Nickel-based Superalloy Inconel Research Articles

Crack inhibition of non-weldable Inconel 738 alloy in ultrasound-assisted laser directed energy deposition

High crack susceptibility restricts reliable laser directed energy deposition (L-DED) and repair of γ′ precipitation-strengthened Nickel-based superalloy Inconel 738. This study investigates the effects of ultrasonic assistance synergized with reduced heat input on microstructures and mechanical properties of the L-DED Inconel 738 alloy. The mechanisms of inhibiting crack initiation and propagation of are studied. Results demonstrate that grain refinement and suppression of epitaxial growth of L-DED Inconel 738 alloy are achieved by ultrasonic assistance. The microstructures evolve from coarse columnar grains (∼82.6 μm) to a bimodal structure of shorter columnar and finer equiaxed grains (∼40 μm). The morphologies of MC carbides transform from a continuous distribution of larger sizes to a discrete distribution of finer sizes. Cracks are highly susceptible to propagate along the long, straight grain boundaries of the coarse columnar grains in deposit without ultrasonic assistance, while tortuous grain boundaries induced by ultrasonic assistance enhance crack resistance and inhibit crack propagation. As a result, crack-free L-DED Inconel 738 alloys with excellent ultimate tensile strength of 1478–1490 MPa and elongation of 15.3–17.8 % are achieved via ultrasonic assistance and are significantly higher than cast Inconel 738 (945 MPa, 7.5 %), indicating the feasibility of utilizing ultrasonic assistance to inhibit cracking in L-DED Inconel 738 alloy.

Quantitative characterization and mapping relationship between microstructure, composition, orientation, and mechanical properties of nickel-based superalloy Inconel 718

Abstract This study explores the relationship between the microstructure, composition, orientation, and mechanical properties of the nickel-based superalloy Inconel 718. Employing scanning electron microscopy (SEM), electron microprobe (EMP), nano-indentation, and other techniques, the study observes the structure, confirms the composition, determines orientation, and tests mechanical properties in specific micro-zones. Findings reveal a uniform grain distribution in Inconel 718, with a minor δ-phase presence at grain boundaries. There is a notable enrichment of Nb at the grain boundaries, whereas Fe and Cr levels are lower at these boundaries compared to the grain interiors. The indentation hardness and modulus at the grain boundaries are markedly higher than those within the grains. Moreover, grains with different orientations exhibit diverse microscale mechanical properties, such as hardness and elastic modulus. This research establishes a quantitative mapping relationship between the microstructure, composition, orientation, and mechanical properties of Inconel 718, providing a foundation for future multiscale (micro to macro) mechanical property investigations.

Fabrication and tribological properties of WC-reinforced Inconel X-750 alloy at elevated temperature

The nickel-based superalloy Inconel X-750, valued for its exceptional mechanical properties, is used in gas-lubricated foil bearings. However, prolonged exposure to high temperatures can lead to wear failure, affecting their service life. Here, we propose a novel method named ultrasonic strengthening grinding (USG) that applies a WC coating on Inconel X-750. Friction tests reveal that at 600 °C, the friction coefficient and wear rate of the USG-treated samples were reduced by 30.2 % and 79.7 %, respectively. Detailed experiments and analysis demonstrate that the surface grain refinement and the WC-rich coating cooperate to improve the high-temperature tribological properties. These findings offer new insights into the design of wear-resistant coatings for enhancing the high-temperature tribological performance of Inconel X-750 Alloy.

Study on the effect of multi-walled carbon nanotube (MWCNT) addition on the microstructure, mechanical and cutting performance of silicon nitride ceramic tools

Silicon nitride (Si3N4) ceramics incorporated with 0–1.5 wt% multi-walled carbon nanotubes (MWCNTs) were synthesised by the spark plasma sintering technology. The effects of the low-content MWCNT addition on the microstructure, density, mechanical properties and cutting performance against nickel-based superalloys (Inconel 718) of the Si3N4/MWCNTs ceramic tools were investigated by the X-ray diffraction, field emission scanning electron microscope, Vickers hardness tester, universal tester, ball-on-disk reciprocating tester and cutting experiment. The results showed that the incorporation of MWCNTs enhanced the conversion rate of Si3N4 structure from the polar α form to the polar β form and reduced the friction coefficient of the composite. However, due to the agglomeration of MWCNTs, the hardness and fracture toughness of the Si3N4/MWCNTs ceramics were observed to decrease by 5.03 % and 13.97 %, respectively, compared to pure Si3N4 ceramics. A higher addition rate of the MWCNT would further accelerate tool wear and significantly diminish tool life. The predominant wear mechanism of the Si3N4/MWCNTs ceramic tools when milling Inconel 718 was groove-shape wear and adhesive wear.

