Correspondence between microstructural evolution mechanisms and hot processing parameters for Ti-13Nb-13Zr biomedical alloy in comprehensive processing maps

As for the hot forming process design of Ti-13Nb-13Zr biomedical titanium alloy, it is a significant issue to achieve optimized processing parameters corresponding to reasonable microstructures. In this work, a series of isothermal compression tests were implemented to acquire the basic stress-strain data at the deformation temperature range of 923-1123 K (across b-transus) and the strain rate range of 0.01-10 s(-1). Based on these stress-strain data, a comprehensive evaluation of the hot workability in this alloy was performed according to the constructed activation energy maps, continuous three-dimensional (3D) maps and improved processing maps (including three indicators, i.e. instability parameter, power dissipation and activation energy). The safe domains with expected deformation stability and unsafe regions with unexpected deformation instabilities were clarified clearly, and the relative microstructural evolution mechanisms in different parameter regions were identified. The optimized parameter domains are as follows: as epsilon = 0.3, domain: 1015-1120 K & 0.01-0.32 s(-1); as epsilon = 0.5, domain: 1023-1103 K & 0.018-0.32 s(-1); as epsilon = 0.7, domain: 1025-1108 K & 0.032-0.32 s(-1); as epsilon = 0.9, domain: 1002-1045 K & 0.022-0.32 s(-1), and 1045-1123 K & 0.07-0.32 s(-1). Microstructure observations validated the comprehensive evaluation of hot workability, and illustrated the main stable mechanisms such as globularization, dynamic recovery (DRV) and dynamic recrystallization (DRX), and the main unstable mechanisms such as cracks and voids. (C) 2016 Elsevier B.V. All rights reserved.