Inconel Research Articles

Microstructure, Mechanical Properties, and Corrosion Resistance of Dissimilar Weld Joints between SS304 and Inconel 600 Welded using Gas tungsten arc welding

The microstructure, mechanical characteristics, and corrosion resistance of dissimilar gas tungsten arc welding (GTAW) joints of 304 stainless steel (SS304) to Inconel 600 (IN600) with Inconel 600, using ERNiCr-3 and ERSS308 filler metals were investigated. The welding process was executed at a current of 110 Amps under argon shielding gas, and all fabricated welds successfully joined SS304 to IN600 without visible cracks or porosity at the weld metal interface. Microstructural analysis with optical and scanning electron microscopy revealed a mix of columnar and equiaxed dendritic structures in the weld zone for all samples. An unmixed zone was noted at the interface on the SS304 side when welded with Inconel 600 and ERNiCr-3, attributed to the differing melting points and chemical compositions of these fillers compared to SS304. The presence of Nb and Ti in the ERNiCr-3 filler facilitated the formation of TiC and NbC carbides in the welded metal structure, resulting in higher hardness compared to other specimens. Mechanically, the ERNiCr-3 welded sample exhibited superior hardness, with the highest microhardness values recorded in the ERNiCr-3 weld metal (197-207 HV) and higher values on the SS304 side (176-194 HV) compared to the IN600 side (164-176 HV). Corrosion tests, including Tafel and Electrochemical Impedance Spectroscopy, indicated that the ERNiCr-3 weld metal had better corrosion resistance than the IN600 weld metal. Due to the differences in chemical compositions of the base metals SS304 and IN600, it is necessary to consider an appropriate filler for welding these materials. ERNiCr-3 demonstrated increased hardness due to the formation of TiC and NbC carbides, along with enhanced corrosion resistance. These properties make it a promising material for industrial applications that require durability, strength, and resistance to corrosion, particularly in high-temperature or corrosive environments.

Heat treatments-induced wear resistance of Inconel 718 superalloy fabricated via Laser based Powder Bed Fusion

Laser based Powder Bed Fusion (LPBF) stands out among Additive Manufacturing (AM) techniques for its ability to fabricate intricate geometries with high precision. However, LPBF produced parts, particularly Inconel 718 (IN718) superalloys, demand further exploration in microstructural and mechanical properties aspect. This study explores the effect of heat treatments on LPBF fabricated Inconel 718. Three distinct heat treatments involving diverse solutionizing temperatures and ageing steps were applied to the LPBFed IN718 alloy. As-printed samples showed columnar dendritic microstructure. The heat treatments led to precipitation of strengthening γ′′ and γ′ phases. A substantial increase in microhardness was observed after heat treatments. Wear tests revealed as-printed specimens suffered higher wear loss (∼889 μm) and coefficient of friction (COF) (∼0.627) attributed to Laves phase and low hardness of the matrix. However, heat-treated specimens exhibited substantially lower wear loss (∼217 μm) and COF (∼0.342), with HT2 condition demonstrating superior wear resistance attributed to a homogeneous microstructure.

Investigating the effect of nanobubble-based cutting fluid on tool wear and cutting forces in milling of Inconel 718

Machining of Nickel-Based Superalloys (NBSAs) is characterized by rapid work hardening, low thermal conductivity, and extreme abrasive behavior. Due to such characteristics of NBSAs, the machining of materials like Inconel 718 (IN718) results in extensive tool wear and high cutting forces. The present study employs nanobubble-based cutting fluid during machining of IN718 and investigates its effect on tool wear and cutting forces. The trochoidal milling experiments were conducted on an IN718 workpiece with nanobubble-based and normal cutting fluid at varying surface speeds. The evolution of tool flank wear area and peak resultant cutting force were recorded and compared to evaluate the effectiveness of nanobubble-based cutting fluid over normal cutting fluid. The results showed that nanobubble-based cutting fluid lowers the tool wear rate by enhancing heat dissipation and reducing abrasion wear. However, higher cutting forces were observed with nanobubble-based cutting fluid due to increase in hardness of the workpiece. Also, it is realized that using nanobubble-based cutting fluid can significantly improve the lifespan of the tool, leading to sustainable manufacturing.

