Micro and Macro Analysis of Additively Manufactured Superalloys for Use in the Aerospace Gas Turbine Industry

Date of Award

6-2025

Degree Name

Doctor of Philosophy

Department

Mechanical and Aerospace Engineering

First Advisor

Daniel Kujawski, Ph.D.

Second Advisor

Jinseok Kim, Ph.D.

Third Advisor

Pnina Ari-Gur, D.Sc.

Fourth Advisor

Ralph Worthington, Ph.D.

Keywords

Additive manufacturing, Haynes 282, Inconel 718, laser powder bed fusion, material characterization

Abstract

Laser powder bed fusion (L-PBF) is an additive manufacturing (AM) technology that enables the production of complex geometries by selectively fusing layers of powdered metal. This process can offer significant advantages, including reduced material waste, enhanced design flexibility, and cost benefits, making it particularly suited for applications within the aerospace gas turbine industry. However, challenges such as anisotropic material properties, porosity, solidification cracking, surface roughness, and sensitivity to process parameters can impact the mechanical performance and reliability of L-PBF produced components. Understanding the relationships between processing conditions, microstructure, and mechanical properties is essential for successfully integrating L-PBF into the production of safety critical components in the aerospace gas turbine industry.

This body of work focuses on the characterization and development of two Nickel based superalloys: Inconel 718 and Haynes 282. Inconel 718, widely used in aerospace gas turbines in its conventional form, is known for its high strength and weldability but is thermally limited above 677°C. The comprehensive characterization of L-PBF Inconel 718 includes evaluations of microstructure, porosity, surface roughness, and mechanical properties, such as tensile strength, fatigue resistance, crack growth behavior, and stress rupture performance. Results reveal that tensile and fatigue properties of L-PBF Inconel 718 are comparable to wrought material and superior to cast material. However, stress rupture tests indicate notch sensitivity similar to cast forms. Fatigue testing highlights the critical influence of surface roughness, temperature, and specimen configuration on fatigue life, with hollow fatigue specimens providing a conservative approach for assessing as-printed surface conditions. Additionally, an energy density variation study identifies the stable process parameter window that produces acceptable L-PBF Inconel 718 material with consistent properties.

Haynes 282 offers superior thermal stability compared to Inconel 718, making it a potential alternative material choice for applications exceeding 677°C. However, limited data exists on its performance when produced by L-PBF processes. This study develops L-PBF process parameters for Haynes 282 using Inconel 718 process parameters as a baseline. Key process parameters, including laser power, scan speed, and hatch spacing, are varied to produce fully dense, crack free material. Tailored post processing profiles, including stress relief, hot isostatic pressing (HIP), solution annealing, and precipitation aging, are developed to control the microstructure, minimize grain growth, and achieve isotropic mechanical properties. Mechanical testing confirms that L-PBF Haynes 282 achieves tensile and fatigue properties comparable to its conventionally manufactured counterparts, with anisotropic behavior limited to under 10%, demonstrating its feasibility to be produced by L-PBF processes.

Collectively, this research provides significant insights into the complex relationships between L-PBF process parameters, material microstructure, and mechanical performance for both Inconel 718 and Haynes 282. By thoroughly analyzing these relationships, it establishes a framework for developing and optimizing L-PBF process parameters to meet the stringent requirements of the aerospace gas turbine industry. Furthermore, the findings offer a solid foundation for aerospace manufacturers to confidently integrate L-PBF produced materials into safety critical applications within the aerospace gas turbine industry.

Access Setting

Dissertation-Abstract Only

Restricted to Campus until

6-1-2035

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