Damage development of Inconel 718 due to laboratory simulated creep (original) (raw)
Journal of Nuclear Science and Technology, 2012
The effects of directional coarsening of g 0 precipitates in nickel-based superalloy on ultrasonic attenuation coefficient and nonlinearity during creep exposure were investigated in this study. The cuboidal g 0 precipitates coarsened preferentially in the direction perpendicular to the applied stress axis during the creep deformation. The length (a) of the g 0 precipitates increased with creep time, while the width (b) increased slightly. Here, the increase in ultrasonic attenuation coefficient and nonlinearity with increasing creep time is discussed in relation to the directional coarsening of g 0 precipitates, which was closely related to the scattering and distortion of the ultrasonic waves. We suggest that ultrasonic attenuation coefficient and nonlinearity can potentially be used for characterization of creep damage in nickel-based superalloys.
2017
Process compensated resonant testing (PCRT) is a full body nondestructive evaluation (NDE) method that measures the resonance frequencies of a part and correlates them to the part's material state, structural integrity, or damage state. This paper describes the quantification of creep damage in a virtual part population via the correlation of PCRT parameters to creep strain using inversion methods and vibrational pattern recognition (VIPR) analysis. Modeled populations were created using the finite element method (FEM) for single crystal (SX) nickel-based superalloy dogbone and turbine engine airfoil geometries. The modeled populations include nominal variation in crystallographic orientation, geometric dimensions, and material properties. Modeled populations also include parts with variable levels of creep strain, allowing for NDE sensitivity studies. FEM model inversion tools quantified creep strain and distinguished it from other variations in the part populations. Resonant modes that were found to be particularly sensitive to creep strain were evaluated using VIPR algorithms to correlate and quantify creep strain with PCRT metrics. The results for PCRT forward models, model inversion, and VIPR correlations were verified with experimental creep strain measurements made for dogbone specimens. This verification demonstrated that PCRT inspections can be trained through forward models to detect and quantify creep damage in a part.
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.
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.
Creep Characterization of Ni-Based Superalloy IN-792 Using the 4- and 6-θ Projection Method
Journal of Engineering Materials and Technology, 2013
This paper studies the accuracy of a technique which is capable of predicting and modeling a wide range of creep life in Ni-based superalloys. The θ-projection method was applied to characterize the creep behavior of the Ni-based superalloy IN-792 at 800 °C. Constant load creep tests have been carried out over a wide range of loads at the constant operating temperature. Creep curves were fitted using either 4-θ or 6-θ equation by the use of a nonlinear least-square technique. The results showed that both 4- and 6-θ projection parameters revealed a good linearity as a function of stress. Comparison of experimental creep curves with those predicted using both of the utilized θ-projection techniques showed that the techniques fit the experimental data at high strain values very well while the 6-θ approach describes much better the creep curves at low strain region.
Ultrasonic quantification of high temperature cyclic damage in an advanced nickel based superalloy
Materials Science and Engineering: A, 2015
Present paper discusses about a new methodology to quantify cyclic damage through ultrasonic measurement. Based on experimental results, correlations have been made between damage accumulated inside the material due to strain excursions and corresponding ultrasonic parameters. It has been proposed that based on the existing correlation between attenuation coefficient and number. of cycles to failure, fatigue failure characteristics can be partitioned into two regimes (a) failures due to early nucleation and rapid propagation of cracks and (b) failures due to delayed propagation and crack coalescence. Plastic strain accumulation and surface crack density have been chosen as two physical parameters directly influencing attenuation coefficient and it has been observed that with increasing plastic strain accumulation, ultrasonic attenuation increases. Between two primary echoes of ultrasonic spectra, some secondary defect echoes have been found. A damage descriptor has been introduced by taking difference between the bandwidth of defect echo and backwall echo normalized by overall amplitude frequency distributions of backwall echo. It has been found to bear sensitivity towards surface crack density. This quantitative estimation differentiates between the classical descriptions of damage due to dislocation mediated plasticity, micro crack generation and coalescence.
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.
Effect of Double Aging Heat Treatment on the Short-Term Creep Behavior of the Inconel 718
Journal of Materials Engineering and Performance, 2016
This research studies the effect of double aging heat treatment on the short-term creep behavior of the superalloy Inconel 718. The superalloy, received in the solution treated state, was subjected to an aging treatment which comprises a solid solution at 1095°C for 1 h, a first aging step of 955°C for 1 h, then aged at 720 and 620°C, 8 h each step. Creep tests at constant load mode, under temperatures of 650, 675, 700°C and stress of 510, 625 and 700 MPa, were performed before and after heat treatment. The results indicate that after the double aging heat treatment creep resistance is increased, influenced by the presence of precipitates c¢ and c¢¢ and its interaction with the dislocations, by grain size growth (from 8.20 to 7.23 ASTM) and the increase of hardness by approximately 98%. Creep parameters of primary and secondary stages have been determined. There is a breakdown relationship between _ e s and stress at 650°C of Inconel 718 as received, around 600 MPa. By considering the internal stress values, effective stress exponent, effective activation energy, and TEM images of Inconel 718 double aged, it is suggested that the creep mechanism is controlled by the interaction of dislocations with precipitates. The fracture mechanism of Inconel 718 as received is transgranular (coalescence of dimples) and mixed (transgranular-intergranular), whereas the Inconel 718 double aged condition crept surfaces evidenced the intergranular fracture mechanism.