Abstract
The microstructure and mechanical properties of IN718 alloy fabricated by laser metal deposition were investigated. The continuous dendritic Laves generated by Nb/Mo microsegregation is dissolved by homogenization, the strengthening phase γ" with dimension about 30 nm precipitates during full heat treatment. The ambient temperature tensile strength of laser metal deposited (LMDed) IN718 alloy is enhanced by heat treatment, and the elevated temperature mechanical properties vary with heat treatment temperature and forming direction. Laves dissolution and complete/partial recrystallization depend on heat treatment, stress release and Nb/Mo concentration gradient. The anisotropy of elevated temperature mechanical properties of LMDed IN718 alloy is caused by the combined effect of directional grains size, higher relative content of texture, superior intergranular strength and residual Laves particles. The fracture mechanism of LMDed IN718 alloy varies with heat treatment temperature. The LMDed IN718 alloy with full heat treatment exhibits superior elevated temperature mechanical properties at 650 °C along building direction. The elevated temperature tensile fracture surfaces consist of cleavage plane and/or dimples, the microvoid coalescence (MVC) occurs in the alloy with full heat treatment, the intergranular (IG) fracture and cleavage plane or quasicleavage (QC) exist in the alloys with 980STA and double ageing.
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