Effect of standard heat treatment on the microstructure and mechanical properties of hot isostatically pressed superalloy inconel 718 (original) (raw)
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Superalloys 718, 625, 706 and Various Derivatives (2001), 2001
Inert gas atomized superalloy Inconel 718 powder was hot isostatically processed (HIPed) at 1200 "C / 120 MPa / 3h. This material was then subjected to a standard heat treatment schedule adopted for wrought IN 718 (955 "C / 1 h. / water quenching and twostep ageing at 720 "C / 8 h. / furnace cooling to 620 "C / 8 h. 1 followed by air cooling to room temperature), which showed substantial improvement in strength but a drastic decrease in ductility. Since, the solution treatment temperature has a significant influence on microstructure development, the HIPed compacts were subjected to various solution treatment temperatures between 850 and 1270 "C, while the same ageing treatment was retained. The microstructure of the compacts in the as-HIPed, solution treated and aged conditions was studied in detail. The tensile properties of these samples were evaluated at room temperature and at 650 "C. The microstructure corresponding to the solution treatment temperature of 1270 "C, showed incipient melting at the particle boundaries leading to enhanced bonding across the particles and resulting in a considerable improvement of ductility.
Improvement in the Microstructure and Tensile Properties of Inconel 718 Superalloy by HIP Treatment
MATERIALS TRANSACTIONS, 2006
Hot Isostatic Pressing (HIP) is a process that uniquely combines higher pressure and temperature to produce materials and parts with substantially better properties than those by other methods. The aim of this paper is to discuss the methods and to find a suitable process of HIP for Inconel 718 superalloy. In this study, the HIP process parameters considered were; temperatures: 1423, 1448, 1453 and 1478 K, pressures: 100, 150, 175 and 200 MPa, and soaking times of 2, 3 and 4 hours. The Inconel 718 superalloy is used throughout this study. To evaluate the effects of microstructure and tensile properties of 718 alloy by HIP process, tensile test at two different strain rates at room and high temperature were evaluated. The microstructure, TEM and XRD inspections were performed. The experiment results show that at 1453 K, 175 MPa, 4 hours of HIP treatment for Inconel 718 superalloy was optimal. It can improve the microstructure and tensile properties of 718 castings. Through the optimal HIP treatment, the grain sizes are uniform and the segregated structure is improved. At fast strain rate (0.001 s À1), it increased the tensile strength by 31% at 298 K, 27% at 813 K, and 24% at 923 K. The 0.2% yield strength increased 40% at 298 K, 31% at 813 K, and 28% at 923 K. Meanwhile the elongation increased 100% at 298 K, 130% at 813 K, and 60% at 923 K after tension tests. When the strain rate was very slowly (0.0001 s À1), it also increased the tensile strength by 24% at 298 K and 20% at 813 K. The 0.2% yield strength increased 29% at 298 K and 27% at 813 K. The elongation increased 54% at 298 K and 282% at 813 K.
Microstructural studies on Alloy 693
Journal of Nuclear Materials, 2014
Superalloy 693, is a newly identified 'high-temperature corrosion resistant alloy'. Present study focuses on microstructure and mechanical properties of the alloy prepared by double 'vacuum melting' route. In general, the alloy contains ordered Ni 3 Al precipitates distributed within austenitic matrix. M 6 C primary carbide, M 23 C 6 type secondary carbide and NbC particles are also found to be present. Heat treatment of the alloy at 1373 K for 30 min followed by water quenching (WQ) brings about a microstructure that is free from secondary carbides and Ni 3 Al type precipitates but contains primary carbides. Tensile property of Alloy 693 materials was measured with as received and solution annealed (1323 K, 60 min, WQ) and (1373 K, 30 min, WQ) conditions. Yield strength, ultimate tensile strength (UTS) and hardness of the alloy are found to drop with annealing. It is noted that in annealed condition, considerable cold working of the alloy can be performed.
In-situ SEM study of temperature-dependent tensile behavior of Inconel 718 superalloy
Journal of Materials Science , 2021
The effect of deformation temperature on tensile behavior of Inconel 718 alloy has been studied by a self-developed in-situ high-temperature tensile stage inside a scanning electron microscopy at a temperature range from room temperature (RT) to 750°C. The dynamic microstructure evolution and mechanical properties at different temperatures were performed and compared by the uniaxial tensile tests. The in-situ test results showed that the mechanical properties and fracture mechanisms of Inconel 718 alloy were sensitive to deformation temperatures. From RT to 650°C, the yield stress and ultimate tensile strength decrease slightly and the tensile ductility is comparable. While up to 750°C, the yield stress and ultimate tensile strength decrease significantly, the elongation and reduction of cross section also showed a significant decrease from RT to 750°C. It was found that at RT and 650°C, tensile cracks tended to initiate around the carbide particles and the triple junctions of grain boundaries, also propagated transgranularly; at 750°C, the cracks initiated at grain boundaries and propagated intergranularly. In fact, with the increase in deformation temperature, the fracture mechanism transformed from the ductile transgranular fracture to the brittle intergranular fracture.
