Laser Powder Bed Fusion in GE LEAP Fuel Nozzle

i Individual Coursework 2 Report on Laser Powder Bed Fusion in GE LEAP Fuel Nozzle By Mr. Hansraj Ashutosh Gaikwad (20795643) MSc. Additive Manufacturing and 3D Printing Date – 29th November 2025. Module Advanced Technology Review (MMME4052 UNUK) (AUT2 25-26) University of Nottingham Department of Mechanical, Materials & Manufacturing Engineering ii Table of Contents List of Figures ................................................................................................................................ iii List of Tables .................................................................................................................................. iv Laser Powder Bed Fusion and its Application in GE LEAP Fuel Nozzle ...................................... 1 Appendix A ..................................................................................................................................... 8 Appendix B ..................................................................................................................................... 8 Appendix C ..................................................................................................................................... 8 References ....................................................................................................................................... v iii List of Figures Figure 1: GE LEAP fuel nozzle [4]. ............................................................................................... 1 Figure 2: Schematic of a typical LPBF machine [9]. ...................................................................... 2 Figure 3: Schematic of direct energy deposition processes [10]. ................................................... 3 Figure 4: Evolutions of melt pool and vapor depression under stationary laser illumination [15]. ......................................................................................................................................................... 4 Figure 5: (a) plot of nominal absorptivity and energy gain versus input laser power. (b) and (c) show melt pool morphology for P80 and P200 cases, respectively [16]. ....................................... 4 Figure 6: Longitudinal view showing the free surface along with porosity distribution[16]. ........ 5 iv List of Tables Table 1: Functional Requirements and Material Properties ............................................................ 2 Table 2: Comparative Advantages of LPBF (L-PBF) over DED (L-DED) .................................... 3 Table 3: LPBF Process Defects and Their Effects .......................................................................... 5 Table 4: Post-Processing Techniques .............................................................................................. 6 1 Laser Powder Bed Fusion and its Application in GE LEAP Fuel Nozzle The GE LEAP fuel nozzle, shown in figure 1, is a flagship example of successful metal additive manufacturing (AM) implementation in the aerospace industry. GE Aviation announced in 2015 that the next LEAP engine would incorporate nearly 20 3D-printed fuel nozzles. The integration of AM allowed for substantial performance improvements and design simplification [1]. The resulting component is 25% lighter and stronger than the original nozzle. Crucially, it contributes to boosting the engine’s fuel efficiency by up to 15% compared to the CFM56 engines [2]. Furthermore, LPBF enabled a major reduction in complexity: the fuel nozzles were reported to be five times more durable than the previous model and reduced the component count from 25 separate parts down to a single piece or assembly of five parts [3]. GE leads the industry in AM volume and machine capacity, having printed over 100,000 parts by 2020 [1]. Figure 1: GE LEAP fuel nozzle [4]. Components destined for the hot sections of aeroengines, such as the LEAP fuel nozzle, require materials with superior performance under extreme conditions [5]. The nickel-based superalloy Inconel 718 (IN718) is the most common alloy utilized in the aerospace industry for these hightemperature applications due to its mechanical strength at elevated temperatures [2] shown in Table 1. The microstructure of IN718 consists of the γ (gamma) matrix phase. Its mechanical properties rely heavily on precipitation hardening, primarily through the metastable γ'' (gamma double prime) phase, which provides excellent high-temperature strength [6]. 