Low-temperature superplasticity in nanostructured nickel and metal alloys

Superplasticity-the ability of a material to sustain large plastic deformat ion-has been demonstrated in a number of metallic, intermetallic and cerami c systems, Conditions considered necessary for superplasticity(1) are a sta ble fine-grained microstructure and a temperature higher than 0.5 T-m (wher e T-m is the melting point of the matrix). Superplastic behaviour is of ind ustrial interest, as it forms the basis of a fabrication method that can be used to produce components having complex shapes from materials that are h ard to machine, such as metal matrix composites and intermetallics, Use of superplastic forming may become even more widespread if lower deformation t emperatures can be attained. Here we present observations of low-temperatur e superplasticity in nanocrystalline nickel, a nanocrystalline aluminium al loy (1420-Al), and nanocrystalline nickel aluminide (Ni3Al). The nanocrysta lline nickel was found to be superplastic at a temperature 470 degrees C be low that previously attained(2): this corresponds to 0.36T(m), the lowest n ormalized superplastic temperature reported for any crystalline material. T he nanocrystalline Ni3Al was found to be superplastic at a temperature 450 degrees C below the superplastic temperature in the microcrystalline regime (3).