Microstructure and stress-rupture property of DD32 nickel-based single crystal superalloy fabricated by additive manufacturing

Abstract

Additive manufacturing (AM) technology is currently undergoing rapid development in the aerospace field. However, due to the intense cracking susceptibility, additive manufacturing of nickel-based single-crystal (SX) superalloys still presents major challenges. In this paper, the crack-free SX superalloy is fabricated directly using pulsed laser. The microstructure and stress rupture property of the additively manufactured SX superalloy after heat treatment are carefully investigated and compared with conventional cast alloy. The results show that the stress rupture life of the AM sample (66.4 h) is longer than that of the cast sample (59.1 h). This is related to the difference of microstructure between AM and cast samples. AM samples have a finer dendritic structure and lower inter-dendritic segregation, which is conducive to solution strengthening and avoids the formation of TCP phase. Besides, the carbides in the AM sample is finer and evenly distributed, which is conducive to precipitation strengthening; The fine carbides are enveloped within layers of γ′ in the AM samples, which avoids the formation of cracks caused by separation of carbides and the matrix. All of those are beneficial to improve stress rupture properties.