Prediction of grain boundary evolution in an titanium alloy substrate using a novel phase field model coupled with a semi-analytical thermal solution

Thomas Flint, Qingrong Xiong, Yongle Sun, Anastasia Vasileiou, Michael Smith, John Francis

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review

Abstract

Grain boundary migration in the presence of concentrated sources of heat is a complex process that has a considerable impact on resultant material properties. The large thermal gradients generated during welding cause grain boundaries to migrate in order to minimise the total free energy of the system. It is important to consider both the thermal gradient driving force, as well as the local curvature driving force of the grain boundaries which both play a significant role in the evolution of the micro-structure in the weld region. In this work a multi-phase field model is used to predict the grain boundary evolution in a Ti6Al4V substrate subjected to a heat source representative of the electron beam (EB) welding process. While numerical simulations incorporating the mass transfer and complex flow dynamics associated with high energy density welding processes are favourable in that they consider the physical processes occurring in the weld explicitly, they are also extremely computationally expensive. As such, the thermal field, on which the phase field model is dependent, is computed using a semi-analytical solution technique. In this approach the complicated flow
dynamics of the EB process are represented as a four-quadrant volumetric heat source, the recently published DEC heat source which has shown to be a good thermal representation of EB processes. Using a Green’s function approach, the time and position dependent thermal field is obtained for this DEC heat source in motion is found, free from numerical errors. Predicted grain size distributions are presented for various energy inputs and conclusions drawn based on the applied driving forces, captured in the phase field model.
Original languageEnglish
Title of host publicationMathematical modelling of weld phenomena 12
PublisherVerlag der Technischen Universität Graz
Number of pages14
ISBN (Print) 978-3-85125-615-4
DOIs
Publication statusPublished - Sept 2018

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