Ostwald Ripening and Phase Transformations of Tic: Enhancing Effects on Grain Refinement in Al-Ti-C Refiners

Abstract

The refining performance of Al-Ti-C refiners is predominantly governed by the particle size and number density of TiC, which are influenced by the phase transformations and Ostwald ripening of TiC. However, the intricate mechanisms underlying these evolutionary processes maintain open. This study aims to elucidate the effects of phase transformations and Ostwald ripening on grain refinement through advanced microstructural characterization and Density Functional Theory analysis. Our findings demonstrate that, except for original homogeneous nucleation from dissolved raw materials, the transformation of Al4C3 into TiC occurs via two distinct mechanisms: solid-phase transformation and homogeneous nucleation. The solid-phase transformation involves the substitution of Ti atoms for Al atoms within the Al4C3 lattice. In contrast, homogeneous nucleation takes place as the concentrations of Ti atoms, released from the dissolution of TiAl3, and C atoms, released from the dissolution of Al4C3, achieve the critical solubility product necessary for TiC nucleation. The enhancement of grain refinement can be attributed to the synergistic effects of phase transformations and Ostwald ripening. Specifically, Ostwald ripening facilitates the growth of TiC particles towards optimal sizes for effective grain refinement, while phase transformations contribute to an increased number density of TiC particles, further enhancing grain refinement. This study elucidates the pivotal roles of phase transformations and Ostwald ripening of TiC in optimizing the performance of Al-Ti-C refiners, providing valuable insights for the development of more effective refiners.

Keywords: Grain refinement, Phase transformation, Ostwald ripening, Aluminum alloys