Grain refinement mechanism of SiC nanoparticles/Mg-9 wt. % Al composite investigated by sharp interface model at microscale and nanoscale

Abstract

The grain refinement mechanism of Mg-9 Al (wt. %) alloy with the addition of SiC nanoparticles (NPs) is studied by a new strategy, a combination of experimental characterizations and sharp-interface model (SIM) simulations. Experiments show that the NPs near grain boundaries form a multilayer coating. Mean grain size is refined with the increase of NPs volume fraction. When the addition level of NPs is raised to 1.0 vol. %, the grain size decreases from 144 µm to 52 µm. The SIM simulations support that the primary interaction between NPs and the moving solid-liquid interface is NPs being pushed to the vicinity of grain boundaries. An equivalent solute-diffusion coefficient for the liquid phase is numerically determined based on iterative SIM simulations. Three possible refinement mechanisms are numerically examined at the microscale and nanoscale. It is the first SIM nanoscale simulation of the Gibbs-Thompson pinning effect. The growth restriction through blocking solute diffusion is identified as the dominant mechanism in the present experiment. The modification of thermal condition and the Gibbs-Thompson pinning effect is less critical. The Gibbs-Thompson pinning is the most promising mechanism for producing nanocrystalline metals with a strict dependence on the uniform dispersion of NPs. This work provides deep insights for controlling grain refinement of Mg matrix composites and shows a new synthetic way, the experiment-sharp interface model, to obtain equivalent solute-diffusion coefficients.