Deciphering the solidification mechanisms of multi-scaled TiCN particles tailoring the abnormal grain coarsening during fast cooling

Abstract

Well-tuned microstructure often grants a fairly predictable performance. Wherein, fast cooling is a universally acknowledged tuning approach to deliver a fine and equiaxed solidification microstructure. Conversely, abnormal coarsening and equiaxed-to-columnar transition were triggered with increased cooling rates in this work. To tailor this counterintuitive response, we proposed a facile, economical yet sustainable method, i.e., inoculant-aided solidification by self-incorporation of nucleating particles assisted ultrasonic vibration. Micro-scaled, nano-scaled, and hybrid-scaled TiCN particles (TiCN_p), i.e., TiCN_mp, TiCN_np, and TiCN_bp, were leveraged to tailor the solidification behaviors under various solidification conditions. Compared with the TiCN_mp, both TiCN_np and TiCN_bp not only manifested far superior resistance to the grain coarsening but conferred more isotropic and equiaxed solidification, which therefore enabled a substantial transition from coarse and directionally oriented columnar to wholly fine and randomly oriented equiaxed grains. Specially, solidification thermodynamics and kinetics behaviors, over a wide range of local temperature fields and inoculating conditions, were thoroughly investigated to uncover the nature of abnormal coarsening at high cooling rates. This work offers promise to deliver a controllable solidification microstructure and hence broaden the application prospects of Al alloys.