2019
Severe plastic deformation (SPD) techniques impose very high level of strains and it can enhance the strength of a material several folds. In the current work, Inconel 718 alloy was severely deformed by machining process resulting in inherently "bi-modal" grain size distribution consisting of sheared zone with nano-structured grains and moderately refined grain zone. Hardness of machined chips were found to be much higher than that of bulk and increased further upon giving heat-treatment because of precipitation of γ'' and γ' nano-precipitates. However, as with most severely deformed materials, ductility of the machined chip is known to be very low, primarily because of the presence of large fractions of dislocation-saturated nanostructured grains which hinder any more dislocation generation or movement. In this work, we gave short heat-treatment to these deformed samples at elevated temperature to ensue controlled recrystallization in the sheared zone. However, heat-treatment is also expected to result in coarsening of precipitates as well as the grains of the matrix. This phenomenon may, not only reduce the strength, but may also reduce the pinning ability of the precipitates which endow the microstructure with thermal stability. Hence, the specific objective of this work is to understand the interplay of grain boundary pinning and recrystallization, both of which occur at elevated temperatures. Short heat-treatment of the severely deformed samples was performed for 15 minute between 700 °C to 900 °C. It was found that temperatures up to 800 °C do not lead to appreciable recrystallization, while 900 °C heat-treatment can cause appreciable recrystallization, albeit, limited to the shear zone. Size of precipitates was also found to grow with increasing temperature, nonetheless, samples heat-treated at 900 °C were found to be thermally stable with a good fraction of coincidence site lattice boundaries, low grain size and improved hardness.
High strain-rate behaviour of as-cast and as-build Inconel 718 alloys at elevated temperatures
Mechanics of Materials, 2021
The restoration of Inconel 718 components through conventional processes typically require cost-intensive machining operations. Moreover, the refurbishment and reuse are extremely important in structural components likely to be subjected to harsh operating conditions (dynamic loads and elevated temperatures). That is why additive manufacturing processes are rising as disruptive techniques for the restoration of Inconel 718 components. However, a limited number of studies have evaluated the mechanical properties of this nickel-base superalloy in harsh conditions. The objective of this study is to evaluate the coupled effect of strain-rates (0.001, 200 and 800 s − 1) and temperatures (20, 350 and 550 • C) on Inconel 718 additive manufactured samples produced by Direct Energy Deposition. A raw Inconel 718 material for the preparation of as-cast samples has been also investigated, and the mechanical results have been compared. The mechanical characterisation at high strain-rates has been performed through a SHTB equipped with a water-cooled induction heating system. Similar mechanical behaviour has been observed between samples realised with a power laser of 400 W and as-cast samples. A gradual decrease of the mechanical strengths is observed for increasing temperatures. The calibration of the Johnson-Cook strength model highlighted the necessity of using specific thermal softening values as a function of fixed strain-rate and temperature.
Tensile behaviour of Inconel 718 alloys under extreme conditions of temperature and strain-rate
EPJ Web of Conferences
Nickel-based superalloys are widely used in critical applications where structural components are subjected to harsh operating conditions such as elevated temperatures and high strain-rate. These alloys are also among the most hard-to-cut materials. For this reason, some critical components with complex geometrical features along with critical dimensions cannot easily manufactured by conventional technologies. A rising disruptive Additive Manufacturing (AM) technique, namely powder-based Laser Metal Deposition (LMD), is able to overcome these limitations in terms of manufacturing costs, tool wear, as well as lead time. As a consequence, the mechanical response under harsh condition of additively manufactured Nickel-based superalloys has to be accurately understood in order to guarantee the reliability of the structural parts made with them. Presently very few researches were addressed to study the dynamic tensile behaviour of Inconel 718 produced by additive manufacturing under high...
Comparative hot workability of 7012 and 7075 alloys after different pretreatments
Materials Science and Engineering: A, 1995
Hot torsion tests, in the range 250 450 °C and 0.05-5.0 s 1, were performed on A1-Zn-Mg Cu alloys (7012 and 7075), which had been direct chill cast, homogenized and precipitation treated to give fine, well-dispersed precipitates. Additional tests were conducted on material that had been extruded, solution treated or precipitation treated at deformation temperature. The peak flow stress was related to the strain rate by the hyperbolic sine equation; the activation energy for precipitated alloys was close to that of the bulk self-diffusion of pure aluminium. For solution-treated metal, the peak stress was very high at low temperatures due to dynamic precipitation; as a consequence, the activation energy was about 50% higher than that of precipitated alloys. The ductility was almost independent of temperature in the investigated range, but decreased with rising strain rate. The ductility of the extruded alloys was almost double that of the as-cast material, with the exception of the solution-treated material where, at low temperature, the ductility of the extruded alloy was lower. The original grains were elongated with precipitates on the boundaries. The dynamically recovered subgrains exhibited sub-boundaries with a high density of fine precipitates and an interior network of dislocations also tied to precipitates.
Additive Manufacturing (AM), also known as three-dimensional (3D) printing and rapid prototyping, is the technology of making solid objects by adding material layer by layer based on computer-aided design (CAD). Electron Beam Melting (EBM) technology, which is one of the AM technologies, is based on the principle of melting metal powders by a focused electron beam that provides high energy and temperature and is based on the formation of layers by the repetitive welding technique, which is made by joining one on top of the other. Inconel 718 is the most widely used nickel-based superalloy due to its excellent high temperature strength and good oxidation corrosion resistance up to high temperatures. The main areas of use are discs, shafts, cases, stators, blades, gaskets, supports, pipes and fasteners. The main subject of this thesis study is to investigate the effects of hot isostatic pressing and heat treatment by revealing the mechanical and physical properties of Inconel 718 with...