Showing papers on "Inconel published in 2020"

CO2 cryogenic milling of Inconel 718: cutting forces and tool wear

Abstract: Machining Inconel 718 alloy is a challenge due to its low machinability. This thermal resistant alloy combines high strength even at high temperatures with strain hardening tendency that causes high forces and extreme cutting temperatures during the machining. These issues force industries to achieve suitable machining processes to deal with this kind of alloys and the high worldwide competitiveness. Nevertheless, environmental considerations must to be taken into account due to growing environmental concerns. In the work here presented, cryogenic cooling with external MQL lubrication (CryoMQL) working along with CO2 as internal coolant is proposed for milling Inconel 718 with the aim of not only improving from a technical point of view but also environmental. This technique was compared with other lubricooling techniques. The results show that internal CryoMQL improves tool life by 57% in comparison with emulsion coolant, achieving 120% if it is compared with MQL in stand-alone mode.

Laves phase control of inconel 718 superalloy fabricated by laser direct energy deposition via δ aging and solution treatment

Abstract: In order to achieve the microstructure homogeneity at a lower temperature and improve the mechanical properties, a novel post heat treatment was introduced to Inconel 718 fabricated by laser direct energy deposition (LDED), by means of δ aging treatment + solution treatment. The microstructure analysis shows that the fully precipitation of δ phase in LDED Inconel 718 superalloy can “cut” the long strip Laves phase into small pieces. According with the δ phase solution treated at 1020 °C for 30 min, only tiny particle Laves phase was remained. The equilibrium volume fraction of Laves phase after δ phase solution treatment is about 1%, which is much lower than that of the as-deposited sample or the sample only solution treated at 1020 °C. Due to the solution strengthening and precipitation of γ″ phase during aging treatment, the tensile strength of δ aging + δ solution + double aging treated samples was 10.27% higher than that of directed solution + double aging treated samples, as well as a 31.38% and 52.71% increases in elongation and the reduction of area during tensile tests.

The microstructure evolution and tensile properties of Inconel 718 fabricated by high-deposition-rate laser directed energy deposition

Abstract: In order to meet the requirements for rapid manufacturing of large-scale high-performance metal components, the unique advantages of high-deposition-rate laser directed energy deposition (HDR-LDED, deposition rate ≥ 1 kg/h) technology have been attracted great attention. HDR-LDED technology significantly improves the efficiency by simultaneously increasing the mass and energy input on basis of conventional laser directed energy deposition (C-LDED, deposition rate ≤ 0.3 kg/h), which dramatically changes the solidification condition and thermal cycling effect compared to C-LDED processes. Based on this, Inconel 718 bulk samples were fabricated with a deposition rate of 2.2 kg/h and a height of 75 mm. Through experimental observation combined with finite element simulation, the precipitation morphology, thermal cycling effect and tensile properties at room temperature of the block samples at heights of 6 mm (bottom region), 37 mm (middle region) and 69 mm (top region) from the substrate were investigated. The results show that both temperature interval and incubation time satisfy the precipitation conditions of the second phases because of the intense thermal cycling effect so that δ, γ" and γ' phase are precipitated in the bottom and middle region of the as-deposited sample during the HDR-LDED process. As a result, the micro-hardness and the yield strength of the bottom region (385 HV; 745.1 ± 5.2 MPa) are similar to those of the middle region (381 HV; 752.2 ± 12.1 MPa), respectively. And they are both higher than those of the top region (298 HV; 464.7 ± 44.2 MPa). The tensile fracture mechanism is shown in both fracture and debonding of the Laves phase. The inhomogeneous microstructures and corresponding mechanical property differences of Inconel 718 fabricated by HDR-LDED along the deposition direction suggest the necessity to conduct further research of the post heat treatment in the future.

Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Abstract: Dislocation structures, chemical segregation, γ′, γ″, δ precipitates, and Laves phase were quantified within the microstructures of Inconel 718 (IN718) produced by laser powder bed fusion additive manufacturing (AM) and subjected to standard, direct aging, and modified multi-step heat treatments. Additionally, heat-treated samples still attached to the build plates vs. those removed were also documented for a standard heat treatment. The effects of the different resulting microstructures on room temperature strengths and elongations to failure are revealed. Knowledge derived from these process-structure-property relationships was used to engineer a super-solvus solution anneal at 1020 °C for 15 min, followed by aging at 720 °C for 24 h heat treatment for AM-IN718 that eliminates Laves and δ phases, preserves AM-specific dislocation cells that are shown to be stabilized by MC carbide particles, and precipitates dense γ′ and γ″ nanoparticle populations. This “optimized for AM-IN718 heat treatment” results in superior properties relative to wrought/additively manufactured, then industry-standard heat treated IN718: relative increases of 7/10 % in yield strength, 2/7 % in ultimate strength, and 23/57 % in elongation to failure are realized, respectively, regardless of as-printed vs. machined surface finishes.

Properties and High Temperature Dry Sliding Wear Behavior of Boronized Inconel 718

Abstract: Silicide-free boride layers were grown on Inconel 718 Ni-based superalloy surface at 850 °C, 950 °C, and 1050 °C for 2, 4, 6 hour by the powder pack-boronizing process using nano-sized B4C powders. The coatings were examined using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, 3D profilometry, and microhardness measurements. Wear experiments were carried out on untreated and boronized Inconel 718 using a ball-on-disk tribometer under dry sliding conditions at temperatures of 25 °C, 400 °C, and 750 °C. An increase in boronizing temperature and duration increased the thickness and hardness of the obtained boride layers, which resulted in low coefficient of friction values and decreased wear rates. Scanning electron microscopy images of the worn surfaces revealed two-body abrasion as the effective wear mechanism in the untreated samples, and three-body abrasion assisted by microcracking and spalling as the dominant wear mechanism in the boronized samples. A transition from mild to severe wear occurred in the untreated samples, while wear rates remained low in the boronized samples up to 750 °C. In conclusion, boronized Inconel 718 was capable of sustaining its boride layers under 5 N for 1800 m at wear-test temperatures up to 750 °C.

Effect of novel hybrid texture tool on turning process performance in MQL machining of Inconel 718 superalloy

Abstract: Higher cutting zone temperatures are responsible for poor turning process performance during dry machining of Inconel 718 material. In the present work, a novel hybrid surface texture tool under mi...

Prediction of solidification cracking by an empirical-statistical analysis for laser cladding of Inconel 718 powder on a non-weldable substrate

Abstract: This paper presents an empirical-statistical approach to predict solidification cracking during laser cladding of Inconel 718 powder on A-286 Fe-based superalloy. This approach is based on a linear regression analysis and empirical-statistical correlations between the key processing parameters (laser power, P; powder feed rate, F; and scanning speed, V) and the geometrical attributes of single laser cladding tracks. These correlations were used for the development of a processing map which assesses the effects of the geometrical characteristics on the solidification cracking and the required conditions to obtain crack-free clads. Scanning electron microscopy was used for microstructural characterization. Thermodynamic calculations using the non-equilibrium Scheil solidification model were also employed. The empirical-statistical analysis showed that the processing parameters directly associated with the height and angle of single laser cladding tracks are P 2 F V 2 and P 0.5 F V 1 , respectively. The processing map revealed that the dilution ratio is the governing macrostructural attribute required to avoid solidification cracking. Indeed, a substrate dilution ratio lower than 25% shifts the cladding composition to an alloy regime, which has lower susceptibility to solidification cracking. The role of this macrostructural feature in reducing the susceptibility of the fusion zone to solidification cracking is thoroughly discussed.

