The Microstructure Changes in IN713LC during the Creep Exposure (original) (raw)
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Microstructural analysis of creep exposed IN617 alloy
2010
Nickel base alloys such as IN617 are one of the preferred choices for steam turbine components used by fossil fuelled power generation plants. IN617 is a solid-solutionstrengthened nickel-based superalloy containing ~23% Cr, 12% Co, and 9% Mo with low content of precipitation-strengthening elements Al, Ti and Nb. In the 'as-received' (solution-annealed condition), the microstructure consists of primary carbides (M 23 C 6 ) and occasional TiN particles dispersed in a single-phase austenitic matrix. Owing to high temperature exposure and the creep deformation processes that occur in-service, evolution of the microstructure occurs. This results in secondary precipitation and precipitate coarsening, both on grain boundaries and intragranularly in areas of high dislocation density. The influence of creep deformation on the solution-treated IN617 alloy at an operating condition of 650˚C/574 Hrs, with emphasis on the morphology and distribution of carbide/nitride precipitation is discussed. The applied stress was at an intermediate level.
Microstructural Changes in IN617 Superalloy during Creep at High Temperatures
Procedia Engineering, 2014
In an Ultra super critical power plant, it is considered to be necessary to use Ni-base super alloys with higher strength in addition to conventional heat-resistant steel. Out of various materials in the pipe line, one important alloy i.e. IN 617 super alloy is selected for the Ultra Supercritical power plant applications for operation. Creep is one of the major properties to be assessed for the material to be used in USC power plants. In this paper, creep behaviour of IN 617 super alloy is studied at various stress and temperatures and microstructures are correlated with high temperature properties. Microstructures of crept samples tested at two temperatures of 650 o C and 700 o C at different stress level were analysed and compared using optical and scanning electron microscopy techniques.
Microstructural characterization of Inconel 713 C superalloy after creep testing
2018
The main aim of this investigation was to determine the microstructural degradation of Inconel 713C superalloy during creep at high homologous temperature. The alloy in as cast condition was characterized by large microstructural heterogeneity. Inside equiaxed grains dendrite cores consisted of γ' precipitates surrounded by channels of matrix, whereas enrichment of interdendritic spaces in carbide formers, Zr and B resulted in the formation of additional constituents, namely M3B2, Ni7Zr2 and eutectic island γ/γ'. Directional coarsening of γ′ precipitates (rafting) under applied stress and decomposition of primary MCtype carbides accompanied by the formation of secondary carbides enriched in Cr and γ' phase was observed.
Aging effects on the microstructure and creep behavior of Inconel 718 superalloy
Standard heat treatment (HT1) for Inconel 718 superalloy is solutionizing at 1095 • C, 1 h/AC, then aging at 955 • C, 1 h/AC + 720 • C, 8 h/FC 57 K/h to 620 • C, 8 h/AC. In order to study the aging effects of the ␦ phase, two more conditions HT2 (no aging condition 955 • C) and HT3 (955 • C, 3.5 h/AC) were studied in this research. Lever arm creep tests were performed at 650 • C under constant stress 625 MPa. Since HT2 produces no ␦ phase, the stress rupture life, creep elongation to failure and steady state creep rate of HT2 are largest among these three aging conditions. However, increasing the 955 • C aging time, the stress rupture life, creep elongation and steady state creep rate raise slightly as compared to HT1, because platelet ␦ phase is more uniformly nucleated and more direction oriented at grain boundaries. Fractographs show ductile fracture patterns mostly and, small portion of inter-granular fracture in the HT2 specimens. Generally only inter-granular fracture is observed in the other two cases of HT1 and HT3. Besides twinning and dislocation mechanisms, grain boundary sliding is also activated, so that creep elongation to failure of HT2 specimens could reach 5.6%, whereas 1% for the other two schemes.
Mechanics of Materials, 2017
This manuscript presents the computational modeling and analysis of creep deformation and failure of Nickel-based superalloy, Inconel 617 (IN 617), operating at high temperature. Crystal plasticity finite element (CPFE) approach, considering isothermal and large deformation conditions at the microstructural scale has been extended for creep deformation and rupture modeling of IN 617 at 950 • C. In order to accurately capture the creep strains that accumulate particularly at relatively low stress levels, a dislocation climb model has been incorporated into the CPFE framework. In addition, a cohesive zone (CZ) model is adopted to capture intergranular creep damage, and incorporated into the CPFE framework. The CPFE and the CZ models work in tandem to describe the viscoplastic deformation as well as progressive failure in the material microstructure. The calibration of dislocation climb and CZ parameters is performed based on experimental data. The microstructure model is validated using independent creep experiments performed at various stress levels. Microstructural analysis of the stress and damage distributions as well as their time-dependent evolution is carried out to provide insight into the dominant microscale deformation and failure mechanisms. Creep life predictions are performed to describe rupture life as a function of load amplitude at high temperature.
