Papers by Keyword: Superalloy

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Authors: Ralph Gilles, Debashis Mukherji, H. Eckerlebe, Pavel Strunz, Joachim Rösler
Abstract: Single crystal Ni-base superalloys based on the  /  system are widely used in gas turbine applications. To understand the formation of  precipitates, including size distribution and growth, we performed in situ small-angle neutron scattering (SANS) measurements at elevated temperatures and - together with TEM as well as , SEM imaging - studied changes in the precipitates in short and long time scale. In the early stages, a bimodal precipitate size distribution of precipitate is observed, which (depending on the annealing temperature) changes to a cuboidal or nearly spherical morphology with almostmore or less uniform ( unimodal?) size distribution. [Note: The term "more or less" is several times repeated in the text. I cannot imagine what it in fact means. Could you change it or explain in a more clear way?]
Authors: Mustapha Jouiad, J. Ghighi, Jonathan Cormier, E. Ostoja-Kuczynski, G. Lubineau, J. Mendez
Abstract: An unprecedented investigation consisting of the association of X-Ray tomography and Scanning Electron Microscopy combined with Focus Ion Beam (SEM-FIB) is conducted to perform a 3D reconstruction imaging. These techniques are applied to study the non-isothermal creep behavior of close (111) oriented samples of MC2 nickel base superalloys single crystal. The issue here is to develop a strategy to come out with the 3D rafting of γ’ particles and its interaction whether with dislocation structures or/and with the preexisting voids. This characterization is uncommonly performed away from the conventional studied orientation [001] in order to feed the viscoplastic modeling leading to its improvement by taking into account the crystal anisotropy. The creep tests were performed at two different conditions: classical isothermal tests at 1050°C under 140 MPa and a non isothermal creep test consisting of one overheating at 1200°C and 30 seconds dwell time during the isothermal creep life. The X-Ray tomography shows a great deformation heterogeneity that is pronounced for the non-isothermal tested samples. This deformation localization seems to be linked to the preexisting voids. Nevertheless, for both tested samples, the voids coalescence is the precursor of the observed damage leading to failure. SEM-FIB investigation by means of slice and view technique gives 3D views of the rafted γ’ particles and shows that γ corridors evolution seems to be the main creep rate controlling parameter.
Authors: Gouthama, Bollineni Yugesh
Abstract: Abrasive Water jet cutting (AWJ) is a process used to cut materials using a jet of pressurized water. These water jets are capable of cutting a variety of materials like superalloys, titanium alloys, stainless steel, tool steels, ceramics, armor tool and granite. In the present study an attempt has been made to investigate microstructural changes taking place in the sub-surface as a result of AWJ cutting using cross-sectional Transmission Electron Microscopy (TEM). TEM analysis shows that the sub-surface of the AWJ machined sample surface experienced severe deformations. The surface microstructure is observed to contain extremely fine sized grains, going down from sub-micrometer to nanometer range. The selected area diffraction pattern analysis also confirms the presence of extremely fine grained microstructure.
Authors: Jie Zhang, Mao Cai Wang, Yu Chun Zhai
Abstract: Gas turbine components are subjected to high temperature and high stress during engine operation, so they often become physically damaged due to the formation of cracks, voids and worn surfaces. In order to develop a new process for repairing gas turbine components with high strength filler materials, an attempt has been made to prepare IN738/NiCrSi/IN738 sandwich-like coating on thermal sensitive superalloy IN738 substrate and heat-treat it in a vacuum furnace. The microstructure morphologies, hardness and element distribution of as-deposited and as- heat-treated coatings have been investigated. The results showed that there were lot of cracks and voids in the deposited ‘sandwich-like’ coating but they could be eliminated by heat treatment. The diffusion of activated element Si in the sublayer NiCrSi of ‘sandwich-like’ coating was beneficial to healing cracks.
Authors: Roland Mücke
Abstract: Modern gas turbines utilize single crystal (SX) and directionally solidified (DS) nickel superalloys which hold a higher cyclic life resistance and an improved creep rupture strength compared to their conventionally cast (CC) version. Both, SX and DS materials feature a significant direction dependence of material properties, which needs to be considered in the constitutive and lifing models. In this context, the paper presents a mathematical framework of cyclic life prediction. Although the method is developed for DS nickel alloys with transverse isotropic material behaviour, a generalisation to common orthotropic materials inclu¬ding SX is straightforward. The proposed procedure is validated by two examples. Moreover, an application to turbine components is shown.
