Fine Grain Formation in as Cold Worked SP700 Titanium Alloy and Its Effect on Mechanical and Superplastic Properties

The aim of this research is to study the effect of fine grain structure on the mechanical and superplastic properties of cold worked SP700 alloy. Thickness reductions of 20%, 40%, and 60%. were applied during cold rolling. Then the specimens were annealed at 700°C, 750°C, and 800°C for 40 minutes. The tensile test was applied at 25, 700oC, 750°C, and 800°C with strain rates of 0.01s^-1 , 0.005s^-1 and 0.001s^-1. The SEM and OM were used to analyze the specimens microstructures. The alloy cold rolled to 40% reduction and annealed at 700°C exhibited a maximum elongation of 1380% at a stress level of 30 MPa and a strain rate of 0.005 s^-1 at 700°C. Microstructural evlauation showed that during the superplastic test, dynamic recrystallization took place. The strain rate sensitivity varied in the range of 0.32 to 0.46. Fundamental equations were also used to determine the mechanism of superplasticity. The activation energy is obtained as 385 kJ.mol^-1. Results validated that the Rachinger sliding is the main superplastic mechanism in the SP700 alloy.