Nanostructured intermetallic samples (Ni-8.5Al-7.8Cr-0.6Zr-0.02wt%B), with an average grain size of 50nm, were produced by means of severe plastic deformation. Diffraction and high-resolution electron microscopy were used to examine specimens which had been annealed at 650C or 750C, as well as material taken from the gauge section of a specimen which had been superplastically deformed to about 300% elongation at 650C. Examination of samples annealed at 650C showed that the grain boundaries remained in high-energy non-equilibrium configurations. The samples annealed at 750C contained grain boundaries with a high density of dislocations. The superplastically deformed samples exhibited no visible distortion of the crystal lattice near to the grain boundary. Observations of twin boundaries in deformed specimen revealed no trapped lattice dislocations; thus suggesting that grain boundary sliding was accommodated by diffusion.

TEM/HREM Observations of Nanostructured Superplastic Ni3Al. Valiev, R.Z., Song, C., McFadden, S.X., Mukherjee, A.K., Mishra, R.S.: Philosophical Magazine A, 2001, 81[1], 25-36