Microstructure and Texture Evolution during Superplastic Deformation of SP700 Titanium Alloy

The superplastic tensile test was carried out on SP700 (Ti-4.5Al-3V-2Mo-2Fe) titanium alloy sheet at 760 degrees C by the method of maximum m value, and the microstructure characteristics were investigated to understand the deformation mechanism. The results indicated that the examined alloy showed an extremely fine grain size of ~1.3 mu m and an excellent superplasticity with fracture elongation of up to 3000%. The grain size and the volume fraction of the beta phase increased as the strain increased, accompanied by the elements' diffusion. The beta-stabilizing elements (Mo, Fe, and V) were mainly dissolved within the beta phase and diffused from alpha to beta phase furthermore during deformation. The increase in strain leads to the accumulation of dislocations, which results in the increase in the proportion of low angle grain boundaries by 15%. As the deformation process, the crystal of alpha grains rotated, and the texture changed, accompanied by the accumulation of dislocations. The phase boundary (alpha/beta) sliding accommodated by dislocation slip was the predominant mechanism for SP700 alloy during superplastic deformation.

Automated summary

The SP700 titanium alloy exhibited excellent superplasticity with fine grain size and increased volume fraction of the beta phase as strain increased. The beta-stabilizing elements were mainly dissolved within the beta phase and diffused from alpha to beta phase during deformation. The increase in strain led to the accumulation of dislocations and an increase in the proportion of low angle grain boundaries.