Thermal Analysis of Micro-Channel Internal Cooling in Cutting Tools: A Machine Learning Approach

The use of coolants for cutting process in metal cutting operations is customary. Turning causes high cutting heat in nickel base super alloy Inconel 718. Nonetheless, it should be acknowledged that although flooding techniques are commonly used in the machining of super alloys, these flood cooling methods have extremely poor efficiencies. Another alternative to increase the cooling capabilities of fluids would be an internal-cooling approach that would enable to lower machining temperatures significantly. The heat dissipation ability in the tool is also greatly influenced by the micro-channel diameter of tool which further causes a significant effect on the coolant outlet velocity. A design of an internal-cooling single point cutting tool with micro channel structures for enhanced coolant heat transfer capability and reduced machining temperature is used for turning Inconel 718 under dry, flooded cooling and internal cooling to study the effects of cooling conditions on cutting force, cutting temperature and surface quality. A regression model is built using the Random Forest (RF) and Support Vector Regression (SVR) methods in machine learning framework. These models were then used to forecast input parameters, such as channel diameter and inlet pressure, which made it easier to obtain output data, such as pressure and maximum velocities at different notches. Eighty percent of the data in the dataset is used to train the model and with the remaining twenty percent set aside for evaluating the model's functionality. When comparing internal-cooling technology to traditional flood cooling, there are clear benefits including increased heat transfer efficiency, which leads to lower cutting temperatures, less cutting force, and better surface quality. More specifically, in the internal-cooling configuration, a direct relationship is shown between rising coolant inlet pressure and falling cutting force and temperature over time. Further highlighting the advantages of this cooling strategy is the relationship between increased intake pressure and decreased surface roughness.

Grain size sensitive modelling of the nonlinear behaviour and fatigue damage of Inconel 718 superalloy

Fatigue tests conducted on various types of materials often exhibit significant scatter, particularly in High Cycle Fatigue tests, attributed to imperfections located at the scale of the microstructure. In metallic materials, one contributor to this dispersion, but not the only one, is the variation in grain size, which cannot be uniform in a structure that has undergone a complex thermal history during its manufacturing process. This paper introduces a new model for predicting the evolution of the grain size in the nickel-based superalloy Inconel® 718 based on the applied thermal load and explores its impact on cyclic elasto-viscoplastic behaviour and fatigue life predictions. The proposed approach is applied to a complete numerical life analysis of an aircraft turbine disk.

Modeling of laser-assisted micro-milling Inconel718

Nickel-based superalloy Inconel718 is a typical difficult-to-machine material with the characteristic of high strength and hardness. Demands for micro parts of nickel-based superalloy Inconel718 are growing in aerospace, biomedical and other fields. Laser-assisted micro-milling (LAMM) can realize precision machining of the workpiece because of its lower cutting force. However, the machining mechanism and the change law of cutting force during LAMM of nickel-based superalloy Inconel718 are still unclear. There is a crucial need for modeling of LAMM Inconel718. This paper explores LAMM of nickel-based superalloy Inconel718 and realizes the simulation of LAMM process. A three-dimensional transient heat transfer finite element (FE) model is established to predict the temperature distribution of a Gaussian heat source in LAMM. Multiple sets of simulations of laser pre-heating with various laser power are conducted to analyze the temperature fields of workpiece and determine the appropriate laser parameters. A novel 3D model of the full machining process of LAMM Inconel 718 is constructed by ABAQUS with multi-subroutine, a fully coupled thermal-mechanical process is achieved. A modified Johnson-Cook constitutive model is used to reflect the size effect and flow stress of LAMM Inconel 718. Finally, the validity of the models is verified by experiments. Based on the verified model, the appropriate laser pre-heating parameters are obtained, and the prediction of cutting forces of LAMM Inconel718 is achieved.

