Showing papers on "Inconel published in 2016"

Effects of laser processing parameters on thermal behavior and melting/solidification mechanism during selective laser melting of TiC/Inconel 718 composites

Abstract: A three-dimensional finite element model is proposed to study the effects of laser power and scan speed on the thermal behavior and melting/solidification mechanism during selective laser melting (SLM) of TiC/Inconel 718 powder system. The cooling time during powder delivery is taken into account to simulate the actual production process well. It shows obviously the existence of heat accumulation effect in SLM process and, the tailored set of cooling time of 10 ms during powder delivery alleviates that effectively. The maximum temperature gradient in the molten pool slightly increases from 1.30×104 °C/mm to 2.60×104 °C/mm as the laser power is increased from 75 W to 150 W. However, it is negligibly sensitive to the variation of scan speed. There is a positive corresponding relationship between the maximum rate of temperature change and processing parameters. A low laser power (75 W) or a high scan speed (300 mm/s) is more energy efficient in Z-direction of the molten pool, giving rise to a deep-narrow cross section of the pool. Whereas, a high laser power (150 W) or a low scan speed (50 mm/s) causes a shallow-wide cross section of the molten pool, meaning it is more energy efficient in the Y-direction of the melt. The combination of a laser power of 125 W and a scan speed of 100 mm/s contributes to achieve a sound metallurgical bonding between the neighbor layers and tracks, due to the proper molten pool size (width: 109.3 µm; length: 120.7 µm; depth: 67.8 µm). The SLM experiments on TiC/Inconel 718 powder system are performed to verify the reliability and accuracy of the physical model and, simulation results are proved to be correct.

On the microstructural and mechanical properties of post-treated additively manufactured Inconel 718 superalloy under quasi-static and cyclic loading

Abstract: Inconel 718 specimens were additively manufactured via selective laser melting (SLM) and subjected to different post-process heat treatments. Performance under monotonic and cyclic loading in the low-cycle fatigue (LCF) regime was investigated at room temperature (RT). Hot isostatic pressing (HIP) was employed in order to reduce the porosity typically present after SLM. Prior functional encapsulation with a Ni-20Cr coating applied by cathodic arc deposition (Arc-PVD) was applied to achieve full densification. The results show that after Arc-PVD and HIP, the mechanical properties are not only affected by reduced porosity but also by substantial microstructural changes. Precipitates, i.e. Laves phase, already present in the as-built condition can be dissolved by solution heat treatment. HIP leads to recrystallization and thus significantly changes microstructural appearance. Elongated grains and sub-micron sized cell structures stemming from SLM processing are eliminated by HIP. Aging leads to evolution of strengthening γ″ precipitates. Concurrently, δ phase forms upon HIP and aging. In comparison to aged conditions that were not subjected to HIP, microstructure upon HIP and aging results in improved ductility under monotonic loading, however, concomitantly deteriorates fatigue properties at RT.

Influence of hatch spacing on heat and mass transfer, thermodynamics and laser processability during additive manufacturing of Inconel 718 alloy

Abstract: A transient three-dimensional powder-scale model has been established for investigating the thermodynamics, heat and mass transfer and surface quality within the molten pool during selective laser melting (SLM) Inconel 718 alloy by finite volume method (FVM), considering the powder-solid transition, variation of thermo-physical properties, and surface tension. The influences of hatch spacing (H) on the thermodynamics, heat and mass transfer, and resultant surface quality of molten pool have been discussed in detail. The results revealed that the H had a significant influence on determining the terminally solidified surface quality of the SLM-processed components. As a relatively lower H of 40 μm was used, a considerable amount of molten liquid migrated towards the previous as-fabricated tracks with a higher velocity, resulting in a stacking of molten liquid and the attendant formation of a poor surface quality with a large average surface roughness of 12.72 μm. As an appropriate H of 60 μm was settled, a reasonable temperature gradient and the resultant surface tension tended to spread the molten liquid with a steady velocity, favoring the formation of a flat surface of the component and an attendant low average surface roughness of 2.23 μm. Both the surface morphologies and average surface roughness were experimentally obtained, which were in a full accordance with the results calculated by simulation.

