Comprehensive study on hot deformation behaviour and mechanism of Ti-900 alloy: Insights from experimental study, neural network modeling and finite element simulation

Thermomechanical processing plays a key role in shaping and refining the microstructure of structural components. This study examines the high-temperature deformation behaviour of equiaxed Ti-900, an alpha + (3 titanium alloy, through hot compression tests conducted at temperatures ranging from 850 degrees C to 1050 degrees C, strain rates from 0.001 s-1 to 10 s-1, and two different strain levels. An artificial neural network (ANN) model, optimized using a backpropagation algorithm, predicts flow stress with high accuracy. Processing maps are developed to assess deformation efficiency at different reduction ratios. As strain increases, the stable deformation efficiency region becomes more confined. Flow stress increases with a higher reduction ratio, while high strain rates cause instability from flow localization and adiabatic shear, leading to crack formation. Q-Form simulations validate the deformation behaviour across different processing regions, aiding in the defect-free manufacturing of gas turbine compressor stator blades. A significant variation in effective stress is observed in samples deformed within the unstable regions identified from the processing map, whereas effective stress remains more uniformly distributed in stable regions. The deformation mechanism of the alloy is developed, highlighting the influence of temperature and strain rate on flow softening mechanisms such as dynamic recovery (DRV) and dynamic recrystallization (DRX). At a constant deformation temperature, lower strain rates promote a higher degree of DRX compared to higher strain rates. Deformation just below the (3 transus temperature favours continuous dynamic recrystallization (CDRX), while deformation above the (3 transus temperature facilitates DRX within the (3 phase.