Superplasticity of multiphase fine-grained Nb–16Si–2Fe refractory alloy

Nb–16Si–2Fe refractory alloy consisting of an Nb solid solution and intermetallic phases Nb3Si, Nb5Si3 and Nb4Fe3Si5 was synthesized by hot press sintering to yield a fine microstructure with all four phases being in the size range of micrometer. This alloy exhibits excellent superplasticity with the presence of a significant amount of liquid phase Nb4Fe3Si5 at a temperature which is 91 °C higher than the solidus temperature of 1359 °C. A tensile elongation of 512% is measured at 1450 °C. Microstructures of the deformed specimen and the DSC (differential scanning calorimetry) analysis indicate that the dominant mechanism for superplastic deformation is viscous flow of the liquid phase Nb4Fe3Si5. This superplastic phenomenon is apparently different from that observed in conventional magnesium-based and aluminum-based composites in which the superplastic deformation is grain boundary sliding but the sliding strain was accommodated by liquid phases.