Abstract
This work uses flow stresses obtained experimentally at different strain rates and temperatures to validate flow modelling results. Flow curves of Ti6Al4V are measured via torsion experiments with a Gleeble® 3800 up to effective strains of 8. A physically based model that describes the evolutions of microstructure and the flow stress in the β-phase field was developed. A model of continuous dynamic recrystallization (CDRX) based on the work of Gourdet and Montheillet [1] for aluminium alloys is combined in this work with elements taken from Kocks and Mecking [2]. The model consists of a detailed description of the microstructure, based on different dislocation density populations and grain boundaries. All these internal variables evolve according to a production and a recovery term correlated mathematically with the temperature and the strain rate. The modelled output variables besides the flow stress are the total, the interior and the wall dislocation densities as well as the subgrain and grain sizes developed by continuous dynamic recrystallization. The model describes the softening occurring during large strain deformations, which is partly produced by the formation of new high angle grain boundaries (HAGB). The fraction of HAGB was used to determine the recrystallization grade, validated with microstructural characterization.
Highlights
To optimize and design hot deformation processes of the most frequently used titanium alloy Ti-6Al-4V (Ti64), the underlying metallurgical phenomena need to be described and correlated with the flow stresses evolution
Regarding moderate stresses a satisfying degree of predictability of the flow behaviour is reached with the existing methods. [5], [6] Contrary, for large strains only few attempts have been made to model the flow behaviour. [7], [8] This work presents the first physicallybased model based on one constitutive equation valid for all regions of strain to describe the flow behaviour and the microstructure evolution of Ti64 during hot torsion
Larger grains and a high grade of recrystallization were observed for slow strain rates, while the temperature difference of 40°C seems not to impact the recrystallization grade and grain size for a given strain rate
Summary
To optimize and design hot deformation processes of the most frequently used titanium alloy Ti-6Al-4V (Ti64), the underlying metallurgical phenomena need to be described and correlated with the flow stresses evolution. This can be achieved by physically-based flow models. During deformation at large strains, recrystallization processes occur in high stacking fault energy materials, namely continuous dynamic recrystallization (CDRX). [7], [8] This work presents the first physicallybased model based on one constitutive equation valid for all regions of strain to describe the flow behaviour and the microstructure evolution of Ti64 during hot torsion Regarding moderate stresses a satisfying degree of predictability of the flow behaviour is reached with the existing methods. [5], [6] Contrary, for large strains only few attempts have been made to model the flow behaviour. [7], [8] This work presents the first physicallybased model based on one constitutive equation valid for all regions of strain to describe the flow behaviour and the microstructure evolution of Ti64 during hot torsion
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