similar to the theoretical consideration brought forward in the study of LME (liquid metal embrittlement) described in the previous chapter - no electronic consideration. As shown in Table 2, all superplastic alloys of binary system are found either at eutectic or eutectoid compositions. This is illustrated in Fig. 14 in which a few binary phase diagram involving superplastic alloys are shown. However, the people who made efforts in the formulation of theories did not consider this well-known fact important enough to incorporate into their theory formulation [24], In fact, this observation is so consistent one should ask the question of the special attributes associated with eutectic or eutectoid composition. Or the fact that the intermetallic compounds with superelastic property are all of the peritectic type. It must be emphasized that to this date there is no report of finding superplasticity in congruently-melting compounds. 

Superplasticity is a very promising property, not only because, like in metals, the superplastic formation opens a way for the manufacturing of complex ceramic pieces for industrial applications, but also because the combination of GBS and diffusional processes makes superplasticity an interesting tool for joining ceramic pieces in shorter times and lower temperatures than the diffusional joining technique. 

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