Research On The Brazability Of Selective Laser Melted Inconel 718 Superalloy

Inconel 718 superalloy is a kind of Ni-Cr alloy with high strength,high stress fracture,corrosion resistance and limited ductility as well as good castability,hot workability and weldability.It is widely used in high-tech fields such as gas turbine disk,rocket engine,spacecraft,nuclear reactor,pump and tooling.Inconel 718 superalloy fabricated by selective laser melting?SLM?has good forming quality.It could be seen from optical structure that no obvious defect formed and microstructure presented plenty of columnar dendrites.SEM results showed that a large amount of brittle Laves phases precipitated in crystalline grains,which was due to high laser heat source and fast cooling rate.The average microhardness was315.8HV.Firstly,amorphous BNi2 and AgCu were used to braze SLMed Inconel 718 superalloy to research its brazability.The results showed that both these two filler metals could braze SLMed Inconel 718 superalloy sucefully.When BNi2 was used under 1060?brazing temperature and 30min holding time,brazing seam completed isothermally solidified process and formed isothermally solidified zone,which composed of?-Ni solid solution and had good properties.Shear strength of BNi2 brazed joint was up to 802MPa,and fracture presented mixed ductile-brittle fracture.When AgCu was used to braze SLMed Inconel 718 superalloy,the solid solution reaction between Ni and Cu was the key to ensure successful brazing.Shear strength of AgCu brazed joint was up to 502MPa,and fracture presented ductile fracture.Then this paper studied the brazing between SLMed Inconel 718 superalloy and Si₃N₄ceramics.Both AgCuTi,particle reinforced AgCuTi+W and composited Cu foam filler metal could braze SLMed Inconel 718 superalloy and Si₃N₄ sucessfully.When AgCuTi was used to braze SLMed Inconel 718 superalloy and Si₃N₄,brazed joint composed of Si₃N₄/TiN+Ti₅Si₃diffusion layer/Ag?s,s?+Cu?s,s?/Ti₂Cu/Fe₂Ti/Ag?s,s?/SLMed Inconel 718.Shear test results showed that fracture originated in near brazing seam zone of Si₃N₄,then extended to brazing seam.Shear strength was up to 339MPa.W particle could decrease the mismatch of coefficient of thermal expansion?CTE?between brazing filler metal and base materials,and provided more nucleation positions for Ag-Cu eutectic,which could enhance shear strength to 352MPa.Cu foam could increase Cu content substantially and formed more Ti₂Cu,which had lower CTE.The formation of Ti₂Cu could avoid forming excessive Fe₂Ti brittle compounds to enhance shear strength to 395MPa.Solid solution+double ageing heat treatment was conducted on SLMed Inconel 718 superalloy.Brittle Laves phases dissolved and precipated plenty of main strengthing phase????Ni₃Nb?.Microhardness of SLMed Inconel 718 superalloy after heat treatment raised to 462HV,and the performance improved greatly.BNi2 was used to braze SLMed Inconel 718 superalloy after heat treatment.Because plenty of????Ni₃Nb?precipated in grains,precipates CrB₂ and Ni₃Si distributed in fine granular in diffusion-affected zone?DAZ?,not continuously.So shear strength of the brazed joint raised to 884MPa.When AgCuTi was used to braze SLMed Inconel 718 superalloy after heat treatment and Si₃N₄,the distance of stress concentration zone of Si₃N₄ side and stress concentration zone of SLMed Inconel 718 superalloy after heat treatment side increased,which lead fracture could not extended to brazing seam.So shear strength of the brazed raised to 384MPa.