Additive Manufacturing Inconel Research Articles

Microstructure and Mechanical Properties of Additive Manufactured Inconel 718 Alloy by Oxide Dispersion Strengthening of Sc Addition

Microstructure and Mechanical Properties of Additive Manufactured Inconel 718 Alloy by Oxide Dispersion Strengthening of Sc Addition

Study of Microstructure and Mechanical Properties of As-built and Heat-treated Additive Manufactured Inconel 718 Alloy

Additive manufacturing technology is becoming popular in the industry because it allows the manufacturer to fabricate cost-effective, strong, lightweight, and complex-shaped parts directly from 3D design data as compared with the conventional manufacturing method. Inconel 718 alloy is the most demanding material in aviation as well as in the automobile industry, in terms of manufacturing high-performance parts. In this study, Inconel 718 samples were built using the direct metal laser sintering process, and standard heat treatment was performed on the samples to improve their microstructure and mechanical properties. The as-built samples exhibited good grain structure with fine laves phases, but the matrix was free from ?' and ?" phases. During the heat treatment, the strengthening phases ?' and ?" precipitated. The mechanical properties of as-built and heat-treated samples were analysed and compared. Tensile tests revealed that the direct-aged sample had the higher tensile strength compared with the other conditions, whereas the as-built samples had higher ductility. Finally, fractography and microstructure analysis were performed to measure the failure modes of tensile specimens.

High Strain Rate Yielding of Additive Manufacturing Inconel 625 by Selective Laser Melting.

Nickel-based alloy Inconel 625, produced by the selective laser melting method, was studied experimentally for its mechanical performance under strain rate loading using Hopkinson bars. Both compression and tensile tests were carried out, with the former also being conducted at 500 °C. The strain rate was in the range of 300 to 3500 s−1 at ambient temperature, and 1200 to 3500 s−1 at the elevated temperature, respectively, for compression tests, and 900 to 2400 s−1 for tensile tests. Results show that the alloy has a strong rate sensitivity with the dynamic yield stress at 3500 s−1, almost doubling the quasistatic value. The test results also show that, even though the temperature elevation leads to material softening, the strain rate effect is still evidential with the dynamic compressive yield stress at the rate 103 s−1 and 500 °C still being higher than the quasistatic one at ambient temperature. It is also observed that dynamic tensile strengths are generally higher than those of compressive ones at room temperature.

Solid-State Transformation of an Additive Manufactured Inconel 625 Alloy at 700 °C.

Inconel 625, a nickel-based superalloy, has drawn much attention in the emerging field of additive manufacturing (AM) because of its excellent weldability and resistance to hot cracking. The extreme processing condition of AM often introduces enormous residual stress (hundreds of MPa to GPa) in the as-fabricated parts, which requires stress-relief heat treatment to remove or reduce the internal stresses. Typical residual stress heat treatment for AM Inconel 625, conducted at 800 °C or 870 °C, introduces a substantial precipitation of the δ phase, a deleterious intermetallic phase. In this work, we used synchrotron-based in situ scattering and diffraction methods and ex situ electron microscopy to investigate the solid-state transformation of an AM Inconel 625 at 700 °C. Our results show that while the δ phase still precipitates from the matrix at this temperature, its precipitation rate and size at a given time are both smaller when compared with their counterparts during typical heat treatment temperatures of 800 °C and 870 °C. A comparison with thermodynamic modeling predictions elucidates these experimental findings. Our work provides the rigorous microstructural kinetics data required to explore the feasibility of a promising lower-temperature stress-relief heat treatment for AM Inconel 625. The combined methodology is readily extendable to investigate the solid-state transformation of other AM alloys.

The influence of microstructural anisotropy on the hot deformation of wire arc additive manufactured (WAAM) Inconel 718

Hybrid additive manufacturing, incorporating additive manufacturing (AM) and other thermo-mechanical processes, has been developed to improve AM mechanical properties by modifying the as-deposited microstructure and eliminating defects. Additive manufactured parts present strong anisotropic properties, as shown by the anisotropic columnar grain morphology and texture. Samples of AM Inconel 718 were tested at high temperature and under uniaxial compression over a range of conditions. The evolution of microstructural anisotropy and the viscoplastic behaviour under these hot deformation processes was studied. The microstructure and texture evolution were characterised with optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The results show that the initial anisotropic microstructure had a negligible effect on flow stress and slip system activation during the hot deformation. The shape of original grains did, however, play a predominant role in determining the final microstructure. When the compression direction was perpendicular to the longitudinal of columnar grains, a more uniform microstructure was obtained under high-flow-stress conditions. This preferred compression direction provides guidance for hot deformation in hybrid additive manufacturing practice. Furthermore, for the nickel alloy studied, controlling the deformation direction to achieve a fine grain structure at a lower temperature (950 °C, lower than δ-solvus) brings practical benefits in the form of possible further δ grain refinement and less demanding thermal conditions during subsequent deformation processes.