Recyclability Study on Inconel 718 and Ti-6Al-4V Powders for Use in Electron Beam Melting

Abstract: Powder bed-based additive manufacturing technologies offer a big advantage in terms of reusability of the powders over multiple cycles that result in cost savings. However, currently there are no standards to determine the factors that govern the powder reuse times. This work presents the results from a recyclability study conducted on Inconel 718 and Ti-6Al-4V powders. It has been found that the Inconel 718 powders are chemically stable over a large number of cycles and their reuse time is limited by physical characteristics of powders such as flowability. Ti-6Al-4V, on the other hand, finds its reuse time governed by the oxygen pick up that occurs during and in between build cycles. The detailed results have been presented.

Selective Laser Melting of Duplex Stainless Steel Powders; an Investigation

Abstract: Selective laser melting gained substantial momentum in the recent past and quite a few alloy systems have been researched and made available for commercial use; titanium, aluminum, stainless and tool steels, cobalt chrome, and Inconel being the most popular examples. Despite the application potential, and the successful processing of powder forms by traditional powder metallurgy methods, selective laser melting of duplex stainless steels was not attempted so far. The response of a duplex stainless steel alloy to processing by selective laser melting with varying process conditions is evaluated in the current research. Experimental results ascertained that the complete cycle starting from duplex powders, consolidating into 3D forms by selective laser melting and then post-process heat treatment to bring the microstructures back to duplex forms is feasible. Within the current experimental domain, the multi-layer samples are close to 90% density and showed a maximum dimensional variation of 2–3%, while the a...

Optimizing Quality of Additively Manufactured Inconel 718 Using Powder Bed Laser Melting Process

Abstract: Inconel 718, a widely used nickel based super alloy, is of special interest to the aerospace and automotive fields for its highly desirable and consistent material properties over a large range of temperatures. The objective of this research is to understand the effect of process parameters of a Direct Metal Laser Sintering (DMLS) machine, concerning mainly beam power between 40 W and 300 W and scan line speed between 200 mm/s and 2500 mm/s on scan line quality, line geometry and dimensions, and melt pool geometry in laser melted Inconel 718 line scans. A beam power that is too low (40 W) does not provide enough energy to maintain a continuous line. It was shown that mid-range beam powers (100 W and 150 W) result in the best and most uniform scan lines with minimal voids and shallower melt volumes. Higher power runs resulted in voids forming in the bottom of the melt pool and were consistent with either electron beam welding or melting processes operating at higher temperatures. Laser energy density (LED), a method of correlating the effects of scan speed and beam power into one characteristic process parameter, was also investigated. This ratio of beam power to scan speed follows a second order polynomial trend line for melt pool width and a logarithmic trend for average line width. LED values for melt pool depth are separated to show two trend lines as two mechanisms operate at low values below 0.25 J/mm and high values above 0.25 J/mm. LED values above 0.21 J/mm are desired for a continuous fill percentage in the formed lines, however dimensional accuracy of the line is sacrificed significantly at values over 0.2 J/mm.

Microstructure Development in Electron Beam-Melted Inconel 718 and Associated Tensile Properties

Abstract: During the electron beam melting (EBM) process, builds occur at temperatures in excess of 800°C for nickel-base superalloys such as Inconel 718. When coupled with the temporal differences between the start and end of a build, a top-to-bottom microstructure gradient forms. Characterized in this study is a microstructure gradient and associated tensile property gradient common to all EBM Inconel 718 builds, the extent of which is dependent on build geometry and the specifics of a build’s processing history. From the characteristic microstructure elements observed in EBM Inconel 718 material, the microstructure gradient can be classified into three distinct regions. Region 1 (top of a build) is comprised of a cored dendritic structure that includes carbides and Laves phase within the interdendritic regions. Region 2 is an intermediate transition zone characterized by a diffuse dendritic structure, dissolution of the Laves phase, and precipitation of $$\delta $$ needle networks within the interdendritic regions. The bulk structure (Region 3) is comprised of a columnar grain structure lacking dendritic characteristics with $$\delta $$ networks having precipitated within the grain interiors. Mechanically, at both 20°C and 650°C, the yield strength, ultimate tensile strength, and elongation at failure exhibit the general trend of increasing with increasing build height.