Boiling of Coolant Near the Cutting Edge in High Speed Machining of Difficult-to-Cut Materials

This study investigates film boiling of coolant as a cooling inhibitor in a narrow wedge-shaped space between the tool flank face and the machined surface of a workpiece, observed during high-speed turning of stainless steel SUS304 and nickel-based superalloy Inconel 718. The boiling, likely triggered by high surface temperatures at both the face and surface close to the cutting edge, impedes coolant access to the tool tip area and efficient cooling. Therefore, the impact of coolant pressure on the boiling zone size was initially explored across pressures ranging from 0.1 to 20 MPa. A burn mark band due to coolant boiling, distinctly visible on the flank face of an insert with a yellow hard coating, expanded over cutting time. The film boiling area width, or the distance from the flank wear area to the band, decreased with increasing coolant pressure, reflecting the enhanced cooling ability and tool life with high-pressure coolant. Applying Boyle–Charles’ law to film boiling indicated that vapor pressure was directly related to coolant velocity rather than pressure. In contrast, the boiling area width increased with increasing cutting speed.

Hot Corrosion Behavior of Plasma-Sprayed Gd2Zr2O7/YSZ Functionally Graded Thermal Barrier Coatings

The development of advanced thermal barrier coating (TBC) materials with better hot corrosion resistance, phase stability, and residual stresses is an emerging research area in the aerospace industry. In the present study, four kinds of TBCs, namely, single-layer yttria-stabilized zirconia (YSZ), single-layer gadolinium zirconate (GZ), bilayer gadolinium zirconate/yttria-stabilized zirconia (YSZ/GZ), and a multilayer functionally graded coating (FGC) of YSZ and GZ, were deposited on NiCrAlY bond-coated nickel-based superalloy (Inconel 718) substrates using the atmospheric plasma spray technique. The hot corrosion behavior of the coatings was tested by applying a mixture of Na2SO4 and V2O5 onto the surface of TBC, followed by isothermal heat treatment at 1273 K for 50 h. The characterization of the corroded samples was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) to identify physical and chemical changes in the coatings. GIXRD was used to analyze the residual stresses of the coatings. Residual stress in the FGC coating was found to be −15.2 ± 10.6 MPa. The wear resistance of TBCs is studied using a linear reciprocating tribometer, and the results indicate that gadolinium zirconate-based TBCs showed better performance when deposited in bilayer and multilayered functionally graded TBC systems. The wear rate of as-coated FGC coatings was determined to be 2.90 × 10−4 mm3/Nm, which is lower than the conventional YSZ coating.

Research on microplastic deformation of Inconel718 under the conditions of high temperature and high strain rate

The compression experiments of the nickel-based superalloy Inconel718 were carried out with the help of split Hopkinson pressure bar device, and the microstructure evolution law in the compression deformation of the alloy was studied by means of optical microscopy, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dislocation theory, a three-dimensional discrete dislocation dynamics model is established. By simulating the dynamic evolution of the discrete dislocation, the interaction of the dislocation itself and the formation of the dislocation microstructure were captured, and further explore the microplastic deformation process of Inconel718. The results show that deformation conditions significantly affect the rheological behavior and dynamic recrystallization behaviour. The cross slip of dislocations is closely related to temperature and strain rate, which in turn affect the dislocation configuration. The deformation mechanism of Inconel718 under the conditions of high temperature and high strain rate is jointly dominated by dislocation slip and twin deformation. As the temperature increases, the average Schmidt factor increases, and more dislocation slip systems are activated. As the strain rate increases, the number of deformation twins increases, while the thickness of deformation twins decreases.

Fatigue Analysis of the Nickel-Based Superalloy Inconel 617 by Fatigue Experiments and EBSD Data-Based Finite Element Simulations in Correlation with E·m Theories

