Superplastic deformation of engineering materials is often represented by high elongation values obtained in conventional tensile tests carried out in specific ranges of temperatures and strain rates. This behavior is characterized by high strain rate sensitivity (SRS) indices obtained by a variety of techniques. The SRS of a fine-grained Sn–1 wt% Bi alloy, processed by multi-directional forging (MDF) was studied by indentation testing at room temperature (T > 0.6Tm). The microstructural homogeneity increased with increasing the number of MDF passes, and the grain size decreased from 3.2 to 2 μm, as the number of passes increased from 1 to 8. The SRS indices of 0.08, 0.24, 0.31, and 0.49 were obtained for the 2, 4, 6 and 8 passes of MDF, respectively. The high SRS index of 0.49, calculated from different analysis methods of the indentation tests are in good agreement with each other and with those of the other testing methods and severe plastic deformation processes on the same alloy reported in the literature. These SRS indices together with the uniform fine-grained equiaxed microstructure with an average grain size of 2 μm, observed after 8 MDF passes, are indicative of a superplastic deformation behavior dominated by grain boundary sliding