Influence of Heat treatments on Microstructure and Mechanical Properties of Additive Manufactured Inconel 718 Superalloy

Influence of Heat treatments on Microstructure and Mechanical Properties of Additive Manufactured Inconel 718 Superalloy

Laser Welding of Laser Powder Bed Fusion Manufactured Inconel 718: Microstructure and Mechanical Properties

This paper focuses on the laser weldability of additively manufactured (AM) Inconel 718. The experiments of this research were conducted on different series of AM Inconel 718 alloy, i.e. as­-built, heat­ treated (HT), and HT after welding, and comprehensively characterized using optical microscope and electron back scattering diffraction (EBSD). The weld morphology and microstruc­tural evolution of the fusion zone were recorded. The mechanical properties of the welded AM Inconel 718 were evaluated by tensile tests and hardness measurements. It was found that solidification crack and micropore defects are induced in the as­built AM Inconel 718. However, defect­free weld was promoted in the HT alloy. The changes in hardness profiles and tensile strength under the experimen­tal parameters were further reported. Homogenous hardness of 500 HV across the weld was obtained when HT was applied after the LW.

Characterization of Additive Manufactured Inconel 718 Alloy Using Laser Cladding

Laser based metal additive manufacturing (AM) is an emerging technology in various aerospace industries including aero-engine components and turbine manufactures. Laser cladding is a potential process for material deposition and surface enhancement technique that forms a strong metallurgical bond with the substrate. In the present study, Nickel based Inconel 718 (IN718) super alloy which maintains high strength working at elevated temperatures is used as the clad material. The study investigates the processing of Inconel 718 with powder morphology and microstructural properties and also two, three and four-layer deposition. This study explores the possibility of depositing IN718 using laser cladding that can be better considered as metal AM process.

Tribocorrosion Behavior of Inconel 718 Fabricated by Laser Powder Bed Fusion-Based Additive Manufacturing

Additive manufacturing (AM) by laser powder bed fusion (LPBF) has gained significant research attention to fabricate complex 3D Inconel alloy components for jet engines. The strategic advantages of LPBF-based AM to fabricate jet components for aerospace applications are well reported. The jet components are exposed to a high degree of vibration during the jet operation in a variable aqueous environment. The combined vibration and the aqueous environment create a tribological condition that can accelerate the failure mechanism. Therefore, it is critical to understand the tribocorrosion behavior of the Inconel alloy. In the present work, tribocorrosion behavior of the LPBF fabricated standalone coating of Inconel 718 in the 3.5% NaCl aqueous solution is presented. The LPBF fabricated samples are analyzed to determine the impact of porosity, generated as a result of LPBF, on the triobocorrosion behavior of AM Inconel 718. The study includes potentiodynamic tests, cathodic polarization, along with OCP measurements. The corrosive environment is found to increase the wear by 29.24% and 49.5% without the initiation of corrosion in the case of AM and wrought Inconel 718, respectively. A corrosion accelerated wear form of tribocorrosion is observed for Inconel 718. Additionally, the corrosive environment has a significant effect on wear even when the Inconel 718 surface is in equilibrium potential with the corrosive environment and no corrosion potential scan is applied. This study provides an insight into a critical aspect of the AM Inconel components.

Microstructure evolution of laser cladding Inconel 718 assisted hybrid ultrasonic-electromagnetic field

In the present article, the hybrid ultrasonic-electromagnetic (UEM) physics field is introduced into the laser additive manufacturing Inconel 718. The effect of the hybrid UEM field on microstructure evolution is investigated. Obtained results show that when the hybrid UEM is applied, porosity reduces significantly, the columnar dendrites epitaxial growth behavior along the deposition direction depresses and the columnar transition to equiaxed grains improves. Moreover, the average microhardness of the coating increases from 244 HV0.2 to 271 HV0.2.

Microstructures and Mechanical Behaviors of Additive Manufactured Inconel 625 Alloys via Selective Laser Melting and Laser Engineered Net Shaping

Microstructures and Mechanical Behaviors of Additive Manufactured Inconel 625 Alloys via Selective Laser Melting and Laser Engineered Net Shaping

The use of Additive Manufactured Inconel 625 as Bipolar Plate for the High Temperature Proton Electrolyte Membrane Fuel Cell