Investigation of dissolution behavior of laves phase in inconel 718 fabricated by laser directed energy deposition

Abstract: The mechanical properties of Inconel 718 are closely related to the morphology and size of the Laves phase, which must be quantitatively controlled to change the effect of the Laves phase from deleterious to beneficial. In this study, post-heat treatment was used to regulate the morphology and size of the Laves phase in Inconel 718 fabricated using laser directed energy deposition, and the dissolution behavior of the Laves phase during solution heat treatment was investigated. The results indicated that the sharp corners and grooves of the Laves phase preferentially dissolved, causing the morphology of the Laves phase to change from a long-striped to granular shape during dissolution. The dissolution kinetics of the Laves phase were also investigated using the Johnson–Mehl–Avrami–Kolmogorov and Singh–Flemings models. The initial stage of dissolution was controlled by both the long-range diffusion of Nb and the interfacial reaction. However, with decreasing degree of Nb segregation, the interfacial reaction became dominant.

Microstructure and tensile fracture behavior of three-stage heat treated inconel 718 alloy produced via laser powder bed fusion process

Abstract: In this study, Laser Powder Bed Fusion (LPBF) Inconel 718 is subjected to various heat treatments, namely double aging, solid solution + double aging, and homogenization + solid-solution + double aging, to investigate the effect of heat treatment on room- and high-temperature tensile properties. The results show that all three heat treatments increase hardness and room-temperature tensile strength, but greatly reduce ductility. With an increase in tensile test temperature, the stress-induced Portevin-Le Chatelier (PLC) effect can effectively prevent the occurrence of oxidation at grain boundaries and maintain a certain ductility in the range of room temperature to 600 °C. However, when the temperature is 650 °C, the PLC effect disappears, resulting in a high-temperature embrittlement effect.

Comparative study on the microstructure evolution of selective laser melted and wrought IN718 superalloy during subsequent heat treatment process and its effect on mechanical properties

Abstract: The microstructure evolution of Inconel 718 (IN718) superalloy fabricated by selective laser melting (SLM) and wrought process during subsequent heat treatment process and their corresponding mechanical properties were comparatively studied in our work After the same solution heat treatment at 1080 °C, the grain size of the SLM-IN718 keeps unchanged and also its dislocation subgrain structure is retained, whereas the grains of wrought IN718 is coarsened obviously Due to the existence of dislocation subgrain structure and higher residual stress in the SLM-IN718 matrix, the precipitation of γ'' strengthening phase is improved a lot during the subsequent aging process in the SLM-IN718 specimen compared to that in wrought IN718 specimen Consequently, the hardness and strength of SLM-IN718 are significantly enhanced, which far exceed that of wrought IN718 By adjusting the aging treatment, the precipitation of γ'' strengthening phase can be further optimized and the corresponding mechanical properties of SLM-IN718 are improved significantly Especially, the elongation of SLM-IN718 at room temperature is significantly increased to 29% with only a little decrease in the strength

Inhibition of cracking by grain boundary modification in a non-weldable nickel-based superalloy processed by laser powder bed fusion

Abstract: A TiC nanoparticle modified non-weldable nickel-based superalloy Inconel 738LC has been fabricated via laser powder bed fusion. The formation of refined grains with a larger high angle grain boundary length density and zigzag grain boundaries inhibits the initiation and propagation of hot cracks, leading to a 97% reduction in cracking and improved mechanical properties.

A study on the influence of substrate pre-heating on mitigation of cracks in direct metal laser deposition of NiCrSiBC-60%WC ceramic coating on Inconel 718