Nickel-based superalloys exhibit pronounced elastic anisotropy and, hence, the local grain orientation strongly affects the stress and strain distribution in the material under mechanical loadings. Therefore, the crack initiation and failure behaviour of components made from nickel-based superalloys are complex and hardly predictable. A better fundamental understanding of the phenomena that occur in nickel-based superalloys under a quasistatic and cyclic load is therefore desired. Previously, a continuum mechanics-based model has been successfully developed, considering the grain structure, the elastic anisotropy, and the Schmid factor, based on data from electron backscatter diffraction (EBSD). The E·m model was confirmed by the finite element method (FEM) simulations and experimental observations regarding the resulting average stresses and strains in the individual grains as well as the formation of slip bands under a quasistatic load with few restrictions. The behaviour under cyclic loadings has been investigated in this work to correlate the mechanical behaviour, simulated by the previously developed FE models, with the local stiffness and Schmid factors considering fatigue failure. For this purpose, the fatigue behaviour of Inconel 617 samples was characterised up to the high-cycle fatigue (HCF) regime, accompanied by EBSD measurements for stress amplitudes that resulted in strains close to the elastic–plastic regime. The EBSD data were used to create digital twins of the samples to simulate the mechanical reaction to a displacement similar to the associated strain of the fatigue tests. An analysis of the fractured samples by scanning electron microscopy was performed to retrace the location of the crack initiation supported by the EBSD measurements before and after fatigue testing. Two samples were investigated in detail that showed different fracture types. Sample 1 showed transcrystalline failure in a grain that showed a high Young’s modulus, Schmid factor, and resolved shear stress that indicates a failure due to the properties of the grain itself. In contrast, an intercrystalline failure was observed for sample 2 that showed large differences in the orientation and, hence, largely different mechanical properties in the area of failure as well. The observed failure types, the resulting stresses and strains calculated by the FE model, and the consideration of the E·m model showed an agreement of all the methods. Therefore, the findings of this work complement previous investigations of the mechanical behaviour of coarse-grained anisotropic nickel-based superalloys with a focus on the orientations of the grains towards the loading direction.

Process qualification, additive manufacturing, and postprocessing of a hydrogen peroxide/kerosene 6 kN aerospike breadboard engine

This contribution addresses the complete process chain of an annular aerospike breadboard engine fabricated by laser powder bed fusion using the nickel-based superalloy Inconel® 718. In order to qualify the material and process for this high-temperature application, an extensive material characterization campaign including density and roughness measurements, as well as tensile tests at room temperature, 700, and 900 °C, was conducted. In addition, various geometric features such as triangles, ellipses, and circular shapes were generated to determine the maximum unsupported overhang angle and geometrical accuracy. The results were taken into account in the design maturation of the manifold and the cooling channels of the aerospike breadboard engine. Postprocessing included heat treatment to increase mechanical properties, milling, turning, and eroding of interfaces to fulfill the geometrical tolerances, thermal barrier coating of thermally stressed surfaces for better protection of thermal loads, and laser welding of spike and shroud for the final assembly as well as quality assurance. This contribution goes beyond small density cubes and tensile samples and offers details on the iterations necessary for the successful printing of large complex shaped functional parts. The scientific question is how to verify the additive manufacturing process through tensile testing, simulation, and design iterations for complex geometries and reduce the number of failed prints.

Parametric optimization to establish eco-friendly nanofluid minimum quantity lubrication (NMQL) practice for turning superalloy Inconel 718

Purpose The purpose of this paper, an experimental study, is to investigate the optimal machining parameters for turning of nickel-based superalloy Inconel 718 under eco-friendly nanofluid minimum quantity lubrication (NMQL) environment to minimize cutting tool flank wear (Vb) and machined surface roughness (Ra). Design/methodology/approach The central composite rotatable design approach under response surface methodology (RSM) is adopted to prepare a design of experiments plan for conducting turning experiments. Findings The optimum value of input turning parameters: cutting speed (A), feed rate (B) and depth of cut (C) is found as 79.88 m/min, 0.1 mm/rev and 0.2 mm, respectively, with optimal output response parameters: Vb = 138.633 µm and Ra = 0.462 µm at the desirability level of 0.766. Feed rate: B and cutting speed: A2 are the leading model variables affecting Vb, with a percentage contribution rate of 12.06% and 43.69%, respectively, while cutting speed: A and feed rate: B are the significant factors for Ra, having a percentage contribution of 38.25% and 18.03%, respectively. Results of validation experiments confirm that the error between RSM predicted and experimental observed values for Vb and Ra is 3.28% and 3.75%, respectively, which is less than 5%, thus validating that the formed RSM models have a high degree of conformity with the obtained experimental results. Practical implications The outcomes of this research can be used as a reference machining database for various metal cutting industries to establish eco-friendly NMQL practices during the turning of superalloy Inconel 718 to enhance cutting tool performance and machined surface integrity. Originality/value No study has been communicated till now on the turning of Inconel 718 under NMQL conditions using olive oil blended with multi-walled carbon nanotubes-based nanofluid. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-10-2023-0317/

Analyzing microstructural, residual stress, and mechanical characteristics in dissimilar welds of Inconel 59 and AISI 904L through double-pulsed gas metal arc welding