Inconel 625 is a promising candidate as base material for bipolar plates in the High Temperature Proton Electrolyte Membrane Fuel Cell (HT-PEMFC), due to its mechanical strength and anti-corrosive properties. Due to its often complicated flow channel networks both internally and externally, production time and costs are significant factors to the total fuel cell manufacturing costs. Additive manufacturing (AM) might be a promising production method, though it is important that the material have its desirable properties intact. This includes corrosion resistance towards concentrated phosphoric acid (H3PO4) at elevated temperatures (120 °C- 200 °C) and exposed to different voltage values. In this work, flat Inconel 625 samples have been manufactured using AM followed by post-machining of its surface to an arithmetic roughness average (Ra) of ~0.3 |j.m. These samples were electro-chemically tested for its anti-corrosive properties while exposed to concentrated H3PO4 at 150 °C and a potential of 0.65 V vs the reversible hydrogen electrode (RHE). The sample surfaces were analysed using scanning electron microscopy (SEM) before and after the corrosion experiment. The interfacial contact resistance (ICR), a measure for the resistance towards electron conductivity through the corrosion-exposed surface with an adjacent conducting material, was also measured before and after the corrosion tests. For comparison, hot rolled Inconel 625 sample commercially purchased and post-machined to the same Ra-value was tested for its corrosion properties and compared to the AM-produced Inconel 625 sample. The AM-sample had a higher corrosion rate compared to the commercial with a corrosion penetration rate (CPR) almost twice as high. The measured ICR of the commercial sample was over 3.5 times higher than for the AM-sample after the corrosion test, indicating a less successful formation and thickness development of a protective phase on the AM-sample surface. Despite of equivalent surface roughness, the corrosion properties between the two production methods are significantly different, which are thought to be linked to different microstructures formed during their manufacturing.

Understanding the Low Cycle Fatigue of Additive Manufactured Inconel 718: A Crystal Plasticity Modeling Approach

Understanding the Low Cycle Fatigue of Additive Manufactured Inconel 718: A Crystal Plasticity Modeling Approach

A comparative analysis of Inconel 718 made by additive manufacturing and suction casting: Microstructure evolution in homogenization

Homogenization is one of the critical stages in the post-heat treatment of additive manufacturing (AM) component to achieve uniform microstructure. During homogenization, grain coarsening could be an issue to reserve strength, which requires careful design of both time and temperature. Therefore, a proper design of homogenization becomes particularly important for AM design, for which work hardening is usually no longer an option. In this work, we discovered an intriguing phenomenon during homogenization of suction-cast and AM Inconel 718 superalloys. Through both short and long-term isothermal heat treatments at 1180 °C, we observed an abnormal grain growth in the suction-cast alloy but continuous recrystallization in the alloy made by laser powder bed fusion (LPBF). The grain size of AM samples keeps as small as 130 μm and is even slightly reduced after homogenization for 12 h. The homogeneity of Nb in the AM alloys is identified as the critical factor for NbC formation, which further influences the recrystallization kinetics at 1180 °C. Multi-type dislocation behaviors are studied to elucidate the grain refinement observed in homogenized alloys after LPBF. This work provides a new pathway on microstructure engineering of AM alloys for improved mechanical performance superior to traditionally manufactured ones.

Using SXRR to Probe the Nature of Discontinuities in SLM Additive Manufactured Inconel 718 Specimens

The utilization of additive manufacturing (AM) to fabricate robust structural components relies on understanding the nature of internal anomalies or discontinuities, which can compromise the structural integrity. While some discontinuities in AM microstructures stem from similar mechanisms as observed in more traditional processes such as casting, others are unique to the AM process. Discontinuities in AM are challenging to detect, due to their submicron size and orientation dependency. Toward the goal of improving structural integrity, minimizing discontinuities in an AM build requires an understanding of the mechanisms of formation to mitigate their occurrence. This study utilizes various techniques to evaluate the shape, size, nature and distribution of discontinuities in AM Inconel 718, in a non-hot isostatic pressed (HIPed) as-built, non-HIPed and direct age, and HIPed with two step age samples. Non-destructive synchrotron radiation refraction and transmission radiography (SXRR) provides additional information beyond that obtained with destructive optical microscopy. SXRR was able to distinguish between voids, cracks and lack of melt in, due to its sensitivity to the orientation of the discontinuity.

Further Studies into Crack Growth in Additively Manufactured Materials.

Understanding and characterizing crack growth is central to meeting the damage tolerance and durability requirements delineated in USAF Structures Bulletin EZ-SB-19-01 for the utilization of additive manufacturing (AM) in the sustainment of aging aircraft. In this context, the present paper discusses the effect of different AM processes, different build directions, and the variability in the crack growth rates related to AM Ti-6Al-4V, AM Inconel 625, and AM 17-4 PH stainless steel. This study reveals that crack growth in these three AM materials can be captured using the Hartman–Schijve crack growth equation and that the variability in the various da/dN versus ΔK curves can be modeled by allowing the terms ΔKthr and A to vary. It is also shown that for the AM Ti-6AL-4V processes considered, the variability in the cyclic fracture toughness appears to be greatest for specimens manufactured using selective layer melting (SLM).

