Enhanced mechanical properties of TiAl alloy through Nb alloying by Triple-wire arc directed energy deposition

Abstract

The introduction of alloying elements is an effective strategy to enhance the performance of titanium aluminides (TiAl). Wire arc directed energy deposition (DED) has cost advantages and high deposition rate, making it an emerging technology for fabricating TiAl alloys with promising application prospects. However, the efficient and flexible introduction of alloy elements for wire arc DED fabricated TiAl alloys is a key concern. In the present research, niobium (Nb) was selected as the alloying element, pure Ti, Al, and Nb wires were used as raw materials to introduce Nb into TiAl alloy via in-situ alloying using Triple-wire arc DED. This approach successfully fabricated the high Nb TiAl alloy Ti-45Al-8Nb and the feasibility of this method was confirmed. By comparing the phase composition, microstructure, and mechanical properties of Nb-containing Ti45Al8Nb and Nb-free Ti45Al fabricated by wire arc DED, the influence of Nb on the microstructure and strengthening mechanisms of TiAl alloys was revealed. The results indicate that Nb alloying significantly reduces internal defects, promotes the formation of the B2 phase, increases the content of γ phase and lamellar spacing, and refines the lamellar colonies. The solid solution strengthening, grain refinement strengthening, and dislocation strengthening effects induced by Nb alloying substantially enhanced the tensile strength and elongation of the TiAl alloy. The process for fabricating ternary TiAl alloys via wire arc DED proposed in this study utilizes three pure metal wires as raw materials without relying on the expensive and difficult-to-obtain pre-alloyed materials required in traditional processes. This approach demonstrates the capability of wire arc DED in fabricating multi-component TiAl alloys with controllable compositions.