Hierarchical Microstructure Modulation of Ti–Co–Al Alloy by Rapid Die Casting Under Simulated Space Condition

The space simulation manufacture of Ti_61.1Co_28.1Al_10.8 alloy from three original states including superheated liquid, undercooled liquid, and semi-solid alloy was accomplished by electromagnetic levitation coupled with die casting (EML-DC) technique. The microscopic segregation was eliminated through remarkable solute trapping under the effects of electromagnetic stirring, microgravity processing and rapid die casting. The hierarchical microstructures with both phase constitution difference and grain size gradient were formed due to the high pressure and rapid quenching by die casting. Furthermore, the efficient modulation of this hierarchical microstructure was achieved by adjusting the original states of alloy before die casting. The hierarchical microstructures displayed gradient micromechanical properties. The ultrafine ternary eutectics at the surface region exhibited high elastic recovery, whereas the microstructures composed of primary TiCo dendrites and TiCo + (βTi) eutectics at the middle region showed lower elasticity but higher hardness.