EFFECTS OF REFINED MICROSTRUCTURES ON DUCTILITY AND TOUGHNESS AT ROOM-TEMPERATURE IN NICKEL-RICH NIAL

Melt-spun Ni-34.6 at%Al ribbons with a minimum average grain size of 2.2 mum were prepared and the microstructures at room temperature were investigated. Refining the sizes of grains and other substructures resulted in interfaces of different types with very high density and uniform distribution. The reaction between the interfaces and propagating microcracks led to plastic deformation ahead of the crack tips and in larger regions with very fine grains, about 0.2 mum. Deflection, twisting and branching of the microcracks also resulted. The results indicate that the ductility and toughness of the nickel-rich NiAl all were considerably improved, which is consistent with previous test results. A simplified model based on the experimental results was used to analyse the mechanism of toughening NiAl. The important role of the interfaces in improving ductility and toughness of NiAl at room temperature is discussed.