Additive Manufacturing Inconel Research Articles

Study on improving surface integrity for additively manufactured Inconel 718 via high-speed micromilling

ABSTRACT The surface finish required for the application of products to aerospace and defense sectors cannot be produced by additive manufacturing (AM), and hence, a secondary finishing process is required post-additive manufacturing. Consequently, the current study analyses the ability of micromilling to enhance surface integrity for AM Inconel 718. Micromilling has been performed at three different levels of cutting conditions. The force induced during micromilling, surface finish, and top burr width for machined workpieces has been analyzed. A minimum value of 50 nm has been achieved for surface finish post-machining at a feed of 2 µm/flute and a speed of 50,000 rpm. An upmilling strategy has been found to be generating a lower top burr width compared to downmilling with a minimum value of 141 µm. A stability plot has also been constructed for the micromilling of AM Inconel 718 and compared with the stability lobe for wrought Inconel at different cutting speeds.

Relation Between Striations Spacing and Fatigue Crack Growth Rates for Additive Manufactured Inconel 625

ABSTRACTThe principles of the mechanisms for fatigue crack propagation in metals have been established several decades ago. By definition, fatigue might be summarized as a damage process imparted to a material under the action of cyclic loads. The relation between fatigue crack growth rates (FCGRs) and formation of striation marks has been a controversial topic. Some authors stated that, in certain fatigue regimes, several fatigue cycles are required to form a single striation. The disagreement found was the motivation for the present work. This study's main goal is to provide a comparison between the striation spacing and the respective FCGR. These analyses will be performed in a Nickel superalloy, Inconel 625, obtained via directed energy deposition. Investigation of the striations spacing are compared with data obtained from FCGR tests. A good agreement between striation spacing and FCGRs was found to intermediate and large values of stress intensity factor.

On the feasibility of a predictive model of mechanical properties of AM Inconel 718 thin wallets produced by DED-LB process monitored with thermal methods

AbstractNickel-based superalloys are widely used in applications requiring resistance to high temperatures and high strain rates. Various additive manufacturing (AM) processes, such as Laser Metal Deposition (LMD), a Directed Energy Deposition (DED) process, can be used to produce these components. The quality of the components depends on the process parameters, so it is crucial to investigate the influence of each parameter and their combinations through extensive experimental campaigns. In this scenario, it would be very important to predict the mechanical properties of the produced components through the online monitoring of the process parameters using non-destructive techniques, such as thermography. The aim of this work was to explore the feasibility to predict the mechanical properties of Inconel 718 thin wallets around 10 mm produced by DED-LB, based on the extraction of suitable thermal features directly during the production. An experimental campaign analysed the effect of different process parameters (laser power, scan speed, powder flow rate, and energy density) on the mechanical properties achieved. All sample production was monitored with an infrared uncooled camera integrated with the laser head moving at the same scan speed. After the process, hardness measurements and tensile tests in both growth directions were carried out for each sample to evaluate the mechanical behaviour of the "as-built" coupons and the influence of selected process parameters. Macrographic analyses of the material structure were performed to determine the morphology of the passes and the degree of overlap between different passes and layers. Various thermal features and statistical models were considered to demonstrate the possibility of establishing a predictive model. The obtained results demonstrated the correlation between the hardness and the apparent temperature assuming a confidence level of 95%, and the possibility of predicting in this sense the final macrostructure and the mechanical behaviour of the printed material considering an empirical model with the R2 coefficient around 0.8.

Investigation of Corrosion Behavior of Wrought and Wire + Arc Additive Manufactured Inconel 625 in Air and Molten Salts at High-Temperature Environments

Investigation of Corrosion Behavior of Wrought and Wire + Arc Additive Manufactured Inconel 625 in Air and Molten Salts at High-Temperature Environments

A Quantitative Approach to Precipitate Characterization in Wire Arc Additive Manufactured Inconel 600 Series Alloys

A Quantitative Approach to Precipitate Characterization in Wire Arc Additive Manufactured Inconel 600 Series Alloys

Magnetron Sputtering as a Microstructural Screening Tool for Laser Additive Manufacturing: Study on Ni Superalloys

