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Highlights • Formed by HDR-LMD, IN625 seem have finer microstructure than that of IN718. • With approx. 2 kg/h deposition rate, IN625 is nearly whole density, IN718 porous. • There exists stronger convection in the melt pool of IN625 than in IN718. • The convection may cause faster heat transfer so that accelerates the solidification. • The convection may promote the escape of the gas that trapped in the process. Abstract Nickel-based super-alloys Inconel 718 (IN718) and Inconel 625 (IN625) have comparable chemical composition and similar physical constants such as density and melting range; however, in high-deposition-rate laser metal deposition (HDR-LMD), processes with IN625 are not transferable to that with IN718. In order to compare HDR-LMD process with IN718 and IN625, the current study has been conducted. Initially, parallel experiments have been performed, and the metallurgical analysis for macro- and microstructures have been carried out. Then, the strengthening effects of HDR-LMD for both alloys have been compared. Finally, in order to understand and explain the obtained results, both processes have been characterized by using a high-speed camera. According to the study, the following conclusions have been drawn: in comparison to IN718, there seems to have a stronger convection in the melt pool of IN625; this convection could be the reason for the faster solidification of IN625 since it may accelerate the dissipation of heat; As a further consequence of the stronger convection, the degassing during the solidification can be enhanced. [ABSTRACT FROM AUTHOR]

As precipitation hardening nickel-based super-alloy, the mechanical properties of Inconel 718 (IN718) formed by high deposition-rate LMD (HDR-LMD) are far lower than the relevant specifications, making it unable to be used in practical industry applications. With the purpose of improving its material performance, the current study has been carried out. The microstructure characteristics of the as-deposited IN718 have been analysed, and the mechanical properties of it have been tested. Based on which, reasons that result in its poor mechanical properties have been identified. Furthermore, aiming to solve these problems the methods in order to improve material performance have been studies. It is found: the poor mechanical properties of the as-deposited IN718 could be significantly improved by HIPing (Hot Isostatic Pressing) and proper heat treatments. In addition, the mechanical properties of the heat-treated material are superior to AMS specifications for IN718 fabricated by conventional manufacturing processes. It concluded: HIP can dramatically reduce the porosity of the as-deposited material; the columnar grains can be transformed to equiaxed grains by homogenization, eliminating material anisotropy; Laves phase could be dissolved by solution treatment, transforming to needle-like δ phase; strengthening phases will be precipitated by double aging, therefore strengthening/hardening the material. [ABSTRACT FROM AUTHOR]