MATEC Web Conf.
Volume 321, 2020The 14th World Conference on Titanium (Ti 2019)
|Number of page(s)||9|
|Published online||12 October 2020|
Phase transformation sequence of Ti-6Al-4V as a function of the cooling rate
1 Christian Doppler Laboratory for Design of High-Performance Alloys by Thermomechanical Processing, Graz, Austria
2 Institute of Materials Science, Joining and Forming at Graz University of Technology, Graz, Austria
3 voestalpine BÖHLER Aerospace GmbH & Co KG, Kapfenberg, Austria
The growth kinetics of allotriomorphic α along the prior β grain boundaries and of globular primary α in Ti-6Al-4V during continuous cooling is described. A physical model is developed based on classical nucleation and growth of platelets for the allotriomorphic α. The growth of the primary α is modelled based on the growth of spherical particle immerged on a supersaturated β-matrix. Continuous cooling tests at two different holding temperatures in the α+β field, 930°C and 960°C, and five different cooling rates, 10, 30, 40, 100 and 300°C/min, are conducted to validate the proposed models and elucidate the growth sequence of those α morphologies. Additionally, interrupted tests at different temperatures are conducted to determine the progress of growth of primary α and formation allotriomorphic α during cooling. The size of primary α increases while its size distribution broadens with a decrease in cooling rate. Area fractions of primary α decrease with increasing cooling rate and increasing holding temperature. Moreover, the lower the cooling rate, the thicker the plates of allotriomorphic α. At the beginning of the cooling, growth of primary α, as well as formation of allotriomorphic α plates is observed. The experimental and modelled results show good agreement.
Key words: Ti-6Al-4V / primary alpha phase / allotriomorphic alpha / materials modelling / continuous cooling
© The Authors, published by EDP Sciences, 2020
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