Crystal plasticity-driven evaluation of notch fatigue behavior in IN718

The aim of this study was to establish a method for evaluating notch fatigue behavior through crystal plasticity finite element (CPFE) simulations based on the actual microstructure of the nickel-based alloy Inconel 718 (IN718). Initially, the equivalent plastic strain, εeps, which reflects the comprehensive slip at the grain scale, was employed to analyze the fatigue crack initiation mechanism of IN718, revealing that twinning and triple junctions of grain boundaries were high-risk locations for fatigue crack initiation. Next, fatigue simulations were performed on notched specimens using the CPFE model, with a material-level CPFE model particularly employed at the notch root. The increment of εeps, Δεeps, in a stable cycle was used as the fatigue damage control parameter and correlated with the fatigue life, Nf, revealing that the Δεeps-Nf relationship at material-level satisfied the form of the Mason-Coffin model. Finally, fatigue life prediction of IN718 notched specimens was carried out based on the Δεeps-Nf relationship, with the predicted results falling within the 2-fold scatter band, demonstrating good prediction accuracy.

Enhanced high temperature mechanical and oxidation behavior of direct energy deposited TiC/Inconel 718 gradient coatings

While Inconel 718 is commonly employed in high-temperature settings, its performance at elevated temperatures is notably diminished in comparison to its performance under ambient conditions. In this study, Inconel 718 (IN718), Inconel 718 with 5 layer of Inconel 718–5 wt% TiC gradient coatings (CG-5), and Inconel 718 with 5 layer of Inconel 718–10 wt% TiC gradient coatings (CG-10) were fabricated using direct energy deposition (DED) to investigate the influence of TiC content on the mechanical and oxidation properties at elevated temperatures through the regulation of microstructural changes. Following the incorporation of TiC, the microstructures underwent a transformation into refined equiaxed crystals, carbides, and columnar crystals, replacing the coarsened columnar crystals and Laves phase present in IN718. Compared to IN718, the high-temperature tensile strength of CG-5 and CG-10 has increased by 80% and 180% at 900 ℃. Meanwhile, the mass gain due to oxidation per unit area of CG-5 and CG-10 has decreased by 23% and 11%, respectively. The results indicate that CG-10 exhibits a combination of highest high-temperature tensile strength and the enhanced resistance to high-temperature oxidation when compared to IN718 and CG-5.

Microstructural Stability of IN625 Reinforced by the Addition of TiC Produced by Laser Powder Bed Fusion after Prolonged Thermal Exposure.

This paper deals with the development and characterization of an Inconel 625 (IN625) reinforced with 2 wt.% of sub-micrometrical TiC particles produced by the laser powder bed fusion (LPBF) process. IN625 and IN625 2 wt.% TiC microstructural evolution was evaluated in the as-built, solution-annealed (2 h at 1150 °C), and prolonged heat-treated (2 h at 1150 °C + 100 h at 1000 °C) conditions. The IN625 and IN625 + TiC samples were successfully produced with low residual porosity (<0.15%). In the as-built conditions, both materials developed mainly columnar grains elongated to the building direction with melt pools, fine dendric structures, and small fractions of recrystallized grains. Some TiC segregations were observed in the composite, preferentially located at the melt pool boundaries. The heat treatments led to a different microstructural evolution between the base alloy and the composite. After solution annealing, the IN625 alloy was subjected to full recrystallization with a drastic reduction in hardness. Afterward, the prolonged thermal exposures for 100 h at 1000 °C provoked the formation of carbides, increasing the hardness. On the contrary, the composite retained the as-built microstructure with columnar grains in the solution-annealed and prolonged heat-treated conditions, revealing a limited formation and growth of carbides, thus resulting in a reduced hardness variation. The addition of TiC inside the IN625 enhanced the microstructural stability of the composite, preventing the recrystallization and the growth of phases occurring under prolonged thermal exposures. The current study therefore reported the effect of TiC particles on the microstructural stabilization of LPBFed IN625, with a peculiar focus on the prolonged thermal exposure at 1000 °C.