In this work, magnetron sputtering coupled with a heat treatment is demonstrated as a route to obtain surrogate microstructures comparable to those achieved by laser‐based additive manufacturing (AM) for Ni superalloys. Furthermore, this technique is shown to be a novel and efficient way of screening elemental additions with high compositional resolution for AM, without the need for designing and characterizing custom‐atomized powders. Herein, Inconel 718 films are sputtered from both arc‐melted and AM targets to capture any compositional changes and to develop a comprehensive methodology. Films are characterized via electron microscopy techniques to establish similarities between sputtered plus heat‐treated films and bulk AM Inconel 718 microstructures reported in literature. Since Inconel 718 is susceptible to high‐temperature S embrittlement, films were then co‐sputtered with small amounts of Zr or Hf, which are found to facilitate sulfur segregation via nano secondary ion mass spectrometry analysis. Overall, this work highlights how magnetron sputtering plus heat treatment can be leveraged to rapidly screen novel AM microstructures, thereby accelerating the development and deployment of AM materials.

Study on the influence of the dendritic microstructure on the turning of Wire and Arc Additive Manufacturing Inconel 718

Study on the influence of the dendritic microstructure on the turning of Wire and Arc Additive Manufacturing Inconel 718

Impact of radial rake angle and machining constraints on the machining behavior and functionality of additive manufactured inconel 718 alloy

The Additive manufactured (direct metal laser sintering) samples has shown greater surface roughness which leads to reduce the functionality of the components. Additionally, the cutting force requirement and obtainable surface finish show the vigorous role during the slot milling process of many materials. In this study, the slot milling process has been conducted on the Additive Manufactured (AM) Inconel 718 alloy under numerous cutter nomenclature such as −7°, 0° and +7° in radial rake angle and machining circumstances such as a cutting feed (5, 15, and 25 mm min−1) and cutting speed (14.13, 28.26, and 42.39 m min−1) to analyze its impact on the cutting force requirement and surface roughness of AM Inconel 718 alloy through TOPSIS statistical tool. Through the above analyses, it is found that the cutter nomenclature plays a vigorous role in the cutting force requirement and obtainable surface roughness followed by the cutting feed and cutting speed, owed to the establishment of moderate strain strengthening and thermal soothing effect.

A Comparative Investigation of Machine Learning Algorithms for Pore-Influenced Fatigue Life Prediction of Additively Manufactured Inconel 718 Based on a Small Dataset.

Fatigue life prediction of Inconel 718 fabricated by laser powder bed fusion was investigated using a miniature specimen tests method and machine learning algorithms. A small dataset-based machine learning framework integrating thirteen kinds of algorithms was constructed to predict the pore-influenced fatigue life. The method of selecting random seeds was employed to evaluate the performance of the algorithms, and then the ranking of various machine learning algorithms for predicting pore-influenced fatigue life on small datasets was obtained by verifying the prediction model twenty or thirty times. The results showed that among the thirteen popular machine learning algorithms investigated, the adaptive boosting algorithm from the boosting category exhibited the best fitting accuracy for fatigue life prediction of the additively manufactured Inconel 718 using the small dataset, followed by the decision tree algorithm in the nonlinear category. The investigation also found that DT, RF, GBDT, and XGBOOST algorithms could effectively predict the fatigue life of the additively manufactured Inconel 718 within the range of 1 × 105 cycles on a small dataset compared to others. These results not only demonstrate the capability of using small dataset-based machine learning techniques to predict fatigue life but also may guide the selection of algorithms that minimize performance evaluation costs when predicting fatigue life.

Experimental Tribological Study on Additive Manufactured Inconel 718 Features Against the Hard Carbide Counter Bodies

Abstract In past years, machining processes have been required when fabricating the complex Inconel 718 parts, and these processes cause undesired tensile residual stresses. Inconel 718 also exhibits extreme work hardening throughout the machining process. To avoid these issues, recently, Inconel 718 parts with high geometric complexity and dimensional accuracy, the laser powder bed fusion (LPBF) process, which belongs to additive manufacturing, has been extensively used. These Inconel 718 parts with LPBF processing are frequently utilized in various industries, including aerospace, automotive, pharmaceutical, and food processing, because of their high strength, biocompatibility, and corrosion resistance. Wear resistance is essential in addition to these properties for designing and crushing applications. In this paper, tribological tests were conducted on the LPBF-processed Inconel 718 parts and compared to casted Inconel 718 parts against the four types of counter bodies, namely boron carbide, silicon carbide, tungsten carbide, and titanium carbide. The studies were carried out for 30 min with a constant load of 5 N, frequency of 10 Hz, and stroke length of 1 mm. In comparison to casted samples, LPBF-processed samples showed low coefficient of friction (COF) values. The highest COF was observed on the cast Inconel 718 against the tungsten carbide counter body. The wear mechanisms were studied using scanning electron microscopy.