Creep Fracture Mechanism of Polycrystalline Ni-based Superalloy with Diffusion Coatings
Diffusion coatings are widely used to increase oxidation and corrosion resistance of hot superalloy components for gas turbines. The aim of this study is to investigate the effect of coatings (NiAl and PtAl) on the creep fracture mechanism of samples with a substrate of IN792. The samples have been creep tested at two temperatures (850 °C and 950 °C) and different applied tensile stresses, until failure between 205 and 21000 hrs. The observation of cross-sections by SEM shows that the microstructural evolution in the coating is dependent on the diffusion of alloying elements in the sample. Furthermore the time and temperature induced growth of the coating is found to be controlled only by inward diffusion of Al. Grain-boundary cracking is the basic fracture mode in the substrate in all samples irrespective if the crack is initiated from coating or substrate. The analysis of microstructure shows that the diffusion coatings display two types of mechanical behavior-being easily plasticized or cracked-dependent on temperature and type of coating, and therefore can be considered as non-load carrying regions. After recalculating the creep stress to exclude the final effective coating thickness from the total sample thickness, the coated samples showed similar creep rupture behavior as the uncoated samples in the Larson-Miller diagram.
Archives of Foundry Engineering, 2015
The results of structure observations of Ni base superalloy subjected to long-term influence of high pressure hydrogen atmosphere at 750K and 850K are presented. The structure investigation were carried out using conventional light-, scanning- (SEM) and transmission electron microscopy (TEM). The results presented here are supplementary to the mechanical studies given in part I of this investigations. The results of study concerning mechanical properties degradation and structure observations show that the differences in mechanical properties of alloy subjected different temperature are caused by more advanced processes of structure degradation during long-term aging at 850K, compare to that at 750K. Higher service temperature leads to formation of large precipitates of δ phase. The nucleation and growth of needle- and/or plate-like, relative large delta precipitates proceed probably at expense strengthening γʺ phases. Moreover, it can’t be excluded that the least stable γʺ phase is...
Creep and Mechanical Behavior Study of Inconel 718 Superalloy
Materials Research, 2022
Over the years, the demand for high engine efficiency has resulted in the development of new generation superalloys with improved elevated temperature properties, especially creep resistance. This study aimed to evaluate creep and mechanical behavior of Inconel 718 superalloy. Creep tests were performed at temperature range of 650 to 700 °C and stress range of 625 to 814 MPa. Hot tensile and oxidation tests were performed and the characterization techniques used in this study were scanning electron microscopy (SEM) for microstructural and fracture surface analysis, transmission electron microscopy (TEM) for precipitates analysis; grazing X-ray diffraction for analysis of oxide formation and Vickers microhardness. The analyze of stress exponent value (n = 36.48) and activation energy (Q c = 512.97 kJ/mol), suggested that creep mechanism at 650 °C was the climb dislocation mechanism. The Inconel 718 presented ductile fracture at 650 and 700 °C and intergranular fracture to 675 °C.
Degradation of creep properties in a long-term thermally exposed nickel base superalloy
Materials Science and Engineering: A, 2004
When exposed for long time at elevated temperatures of 430 and 650 • C the nickel base superalloy EI 698 VD can experience a significant decrease in creep resistance. The cause of the creep degradation of nickel base superalloy is generally attributed to the microstructural instability at prolonged high temperature exposure. In this article, the creep-life data, generated on long thermally exposed nickel base superalloy EI698 VD were related to the local microstructural changes observed using SEM and TEM analysing techniques. While structure analysis provided supporting evidence concerning the changes associated with grain boundary carbide precipitation, no persuasive evidence of a morphological and/or dimensional gamma prime change was showed. For clarifying of the role of gamma prime precipitates on alloy on creep degradation, the SANS (small angle neutron scattering) experiment was crucial in the characterization of the bulk-averaged gamma prime morphology and its size distribution with respect to the period of thermal exposure.
5428 - Experimental and Numerical Investigation on the Creep Crack Growth in IN718
Icf11 Italy 2005, 2013
Creep crack growth (CCG) behaviour of Inconel 718 superalloy are investigated by means of experimental tests and numerical simulation at the temperature of 687 °C. The CCG tests are carried out with different initial values of the stress intensity factor on a standard compact-tension specimen. Creep crack growth are simulated using the finite element code ABAQUS and creep constants obtained from creep tests. C* parameter is used for characterizing CCG behaviour under the steady-state condition. Experimental and numerical results will be compared. Moreover Nikbin, Smith and Webster approach, for the evaluation of the time of crack initiation and the rate of damage accumulation, will be assessed.