Effect of Machining Parameters on Surface Integrity in High Speed Milling of Super Alloy GH4169/Inconel 718

Abstract: Control of surface integrity is a vital consideration in the machining of components subjected to fatigue loading, for example, critical components of aerospace engines. In this research, three important aspects of surface integrity of a machined part—surface roughness, micro-hardness, and residual stresses—were analyzed for their variations with the cutting parameters. Finish milling of super alloy GH4169/Inconel 718 was carried out using coated cemented carbide and whisker-reinforced coated ceramic inserts. All of the three machining parameters—cutting speed, feed rate, and depth of cut—were found to have a substantial effect on the surface integrity of the finished part. Although different cutting parameters gave different effects for the two types of cutting inserts, overall better surface integrity was obtained at minimum cutting feed and medium cutting speed and depth of cut value. Moreover, carbide inserts produced better surface integrity of the finished part, whereas ceramic inserts generated ver...

Effects of tailored gradient interface on wear properties of WC/Inconel 718 composites using selective laser melting

Abstract: The WC/Inconel 718 composites were fabricated by selective laser melting (SLM). The laser processing parameters played an important role in determining the microstructure and performance of the WC/Inconel 718 composite parts. With the decrease in the laser scanning speed, the densification rate increased and achieved 97.8% at a scanning speed of 350 mm/s. As an optimal scan speed of 450 mm/s was applied, the WC/Inconel 718 composite part obtained a mean microhardness as high as 393.2 HV 0.1 . At the same time, a regular and orderly gradient interface with a mean thickness of 0.27 μm surrounded by a diffusion layer was obtained. What is more, the chemical composition of the gradient interface and the diffusion layer were X 3 C 17 and XC 4 (X = W, Ni, Cr, Fe), respectively. Meanwhile, the composite acquired a considerably low coefficient of friction (COF) of 0.35 with almost no fluctuation and attendant wear rate of 2.5 × 10 − 4 mm 3 N − 1 m − 1 and the wear mechanism changed continuously from severe abrasive wear to adhesive wear. Subsequently the effects of the tailored gradient interface on wear performance were discussed. It revealed that the existence of gradient interface showed a very important role in improving the wear performance of the SLM-processed WC/Inconel 718 composite parts.

Mean field modelling of dynamic and post-dynamic recrystallization during hot deformation of Inconel 718 in the absence of δ phase particles

Abstract: Dynamic and post-dynamic recrystallization kinetics were investigated during hot-working of Inconel 718 as a function of temperature, strain and strain rate in the single phase domain. The post-dynamic evolution was found to be extremely fast and impacting significantly the grain size. A two-site mean field model including both dynamic and post-dynamic evolution was used to predict the recrystallized fraction, the average grain size and the stress–strain curves in different thermomechanical conditions.

Microstructure and directional fatigue behavior of Inconel 718 produced by selective laser melting

Abstract: Recent research efforts in additive manufacturing have focused on developing parts made of Inconel 718 (IN 718), a nickel-based superalloy, which is an attractive material for aerospace and energy high-temperature applications. Here the selective laser melting (SLM) process is used to transform alloy powder into a solid IN 718 parts followed by optimal stress-relief and subsequent precipitation hardening treatment. Two main aspects were investigated. The IN 718 microstructure generated by the SLM process was characterized using metallographic techniques and found to be distinctly directional because it is a result of a layer-by-layer material build-up typical of the SLM process. The high cycle fatigue behavior of SLM IN 718 was determined using a novel test method designed to determine and quantify the directional material behavior, which is important information for part design and process optimization. The fatigue S-N data show that the direction parallel to the build direction is associated with the lowest fatigue strength. The role of the as-produced surface characteristics on fatigue crack initiation is discussed.

Influence of cutting parameters on work hardening behavior of surface layer during turning superalloy Inconel 718

Abstract: The use of superalloy Inconel 718 is increasing inmost of sophisticated applications such as aircraft and rocket engines. However, the high work hardening behavior of Inconel 718 has not been studied sufficiently yet. In the present work, an experimental work was made to study the relationship between work hardening and cutting parameters (cutting speed and feed rate) in turning Inconel 718. Depths of work hardening and degree of work hardening (DWH) at different depths beneath the machined surfaces were investigated to determine and understand the integrity of machined surfaces. It is observed that there was no significant difference with work hardening characteristics in this experiment to consider the error of measurement. The parameters (v = 50 m/min, f = 0.2 mm/r) may be better than others. An empirical model based on Meyer’s index with a view was utilized to understand the characteristics of machining-affected layers. From the obtained data, the work hardening can be better understood and controlled, which can be used to enhance the machinability and surface integrity characteristics of superalloy Inconel 718.