Superplasticity of Ti2448 Alloy with Nanostructured Grains

Abstract

Ti-24Nb-4Zr-8Sn, abbreviated as Ti2448 from its chemical composition in weight percent, is a multifunctional beta type titanium alloy with body centered cubic (bcc) crystal structure, and its highly localized plastic deformation behavior contributes significantly to grain refinement during conventional cold processing. In the paper, the nanostructured (NS) alloy with grain size less than 50 nm produced by cold rolling has been used to investigate its superplastic deformation behavior by uniaxial tensile tests at initial strain rates of 1.5x10(-2), 1.5x10(-3) and 1.6x10(-4) s(-1) and temperatures of 600, 650 and 700 degrees C. The results show that, in comparison with the coarse-grained alloy with size of 50 mu m, the NS alloy has better superplasticity with elongation up to,similar to 275% and ultimate strength of 50-100 MPa. Strain rate sensitivity (m) of the NS alloy is 0.21, 0.30 and 0.29 for 600, 650 and 700 degrees C, respectively. These results demonstrate that grain refinement is a valid way to enhance the superplasticity of Ti2448 alloy.