Effects of hatch spacing on densification, microstructural and mechanical properties of β-solidifying γ-TiAl alloy fabricated by laser powder bed fusion

Abstract

beta-solidifying gamma-titanium aluminide (gamma-TiAl) alloys, which typically contain beta-phase stabilizers such as Nb and Cr, hold great promise for the aerospace industry and can potentially be processed through additive manufacturing to realize performance unachievable using conventional methods. However, the effects of laser powder bed fusion (L-PBF) parameters on the characteristics of the thus obtained samples remain underexplored. To address this gap, we herein examined the effects of hatch spacing on the densification, microstructural, and mechanical properties of L-PBF-fabricated Ti-44Al-6Nb-1.2Cr (at.%) alloy samples, revealing that the strong influence on thermal history induced the variation in densification and formation of two microstructure types. 0.01 mm hatch spacing resulted in repetitive slow cooling and sufficiently remelting, thus suppressing crack formation, promoting high densification, and inducing a complex phase transformation involving the formation of a basketweave-structured alpha 2 phase and the < 001 > alignment of the beta phase along the build direction. 0.06 mm hatch spacing resulted in rapid cooling and insufficient heat accumulation, favoring the massive phase transformation, a jagged morphology alpha 2 phase with a randomly distributed crystallographic texture. Hardness was mainly correlated with phase constitution and volume fraction, whereas compressive properties were jointly determined by additional effects of multiple factors such as grain size and crystallographic texture. This work provides the fundamental insights required to suppress defect formation in beta-solidifying gamma-TiAl alloys and tailor their microstructure for mechanical property enhancement.