Abstract
Fabricating an Inconel 718 superalloy using electromagnetic stirring assisted laser solid forming (EMS-LSF) is a novel method to modify its microstructure and mechanical properties by consuming the Nb element in the γ phase to alleviate interdendritic segregation. The precipitate of the δ phase at 950 °C after EMS-LSF can help to achieve the uniform diffusion of Nb, and can also improve its mechanical properties. The precipitation behavior of the δ phase in an EMS-LSF Inconel 718 superalloy with different heat treatment processes has been investigated. The results show that the morphology of the δ phase changes from rod-like to a long-needle shape and tends to grow from the inter dendrite to the core dendrite with electromagnetic field intensity increasing, which is accompanied by the “cutting” and “dissolution” of the Laves phase. Through precipitation kinetics analysis, the precipitation rate of the δ phase is seen to increase with the electromagnetic field intensity increasing. Under a combination of electromagnetic stirring and laser solid forming, the microhardness of the Inconel 718 samples increased slightly due to the fact that a higher content of Nb was distributed in the core dendrite resulting from the serious convection of liquid metal, which can strengthen the matrix.
Highlights
The Inconel 718 superalloy is a Ni-Fe-Cr based and precipitation-hardening superalloy
This result is due to the fact that the nucleation and growth of the δ phase need the Nb concentration to remain above 6% molar fraction [29], and the Laves phase can provide enough Nb to precipitate the δ phase
Electromagnetic stirring assisted laser solid forming in an Inconel 718 superalloy makes the distribution of the alloying elements more homogeneous
Summary
The Inconel 718 superalloy is a Ni-Fe-Cr based and precipitation-hardening superalloy. It is widely used in various kinds of disks, rotors, shafts, fasteners, and other components because of its excellent strength, good corrosion resistance, and favorable weldability [1]. It has been proven that LSFed Inconel 718 parts have superior performance, such as in their tensile properties, compared to forged components [2]. Studies on LSFed Inconel 718 have mainly focused on its forming process, microstructure, and mechanical properties [4,5,6,7,8,9,10,11]. It can be found that Nb is highly susceptible to segregation and leads to the precipitation of some brittle phases, such as the Laves phase in the LSFed
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