Authors: Ciro Caramiello, Stefania Iannuzzi, Alessandro Acernese, Doriana M. D’Addona
Abstract: We account for the problem of optimal control of ceramic mould manufacturing in lost wax cast processes with the aid of a mixed linear algebraic-statistical approach based on the employment of Singular Value Decomposition (SVD) and Neural Networks (NN).We consider the peculiar aspect of minimizing ceramic inclusions occurrence in equiaxed superalloy turbine components which are manufactured resorting to gravitational pouring. The optimization consists in finding optimal extrema of scalar and/or vectorial functions of the type Rk->Rm i.e. Key Process Variable domain (KPV) vs. Target Variable domain (TV) over a large set of experimental data affected by acquisition noise leading to a typical sparse multiblock array.The goal of the work consists in the assessment of possible significant statistical multivariate correlations amongst the KPV and TV when the dimension of domain space, k, has an order of magnitude of tens, in the presence of quasi-rank deficient input matrix.
Authors: Gilles Damamme, David Piot, Frank Montheillet, S. Lee Semiatin
Abstract: A simple mesoscale model was developed for discontinuous dynamic recrystallization. The material is described on a grain scale as a set of (variable) spherical grains. Each grain is characterized by two internal variables: its diameter and dislocation density (assumed homogeneous within the grain). Each grain is then considered in turn as an inclusion, embedded in a homogeneous equivalent matrix, the properties of which are obtained by averaging over all the grains. The model includes: (i) a grain boundary migration equation driving the evolution of grain size via the mobility of grain boundaries, which is coupled with (ii) a dislocation-density evolution equation, such as the Yoshie–Laasraoui–Jonas or Kocks–Mecking relationship, involving strain hardening and dynamic recovery, and (iii) an equation governing the total number of grains in the system due to the nucleation of new grains. The model can be used to predict transient and steady-state flow stresses, recrystallized fractions, and grain-size distributions. A method to fit the model coefficients is also described. The application of the model to pure Ni is presented.
Authors: Sridhar Kompella, Kai Zhang, Rajeev Pakalapati
Abstract: The use of cubic boron nitride (CBN) over conventional abrasives in ferrous and superalloy grinding has resulted in improved manufacturing throughput and beneficial mechanical properties on workpiece surfaces. However, through the innovative use of crystal synthesis techniques, the grinding performance can be further improved over existing CBN crystals. In this study, such a new CBN crystal is developed, characterized, and its grinding performance is compared to a commercially available CBN crystal. Grinding tests are conducted in AISI M2 steel and Inconel-718 superalloy using a vitrified bond configuration with applicability in a wide range of end-use applications.
Authors: Huai Zhong Li, Jun Wang
Abstract: nconel 718 is one of the most commercially important superalloys but with very poor machinability. It has a very high yield stress and a high tendency to adhesion and work-hardening. A recent trend of improving the machining processes of difficult-to-cut materials is to move towards dry cutting operations. This paper presents an experimental study of the cutting forces in high speed dry milling of Inconel 718 using a milling cutter with coated carbide inserts. It is found that the peak cutting forces increase with an increase in chip load in a nonlinear way, but cutting speed does not show a significant influence on the cutting force for the range of cutting speeds tested in this study.
Authors: Marta Kianicová, Jan Kafrik
Abstract: The microstructure and corrosion behaviour was studied for a diffusion β-NiAl and Si modified β-NiAl coatings formed on the superalloy MAR-M 247. First type, β-NiAl coating was applied with the help of method “out-of-pack”. Second type, Si modified β-NiAl coating was applied by method “pack-cementation”. Diffusion coatings created protective, heat-activated layer which separated superalloy from aggressive environment. Corrosive environment was created by tablets Na2SO4 at 900°C. Technique of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDS) was used to characterize the corrosion products. Experiment confirmed the advantages relating to the application of diffusion coating in aggressive environment which imitated environmental condition during operation of turbine engine. This experiment was made in cooperation with company PBS Velká Bíteš a. s., Velká Bíteš, Czech Republic and The Silesian University of Technology, Faculty of Materials Science and Metallurgy, Katowice, Poland.
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