Predicting rapid growth behavior in solidified eutectic ceramic composites using infrared thermal imaging and thermal field simulation during laser directed energy deposition

Abstract

Cylindrical Al2O3/GdAlO3 binary in situ oxide eutectic ceramic composite, with a glossy surface and high relative density, has been fabricated using the laser directed energy deposition method (LDED) with optimized process parameters. In a novel and innovative approach, infrared thermal imaging and the finite element method (FEM) have been combined for the first time to capture the temperature field distribution across different regions of the molten pool during the LDED processing of the binary oxide eutectic ceramic composite, thereby synergistically obtaining the solidification characteristics. With an increase in the scanning rate, the temperature gradient within the molten pool decreases from 3.38 × 105 K/m to 1.62 × 105 K/m, while it shows minimal variation with fluctuations of the laser power. Under the conditions of high temperature gradients and rapid non-equilibrium solidification characteristic of LDED, the Al2O3/GdAlO3 (GAP) binary eutectic ceramic composites, which exhibit typical high melting entropy and faceted/non-faceted growth modes, exhibit complex and variable microstructure morphology. A combination of regular/irregular models, including JH (Jackson-Hunt), MK (Magnin-Kurz), GK (Guzik-Kopyciński) and TMK (Trivedi-Magnin-Kurz), is employed to investigate and predict the growth and transformation of microstructures. The JH and TMK models fairly predict the rod-like regular eutectic microstructure inside the colony and lamellar regular eutectic within adjacent layers, respectively. The “Chinese-script” irregular microstructure at the interface between the colony and the layers is consistent with the MK and GK models. The as-deposited eutectic ceramic composite presents ultra-fine microstructures, clear and strongly bonded phase interfaces with low strain energy, contributing to its microstructure stability after high temperature heat treatment at 1773 K for 200 h, and achieving a minimum microstructure coarsening rate of 0.0005 μm/h.