Microstructure characterization of gradient composition between TC25G and TiAl alloys prepared by directed energy deposition technique

Abstract

Graded Materials are now used widely as structural components due to their specific properties. Researching on microstructure evolution of the transition region in graded materials is important to control the entire property of the graded materials. In this study, three alloys with the typical compositions were made by directed energy deposition (DED), which were correlated to the transition zone of the TC25G/TiAl graded material. Results indicate that the DEDed TiAl alloy consists of a duplex microstructure with γm and (α2 + γ) lamellar. For sample AD75 (mixed of 75 wt% TiAl and 25 wt% TC25G powder), the microstructure changes to B2 + α + γm + (α2 + γ). The continuing increase of TC25G alloy content causes the microstructure transfer to β/B2 + α + ω + (α + α2) and β + α + (α + α2) for sample AD50 (mixed of 50 wt% TiAl and 50 wt% TC25G powder) and AD25 (mixed of 25 wt% TiAl and 75 wt% TC25G powder) alloy consequently. Besides, the microstructure of TC25G alloy is β + α + α2. The highest hardness is found in AD75 alloy, followed by AD50, TC25G, AD25 and TiAl alloy, which is attributed to a large amount of B2 and α2 phase formation.