2 Table 1: Functional Requirements and Material Properties Property Metric Operating Temperature Capability Close to melting point, 1336 °C [7] Matrix Phase Stability High phase stability (Face - Centred - Cubic nickel matrix) [1] Primary Strengthening Phases γ' and γ ' ' nano - precipitates (precipitation strengthened) [ 6 ] Application Environment High thermal stability and thermal oxidation resistance [ 8 ] Manufacturing the intricate geometry of a modern fuel nozzle using traditional methods presents significant challenges. Conventional techniques like casting or forging struggles with complex geometries, consuming more time or being incapable of achieving structures like conformal cooling channels [5]. Advanced alloys like nickel and titanium superalloys are difficult and expensive to machine due to their natural tendency for work hardening [1]. The conventional manufacturing route for superalloy components, such as turbine blades, involves numerous complex steps—including investment casting and precision machining—which result in substantial material waste. Historically, only about 10% of the initial superalloy feedstock might end up in the final component [5]. The inherent difficulty in machining and the high material waste associated with conventional processes make the manufacturing cost prohibitive and the complexity difficult to manage. Laser Powder Bed Fusion (LPBF), shown in figure 2, also known as selective laser melting (SLM), is a prominent metal additive manufacturing (AM) technology [2]. Figure 2: Schematic of a typical LPBF machine [9]. 3 Figure 3: Schematic of direct energy deposition processes [10]. LPBF enables complex geometries to be produced directly from a digital model [12]. This process is favoured over other AM processes like Directed Energy Deposition (DED), shown in figure 3, due to its high resolution and ability to produce high-quality metal parts shown in Table 2. LPBF drastically reduces material wastage, sometimes yielding waste levels as low as ~ 5% [1]. Table 2: Comparative Advantages of LPBF (L-PBF) over DED (L-DED) Feature L-PBF (Typical) L-DED (Typical) Process Control/Accuracy High resolution and accuracy [1] Generally, very low resolution, rough surface [1] Component Count Reduction High (e.g., 25 parts to 5 for nozzle) [1] Moderate (often used for repair work) [1] Cooling Rate High (~ 10 4 – 10 6 K/s) [13] Lower (~ 100x different than LPBF) [6] As-Built Hardness (IN718) Higher (323.4 to 342.6 HV) [6] Lower (246.4 to276.4 HV) [6] Laser Parameters Smaller beam (~ 1x magnitude difference); P ≤ 500W [13] Larger beam; P ≥ 2x L-PBF power [6] LPBF involves scanning a laser beam (with spot sizes around 20 – 100 µm) across fine powder layers (thickness ≤ 100 µm) at high speeds (~ 0.05 – 4 m/s). Physics of this process dictates extreme thermal conditions [14]. When the temperature of the material exceeds its boiling point, the process shifts from conduction mode (shallow, rounded melt pool shown in figure 4) to keyhole mode. Keyhole mode is characterized by the laser fluence causing vaporization and generating sufficient recoil pressure to depress the liquid metal surface, forming a deep, high aspect ratio vapor cavity [14]. 4 Figure 4: Evolutions of melt pool and vapor depression under stationary laser illumination [15]. The formation of the keyhole is crucial because it dramatically enhances laser energy absorption. This occurs due to multiple reflections of the laser beam inside the depression, allowing the laser energy to transfer more efficiently to the powder layer [16]. For example, simulations show that as laser power increases beyond the 110W threshold, shown in figure 5, the nominal absorptivity sharply increases due to keyhole formation and ray-entrapment. The resulting melt pool is subject to steep thermal gradients and high cooling rates (~ 104 – 106 K/s) [14]. Figure 5: (a) plot of nominal absorptivity and energy gain versus input laser power. (b) and (c) show melt pool morphology for P80 and P200 cases, respectively [16]. Despite its advantages, LPBF introduces intrinsic defects, given in Table 3, that can badly deteriorate the part's performance, particularly relevant for safety-critical components like fuel nozzles [12]. 5 Figure 6: Longitudinal view showing the free surface along with porosity distribution[16]. A detailed parametric study on Ti6Al4V confirmed that increasing laser power above a certain threshold (e.g., from 110W to 140W) rapidly transitions the process to the unstable keyhole regime, sharply increasing the melt pool volume (from 1.8x to 5x relative to 50W) and initiating porosity formation, shown in figure 6. The frequency and size of keyhole pores are highly dependent on the process parameters[16]. Table 3: LPBF Process Defects and Their Effects Defect Type Cause Characteristics Numerical Data (Ti6Al4V) Lack-ofFusion Porosity Insufficient heat input; incomplete melting [5] Irregular shape, large size; reduced density [8] N/A (occurs at low power) Keyhole Porosity Excessive heat input; unstable keyhole collapse [14] Spherical, small size; detriment to fatigue life [13] 35 – 95 µm diameter [16]