Showing papers on "Inconel published in 2021"

The effects of shot peening, laser shock peening and ultrasonic nanocrystal surface modification on the fatigue strength of Inconel 718

Abstract: As most of the failures in engineering components initiate from the surface layer, applying surface treatments can play a crucial role in controlling material performance and lifetime. In this study, different surface severe plastic deformation techniques including severe shot peening, laser shock peening and ultrasonic nanocrystal surface modification have been considered. The effects of process parameters and the kinetic energy of each treatment on the microstructure, mechanical properties and fatigue behavior of nickel-based super-alloy Inconel 718 have been investigated. The results revealed that using the proper parameters to increase the kinetic energy of the applied surface treatments, it is possible to effectively promote surface grain refinement and induce a deep compressive residual stress field in Inconel 718 samples. Among the applied treatments, ultrasonic nanocrystal surface modification was found to be the most efficient one in improving the mechanical properties as it led to the most significant fatigue performance, followed by severe shot peening and laser shock peening.

Strengthening mechanisms in selective laser-melted Inconel718 superalloy

Abstract: The microstructures and mechanical properties of Inconel 718 (IN718) alloy fabricated by selective laser melting (SLM) are evaluated in as-built, direct aging (DA), and homogenization + aging (HA) conditions on considering the effect of applied loading direction. The results show that the microstructure of as-built and DA specimens consist of the intracrystalline fine degenerated dendritic structures (0.6–1 μm in spacing) with a high density of dislocations (1013–1014 m−2). Fine dendritic structures disappear after HA treatment, and the average geometrically necessary dislocation (GND) density decreases to 1012 m−2. A quantitative analysis of strengthening mechanisms is established by taking into consideration the grain boundary, solid solution, precipitation and dislocation strengthening. For the as-built and DA specimens, the contribution to the yield strength by dislocation strengthening is ~85 MPa in vertical deposition and ~170 MPa in horizontal deposition, respectively, and the Laves phases provide approximately 100–110 MPa. The contribution of precipitation strengthening to the strength increment in the DA and HA specimens is 590–600 and 830–850 MPa, respectively. The precipitation strengthening is mainly contributed by shearing mechanisms among which coherency strengthening plays dominant effect rather than order strengthening. For as-built, DA, and HA regimes, the specimens always exhibit higher strength along the horizontal direction than that along the vertical direction. The anisotropy of yield strength in the as-built and DA specimens is mainly attributed to the difference in dislocation density and effective grain size, and the anisotropy of yield strength in the HA specimens is mainly caused by the difference in effective grain size and Taylor factor.

Machinability of Inconel 718: A critical review on the impact of cutting temperatures

Abstract: The demand for high temperature-resistant superalloys such as Inconel 718 is increasing rapidly, as they possess superior mechanical, chemical, and physical properties. Hence, these materials are h...

Pore-affected fatigue life scattering and prediction of additively manufactured Inconel 718: An investigation based on miniature specimen testing and machine learning approach

Abstract: Fatigue life scattering and prediction of Inconel 718 fabricated by selective laser melting were investigated using miniature specimen tests combined with statistical method and machine learning algorithms. The relationship between pore features and fatigue life of the selective laser melting-fabricated specimens was analyzed statistically. The results show that the increase in the size and/or the number of the pores in the specimens, and/or the decrease in the distance from a pore center to the specimen surface degraded the fatigue life. The machine learning and statistical analysis results reveal that the fatigue life are most closely related to the location of the pores compared with the size and the number of pores in the specimens. The finding may provide a potential way to get high-throughput statistical data helping in evaluating defect-dominated scattering and prediction of fatigue life of additive manufactured metallic parts using miniature specimen testing assisted by the machine learning approach.

The effect of homogenization temperature on the microstructure and high temperature mechanical performance of SLM-fabricated IN718 alloy

Abstract: Microstructure, mechanical performances at elevated temperature (650 °C) and their correlation of Inconel 718 manufactured by Selective Laser Melting (SLM) were investigated in this paper. Four kinds of heat treatment schemes including homogenization, solution treatment and conventional aging process were carried out to regulate the microstructure in order to obtain the optimum comprehensive mechanical performances at high temperature. The dimension and morphology of grains, subgrains, different precipitates including δ phase, strengthening phase, carbides and nitrides were investigated. In addition, their evolution mechanism was also analyzed in detail. Furthermore, for figuring out the effects of microstructures on the mechanical performance, creep rupture test and tensile test were carried out to compare the performance differences of heat-treated samples. The results demonstrated that the heat-treated samples show the better creep rupture performance and higher tensile strength at elevated temperature than that of the wrought. In addition, the sample under homogenization heat treatment in 1080 °C, solution treatment in 980 °C and conventional aging treatment shows the optimum mechanical properties at 650 °C.