Defects, microstructure and associated mechanical properties of Inconel 718 fabricated by selective electron beam melting

Comprehensive characterizations and evaluations were conducted on the relationship between process parameters and density in the Inconel 718 (IN718) alloy fabricated by selective electron beam melting (SEBM). Additionally, the microstructure and anisotropy of tensile properties were evaluated in both the as-built state and after solution treatment and aging (STA). During different stages of energy density, the primary contributors to the porosity rate transitioned from the lack of fusion (LF) pores to the inclusion of spherical and shrinkage pores, resulting in a maximum relative density of 98.95 %. The as-built parts displayed notable parallel texture to the building direction, and a significant tensile anisotropy supported by the Taylor factor. The matrix of these parts consisted of δ, γ', γ″, and carbonitrides, with a considerable presence of δ precipitation leading to a reduction in γ″ content and lower strength. After heat treatment, the δ dissolved, and γ″ precipitated extensively, while the carbonitrides and texture were retained. However, unique tensile results contradicting the predictions made by computational modeling were observed, we propose a new insight attributed to the presence of shrinkage pores along the build direction and use finite element analysis to support this view.

Post-Processing of Inconel 718 Alloy Fabricated by Additive Manufacturing: Selective Laser Melting

The review analyses Inconel 718 (IN718) alloy, which is the nickel-based superalloy and has great application in industries due to its superior mechanical properties even at elevated temperatures by means of the solid-solution strengthening and precipitation strengthening. However, because of the tool over-wear, poor part surface integrity, high hardness and low thermal-conductivity properties, it is difficult to manufacture finished products with using conventional machining methods. It is especially urgent for the products of complex designs. In this regard, justification is given for the widespread use of modern additive manufacturing (AM) for the fabrication of the products from IN718. The most popular is AM based on the selective laser melting (SLM) technique, which can fabricate complex geometries with superior material properties. At the same time, the metal parts fabricated by SLM suffer from excessive residual porosity, residual tensile stress in the near-surface layer, and the formation of a relatively rough surface. In addition, the SLM-inherited surface defects can cause stress concentration to initiate cracks, reducing the fatigue strength of the printed parts. The review focuses on identifying potential solutions to the surface-finish complex additive manufactured to improve the surface properties to meet the industry requirements. Therefore, the improvement of the IN718-alloy-parts’ surface properties printed by the SLM becomes especially relevant. Currently, different surface post-processing technologies are being developed to obtain the expected surface quality of the SLM-components. As demonstrated, the finish surface enhancement treatments led to significant improvement in the wear resistance, corrosion resistance, increase in fatigue life, and tensile strength of the metallic materials. Therefore, adapting surface post-processing technologies has become a growing area of interest as an effective tool for improving the functionality and service lifetime of SLM IN718-alloy components. The review aims to analyse the main results of the most systematic studies of the currently developed surface post-treatments aimed to improving the surface-structure quality and properties of the IN718 parts fabricated by SLM. These results contribute to a better understanding of the role of the various-parameters’ effects on the surface improvements during the surface post-processing and changes in the structure–phase state, and physical, chemical and mechanical properties. Examples of the effects of a series of surface post-processing methods are presented: laser polishing, mechanical magnetic polishing, cutting finish-machining operations, shot peening, sandblasting technique, ultrasonic-impact treatment, and electrochemical polishing.

Effects of electrochemical machining on high-cycle fatigue of Inconel 718 blades

Blades made from Inconel718 (IN718) are generally machined using electrochemical machining (ECM), and the high-cycle fatigue (HCF) of such blades significantly impacts the service life of aeroengines. In this study, modal analysis was performed to obtain the blade modal shape and stress distribution at first-order frequency, after which blades were machined at different current densities (9.5A/cm2, 18.2A/cm2, 34A/cm2, 46.7A/cm2, 61.2A/cm2, 70.1A/cm2) and then subjected to detailed surface-integrity analysis and fatigue tests. No surface defects (e.g., intergranular corrosion, recast layers) were observed, the microhardness was unchanged, and new residual stress was not found to be introduced to the machined surfaces. The machined surfaces were uneven and contained micro-pits, and high current density contributed to better surface quality. At a constant load of 520 MPa, the blade machined at 70.1A/cm2 had the best fatigue life of 1.4×106. The blades fractured because of micro-pits, and as the surface quality of the blades improved, so did their fatigue performance. Therefore, the fatigue failure mechanism characterized in this work provides a reference for the HCF behavior of blades machined by ECM.

