Low-temperature superplasticity in nanostructured nickel and metal alloys

Superplasticity-the ability of a material to sustain large plastic deformation-has been demonstrated in a number of metallic, intermetallic and ceramic systems, Conditions considered necessary for superplasticity(1) are a stable fine-grained microstructure and a temperature higher than 0.5 T(m) (where T(m) is the melting point of the matrix). Superplastic behaviour is of industrial interest, as it forms the basis of a fabrication method that can be used to produce components having complex shapes from materials that are hard to machine, such as metal matrix composites and intermetallics, Use of superplastic forming may become even more widespread if lower deformation temperatures can be attained. Here we present observations of low-temperature superplasticity in nanocrystalline nickel, a nanocrystalline aluminium alloy (1420-Al), and nanocrystalline nickel aluminide (Ni(3)Al). The nanocrystalline nickel was found to be superplastic at a temperature 470 degrees C below that previously attained(2): this corresponds to 0.36T(m), the lowest normalized superplastic temperature reported for any crystalline material. The nanocrystalline Ni(3)Al was found to be superplastic at a temperature 450 degrees C below the superplastic temperature in the microcrystalline regime(3).