Evolution of microstructure and mechanical properties in the molten pool of γ-TiAl alloy synthesized in situ by dual-wire-fed electron beam directed energy deposition

Abstract

Dual-wire-fed electron beam directed energy deposition (EB-DED) is a highly efficient technique for additive manufacturing (AM) of TiAl alloys, but research into the evolution of microstructure and mechanical properties within the melt pool is limited. Experimental and numerical simulations are used together to study the evolution along the vertical direction within the TiAl alloy melt pool. The chemical composition, microstructure and microhardness in the top region (TR), middle region (MR) and bottom region (BR) within the melt pool were characterized and comparatively analysed. The results showed that the Al content decreased from 52 at. % to 49 at. % from the top to the bottom, the grain size increased and then decreased, and the grain aspect ratio increased from 1 to over 3. The decreasing size factor and increasing shape factor result in variations in grain size and shape. The improvement in microhardness from 226 HV0.5 to 280 HV0.5 was quantitatively analysed as being mainly due to the reduction in Al content. The results of this study are of paramount importance in facilitating the use of the dual-wire-fed EB-DED technique for the production of high performance TiAl alloy components.

Keywords

• TiAl alloy
• Directed energy deposition
• Microstructure
• Numerical simulation
• Mechanical property