5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Peritectic transitions - characterized by the formation of a secondary phase from decomposition of the primary phase and the melt - are very common in the solidification of metallic alloys. During the peritectic reaction, all three phases are in direct contact, thus forming a trijunction. Already in 1979, Hillert [1] emphasized the important role of the junction force balance in the peritectic reaction and pointed out that opposing capillarity forces are required to meet the local equilibrium conditions at the different boundaries in the vicinity of the junction. However, so far, little attention has been paid to the actual impact of the individual liquid-solid and solid-solid phase boundary energies, which cannot be expected to be equal in real materials. In this work, the multi-phase-field method was applied to study the impact of unequal phase boundary energies by the example of a peritectic TiAl alloy with negligible solid-state diffusion. Simulations were performed under isothermal conditions and systematic variation of the involved interfacial energies. Reaction rates, evaluated after reaching steady-state conditions, are discussed and correlated to the thickness of the peritectic layer. A major result of the case study is that two different growth modes can be distinguished a) when the triple junction is leading and rate-controlling and b) when the peritectic growth front is leading and its tip is rate-controlling. Which of these two growth modes is selected can be described by a critical ratio of the interfacial energies. [1] Hillert M. Solidification and Casting of Metals. London: The Metals Society; 1979.