Fabrication of Inconel 718 composites reinforced with TiCN via laser powder bed fusion: Integration of triply periodic minimal surface lattice structures

The integration of TiCN particles into superalloy composites for laser powder bed fusion (LPBF) and the construction of Triply Periodic Minimal Surface (TPMS) lattice structures have been understudied. This research systematically examines the microstructure and mechanical properties of LPBF-processed 10 vol% micron sized TiCN particle reinforced Inconel 718 (IN718) composites. The compressive behavior of the resultant TPMS lattice structures, derived from the TiCN-IN718 composite, was scrutinized through a combination of experimental testing and Finite Element (FE) simulation. The micro-sized TiCN reinforcement is demonstrated to notably augment the hardness, tensile strength, and wear resistance of the LPBFed TiCN-IN718 composite. Furthermore, the application of homogenization-solution-aging (HSA) heat treatment is shown to provide additional enhancements to the composite's mechanical behavior. Both the TiCN reinforcement and the HSA heat treatment are identified as pivotal factors influencing the compressive response of the TPMS lattice structures. Experimental findings indicate that the HSA-treated D-structure attains the highest compressive strength, reaching 122 MPa, outperforming both the G- and P-structures. During quasi-static compression testing, the D- and G-structures undergo a layer-by-layer collapse, while the P-structure exhibits tilt shear band behavior. The congruence between FE simulation results and experimental data substantiates the simulation's reliability and its capacity to accurately evaluate the mechanical behavior of TPMS lattice structures.

Influence of alloying elements on stacking fault energy in Ni and Ni-based alloy: A first–principles study

The study of the reliability of Ni-based alloys and their performance under high-temperature radiation environments is crucial for nuclear reactor application. The first-principles study has been utilized to investigate the effect of individual alloying elements (Cr, Fe, Mo, Nb) on the stacking fault energy (SFE) of pure Ni in order to understand their specific contribution in the superalloy Inconel 718 (IN718). The result shows that the addition of an alloying element in pure Ni reduces the SFE value with the most significant reduction seen in IN718 alloy. The role of individual alloying element in the reduction of the SFE in IN718 is conjectured. The DOS at EF of all the elemental substitution configurations were also calculated and significant change is seen in the alloy IN718. Such reduction is due to the interrupted distribution of d-electrons and atomic bonding on the stacking fault planes, reflected in the SFE value.

Microstructural characterization and creep deformation response of an Inconel-600/Inconel-625 welded joint obtained by oscillating GMAW process.

This investigation presents the microstructural characterization and creep failure mechanism of a dissimilar weld (DW) of Inconel 600 (IN600) and Inconel 625 (IN625) at a temperature of 675 °C and different stress levels. Optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and Vickers microhardness test were used to characterize the welded joint, the creep rupture features, and microstructural characteristics of the DW respectively. The experimental results show that the crept samples consistently broke on the base material of the IN600 side and that the failure was mainly controlled by the plastic deformation of coarser austenitic grains, dynamic recrystallization, and the coalescence and growth of microcracks that resulted from the evolution of the Cr-rich carbides along the grain boundaries that conducted to a transgranular fracture mode.

