Papers by Keyword: Ni Based Superalloy

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Authors: Vsevolod I. Razumovskiy, A.Y. Lozovoi, Igor M. Razumovskii, Andrei V. Ruban
Abstract: A new approach to the design of Ni-based polycrystalline superalloys is proposed. It is based on a concept that under given structural conditions, the performance of superalloys is determined by the strength of interatomic bonding both in the bulk and at grain boundaries of material. We characterize the former by the cohesive energy of the bulk alloy, whereas for the latter we employ the work of separation of a representative high angle grain boundary. On the basis of our first principle calculations we suggest Hf and Zr as “minor alloying additions” to Ni-based alloys. Re, on the other hand, appears to be of little importance in polycrystalline alloys.
Authors: Anders Engström, Johan Bratberg, Qing Cheng, Lars Höglund, Paul Mason
Abstract: This paper presents a brief review, followed by some new results from recent diffusion simulations in Ni-base superalloy systems, performed by means of a thermodynamic and kinetic modeling approach as taken in the commercial finite-difference code DICTRA. The DICTRA code solves the multi-component diffusion equations, combining assessed thermodynamic and kinetic data in order to determine the full composition dependent interdiffusion matrix. The link between fundamental physics based models and critically assessed data allows simulations to be performed with realistic conditions on alloys of practical importance. Emphasis in this paper is on modeling and simulation of interdiffusion occurring between NiAl coatings and Ni-base superalloy substrates. For this purpose we have used the so-called homogenization approach to diffusion in multi-phase systems, recently implemented into the DICTRA software. The simulation results have been validated against experimental data and the agreement is very satisfactory given the complexity of the problem.
Authors: Xuan Xiao, Xu Le, Zeng Chao, Li Yuan Sheng, Yong An Guo, Lan Zhang Zhou
Abstract: Directionally solidified Ni-based superalloy DZ483 is a kind of potential material for the blade of an advanced heavy duty gas turbine, which has good combination properties. The carbide degradation behaviors of DZ483 alloy during long-term thermal exposures were investigated at different conditions in this paper. The results show that during the long-term exposure, primary carbide will decompose in the form of MC + γ → M23C6 + γ'. Carbide on the grain boundary could be decomposed more easily than intragranular carbide. With the increase of aging time, decomposition could be observed more obviously, carbides on the grain boundary become bigger and the morphology of carbide near the grain boundary tends to be more complex. The fine dispersive particles of M23C6 on the grain boundary will grow up gradually to a thin consecutive chain of carbide with the increase of aging time.
Authors: Dmitry Valerievich Kotoban, Aleksey Petrovich Nazarov, Igor Vladimirovich Shishkovsky
Abstract: The Ni3Al intermetallics involve more attention because of inherent material properties especially interesting in high temperature application. In this study the Selective laser melting (SLM) and Direct laser metal deposition (DLMD) are used to manufacture the single-tracks and layers. For the comparison of the methods, the optical microscopy, SEM, XRD and EDX microelement analysis were involved. The materials show no significant differences but each SLM and DLMD have the target application.
Authors: Xu Dong Lu, Ce An Guo, Jie Wang, Shu Wu Ma
Abstract: The cyclic oxidation behaviour of Ni 5.5Al 2.6Ti 4.8Co 3.9Mo 5.0W 11.0Cr superalloy at 900 °C in air has been investigated by means of measuring the kinetics curves of the oxidation and analysis method of XRD and SEM/EDAX. The results show that the mass gain rapidly increases in the initial stage, and the weight loss and mass gain occurs alternately during the cyclic oxidation. An obvious oxidation and internal oxidation occurs during cyclic oxidation. Ti in the alloy oxidized, diffusing through the Al2O3 and Cr2O3 scales to form faceted TiO2 particle on the surface of the alloy. Al2O3 formed discontinuousness inner oxides in the alloy.
