Microstructure and mechanical properties of Ti-52 at% Al alloy synthesized in-situ via dual-wires electron beam freeform fabrication

Abstract

The in-situ synthesized Ti-52 at% Al alloy was additively manufactured for the first time by electron beam freeform fabrication (EBF3) with pure Ti and Al wires. The chemical compositions, microstructure, crystal orientation and mechanical properties of the Ti-52 at% Al walls were investigated. The results show that the actual Al content was lower than that the designed content due to the evaporation of elements. The microstructure of the as-fabricated walls was composed of γ dendrite which was oriented along the <111> direction. The solidification path was L→ γ phase due to the high cooling rate during EBF3 process. The primary dendrite spacing and the width of the secondary dendrite increased with the building height indicating that the cooling rate decreased. The dendrite disappeared in layer bands due to the repeating thermal cycles. Based on the orientation analysis, the epitaxial growth of the γ phase was found between the dendritic and interdendritice regions and between layers. The microhardness of the dendrite was higher than that of the interdendritic regions. The compressive tests at ambient temperature indicated anisotropic mechanical properties due to the dendrite structure. The compressive strength along the building direction was higher than that along the deposited direction.