Papers by Keyword: IN718

Abstract: The nickel base alloy IN718 was manufactured by Laser Powder Bed Fusion (LPBF) using a laser spot size of 1024 μm and a laser power of 1.3 kW at a layer thickness of 160μm. The resulting porosity, microstructure and mechanical properties are presented. Very coarse and in build direction elongated grains are stacked to form a polycrystalline material with sharp single-crystal-like texture. The appearance of ∑5 grain boundaries between coincidence side lattices is recognized. Tensile testing shows highly anisotropic mechanical properties according to the revealed texture. Increasing the hatch distance reduces the severity of the texture.

Abstract: Tensile and compressive creep behavior of SLMed IN718 alloy under 973K (700°C) were investigated. Crept samples were analyzed by SEM and TEM to expose evolution of microstructure, precipitates and dislocation structure during the creep process. Results show that initial creep rate under compression is higher than under tension for the same creep conditions. Minimum creep rates are approximately the same both in tensile and compressive creep tests. The different creep behaviors may be related to the fact that tension stress promotes precipitations of fine needle-like γ′′ phases, while compression stress promotes precipitations of large size δ phases. The tension-compression asymmetry owns to the increment of chemical potential varying with the stress orientation.

Abstract: Residual stress measurements were successfully performed on the representative IN718 fatigue specimens by X-Ray Diffraction. All surface residual stresses were found to be compressive. A stress gradient normal to the surface was observed on all specimens. The residual stresses tended to become less compressive with increasing depth into the parts. Residual stress measurement is the special requirement for NADCAP CRITERIA AC 7101/7. In this paper, residual stress measurements were successfully performed on two IN718 low cycle fatigue test specimens.

Abstract: Fatigue crack propagation has been measured in flow formed Inconel 718 (IN718). Test pieces were extracted from a flow formed tubular structure in the longitudinal direction, retaining the tube curvature across their width. Crack growth rates (da/dN) were measured at 20, 300, and 400oC. For comparison, tests were repeated on specimens with an identical geometry but machined from conventionally forged IN718. Detailed metallurgy of the flow formed material is presented.

Abstract: Alloy IN718 is a nickel based precipitation hardened material and it has the necessary strength over a range of temperatures which includes the operating range for many rocket propulsion systems and jet engines. This performance is accomplished by a combination of solid-solution strengthening, precipitation strengthening and grain-boundary strengthening. However, it is common for precipitation hardened nickel based superalloys to have a problem of post-weld cracking. In this study, several welding processes are investigated to obtain the optimum welding method of IN718 for elevated temperature forming. These include LBW(Laser Beam Welding), EBW(Electron Beam Welding), HIP(hot isostatic pressing), and solid state diffusion bonding. The result shows that the LBW specimen performs the highest formability at 980°C so that this process can be applied to superplastic forming of IN718 sheet. It is demonstrated that the elevated temperature superplastic forming of nozzle extension with internal cooling channels was possible with laser beam welded IN718 sheet.

Abstract: In this work, the oxidation behavior of Ti₂AlN coating deposited on nickel super alloy IN718 was investigated. The coating was obtained by DC-magnetron sputtering at 540°C and subsequent vacuum annealing at 800°C for 1h. The coating morphology as well as the chemical composition were analyzed using SEM, EDS and XRD, respectively. The XRD results revealed that the coating mainly composed of Ti₂AlN MAX phase. Cycling oxidation was performed at 700 °C and 800 °C in air. The XRD and SEM results proved the interaction between substrate and coating and the formation of the quaternary Ti₃NiAl₂N phase during oxidation at the interface. Due to the Ni diffusion towards the surface, the Ti₃NiAl₂N phase grew continuously and the Ti₂AlN phase decomposed gradually resulting in a coating failure. The results indicate that the oxidation behavior of the coating is essentially controlled by the interdiffusion of Ni from substrate into the coating.

Abstract: Many metals, such as titanium and superalloys, are used for a wide range of aerospace applications, which include aircraft gas turbine engine and space launcher propulsion engine. In order to manufacture a stiffened extension with superplastic blow forming at elevated temperature, the structural integrity of the joint part was investigated since the welded or bonded joint of internal channels should maintain its strength during superplastic blow forming process. Various types of joint methods were performed in order to investigate microstructural and mechanical properties of the bonded specimen at elevated temperature. In this paper, the possibility of manufacturing combustion chamber and other aerospace components with superplastic blow forming of titanium and superalloy was demonstrated. An innovative manufacturing method to produce complex configuration from titanium multi-sheets by superplastic forming with low hydrostatic pressure was presented. The result also shows that the manufacturing method with superplastic blow forming of multi-sheets of IN718 alloy has been successfully demonstrated for near net shape forming of subscale nozzle extension cone with internal channels.

Abstract: The paper introduces an experimental process on measurement of ultra low sulfur in IN718 by using infrared carbon sulfur analyzer. The experimental data shows that, infrared absorption method can be used to analyze and measure the ultra low sulfur in IN718, and the precision and accuracy of this method meets the requirement of ASTM E l019-2000. It can be concluded that it is a feasible method in practice.

Abstract: Blow forming technology has been used to produce glass and plastic components with easy and simple process. In order to apply this technology to metallic system, relatively high formability of material and elevated temperature are required. Since the blow forming temperature is quite high for metallic system, the main difficulty is to obtain adequate mold material which can sustain pressure difference between inside and outside of the tool. The present study demonstrates blow forming process with IN718 and steel can be applied to manufacturing of combustion chamber in liquid propellant rocket engine with complex shape. The result shows that the developed technology to process design of high temperature blow forming by the finite element method can be applied for near net shape forming of a combustion chamber of liquid rocket engine and a cone-shaped chamber extension part with cooling channels.

Abstract: nconel 718 is an age hardenable nickel base supper alloy with high strength at elevated temperatures, and excellent creep properties. It is used extensively in turbine discs, blades where components experience elevated temperatures for prolonged duration, leading to coarsening of the microstructure. To evaluate the life of such components after prolonged exposure to service conditions, LCF properties at such large grain sizes are essential. For this purpose, low cycle fatigue (LCF) behavior of forged Inconel 718 turbine rotor disc having large grain size was studied at room temperature. Total strain controlled fatigue tests were conducted in air at ambient temperature on this alloy in solution treated and aged condition. The results indicated that the material exhibits cyclic strain softening and the cyclic yield strength is lower by 40% compared to the monotonic yield strength. The deformation takes place by multiple planar slip.