The liquid properties of alloys including thermophysical properties and structure characteristics are crucial to the heat and mass transfer, crystal growth, and solidification mechanism. The metastable liquid state brings structural refinement, novel crystalline or amorphous phase, and solid solubility extension, etc., contributing to the improvement of applied performance [1]. In this presentation, we studied the metastable liquid properties and rapid solidification of Ti-Ni-Al, Ti-Ni-Cr-Al and Ti-Ni-Cr-Al-Zr alloys by means of levitation technologies and computational simulation.

The thermophysical properties of Ti-Ni-Al and Ti-Ni-Cr-Al alloys were firstly measured by electrostatic/electromagnetic levitation technologies. Based on this, we proposed a machine learning method to estimate accurately the liquid properties of the alloys within a wide temperature range through deep neutral network potential (DNNP) [2]. The density and surface tension increased linearly, and the viscosity and diffusion coefficient varied exponentially with the decrease of temperature. The Honeycutt-Andersen neighbour analysis and Voronoi polyhedron analysis suggested the increase of the population of high symmetry and high-coordinated clusters with the decreasing temperature. This clustering behavior was essential to the decrease of potential energy and the enhancement of local structure stability, consequently resulting in the variation of thermophysical parameters.

The undercooling dependence of the local structure influences the rapid solidification process. The growth velocity increased significantly with the increase of undercooling. The rapid dendrite growth and the multiple nucleation sites converted from high high-coordinated clusters are responsible for the refinement of primary dendrite. The electrostatic levitation plus quenching processing introduced multiple metastable nanostructures and novel biphase boundary into Ti-Ni-Al alloy, therefore improved the mechanical property of the alloy [3]. For the undercoolled Ti-Ni-Cr-Al and Ti-Ni-Cr-Al-Zr alloys, the solute trapping effect led to the precipitation of Ti2Ni phase from (Ti) phase matrix during rapid solidification.