Authors: Shuho Koseki, Kenichi Inoue, Kazutake Uehara, Hiroshi Usuki, Masahiro Yoshinobu, Ryutaro Tanaka, Masahiro Hagino
Abstract: Ni-based superalloys are typically difficult-to-cut materials. During machining, the cutting forces and temperatures of these superalloys are generally higher than those of other materials. Therefore, the tool life of the coated carbide cutting tools used for superalloy machining is shortened. This study evaluates the damage of the coated end mills during interrupted cutting of alloy 718 and finds the coating properties necessary for improved cutting of Ni-based superalloys. Damage of the PVD-TiN-coated cutting tools was observed by scanning electron microscopy and transmission electron microscopy of the surfaces and cross sections. In addition, friction forces were measured during turning for some coatings, and hardness of the coatings was measured after annealing. Plastic deformation of the coating and crack formation was shown to occur at the coating cross section. In addition, we determined that the major factor for the damage was high friction force between the coating surface and work material at high temperatures. In summary, coatings with stability at high temperatures and low friction forces during machining can reduce the damage of coated cutting tools, thus increasing the tool life.
Authors: Keun Bong Yoo, Han Sang Lee, Kyu So Song
Abstract: Gas turbine components operated by hot combustion gas undergo material degradation due to the thermal cycle by daily startup and shutdown. The failure mechanism of the hot gas components is accompanied by degradation in the properties of high temperature strength and creep rupture time. Many hot gas components in gas turbines are made of Ni-based superalloy because of their high temperature performance. In this work, we survey the time and temperature dependent degradation of Ni-based superalloy. We prepared specimens from Inconel738LC that were then exposed at 871~982°C in 1,000~5,000hours. We carried out stress-rupture tests and microstructural investigation.
Authors: Masakazu Okazaki, Motoki Sakaguchi, Yosuke Sasaki, Koichi Namba
Abstract: Degree of long term degradation damage of a retired gas turbine vane made of a Ni-based superalloy which had been operating for about 20000 hrs in a land-based gas turbine, was experimentally evaluated, through an assessment on the change in fatigue crack propagation resistance. For the purpose, a new testing apparatus has been developed to measure the local area fatigue crack propagation resistance, by extracting the miniature size compact tension specimens from the vane, where the specimens were extracted from the leading and the trailing edge, respectively. It was shown, the propagation rate of the crack that grew at the trailing edge part was significantly higher that that at the leading edge part. It was also shown that the crack propagation rates in the miniature specimen were generally higher than those in the standard size specimen. In order to explore an possibility to recover the degradation damage, the effect of a simple reheat treatment on the fatigue crack propagation resistance was also investigated
Authors: Lembit A. Kommel, Boris B. Straumal
Abstract: Deformation-enhanced diffusion in single-crystalline Ni-based superalloy specimens have been investigated under the conditions of hard cyclic viscoplastic tension-compression deformation. The chemical composition of phases before and after cyclic deformation was investigated by filed-emission scanning electron microscopy. At low strain amplitude values (0-0.05%; 0-0.2%; 0-0.5%) the material shows upscaled viscoelastic behavior and microstructural stability. At the increase of strain amplitude in the γ+γ’-phase (0-1%), the Ni, Re and Co content decreases, whereas Al and Mo content increases significantly. On the contrary, in the single γ’-phase area, the Ni and Co content was increased, which was accompanied by a decrease of Nb, Cr, Ta and Al content. The length of dendrite arms was significantly decreased as compared to primary dendrite arms and γ+γ’-rafts were formed parallel to the stress axis direction. As a result of the deformation-enhanced, diffusion the necking of dendrites accompanied with longitudinal cracking by the dendrite axis and cross-sectional radial cracking by interdendritic region of single crystalline specimen occurs.
Authors: J.Y. Song, Shigeo Sato, Yuichiro Koizumi, Akihiko Chiba
Abstract: The aim of this study was to examine the effect of cobalt addition on the deformation and recrystallization behavior. The prepared material was Inconel 713C nickel base superalloy. In order to improve the deformability, the IN713C was modified by cobalt addition with 5 and 10wt%. Mechanical property was determined by room temperature tensile test with the strain rate of 10-3 s-1.The recrystallization was performed at 1473K for 300sec followed by oil quenching. The final microstructure becomes homogeneous through cobalt addition. Strength and work hardening rate were decreased during room temperature tensile test. By contrast, elongation was increased. Nucleation site was changed by cobalt addition. It was found that kinetics of recrystallization is dependent of the cobalt addition. The cobalt addition is attributed with ductility and recrystallization behavior and the latter is related to change of deformation behavior.
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