Microstructual evolution in Ti-185 alloy prepared using electrostatic levitation and conventional casting techniques

Abstract

Ti and its alloys have been widely applied in various fields of national economy due to their excellent combinations of specific mechanical properties and outstanding corrosion behavior. Among Ti alloys, Ti–1Al–8V–5Fe (Ti-185) alloy is a metastable and low-cost β-Ti alloy, and owns extremely outstanding mechanical performance. In the paper, to overcome the issue of β flecks associated with Fe segregation in conventional ingot metallurgy process, Ti-185 alloy was prepared by electrostatic levitation (ESL) technique at various supercoolings, and its solidification behavior and dendrite growth were systematically analyzed. Moreover, the thermophysical parameters of liquid Ti-185 alloy were tested, and the microstructure, hardness and compressive property were compared to that of cast ingot. Results shown that the maximum supercooling of 311 K in the liquid Ti-185 alloy can be achieved, and a noticeable recalescence phenomenon appears during ESL process. The density and the ratio of specific heat to emissivity of liquid Ti-185 alloy increases linearly with temperature decreasing. Once the crystal nucleus is formed, the nonfacted interface will advance promptly. Moreover, the dendritic growth velocity (v) exhibits an exponential relationship with the supercooling (ΔT), and can be depicted as the equation of v = 1.59·ΔT1.65 mm s−1. Additionally, at a supercooling of 229 K or above, single crystal can be formed using ESL technique. Furthermore, the microhardness, elastic modulus and compressive strength of as-levitated Ti-185 alloy are hardly affected by the supercooling, but the plasticity of as-levitated sample is obviously higher than that of as-cast one.

Keywords

• Ti-185 alloy
• Electrostatic levitation (ESL)
• Casting
• Supercooling
• Microstructure