Selective compositional range exclusion via directed energy deposition to produce a defect-free Inconel 718/SS 316L functionally graded material

Abstract: In this research, additively manufacturing a functionally graded material (FGM) with a compositional range of Ni-based Inconel superalloy (Inconel 718) and Fe-based stainless steel (SS 316L) via directed energy deposition (DED) was examined. The microstructural transformation, defect behavior, and Vickers hardness of the material were each determined as a function of the discrete chemical composition of the FGM varied in steps of 10 wt% of the two materials across its length. In particular, for the specific compositions of 30 wt% Inconel 718/70 wt% SS 316L and 20 wt% Inconel 718/80 wt% SS 316L, critical pores and cracks (defects) initiated by ceramic oxides occurred due to the presence of intermetallic and carbide compounds. In addition, the results of electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analyses of the FGM demonstrate that the thermal and residual stresses due to constitutional supercooling and columnar-to-equiaxial transition (CET) became concentrated at the grain boundaries, thereby further contributing to the formation of the defects. The measured Vickers hardness was inevitably found to be minimal near the defective compositional range regardless of laser parameter optimization due to the reduced generation of segregants in the inter-dendritic regions and the increased formation of precipitates at the grain boundaries. The results of microstructural and mechanical analyses indicate that deliberate and strategic removal of the defective compositional range helped obtain a robust FGM composed of Inconel 718 and SS 316L without noticeable defects.

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

Abstract: 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.

Understanding tensile and creep properties of WC reinforced nickel-based composites fabricated by selective laser melting

Abstract: In this study, submicron-WC reinforced Inconel 718 composites were fabricated by selective laser melting (SLM). They were investigated regarding forming quality, microstructure evolution, tensile and creep properties. The results demonstrated that SLM-processing with decreasing volumetric energy density (Ed), entailed the fabrication of composites with also decreasing density, due to the formation of more pores and cracks. The microstructure of the prepared composites mainly consisted of two different types, namely cellular and columnar dendrites, which formed within the molten pool. The microstructure was more heterogeneous at smaller length scale, whereby reduced grain size and enhanced high angle grain boundaries (HAGBs) were observed. At the optimal Ed of 120 J/mm3, the SLM-fabricated composite was highly dense and exhibited small stress concentration, so that it showed the highest microhardness (361.7 HV0.2), ultimate tensile strength (1030.5 MPa) and elongation (24.8%). Owing to elongated grain boundaries, which were characteristic for the respective microstructure, the composite displayed reduced creep life and ductility. The deformation behaviors during tension and creep were analyzed and they were interrelated to the microstructural defects, grain size, grain boundary morphology, and dislocation density.

Effect of multi-layer laser cladding of Stellite 6 and Inconel 718 materials on clad geometry, microstructure evolution and mechanical properties

Abstract: The multi-layer laser cladding of high temperature resistance alloys i.e., Stellite 6 and Inconel 718 on SS316 was developed with an objective to investigate the effect of cladding materials on clad geometry, microstructure evolution and mechanical properties. The analysis was performed using Optical Microscope, SEM with EDS and Microhardness tester respectively. The results have shown a comparable difference in all the aspects of study. A 50% and 30% increment in clad height is measured while cladding at 12 mm/s and 16 mm/s scan speed as compared to 20 mm/s for both the alloys. The Inconel 718 deposits has shown 15–25% larger clad height, than Stellite 6. Also, under varying process parameters, 15–45% penetration depth and 10–15% higher dilution in Inconel 718 is obtained. SEM results have revealed that the microstructure evolution from top to bottom of the clad is nearly the same except at low laser powers. The decrement in microhardness is observed near the interface due to dilution and is higher in the first layer than the second layer. Whereas, the low dilution obtained in the second layer is because of the newly deposited layer over the substrate. The present work has given the optimum parameters (laser power and scan speed) as 2900 W and 20 mm/s for Stellite 6 and 3400 W, 12 mm/s for Inconel 718 respectively.

Effect of homogenization and solution treatments time on the elevated-temperature mechanical behavior of Inconel 718 fabricated by laser powder bed fusion.

Abstract: In the present study, the effect of homogenization and solution treatment times on the elevated-temperature (650 °C) mechanical properties and the fracture mechanisms of Inconel 718 (IN718) superalloy fabricated by laser powder bed fusion (LPBF) was investigated. Homogenization times between 1 and 7 h at 1080 °C were used, while solution treatments at 980 °C were performed in the range from 15 to 60 min. The as-printed condition showed the lowest strength but the highest elongation to failure at 650 °C, compared to the heat-treated conditions. After heat treatments, the strength of the IN718 alloy increased by 20.3-31% in relation to the as-printed condition, depending on the treatment time, whereas the ductility decreased significantly, by 67.4-80%. Among the heat treatment conditions, the 1 h homogenized conditions at 1080 °C (HSA1 and HSA2) exhibited the highest strength and ductility due to the combined effects of the precipitation hardening and sub-structural changes. Further increases in the homogenization time to 4 and 7 h led to a decrease in the strength and significant ductility loss of the LPBF IN718 due to the considerable annihilation of the dislocation tangles and a greater precipitation of coarse MC carbide particles. Furthermore, it was found that the solution treatment duration had a crucial influence on the mechanical properties at 650 °C due to the increase in the grain boundary strength through the pinning effect of the intergranular δ-phase. In addition, the fracture mechanism of the LPBF IN718 was found to be dependent on the heat treatment time. Finally, this investigation provides a map that summarizes the effect of homogenization and solution treatment times on the high-temperature mechanical behavior of LPBF IN718 by relating it to the corresponding microstructural evolution. This effort strives to assist in tailoring the mechanical properties of LPBF IN718 based on the design requirements for some specific applications.

