Dynamic recrystallization kinetics of a powder metallurgy Ti–22Al–25Nb alloy during hot compression

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2014-06, Vol.607, p.630-639
• Main Authors: Jia, Jianbo, Zhang, Kaifeng, Lu, Zhen
• Format: Article
• Language: English
• Subjects: Applied sciences; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; Deformation; Dynamic recrystallization; Elasticity. Plasticity; Evolution; Exact sciences and technology; Flow behavior; Kinetics model; Materials science; Materials synthesis; materials processing; Mathematical models; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Physics; Powder metallurgy. Composite materials; Production techniques; Strain; Strain hardening rate; Strain rate; Technology; Titanium base alloys; Ti–22Al–25Nb alloy; Treatment of materials and its effects on microstructure and properties
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2014.04.062

The flow behavior of a P/M Ti–22Al–25Nb alloy was evaluated by applying a series of compression tests to a height reduction of 50% performed within the temperature range of 950–1070°C using strain rate range of 0.001–1s−1. The dynamic recrystallization (DRX) behavior at elevated temperature was evaluated by the modified Avrami type equation based on stress–strain data. By means of conventional hyperbolic sine function, the activation energies for DRX were estimated to be 1053.06kJ/mol in the (α2+β/B2+O) phase region and 734.77kJ/mol in the (α2+B2) phase region, respectively. The critical strain (εc) for the onset of DRX, the strain for peak stress (εp) and the strain for maximum softening rate (ε⁎) under different deformation conditions were identified according to the strain hardening rate curves. The DRX kinetics model was proposed to characterize the evolution of DRX volume fraction, which revealed that the DRX exhibited the ‘slow-rapid-slow’ evolution with the increasing strain. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Moreover, the microstructure examination results indicated that the theoretical prediction results were shown to be in good agreement with the statistical results. Finally, the continuous dynamic recrystallization (CDRX) was identified to be the DRX mechanism by referring to a transmission electron microscope (TEM) observation.