Inconel 718 structure in EBM 3D printing: the influence of process parameters on contour characteristics

(HY-industry technical centre)

Shanghai HY Industry Co., Ltd recently demonstrated with the Polymer Laboratory of East China University of Science and Technology “the effect of process parameters on the profile characteristics of Inconel 718 structure by electron beam melting”, further expanding the scope of metal additive manufacturing.

Extensive classification of additive manufacturing processes in metals

Nickel alloy Inconel 718 was used to create samples for analysis because the researchers examined the effect of process parameters on the profile characteristics of the Inconel 718 (IN718) structure manufactured by EBM. Compared with other Ni-based alloys, Inconel 718 has higher Fe, Mo, and Nb contents, while Ti and Al have lower weight percentages, resulting in better strength, corrosion resistance, good weldability and crack resistance.

Parts of EBM machine

Picture of Dr. Li Bo, East China Institute of Technology

The EBM process contains various construction parameters, which can be optimized for the following functions:

  • Beam

  • Speed

  • Focus shift

  • Scanning order

  •  Body temperature

Changes can better control parameters such as molten pool size, molten powder depth, etc.

 


The effect of low focus (left) and high focus (right) on the molten pool

 

Starting from the following characteristics, powder is critical to the quality of the parts:

  • Size distribution

  • chemical composition

  • Morphology

  • fluidity

  • Density

The researchers say: “These characteristics lead to a combination of theoretical and empirical methods.” It is important that the powder has good flowability because it directly affects the density of the part. A larger powder size density (PSD) will result in poorer fluidity, while a smaller PSD density will result in a poorer bulk density. “

Arcam A2X EBM machine internal view (left) external view (right)
Image source Shanghai HY Industry Co., Ltd

The research samples were 3D printed at University West on the Arcam A2X EBM machine. Three construction parameters were changed during the project, including voltage, focus offset, and print speed.

Inconel 718 Element W nominal composition (Persent by weight)

A total of 34 samples were created. Two samples were made with standard parameters and 5mm thickness. Others use 16 different construction parameters for 3D printing, ranging in thickness from 3mm to 5mm. Cut the sample in the build direction and cut at an offset of 1-2 mm at the middle width of the stretch rod.

The researchers explained: “A moderate cutting rate is used, and sufficient cooling fluid is provided to ensure that the sample does not overheat and maintain a straight cut.”

Hardness test according to ISO 6507 test standard

 

After hot mounting and grinding any sharp edges, the samples are polished, then hardness tested, and then microstructured.

Average hardness measurement of various samples under HV1 (1Kg load) test conditions

“For some samples, a large amount of lack of fusion and the presence of surface defects may seriously affect the hardness value.” Placing the hardness indentation close to the hole may result in inaccurate readings. Although the average hardness is determined by a series of indentations, it can still prove that it is only close to the best reading, but not accurate. This article cannot determine the possible role of “γ” in the microstructure through experiments. This is due to the limitations of scanning electron microscopy.

Finally, the nature and formation of the grain size are compared for various process parameters. The grain structure map of each sample obtained from the optical microscope may vary due to factors such as the quality of the surface finish, etching parameters (such as voltage and duration), and optical microscope parameters. The magnification and quality of the image may affect the comparison and research of the grain structure during the project. Although measures have been taken to avoid all sources of errors, they cannot be eliminated completely.
Today, researchers are involved in various projects involving the electron beam melting process (EBM), which are used with materials such as tungsten, in applications such as orthopedics and related to biocompatibility.

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