Liquid state property, structural evolution and mechanical behavior of TiFe alloy solidified under electrostatic levitation condition

Abstract

The thermophysical properties of hypereutectic Ti63.64Fe36.36 alloy at both normal and undercooled states, including density, volume expansion coefficient, ratio of specific heat to emissivity were measured by electrostatic levitation (ESL) method combined with a high-speed photography technique. The enthalpy, specific heat, solute diffusion coefficient and surface tension were simultaneously calculated as functions of temperature by molecular dynamics simulation (MD), from which the emissivity was also derived. The rapid solidification kinetics in the undercooling range from 50 K to a maximum value of 270 K (0.18TL) during ESL experiments was quantitatively studied. As undercooling increases, primary TiFe intermetallic compound evolves from coarse dendrites to refined equiaxed grains, whose volume fraction rises significantly. The growth velocity of primary TiFe phase increases according to a power relation with undercooling to a maximum of 170 mm/s, which agrees well with the calculated results from LKT/BCT model on the basis of above determined thermophysical properties. The inter-correlations among “undercooling-microstructure-hardness” were derived subsequently through experiments. The hardness of both primary TiFe intermetallic compound and Ti63.64Fe36.36 alloy increases almost linearly with the increase of undercooling, and the former one relates to its grain size by Hall-Petch function. Keywords: Rapid solidification, Titanium alloy, Thermophysical property, Microstructure, Mechanical property