Effect of Al content on wear and corrosion resistance of Ni-based alloy coatings by laser cladding

Abstract: Inconel 625 + x Al (x = 0, 2.5, 5.0, 7.5, 10.0) alloy coatings were prepared by laser cladding. The addition of Al promoted the formation of the BCC phase, which changed the coating microstructure from an FCC + δ phase + Laves phase to FCC + BCC + δ phase + Laves phase. Inconel 625 + 2.5 Al alloy showed the greatest corrosion resistance among all samples. The formation of an Al2O3 film improved the corrosion resistance of the coating, but excess Al decreased the Cr2O3 content in the film, which decreased the corrosion resistance of the coating. Increasing the Al content aggravated the lattice distortion and improved the solid solution strengthening effect, while also increasing the amount of BCC phase, which improved the coating hardness. After adding Al, the Inconel 625 + x Al alloy coatings displayed strong plastic deformation resistance, and their wear resistance was improved due to the presence of a hard phase.

Oxidation and hot corrosion resistance of HVOF/EB-PVD thermal barrier coating system

Abstract: Hot corrosion and oxidation cause very destructive damage in thermal barrier coatings (TBCs) during service conditions. In hot corrosion, TBCs exposed to molten salts lose their integrity easily due to the phase transformations while oxygen easily penetrates from the TBCs to bond coats and forms thermally grown oxide (TGO) layer which causes higher stresses at the interface of bond and top coating. In the current study, CoNiCrAlY powders were sprayed by high-velocity oxygen fuel (HVOF) technique on Inconel 718, and then yttria-stabilized zirconia (YSZ) and YSZ/Gd2Zr2O7 ingots were deposited by electron beam physical vapor deposition (EB-PVD) technique on the bond coated substrates. Isothermal oxidation tests were carried out at 1000 °C for 8, 24, 50, and 100 h, while hot corrosion tests were carried out at 1000 °C in the presence of NaCl, Na2SO4, and V2O5 molten salts with 5, 10, 15, and 20 h cycles. The produced coatings, as well as the oxidation and hot corrosion test results, were examined using SEM, EDS, XRD, and image analysis techniques. After the tests, the Gd2Zr2O7 layer was found to exhibit superior oxidation and hot corrosion performance as compared to the conventional YSZ TBC system.

On the influence of heat treatment on microstructure and mechanical behavior of laser powder bed fused Inconel 718

Abstract: A range of heat treatments have been developed for wrought Inconel 718 to obtain desired properties. For additively manufactured Inconel 718, the recently developed standard ASTM F3301 provides guidance for heat treatment of powder bed fusion specimens. Although this standard is based on standards developed for wrought Inconel 718, it does not include direct aging. Since direct aging reduces the number of processing steps, it can result in a post processing cost reduction if the desired properties are obtained. In this study, we characterized the microstructure and tensile behavior of Inconel 718 specimens produced by a laser powder bed fusion process. The specimens were heat treated according to two different routines after stress relieving: a full heat treatment versus a one-step direct aging process. Differences in the resulting texture and grain morphology were observed. The ex-situ stress-strain behavior was broadly similar. However, a slight increase in yield strength was observed for the direct aged specimen. In order to understand this behavior, investigations with in-situ synchrotron energy dispersive X-ray diffraction tensile testing revealed differences in the load partitioning among different crystal directions. Importantly, the elastic anisotropy expressed by the magnitude of the diffraction elastic constants showed a dependency on the microstructures.

Machinability of the laser additively manufactured Inconel 718 superalloy in turning

Abstract: In industrial fields, subsequent machining processing is essential for the laser additively manufactured (LAM) parts to meet the requirements of dimensional accuracy and surface quality in practical applications. Compared with the wrought Inconel 718 superalloy, this research investigated the machinability of the direct laser metal sintered Inconel 718 superalloy. The results indicated that the LAM Inconel 718 superalloy had irregular continuous chips with serrated edges and uncontrollable outflow, small cutting force and cutting vibration due to the poor density of 8.1577 g/cm3 and small microhardness up to 412 HV0.2, and low cutting temperature owing to the high thermal conductivity of 24.7 W/(m•K). The coated carbide tools were suitable for the cutting of the LAM Inconel 718 superalloy. The cutting force, cutting temperature, and cutting vibration of the LAM Inconel 718 superalloy obtained with the coated carbide tools were about 9.63, 6.29, and 16.67% smaller than those of the wrought Inconel 718 superalloy, respectively. The coated carbide tools presented a longer average life of 12.41 min with crater wear, notch wear, and nose breakage in the cutting of the LAM Inconel 718 superalloy, while a shorter life of 3.28 min with crater wear and nose wear in the cutting of the wrought Inconel 718 superalloy, and obtained similar surface roughness of the machined LAM and wrought Inconel 718 superalloys.