Kinetics of orthorhombic martensite decomposition in TC21 alloy under isothermal conditions

• Published in: Journal of materials science 2012, Vol.47 (1), p.521-529
• Main Authors: Tang, Bin, Kou, Hong-Chao, Wang, Yi-Hong, Zhu, Zhi-Shou, Zhang, Feng-Shou, Li, Jin-Shan
• Format: Article
• Language: English
• Subjects: Alloys; Analysis; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Decomposition; Dilatometry; Kinetics; Martensite; Materials Science; Mathematical analysis; Phase transitions; Polymer Sciences; Solid Mechanics; Specialty metals industry; Titanium base alloys
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-011-5829-5

The kinetics of martensite decomposition in TC21 alloy was investigated at isothermal conditions in the temperature range 500–850 °C. The dilatometry technique was utilized to trace the transformation process for different aging temperatures. Within the framework of the Avrami theory, the analysis of the experimental data was made by means of the Johnson–Mehl–Avrami (JMA) equation. A very good correspondence between the calculated and the experimental results was found. The JMA kinetic parameters obtained from different aging temperatures implied different mechanisms of the transformation. The α″ phase transforms to α + α″ (rich) at 500 °C and the transformation is incomplete. Further increase of the temperature to 800 and 850 °C results in directly transformation α″ →α + β. The mechanism of the transformation alters during the course of the transformation for 550, 600, 650, 700, and 750 °C. Moreover, The TTT diagram was constructed for the martensite decomposition in TC21 alloy based on the dilatometry analysis and JMA theory, respectively. Good agreement between experimental and calculated TTT diagram is observed.