Abstract: Direct metal laser deposition of ceramic-metal composite coatings has received much attention in the recent past over other conventional methods due to a large number of advantages. However, formation of cracks due to large thermal gradients and rapid cooling rates limits its application. Therefore, in the present study the influence of cooling rate on crack mitigation in multilayer direct metal laser deposition of NiCrSiBC-60%WC on Inconel 718 substrate has been investigated by monitoring the thermal history of the molten pool using an IR pyrometer. Cracks could not be mitigated by varying the cooling rate through changing the scan speed within the present experimental range of 300 mm/min to 700 mm/min, possibly due to the large thermal gradients build up between the substrate and the deposited clad track. Therefore, in order to decrease the cooling rate and the thermal gradient, and study their effect on crack mitigation pre-heating of the substrates at two different temperatures, 300 °C and 500 °C was employed during the deposition process. Crack-free coatings could be obtained with substrate pre-heating, except at the lower pre-heating temperature of 300 °C and the highest scan speed of 700 mm/min which had yielded a relatively fast cooling rate. Also, at the higher pre-heating temperature of 500 °C and the lowest scan speed of 300 mm/min scan speed micro-cracks were observed inside the coating due to severe dissolution of WC particles making the matrix brittle. Further, residual stresses, hardness and wear resistance of the deposited coating under above experimental conditions were determined and correlated with the cooling rate and the microstructure.

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

Abstract: 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.

Machining performance of Inconel 718 using graphene nanofluid in EDM

Abstract: Inconel 718 in a nickel-based superalloy has excellent mechanical properties such as high tensile and impact strength, excellent oxidation, and corrosion resistance. Unlike most superalloys...

The effect of subsequent heat treatment on the evolution behavior of second phase particles and mechanical properties of the Inconel 718 superalloy manufactured by selective laser melting

Abstract: In this work, the influence of subsequent heat treatment on the evolution behavior of Laves phase, δ phase and carbides, and mechanical properties were investigated systematically for the Inconel 718 superalloy manufactured by selective laser melting (SLM). Two different subsequent heat treatment schemes were employed for SLM manufactured Inconel 718 superalloy in our work: 980 °C * 1 h/AC + 720 °C * 8 h/FC to 620 °C * 8 h/AC (the standard heat treatment scheme, SA980) and 1080 °C * 1 h/AC + 720 °C * 8 h/FC to 620 °C * 8 h/AC (the optimized heat treatment scheme, SA1080). The results show that the δ phase can nucleate around the residual Laves phase, and then the composite phase particles are formed at the subgrain boundaries during SA980 heat treatment of SLM manufactured Inconel 718. Moreover, the entangled dislocations around these composite phase particles can promote the initiation of microcrack during the tensile process at elevated temperature, leading to premature failure. On the other hand, two types of carbides were found to exist in the SA1080 heat-treated samples: the nanoscale TiC particles along subgrain boundaries originally formed during the SLM process, and the large-size NbC particles along the grain boundaries formed during the solution heat treatment process. The heat treatment schemes of SA1080 can achieve excellent combination of strength and elongation at room temperature and elevated temperature, which is more suitable for the subsequent heat treatment of SLM manufactured IN718.

Post-processing effects on the surface characteristics of Inconel 718 alloy fabricated by selective laser melting additive manufacturing

Abstract: This experimental study presents the effects of various post-processes including finish machining (FM), drag finish (DF) and vibratory surface finish (VSF) on surface characteristics and wear performance of Inconel 718 specimens fabricated by selective laser melting additive manufacturing. Concentrated characteristics are surface roughness, surface topography, microstructure, microhardness, XRD pattern and wear resistance. Analysis shows that partially melted powders on the surface and just beneath the surface create an undesired layer and its thickness varies from 80 to 130 µm that leads to poor surface topography and very high surface roughness. FM and DF post-processes are capable of completely removing this layer and in the meantime, up to 96 and 88% lower surface roughness. Post-processes particularly FM leads to occur strain hardening and resulted in up to 21% increase microhardness as compared to as-built material. XRD pattern of as-built and wrought alloys shows substantial difference when considering (111) and (200) planes. This study demonstrates that post-processes enhance the wear performance of SLM manufactured Inconel 718. Coefficient of friction and the wear rate of the as-built specimen decreased more than 10% after FM process.