Determination of Critical Conditions for Dynamic Recrystallization of Commercially Pure Titanium

Abstract

Abstract Microstructural evolution and mechanical properties are controlled by dynamic recrystallization (DRX) during industrial processing. To identify the critical condition for initiation of DRX, hot isothermal compression tests of commercially pure (CP)-70 titanium were conducted in a temperature range of 750°C–1,100°C and strain rate range of 0.001–10 s−1 to a true strain of 0.69. The critical condition for initiation of DRX can be identified from the inflection point on the strain-hardening rate (θ=∂σ/∂ε) versus flow stress (σ) curve. A third-order polynomial equation was fitted to the experimental θ−σ data to find out the inflection point. The results show that the critical stress (σc) for the initiation of DRX can be expressed as σc=−B/3A, where A and B are the coefficients of the third-order polynomial equation. It was observed that critical stress value depends on the deformation condition. The stress-strain curve was then normalized with respect to the peak stress (U=σ/σp vs.W=ε/εp), leading to a normalized value of critical stress, (Uc)=σc/σp=−B′/3A′, where A′ and B′ are the coefficients of the normalized third-order equation. The value of Uc(≈0.95) is a constant and independent of deformation conditions. These parameters were then used to calculate the DRX fraction, and the relationship between DRX fraction and processing variables was established.