Superplastically deformed material gets thinner in a very uniform manner, rather than forming a "neck" (a local narrowing) that leads to fracture.
Some evidence of superplastic-like flow in metals has been found in some artifacts, such as in Wootz steels in ancient India, even though superplasticity was first scientific recognition in the twentieth century in the report on 163% elongation in brass by Bengough in 1912.
The interest in superplasticity rose in 1982 when the first major international conference on 'Superplasticity in Structural Materials, edited by Paton and Hamilton, was held in San Diego.
[7] In metals and ceramics, requirements for it being superplastic include a fine grain size (less than approximately 10 micrometers) and an operating temperature that is often from above a half absolute melting point.
Increment of strain rate in superplastic deformation is generally achieved by reduction of grain size in the ultrafine range from 100 to less than 500 ums.
At the beginning, the blank is brought into contact with the die cavity, hindering the forming process by the blank/die interface friction.
Similar to the cavity forming technology, at the process beginning, the firmly clamped blank is bulged by gas pressure.
Due to a better material use, which is caused by process conditions, blanks with a smaller initial thickness compared to cavity forming can be used.
Product also suffers from poor creep performance due to the small grain sizes and there can be cavitation porosity in some alloys.
For example, the diaphragm-forming method (DFM) can be used to reduce the tensile flow stress generated in a specific alloy matrix composite during deformation.
Superplastically formed (SPF) aluminium alloys have the ability to be stretched to several times their original size without failure when heated to between 470 and 520 °C.
These dilute alloys containing zirconium, later known by the trade name SUPRAL, were heavily cold worked to sheet and dynamically crystallized to a fine stable grain size, typically 4–5 μm, during the initial stages of hot deformation.
The breakthrough for superplastic Al-Cu alloys was made by Stowell, Watts and Grimes in 1969 when the first of several dilute aluminium alloys (Al-6% Cu-0.5%Zr) was rendered superplastic with the introduction of relatively high levels of zirconium in solution using specialized casting techniques and subsequent electrical treatment to create extremely fine ZrAl3 precipitates.
The composites are often fabricated by powder metallurgy to ensure fine grain sizes and the good dispersion of reinforcements.
Just like other superplastic materials, the strain rate sensitivity m is larger than 0.3, indicating good resistance against local necking phenomenon.
[15] The GBS mechanism model predicts a strain rate sensitivity of 0.3, which agrees with most of the superplastic aluminium alloy composites.
The partial melting could lead to the formation of filaments at the fracture surface, which can be observed under scanning electron microscope.
Ti-Al-Mn (OT4-1) alloy is currently being used for aero engine components as well as other aerospace applications by forming through a conventional route that is typically cost, labour and equipment intensive.
Once the set temperature was reached the top chamber was brought down further to effect the required blank holder pressure.
Simultaneously, the linear variable differential transformer (LVDT), fitted at the bottom of the die, was set for recording the sheet bulge.
Once the LVDT reached 45 mm (radius of bottom die), gas pressure was stopped and the furnace switched off.
[clarification needed] The grain size was determined using the linear intercept method in both the longitudinal and transverse directions of the rolled sheet.
It was seen that the rate of forming was rapid initially and decreased gradually for all the temperature and pressure ranges as reported in Table 2.
The strain rate sensitivity parameter (m) and observed maximum elongation until rupture (εr) could be determined and also obtained from the hot tensile test.
Metallographic examinations have shown that the average grain size of large-grained iron aluminides decreased during superplastic deformation.
But for ceramic materials, superplastic deformation has been restricted to low strain rates for most oxides, and nitrides with the presence of cavities leading to premature failure.
Here we show that a composite ceramic material consisting of tetragonal zirconium oxide, magnesium aluminates spinal and alpha-alumina phase exhibit superplasticity at strain rates up to 1.0 s−1.
Superplastic metals and ceramics have the ability to deform over 100% without fracturing, permitting net-shape forming at high temperatures.
The fine grain size of Y-TZP lends itself to be used in cutting tools where a very sharp edge can be achieved and maintained due to its high wear resistance.
Regardless of which, several studies have been performed on superplasticity in doped, fine-grain Al2O3.Demonstrated that the grain size of Al2O3 containing 500-ppm MgO can be further refined by adding various dopants, such as Cr2O3, Y2O3, and TiO2.