New insights into the anisotropic ductility of additively manufactured Inconel 718

Anisotropic ductility in additively manufactured (AM) alloys, namely better ductility along the building direction (BD) has been extensively studied and traditionally attributed to the crystallographic texture. However, recent studies have shown significant ductility anisotropy in weakly or non-textured AM alloys, indicating that other factors may also play critical roles. To explore this, AM Inconel 718 with weak crystallographic texture was selected as the model material, and the in-situ high-energy X-ray diffraction tests together with multiscale microstructural characterization techniques were performed to explore the deformation micromechanisms. The results of this study, for the first time, revealed that the better ductility in the vertical specimen (loading parallel to BD) was partially due to the negative stress triaxiality factor (TF) of the {220} grains during plastic deformation, which results in the shrinkage or even healing of the microvoids. Furthermore, the δ-phase alignment in conjunction with grain boundary orientation were also proved to have a pronounced impact on the anisotropic ductility of AM alloys. On the other hand, though in the overall weak-textured microstructure, the proportion of 〈101〉 grains were marginally over other grains. Thus, the positive effect of {220} grains on ductility was stronger than the negative effect of {200} and {311} grains, contributing to the excellent failure elongation exceeding 12% for both samples. The findings of this study shed new light on the mechanisms underlying the anisotropic ductility of AM alloys and provide insight into strategies for enhancing their performance.

Role of δ-phase on Mechanical Behaviors of Additive Manufactured Inconel 718: Detailed Microstructure Analysis and Crystal Plasticity Modelling

In this work, a multi-scale approach was applied to reveal the evolution mechanisms of the δ (Ni3Nb) phase and the resultant mechanical responses in wire-arc additive manufactured (WAAM) Inconel (IN) 718. Several heat treatment strategies, consist of homogenization, intermediate heat treatment and aging process, were firstly conducted to produce δ phases with different characteristics. The early evolution of the δ phase was then analyzed in detail via transmission electron microscopy. The nanoindentation and tensile tests were also used to verify the strengthen response of δ phase. Moreover, a crystal plasticity finite element (CPFE) model, taking into account the different configurations of δ phase, was developed to study and predict the micro deformation behavior. Results revealed that when the intermediate heat treatment time exceeded 1 h, the formation of the main strengthening phase γ" was constrained by the δ phase, accompanied by the coarsening of γ". The decrease of γ" phase and the destruction of coherent γ"/γ interface are the main causes of strength loss in the WAAMed IN718. The intergranular dislocation transmission was hindered by the δ phase, thereby increasing the grain boundary strength. However, the needle-like δ phase within the grain may cause premature fracture due to strain localization, thereby reducing the material properties. The evolution mechanisms of the δ phase obtained in this study provides theoretical guidance for the optimization of the microstructures and mechanical properties of WAAM Inconel 718.

Effects of TiC on the microstructure refinement and mechanical property enhancement of additive manufactured Inconel 625/TiC metal matrix composites fabricated with novel core-shell composite powder

The flexible product shape of additive manufacturing (AM) is attractive, but the process suffers from a lack of material property diversity due to a limited number of printable alloys and post-processing options. To overcome this problem, the AM of metal matrix composites (MMCs) is a highly suitable solution because the properties of MMC can be tailored using various reinforcements. Therefore, extensive research has been conducted on the AM of MMCs; however, the major huddle for this process has been the difficulties in preparing feedstock powder and operating the AM process. This study introduces an easily synthesizable core-shell composite powder, which was fabricated by a recently developed process called the SMART process. The core-shell powder has a novel morphology, consisting of a metal core and composite shell, distinguishing it from the powders used in conventional AM approaches. Inconel 625/TiCp composites were fabricated using the core-shell composite powder, with various fractions of TiCp up to 10 vol.%. Compared to additive-manufactured Inconel 625, the additive-manufactured MMCs showed enhanced strength with significantly fewer defects. The results of this study may accelerate the application of MMC fabricated by AM, which offers superior properties and reliability compared to casting and powder metallurgy due to the higher degree of dislocation density and reinforcement dispersion.

