Static Globularization Behavior and Artificial Neural Network Modeling during Post-Annealing of Wedge-Shaped Hot-Rolled Ti-55511 Alloy

Abstract

The globularization of the lamellar α phase by thermomechanical processing and subsequent annealing contributes to achieving the well-balanced strength and plasticity of titanium alloys. A high-throughput experimental method, wedge-shaped hot-rolling, was designed to obtain samples with gradient true strain distribution of 0~1.10. The samples with gradient strain distribution were annealed to obtain the gradient distribution of globularized α phase, which could rapidly assess the globularization fraction of α phase under different conditions. The static globularization behavior under various parameters was systematically studied. The applied prestrain provided the necessary driving force for static globularization during annealing. The substructure evolution and the boundary splitting occurred mainly at the early stage of annealing. The termination migration and the Ostwald ripening were dominant in the prolonged annealing. A backpropagation artificial neural network (BP-ANN) model for static globularization was developed, which coupled the factors of prestrain, annealing temperature, and annealing time. The average absolute relative errors (AARE) for the training and validation set are 3.17% and 3.22%, respectively. Further sensitivity analysis of the factors shows that the order of relative importance for static globularization is annealing temperature, prestrain and annealing time. The developed BP-ANN can precisely predict the static globularization kinetic curves without overfitting.

Fragmentation and Branch Elimination of Primary α′ Martensite in Additively Manufactured Ti-6Al-4V Alloy

“…Morphologically, the primary α phase resembles the lamellar microstructure of α phase in the conventionally processed Ti-64 alloy. Semiatin et al and others [21][22][23][24] have established that the lamellar microstructure of the α phase breaks up or globularises both dynamically during deformation and statically during post-deformation annealing in the two-phase field. The AM process has all components including force by the spreading blade [25] and heat dissipation to the previous layers during cooling that can induce the atmosphere for breaking or globularisation of the primary α phase.…”