Metallurgical and mechanical properties of trimetallic functionally graded material fabricated by wire arc additive manufacturing

This study explores the fabrication of a trimetallic functionally graded material (FGM) using stainless steel (ER316L), duplex steel (ER2205), and Inconel 718 (IN718) through a gas metal arc welding (GMAW) based wire arc additive manufacturing (WAAM) process. The metallurgical examination reveals the large columnar austenitic grains and δ-ferrite phase at the grain boundaries along the built direction in the stainless-steel zone. At the interface of ER2205-IN718, a distinct boundary is observed due to the different alloy compositions. Scanning electron microscopy (SEM) shows metal carbide of nickel (Ni), molybdenum (Mo), and niobium (Nb) along the grain boundaries and nodular-shaped Lave phases in the IN718 zone. The energy dispersive spectroscopy (EDS) analysis reveals a gradual variation of Ni and Fe content, indicating the successful fabrication of the FGM. The mechanical characterization reveals that the hardness of the developed FGM steadily increases from bottom to top. However, at the ER2205-IN718 interface, it experiences a sharp decrease, followed by a subsequent increase within the IN718 zone. The tensile test demonstrated an increase in tensile strength along the built direction, accompanied by a reduction in strain. Notably, the minimum strain observed in the developed FGM is approximately equal to that of IN718 alloy.

Corrosion Properties and Passive Film Interface of Inconel 718 in NaNO3 Solution for Laser-Assisted Electrochemical Machining.

Laser-assisted electrochemical machining (ECM) is an ideal manufacturing method for Inconel 718 (IN718) because of the method's high efficiency and good surface quality, and the basis for and key to laser-assisted ECM is its anodic electrochemical dissolution behavior. In this study, IN718 in a 10 wt % NaNO3 solution was subjected to innovative electrochemical testing and laser-assisted ECM experiments to investigate its corrosion properties and the passive film characteristics formed on its surface. The passivation-related behaviors and structures of the passive film were investigated based on open-circuit potentials, dynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. It was found that there was obvious active-passive-transpassive transition behavior, and the structure of the passive film in laser-assisted ECM exhibited pores and defects, resulting in weak corrosion resistance, compared with IN718 under ECM without laser irradiation. The chemical composition of the passive film was obtained by X-ray photoelectron spectroscopy. The results showed that the passive film was composed mainly of a mixture of NiO, Ni(OH)2, Cr2O3, CrO3, Fe2O3, α-Fe2O3, α-FeOOH, Nb2O5, NbO, MoO3, MoO2, and TiO2. The passive film formed by laser-assisted ECM was rich in NiO and TiO2 and lacked Cr2O3 and MoO3, which validated its pores and defect structures. A corresponding schematic model was also proposed to characterize the interface structure between the IN718 substrate and the passive film. Laser-assisted ECM tests were performed under different current densities and machining times, and the corrosion morphology of IN718 was identified. Corrosion pits and a loose product layer appeared on the machined surface at low current densities, and the dissolution mechanism was pitting. The quantity and depth of the corrosion pits dispersed on the machined surface clearly decreased as the current density increased. Finally, a quantitative corrosion model was established to characterize the dissolution behavior of IN718 in NaNO3 solution during laser-assisted ECM.

Additive manufacturing of Inconel 718/CuCrZr multi-metallic materials fabricated by laser powder bed fusion

The multi-metal structure combines the thermal stability and high-temperature resistance of Inconel 718 (IN718) with the excellent thermal conductivity of CuCrZr, making it highly valuable for applications in aero-engines. Nevertheless, it is challenging to fabricate high-strength multi-metallic interfaces due to their large thermophysical differences. In this paper, the interface between IN718 and CuCrZr was well bonded by laser powder bed melting technology and optimizing the process parameters. The effects of process parameters on the interfacial properties of the prepared IN718/CuCrZr were analyzed. The microstructure characteristics, element distribution, microhardness, tensile properties, and thermal conductivity of IN718/CuCrZr were studied. The melting behavior, interface characteristics, and formation mechanism of multi-metallic materials were discussed. The experimental results show that the volumetric energy density range of 209.88–404.76 J/mm3 is suitable for the formation of IN718/CuCrZr. The formation of interface characteristics is mainly attributed to Marangoni convection, which promotes the mixing of Ni and Cu elements, helps form a stable transition layer at the interface, and enables a natural transition between the two metal interfaces. This indicates that there is good metallurgical bonding at the IN718/CuCrZr interface. At the same time, the equiaxed grain structure and grain refinement were observed in the transition zone, which was also reflected in the longitudinal section hardness distribution of the IN718/CuCrZr interface. The tensile test results show the transverse of IN718/CuCrZr (IN718/CuCrZr (T)) and longitudinal of IN718/CuCrZr (IN718/CuCrZr (L)) exhibit different deformation mechanisms. The fracture of IN718/CuCrZr (T) occurs in the CuCrZr region, indicating that the interface is well bonded. The tensile properties of IN718/CuCrZr (L) are higher than that of CuCrZr and lower than that of IN718, and brittle fracture occurs at the interface. The tensile properties of IN718/CuCrZr (T) are dominated by CuCrZr and IN718/CuCrZr (L) is determined by both IN718 and CuCrZr. Compared with IN718, the thermal conductivity of IN718/CuCrZr multi-metallic structure is significantly improved. This will open up the possibility of multi-metallic materials additive manufacturing for the next generation of aerospace structures.

