Phase-field investigation of rod eutectic morphologies under geometrical confinement

Three-dimensional phase-field simulations are employed to investigate rod-type eutectic growth morphologies in small samples. The lateral confinement fixes the spacing between rods, λ, as well as the angle α between the two independent basis vectors of the rod array. Several distinct morphologies are observed when the geometry of the sample is varied, including rods of circular cross-section, rods of distorted (elliptical) cross section, broken lamellae of "peanut-shaped" cross-section, and lamellar structures. For a fixed value of α >10 degrees, the usual arrays of circular rods are stable in a broad range of spacings, with a transition to the broken lamellar structure occurring at large spacings (above 1.5 times the minimum undercooling spacing λ_min), and the advent of rod eliminations at low spacings. Furthermore, a transition from rod to lamellar structures is observed for α values smaller than 10 degrees for the phase fraction of 10.5 % used in the present study.