Abstract
The post-dynamic recrystallization behavior of ultrafine-grained (UFG: 0.44 μm) cp-Ti under annealing, room temperature (RT) monotonic and cyclic loading was investigated across a range of temperatures and deformation rates wherever appropriate. By characterizing the grain and boundary structures, it was confirmed that recrystallization and grain growth occurred due to annealing (≥ 600 °C) and R = − 1 fatigue at RT. There was a noticeable 30 deg aggregation in misorientation distribution, along with the increased grain size. However, the hypothetical correlation between 30 deg aggregation and Σ13a or the other characteristic coincidence site lattice boundaries was found to be weak. The fatigue-induced grain growth is particularly intriguing for two reasons. First, the large monotonic deformation with low strain rate cannot trigger grain growth. Second, fatigue sharpened the basal intensity around the ND and caused a weaker texture component close to TD (load axis along the LD, perpendicular to the TD–ND plane). By contrast, high-temperature annealing only strengthened the UFG processing induced basal pole but without affecting its location. Novel insights into this fatigue-induced texture evolution in UFG cp-Ti has been provided. The lattice rotation during fatigue can be attributed to the combined effect of activation of prismatic langle arangle slip parallel to LD, and basal langle arangle slip perpendicular to it. The theoretically calculated stress to activate dislocation slip by assuming a non-equilibrium grain boundary state lent support to the above assertion. Moreover, the TEM observation evidently showed the characteristics of dislocation cross-slip and multiple slip in the grain interior.Graphical
Highlights
THE generic term recrystallization describes the replacement of cold worked microstructure by forming new grains during annealing at temperatures of ‡ 0.5Tm
The post-dynamic recrystallization behavior of cp-Ti processed by multi-directional forging (MDF), was studied under the following three conditions: annealing, room temperature (RT) monotonic tensile loading, and R = À 1 high-cycle fatigue loading
The main conclusions are summarized as follows: 1) Recrystallization and uniform grain growth occurred at high-temperature (‡ 600 °C) annealing and R = À 1 fatigue
Summary
THE generic term recrystallization describes the replacement of cold worked microstructure by forming new grains during annealing at temperatures of ‡ 0.5Tm. Discontinuous dynamic recrystallization (dDRX) occurs during high-temperature straining. For both cases, recrystallized grains co-exist with the deformed ones, a discontinuous process. The recrystallization mechanism was studied for several decades and a thorough review of the literature was published in 1997.[1] Since electron backscattered diffraction (EBSD) technique has become widespread and it enables mapping crystallographic orientations in a large number of grains with much reduced time compared to transmission electron microscopy (TEM). The paper published in 2014[2] provided a comprehensive review on two types of dynamic recrystallization: dDRX and continuous dynamic recrystallization (cDRX). The evolving recrystallization terms can be attributed to the expansion of processing methods, in particular those arising from severe plastic deformation, SPD.[2]
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