In this research, dissimilar welding of the nickel-based superalloy Inconel 59 and austenitic stainless steel AISI 904L steel was successfully done with double-pulsed gas metal arc welding (DP-GMAW) using the filler ERNiCrMo-13. Macroscopic analysis showed a defect-free weld with an aspect ratio of 2.4, attributed to the efficient heat delivery (0.642 kJ/mm) in DP-GMAW. The microstructure of the weld joint was examined through both optical microscopy and scanning electron microscopy. Examination of the microstructure of the weld interface exposed grain coarsening near the heat-affected zone on the AISI 904L side. In contrast, the weld fusion zone contained fine equiaxed dendrites. Microsegregation and alloying element migration across the entire weld area were assessed through energy dispersive X-ray spectroscopy point analysis and line mapping, revealing controlled microsegregation across the region. X-ray diffraction (XRD) analysis was used to ascertain the average grain size (38.41 nm) and secondary phase composition. The XRD-cosα method was used to assess the residual stress of the weld joint, revealing tensile residual stress in the weld zone and compressive residual stress in other regions. Tensile, Charpy impact, and Vickers hardness tests were conducted in the study to evaluate the strength, toughness, and hardness of a dissimilar weld. The impact of two cryogenic treatments, namely shallow and deep, on tensile and toughness characteristics was investigated in this study. The cryogenic treatments significantly enhanced the mechanical properties of weld samples compared to their as-welded condition, leading to an 11.5% increase in tensile strength and a 10% improvement in toughness.

Surface—subsurface grain structure relationships

Relationships between surface and subsurface grain structure are studied using a large three-dimensional (3D) microstructural dataset of a nickel-base superalloy Inconel 718. Comparative analyses of microstructural features were performed from both an orthographic, two-dimensional (2D) perspective and a full-3D one to underscore their distinctions on a grain-by-grain basis for a given surface microstructure. A positive correlation between grain size and the number of nearest neighbors of surface grains was observed; however, considerable variability exists per grain. We also present a detailed investigation of 3D surface grain structure and highlight the limitations of 2D surface grain characterizations. Several features of subsurface grain structure, including out-of-plane grain boundary inclination angle, surface-to-subsurface feature proximity, and subsurface grain boundary interface geometry are characterized. The analysis reveals a wide array of highly non-columnar subsurface grain structures with many points at the free surface being closer to grain boundaries and triple junctions beneath the surface than in the surface observation plane. Repeating these analyses for a synthetic dataset without twins reveals that our findings apply to other polycrystalline materials with near-equiaxed grains and limited texture.

Experimental investigation of process parameter variations on the microstructure and failure behavior of IN718 structures in PBF-LB/M

Conventional manufacturing technologies, such as milling or casting, are limited in terms of the manufacturable complexity of the parts to be produced. They are also restricted in terms of the local modifiability of the mechanical properties. Additive manufacturing, specifically the Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M), is a novel method, which is capable of addressing both limitations. However, the resulting parts are often prone to cracking during PBF-LB/M and in the service afterward because of high thermally induced local stress intensities. Selectively modifying the process parameters during the fabrication can be a suitable strategy to locally reduce the failure susceptibility. Over the course of this study, samples made from the nickel-based superalloy Inconel 718 were manufactured with varying laser powers, hatch distances, and scan speeds. The samples were divided into stress crack specimens as well as static and dynamic tensile test specimens. The grain structure was investigated, and correlations between the microstructure and the cracking susceptibility were determined. It was found out that variations in the laser power had the most pronounced effect on the grain structure and the failure behavior. An increasing grain size enhanced the fracture resistance in the stress crack samples while the static and dynamic mechanical properties deteriorated. Based on these results, the application area of PBF-LB/M could potentially be widened due to the manufacturability of parts otherwise susceptible to stress-induced cracking. The mechanical properties of as-built parts can remain unchanged utilizing a local process parameter adaption.

A simulation of chip formation mechanism in elliptical vibration assisted cutting of nickel-based superalloy Inconel 718.

This article reveals the chip formation and the reducing of cutting force mechanisms of nickel-based superalloy Inconel 718 under elliptical vibration cutting using finite element analysis software. The results are compared with traditional cutting methods. The elliptical motion trajectory of the tool in elliptical vibration cutting machining is analyzed, and a two-dimensional finite element elliptical vibration cutting model is established. The effects of dynamic impact on the elliptical vibration cutting of Inconel 718 were discussed in terms of the surface morphology, chip formation mechanism, and cutting force reduced mechanism. The simulation results show that (1) compared with traditional cutting, the surface morphology of the workpiece machined by elliptical vibration cutting is better, and the machined surface has obvious elliptic indentation; (2) in traditional cutting, sawtooth chips are formed through shear slip, while in elliptical vibration cutting, the faster relative cutting speed , higher tool-tip temperature, and smaller material removal cross-sectional area cause a more prominent thermal softening effect in the chip formation process than that in traditional cutting, which leads to the plastic flow to be dominant in the material removal process, resulting in the strip chips; and (3) compared with traditional cutting, the normal cutting force and the tangential cutting force in elliptical vibration cutting are separately reduced about 51.4% and 60.8%.