High-speed perforation of IN718 plates by spherical TC4 Ti alloy projectiles: Experiments and modeling

Data and knowledge on ballistic performance of Inconel-718 (IN718) alloy is critical for evaluating the resistance of turbine blades against foreign object impacts in aeronautical and astronautical industries. Ballistic perforation experiments (impact velocity 480 ms−1 to 1340 ms−1) with TC4 spherical projectiles (5-mm-diameter) are conducted on IN718 target plates (2-mm-thick) in this work, along with high-speed photography. The IN718 plates show multiple deformation and failure modes (bulging, dishing, petaling and plugging). The ballistic limit velocity for the investigated projectile/target combination is 823 ms−1. Postmortem material characterizations (optical photography, scanned electron microscopy and energy dispersive spectrometry) are conducted on recovered projectiles and bullet hole inner walls, and the observations indicate adiabatic shearing, surface melting and abrasion of projectile material. A finite element model based on the Johnson–Cook constitutive model and failure criterion is established, and reproduces the ballistic experiments. Dimensionless analyses are conducted on the dimensions of postmortem projectiles and bullet holes, and the projectile residual velocity/mass. On the basis of experimental observations and theoretical analysis of the projectile dynamics, the whole perforation process is divided into three stages (the entering, cratering and plugging stages). A multi-stage analytical model on perforation is then developed considering the effects of cavity expansion, projectile deformation and abrasion, and can well predict the projectile dynamics during entering and cratering stages.

Effect of Electric Pulse Treatment on Microstructure and Mechanical Property of Laser Powder Bed Fused IN718

This study investigated the impact of electric pulse treatment (EPT) on the microstructure and mechanical properties of laser powder bed fused Inconel 718 (IN718). Through a comprehensive experimental characterization, we found that EPT induced significant improvements in the microstructure of IN718. In the YOZ plane of EPT-700, the molten pool diminished and replaced by a grain boundary with granular Ni3Nb precipitates, and the dislocations increased while the irregular porosity decreased. Concurrently, enhanced mechanical properties of EPT-700 were obtained, including a hardness of 354.7 HV, an ultimate tensile strength of 930.21 MPa, and an elongation of 34.35%. Fractographic analysis revealed a transition in fracture mechanisms, highlighting the intricate relationship between microstructural modifications induced by EPT and mechanical response under load. These findings underscore the potential of EPT as a promising post-processing technique for optimizing the microstructure and mechanical properties of IN718 components fabricated via laser powder bed fusion additive manufacturing. This study contributes to the advancement of knowledge in the field of additive manufacturing and provides valuable insights for the development of high-performance metallic components.