Dynamic-loading behavior and anisotropic deformation of pre- and post-heat-treated IN718 fabricated by laser powder bed fusion

The microstructures of additively manufactured (AM) metal components have been shown to be heterogeneous and spatially variable when compared to conventionally manufactured counterparts. Consequently, the mechanical properties of AM-metal parts are expected to vary locally within their volume. For AM structural components intended to operate in extreme environments, including high-strain-rate loading scenarios, there is a need to quantify variability of mechanical behavior within the same AM-build domain at quasi-static and dynamic strain-rates as well as the effect of heat treatment on the mechanical properties. The objective of this study is to investigate the effect of loading direction and direct-age hardening heat treatment on quasi-static and dynamic mechanical response within an Inconel 718 volume produced by laser powder bed fusion using manufacturer-recommended processing parameters. Uniaxial compression tests and a split-Hopkinson pressure bar (SHPB) were used to investigate the quasi-static and dynamic response, respectively, of as-built and heat-treated specimens extracted along the three principal processing directions. Electron backscatter diffraction measurements were made for representative specimens within the build domain to correlate microstructural features to observed location-specific mechanical deformation. Results from both quasi-static and dynamic loading show that the recommended processing parameters yield a homogeneous stress-strain response throughout the material volume in the as-built condition. In the direct-age-hardened condition, statistically significant differences were observed in the stress–strain responses between the build direction and sweep and transverse directions (although the latter two exhibited no statistically significant differences). Deformed specimen geometries showed a systematic and repeatable preferential deformation along the build direction, regardless of condition or loading strain rate when loading was applied in either of the two orthogonal processing directions. The deformation dependence is found to be related to the underlying, process-induced crystallographic texture and grain morphology. This study provides important insight that can be used for qualifying large AM Inconel 718 parts for critical structural applications used in extreme conditions.

The Creep Behavior of Additively Manufactured Inconel 625

Creep tests of additively manufactured (AM) Inconel 625, both hot isostatically pressed (HIPed) and non‐HIPed, are performed at various stresses between 65 and 658 MPa at 650–800 °C. The creep behavior of AM samples are compared with that of (conventional) wrought alloys. Tests are performed over a 24 h period for initial heat‐treated samples and also after heat exposure at the service temperature of 650 °C for 6 months. The 6 month tests consist of a time‐temperature profile similar to Inconel 625 service conditions in jet engines. It is found that the creep strength of AM 625 has equal or superior creep strength at 650–800 °C compared with the wrought alloy, even after 6 months exposure to the test temperature. The HIPed AM alloys has significantly superior ductility over the non‐HIPed AM Inconel 625, as expected. However, the ductility of the HIPed AM Inconel 625 is still substantially lower than the wrought alloy, particularly at the longer exposure times to the test temperatures. The explanation for the dramatic loss of ductility is not clearly identified, but sulfur segregation to grain boundaries and relatively higher oxygen content leading to oxide embrittlement are the possibilities.

Phase Fraction and Evolution of Additively Manufactured (AM) 15-5 Stainless Steel and Inconel 625 AM-Bench Artifacts.

A proper understanding of the structure and microstructure of additively manufactured (AM) alloys is essential not only to the prediction and assessment of their material properties, but also to the validation and verification of computer models needed to advance AM technologies. To accelerate AM development, as part of the AM-Bench effort, we conducted rigorous synchrotron-based X-ray scattering and diffraction experiments on two types of AM alloys (AM 15-5 stainless steel and AM Inconel 625). Taking advantage of the high penetration of synchrotron hard X-rays, we determined the phases present in these alloys under different build conditions and their statistically meaningful phase fractions using high-resolution X-ray diffraction. Using in situ multi-scale X-ray scattering and diffraction, we quantitatively analyzed the phase evolution and development of major precipitates in these alloys as a function of time during stress relief heat treatments. These results serve to validate AM microstructure models and provide input to higher-level AM processing and property models to predict the material properties and performances.

Comparison of carbon-based reinforcement on laser aided additive manufacturing Inconel 625 composites

Abstract In this paper, a comparison study of CNTs and graphite addition in laser aided additive manufacturing (LAAM) Inconel 625 composites was proposed. The difference of microstructure and tensile properties between two modified Inconel 625 alloys was investigated. SEM, EDS and micro-Raman identification results showed that the CNTs structure can be found on columnar dendrite boundaries accompanied with precipitated Laves and γ′ phase in LAAM Inconel 625-CNTs composite. Based on tensile test results, 0.25 wt% of CNTs addition in LAAM Inconel 625 can significantly increase strength and ductility by 20% because of grain refinement and grain boundary pinning reinforcement. However, the graphite addition only raises strength but decreases ductility due to carbon content raise.