Comparative study on mechanical properties and high temperature oxidation behaviour of Hastelloy X and Inconel 718 fabricated by laser directed energy deposition

The high temperature oxidation resistance is crucial to assure the reliability of nickel-based superalloy parts serving at elevated temperature. Hastelloy X is a solid solution strengthening superalloy featured by decent mechanical properties and excellent high temperature oxidation resistance, having the potential to replace the commonly used nickel-based superalloy Inconel 718 in appropriate high-end manufacturing fields. In this work, a comparative study on mechanical properties and high temperature oxidation behaviour of Hastelloy X and Inconel 718 fabricated by laser directed energy deposition was carried out. Under the same processing parameters, the as-built Hastelloy X consisted of columnar and cellular γ phase with dispersed carbides, but Inconel 718 contained columnar γ phase with dispersed carbides and γ′ phase. At ambient temperature, Hastelloy X showed better ductility but inferior strength and hardness. Additionally, the isothermal oxidation tests at 1000 and 1100 °C demonstrated that the oxidation kinetics curves of both as-built superalloys followed the parabolic law. Hastelloy X owned a better high temperature oxidation resistance, which could be attributed to the uniformly distributed dense Cr2O3 and the relatively slight exfoliation of oxides in the oxide scales.

Towards a Simulation-Assisted Prediction of Residual Stress-Induced Failure during Powder Bed Fusion of Metals Using a Laser Beam: Suitable Fracture Mechanics Models and Calibration Methods

In recent years, Additive Manufacturing (AM) has emerged as a transformative technology, with the process of Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M) gaining substantial attention for its precision and versatility in fabricating metal components. A major challenge in PBF-LB/M is the failure of the component or the support structure during the production process. In order to locate a possible residual stress-induced failure prior to the fabrication of the component, a suitable failure criterion has to be identified and implemented in process simulation software. In the work leading to this paper, failure criteria based on the Rice-Tracey (RT) and Johnson-Cook (JC) fracture models were identified as potential models to reach this goal. The models were calibrated for the nickel-based superalloy Inconel 718. For the calibration process, a conventional experimental, a combined experimental and simulative, and an AM-adapted approach were applied and compared. The latter was devised to account for the particular phenomena that occur during PBF-LB/M. It was found that the JC model was able to capture the calibration data points more precisely than the RT model due to its higher number of calibration parameters. Only the JC model calibrated by the experimental and AM-adapted approach showed an increased equivalent plastic failure strain at high triaxialities, predicting a higher cracking resistance. The presented results can be integrated into a simulation tool with which the potential fracture location as well as the cracking susceptibility during the manufacturing process of PBF-LB/M parts can be predicted.

Grain boundary network evolution in electron-beam powder bed fusion nickel-based superalloy Inconel 738

Additive manufacturing (AM) of alloys has attracted much attention in recent years for making geometrically complex engineering parts owing to its unique benefits, such as high flexibility and low waste. The in-service performance of AM parts is dependent on the microstructures and grain boundary networks formed during AM, which are often significantly different from their wrought counterparts. Characteristics such as grain size and morphology, texture, and the detailed grain boundary network are known to control various mechanical and corrosion properties. Advanced understanding on how AM parameters affect the formation of these microstructural characteristics is hence critical for optimising processing parameters to unlock superior properties. In this study, the difficult-to-weld nickel-based superalloy Inconel 738 was fabricated via electron-beam powder bed fusion (EPBF) following linear and random scanning strategies. Random scanning resulted in finer, less elongated, and crystallographically more random grains compared to the linear strategy. However, both scanning strategies achieve unique high grain structure stability up to 1250 ℃ due to the presence of carbides pinning the grain boundaries. Despite significant difference in texture and morphology, majority of grains terminated on {100} habit planes in both linear and random built samples. The results show potential for controlling grain boundary networks during EPBF by tuning scan strategies.