An investigation of defects in the nickel-based superalloy IN738LC fabricated by laser powder bed fusion


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Guo, Chuan (2021). An investigation of defects in the nickel-based superalloy IN738LC fabricated by laser powder bed fusion. University of Birmingham. Ph.D.

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Nickel-based superalloy Inconel 738 LC (IN738LC) can be used for the components in aero-engine due to its excellent high-temperature mechanical properties and oxidation/corrosion resistance. However, this alloy is difficult to be processed due to a high level of defects by laser powder bed fusion (LPBF) technology. Thus, this thesis presents the studies on the formation mechanisms and exposes some potential solutions for the mitigation of these defects during LPBF.

A statistical single variable method of 3 parameters (hatch spacing, scan speed and laser power) in LPBF is applied to understand how processing parameters influence defect formation. It is found that pores can be eliminated using the parameter optimisation method but cracks cannot.

Single-track experiments are performed to study the fluid dynamics and solidification processes during LPBF to explore the pore formation mechanism including lack of fusion and keyholing.

The microstructural characterisation of the as-printed (APed) samples indicates that Zr segregates at the grain boundaries is the main cause of the cracks. And the cracks tend to occur at the grain boundaries with higher misorientation angles.

Different amounts of nanoparticles Y\(_2\)O\(_3\) are added into IN738LC powders by powder mixture, and Y\(_2\)O\(_3\)/IN738LC composite parts are fabricated using LPBF. The addition of 0.05 wt% Y\(_2\)O\(_3\) can effectively mitigate the cracks under the current experimental condition, however, further increases of the Y\(_2\)O\(_3\) nanoparticles to 0.2 wt% and 0.6 wt% aggravate the cracking phenomenon. In addition, both high-temperature strength and oxidation resistance are improved by adding 0.05 wt% Y\(_2\)O\(_3\) nanoparticles compared to the alloy without Y\(_2\)O\(_3\).

Pulsed-wave laser beam also reduces the cracks. Microstructural analysis reveals that the refinement of grains by the application of pulsed-wave mode is the main contributor in reducing the cracks, which results from a higher cooling rate under the pulsed-wave mode.

Type of Work: Thesis (Doctorates > Ph.D.)
Award Type: Doctorates > Ph.D.
Licence: All rights reserved
College/Faculty: Colleges (2008 onwards) > College of Engineering & Physical Sciences
School or Department: School of Metallurgy and Materials
Funders: Other
Other Funders: Southern University of Science and Technology
Subjects: Q Science > QC Physics
T Technology > TS Manufactures


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