Microstructural transition in monotectic alloys: A phase-field study

摘要

In the present study, we employ a multiphase-field model based on the grand chemical potential formulation to simulate the microstructural transition in a binary FeSn monotectic alloy. In a directional solidification environment, we systematically investigate the formation of monotectic microstructures. At equilibrium monotectic composition, we observe that depending on the imposed temperature gradient and the solidification velocity, the liquid L_2 phase transforms into an array of droplets embedded in the solid phase matrix. Initiated at the solidification front, the minor liquid phase undergoes detachment and spherodization to form L_2 droplets as a result of post-solidification ripening behind the growth front. We show that the wavelength of the oscillating phase is critical to observe a lamellar to droplet transition. A microstructural selection map at various growth conditions is delineated to illustrate the different monotectic microstructures. The present phase-field simulations, while providing significant insights into the formation of microstructures closes the gap with the in-situ observations reported earlier. In addition, the influence of lamellar spacing is investigated in detail through the Jackson and Hunt analytical relationship for the present material system.