Simulation and experimental studies on surface quality of vibration-assisted ECM

ABSTRACT Electrochemical machining (ECM) offers a superior technology for manufacturing hard-cutting metals such as modified Inconel 718 (IN718). However, in many cases, poor surface quality arises because of the specific dissolution characteristics of the material, hindering further application of the process. Vibration-assisted ECM (VA-ECM) has been proposed in the hope of solving the problem by oscillating the cathode. A multiphysics model was developed for pulsed ECM (PECM) and VA-ECM. Systematic experiments were performed to clarify the mechanism of cathode oscillation on surface quality and verify the computational results. With 20 Hz vibration frequency and 25% duty cycle, the surface roughness reaches 0.39 µm, show that higher oscillation frequency and lower duty cycle are effective in improving surface quality. Finally, dissolution models of modified IN718 under PECM and VA-ECM are proposed. By oscillating the cathode, electrolyte fluctuation is enhanced, electrolytic products are removed effectively, the surface quality is improved significantly.

Microstructure and mechanical properties of IN718 on 42CrMo for repair applications by laser directed energy deposition

Laser Directed Energy Deposition (LDED) has gained significant attention as a promising additive manufacturing technology for the repair and restoration of worn parts. The objective of this study is to assess the feasibility and performance of repairing 42CrMo substrates using Inconel 718(IN718) powder. In this study, the LDED process was employed to investigate the influence of varying laser power, scanning speed, and feed rate on a single track study. The optimal process parameters for trapezoidal groove repair were determined by comparing and evaluating factors such as dilution, aspect ratio, track continuity, and molten pool shape. Furthermore, the effects of different repair strategies (X-, Y-, Cross-paths) on the microstructure and mechanical properties were investigated. The results indicate that by using suitable process parameters, successful deposition of IN718 on 42CrMo is achieved. The investigation reveals elemental diffusion between the two materials, quenching phase transition on the substrate surface, and the formation of intermetallic compounds in the fusion zone. The fusion zone(FZ) and heat-affected zone(HAZ) exhibited the highest microhardness compared to the substrate. Significant changes in molten pool shape and arrangement were observed using different repair strategies, while the effect on grain size was not significant. Due to the high directionality of the samples fabricated using the LDED process, the samples of the X-path demonstrated the highest ultimate tensile strength and elongation compared to the other two repair strategies. The ultimate tensile strength after repair is comparable to that of the substrate, while the elongation is reduced.

Crystal plasticity quantification of anisotropic tensile and fatigue properties in laser powder bed fused Inconel 718 superalloy

The high thermal gradients during the laser powder bed fusion (LPBF) process induce an inhomogeneous microstructure with anisotropic mechanical properties. This study developed a dislocation-based strain-gradient crystal plasticity finite element (CPFE) model to reveal the microstructure-based deformation mechanisms and quantify their strengthening contributions to the mechanical property anisotropy of LPBF-ed Inconel 718 (IN718) superalloy. The analyzed microstructural attributes included 1- crystallographic orientations/misorientations, 2- solid solutions (SS), 3- grain size and morphologies, and 4- dislocation dynamics, such as statistically stored dislocations (SSDs) and geometrically necessary dislocations (GNDs). The investigated mechanical properties contained tensile strength, fatigue resistance, fracture mechanisms, and their anisotropy under loading towards building (BD) and transverse (TD) directions. The experimentally obtained microstructural features of the as-LPBF-ed IN718 were synthesized into the crystal plasticity representative volume elements (CPRVE) to model the deformation behavior using a user-defined material subroutine (UMAT) in the ABAQUS solver. The energy-based fatigue indicator parameter (FIP) captured the fatigue properties and failure mechanisms. The main slip-strengthening contributions stemmed from SSDs, grain size, SS, and GNDs. in TD. The corresponding order in BD was SSDs, SS, GNDs, and grain size because the grain dimensions were larger in BD than in TD. The grain-size effect had the highest contribution to the tensile property anisotropy, followed by SSDs, GNDs, and SS. Aside from their strengthening effects, crystal texture and grain size induced mechanical property heterogeneity and fatigue sensitivity at grain boundaries, reducing their contributions to fatigue strength relative to tensile. In contrast to the previous findings, local accumulations of SSDs and GNDs at softer sides of grain boundaries during cyclic loading reduced the strength heterogeneity in these areas, improving fatigue properties. The highest slip-strengthening effect for fatigue resistance and anisotropy was under SSDs, followed by GNDs, SS, and grain size.