Investigations on Deposition Geometry and Mechanical Properties of Wire Arc Additive Manufactured Inconel 625

Investigations on Deposition Geometry and Mechanical Properties of Wire Arc Additive Manufactured Inconel 625

Strengthening additively manufactured Inconel 718 through in-situ formation of nanocarbides and silicides

We report additive manufacturing (AM) of a nickel superalloy metallic matrix composite (Ni-MMC) using laser powder bed fusion (LPBF). Nanoceramic-containing composite powders were prepared by high-speed blender declustering and ball milling of as-received SiC nanowires (2 vol%) and Inconel 718 alloy powders, which produced a homogeneous decoration of SiC on the surfaces of Inconel particles. Analysis of the as-printed specimens revealed the dissolution of SiC nanowires during laser melting, leading to the in-situ formation of Nb- and Ti-based silicide and carbide nanoparticles. These in-situ formed nanoparticles resulted in a more desirable solidification microstructure of the AM Inconel 718 with fewer printing defects (cracks and pores) and slightly refined grain sizes. Mechanical characterization of the as-printed Ni-MMCs revealed notable increases in hardness, yield strength (by 16%), and ultimate tensile strength (σUTS, by 12%) compared to the reference samples without SiC addition. After heat treatment, the same composite samples displayed a 10% higher σUTS compared to identically treated unreinforced material while maintaining ∼14% total tensile elongation. We believe this in-situ precipitate formation presents a simple and effective method for strengthening additively manufactured high-temperature materials that could be used in the increasingly harsh environments in energy and propulsion applications.

Effect of titanium nitride inclusions on the mechanical properties of direct laser deposited Inconel 718

Additive manufacturing (AM) of metal is attractive for its ability to fabricate complex and tailored structures. However, unusual thermal history during the manufacturing process creates unique microstructures, which leads to non-uniform mechanical behavior. In this paper, we report the room temperature and high temperature mechanical properties of Inconel 718 fabricated by laser-based directed energy deposition. Surprisingly, failure strain at all tested temperatures exhibited noticeable scatter, which is attributed to the formation of titanium nitride (TiN) inclusions. While heat treatment was conducted on AM Inconel 718 to minimize the influence of the inhomogeneous as-built microstructure, it resulted in significant increase in the volume fraction, number density, and maximum particle radius of the TiN inclusions. Consequently, dispersion of mechanical properties became more severe. Experimental investigation (strain mapping, fractography, and X-ray microscopy) supported by finite element analysis implies that premature failure of AM Inconel 718 is mainly due to transgranular cracks of the TiN inclusions that propagates into the matrix.

Hydrogen Embrittlement of Inconel 718 Manufactured by Laser Powder Bed Fusion Using Sustainable Feedstock: Effect of Heat Treatment and Microstructural Anisotropy

This study investigated the in-situ gaseous (under 150 bar) hydrogen embrittlement behaviour of additively manufactured (AM) Inconel 718 produced from sustainable feedstock. Here, sustainable feedstock refers to the Inconel 718 powder produced by vacuum induction melting inert gas atomisation of failed printed parts or waste from CNC machining. All Inconel 718 samples, namely AM-as-processed, AM-heat-treated and conventional samples showed severe hydrogen embrittlement. Additionally, it was found that despite its higher yield strength (1462 ± 8 MPa) and the presence of δ phase, heat-treated AM Inconel 718 demonstrates 64% lower degree of hydrogen embrittlement compared to the wrought counterpart (Y.S. 1069 ± 4 MPa). This was linked to the anisotropic microstructure induced by the AM process, which was found to cause directional embrittlement unlike the wrought samples showing isotropic embrittlement. In conclusion, this study shows that AM Inconel 718 produced from recycled feedstock shows better hydrogen embrittlement resistance compared to the wrought sample. Furthermore, the unique anisotropic properties, seen in this study for Inconel 718 manufactured by laser powder bed fusion, could be considered further in component design to help minimise the degree of hydrogen embrittlement.

