Abstract
Microstructural conversion mechanisms under hot forging process (at temperatures ranging from 750 °C to 1050 °C and strain rates ranging from 10–3 s–1 to 1 s–1) of a Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy with a lamellar starting microstructure were experimentally identified in this work. After that, constitutive formulae for predicting the microstructural evolution were established followed by calculation using finite-element (FEM) analysis. In the α phase, a lamellae kinking is the dominant mode in the higher strain rate region and dynamic globularization frequently occurs at higher temperatures. On the other hand, continuous dynamic recrystallization is the dominant mode below the transition temperature, Tβ (880~890 °C) in the β phase. And, at conditions of lower strain rates and higher temperatures, dynamic recovery tends to be more active. For microstructural prediction, a set of constitutive equations modeling the microstructural evolution and forging properties are established by optimizing the experimental data followed by implementation in the DEFORM-3D software package. Herein, microstructural evolution on dynamic globularization process, dynamic recrystallization behavior are predicted according to both approaches of physical model and artificial neural network model followed by FEM simulation. In these calculated results, there is a satisfactory agreement between the experimental and simulated results, indicating that the established series of constitutive models can be used to reliably predict the properties of a Ti-17 alloy after forging.
Highlights
Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy, a near-β-type (α+β) alloy with high strength, superior fracture toughness, and excellent creep property, was first developed by GE Aviation,[1] which is being widely used to manufacture fan blades and compressor disks in aircraft engines
According to the results of microstructure, a steady state stress behavior observed in forging conditions at higher temperatures and lower strain rates is attributable to dominant microstructural conversion mode by either dynamic recovery (DRV) or CDRX of β phase
The microstructural evolution under hot forging of the Ti-17 alloy reveals that lamellae kinking is the dominant mode for the α phase at higher strain rates; dynamic globularization of the α phase frequently occurs at high temperatures
Summary
Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloy, a near-β-type (α+β) alloy with high strength, superior fracture toughness, and excellent creep property, was first developed by GE Aviation,[1] which is being widely used to manufacture fan blades and compressor disks in aircraft engines. [3] under hot working of Ti alloys, dynamic microstructural changes such as grain size evolution, change in α phase fraction and dynamic globularization (DG) of α phase occur These microstructural evolutions strongly affect the mechanical properties of Ti-products. The ANN model cannot identify the deformation and microstructural evolution mechanisms, whereas it has a relatively high precision for prediction owing to the advanced statistical approach. These constitutive formulae of physical model and ANN model were implemented in the finite-element method (FEM) software (DEFORM-3D, v.10.2) followed by simulation of microstructures and Vickers hardness
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