Characterization of Properties of Laser Powder Bed Fusion Three-Dimensional-Printed Inconel 718 for Centrifugal Turbomachinery Applications

AbstractThis paper presents the results of a comprehensive effort to characterize the properties of Inconel 718 produced by a form of laser powder bed fusion (LPBF) additive manufacturing (AM) or three-dimensional (3D)-printing, subsequently subjected to hot isostatic pressing (HIP) and heat treatment according to standards F3055-14a and AMS 5663, respectively. Material property data, while broadly available for traditional Inconel 718 presentations (e.g., forgings or castings) is currently lacking for the 3D-printed material. It is expected that while limited in size, the experimental data sets presented provide sufficient information to glean the capability of LPBF Inconel 718. These include: (1) chemical composition, electron backscatter diffraction (EBSD), and X-ray energy dispersive spectroscopy (XEDS) characterization of 3D-printed material structure; (2) tensile properties—0.2% yield stress, ultimate stress, modulus of elasticity, and elongation to failure—based on 108 samples, as functions of temperature and sample print orientation; (3) creep rupture data including the Larson-Miller parameter, based on 21 samples; and (4) high cycle fatigue data based on 21 samples as a function of temperature. Results are compared to available standards and/or data for forged, cast, and other AM Inconel 718. A key observation of this study, based on the EBSD results, is that while the material appears to approach full recrystallization following heat treatment, there is a detectable fraction of the material that does not fully recrystallize, resulting in a material with mechanical properties (e.g., yield stress and creep rupture) measurably lower than those of forgings, but higher than those of castings.

Grain refinement in Wire-Arc Additive Manufactured Inconel 82 alloy through controlled heat input

In the Wire-Arc Additive Manufacturing (WAAM) process, the high heat input led to the formation of a large-sized molten metal pool, producing a coarse columnar grain structure and thus the component exhibits poor mechanical properties. So, it is important to have in-process transformation (CET: columnar to equiaxed transition) of the formed grains. This can be achieved by the proper control of the cooling rate during the solidification process. In this study, four vertical walls consisting of 10, 15, 20, and 25 layers of Inconel-82 alloy were produced using a GTAW-based AM process with varying input parameters. It has been observed that with the variation in travel speed and low frequency pulsed arc (3 Hz) the heat input varied from 705.1 J/mm (maximum) to 301.7 J/mm (minimum) which promoted the in-process grain refinement. The transformation of columnar grains into equiaxed grains having an average grain size of 19 µm was observed in the 15-layer wall. The average micro-hardness of the fabricated thin wall got enhanced from 228 HV in the 10-layer wall to 275 HV in the 15-layer wall owing to the grain refinement. Similarly, the maximum average ultimate tensile strength (UTS) and yield strength (YS) are observed in the transverse direction which is 650 MPa and 325 MPa respectively. The friction coefficient and wear rate are observed to be minimum in the 15-layer wall i.e., 0.42 and 4.7 × 10−4 mm3/Nm respectively. Furthermore, the anisotropy in the tensile properties is observed to be minimum in 15 layer wall (average UTS: 1.9 %; average YS:3.8 %).

Study on the Effects of Different Cutting Angles on the End-Milling of Wire and Arc Additive Manufacturing Inconel 718 Workpieces.

This research presents an analysis of the effects of different cutting angles on the side milling of Inconel 718 products manufactured with the Wire and Arc Additive Manufacturing (WAAM) technique. Considering that this manufacturing technology can build near-net shape products, its surface quality is deemed unqualified as a final product, requiring a post-processing step. In this paper, three different angles—0°, 35°, and 90—are compared, looking for possible differences regarding its machinability. As the alloy in question is a material known for being difficult to machine, and the samples were produced with the additive manufacturing technique that created peculiar characteristics, it was deemed necessary to analyze different aspects of the machining process: the surface quality, tool wear, and cutting forces for all three cases, and to rank the angles regarding these results. With analog experiments with the same alloy but cold-rolled, it was possible to infer that not only is the 0-degree angle is the best option for milling, but the anisotropy of the WAAM samples could be the major source of the differences in the milling results.