Quantitative Microstructural Analysis of a Ni-based Superalloy After Different Heat Treatments (original) (raw)
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Effect of the heat treatment on the microstructural evolution of the nickel based superalloy
Metalurgija, 2011
The effect of heat treatment on the microstructure of cobalt-rich nickel based supperalloy was studied applying scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The aim of the present work was to investigate the formation and evolution of different phases during the heat treatment of superalloy similar to Udimet 500. The presence of a relatively high volume fraction of γ'particles in the γ matrix suggests on inefficient cooling rate during oil quenching from 1150°C. Carbides such as MC primary carbides of the type TiC and MoC as well as secondary carbides M 23 C 6 (Cr 23 C 6 ) were found in grains and at grain boundaries.
Microstructure of an experimental Ni base superalloy under various casting conditions
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2010
The effect of casting parameters such as melt superheat and solidification rate on the microstructure of an experimental Ni-based superalloy made by vacuum melting and investment casting methods was investigated. The results show that the as cast microstructure of this alloy consists of dendritic ␥ matrix, interdendritic ␥/␥ , ␥ phase, MC carbides and minor phases in interdendritic regions. DSC analyses in addition to SEM and EDS proved that the nodular phase found in minor phases is phase, while the phase was found to solidify in two forms; as plate-like and blocky shape. The volume fraction (V f ) of and phases increases as the melt superheat increases and the solidification cooling rate decreases. Additionally, the V f of interdendritic ␥/␥ increases with higher solidification rate and lower melt superheat. It was found that higher melt superheating temperature enlarges the size of the primary ␥ dendrites; however the higher solidification rate diminishes it.
Applied Physics A, 2020
Due to their high thermal stability under severe working conditions and harsh environment, nickel (Ni)-based superalloys, such as Inconel 718, Inconel 738, GTD11, and René 40, are largely used in gas turbine industry. The gamma prime (γʹ) precipitates, that are coherent with the gamma (γ) matrix in these superalloys, provide excellent mechanical properties at high operating temperatures. However, after a long time of functioning, (γʹ) precipitates coarsen and lose their coherency with the matrix, which causes damages in gas turbine blades. The main purpose of this paper is to study the effect of both solid solution and aging heat treatments temperatures on the microstructural evolution in an Inconel 738 superalloy blade, which was received after few tens of thousands of service hours. The resulting microstructures were analyzed by using scanning electron microscopy and optical microscopy along with Vickers microhardness measurements. The obtained results show that the Vickers microhardness of the studied superalloy is related to size, shape, volume fraction, and distribution of the hardening phase (γʹ) [Ni 3 (Al, Ti)], and to its carbides as well. It was found that the microstructural stability is related to the working temperature.
Effect of the cooling rate on microstructure and hardness of MAR-M247 Ni-based superalloy
Materials Letters, 2012
The effect of cooling rate on the microstructure of MAR-IVI247 Ni-based superalloy was investigated via physical simulation of the casting process. Solidification experiments with cooling rates in the range of 0.25-10 K/s showed smooth temperature profiles with measured cooling rates matching the set values. The MAR-IVI247 showed cellular (0.25 K/s) and dendritic (1, 5 and 10 K/s) microstructures. Microconstituents also varied with cooling rates: yy matrix with carbides and yy eutectic at 0.25 K/s, yy matrix with carbides at 1 K/s, and yy matrix with carbides and yMC eutectic at 5 and 10 K/s. Moreover, the secondary dendritic arm spacing decreased and the hardness increased with the increase in the cooling rates.
International journal of electrochemical science
The microstructure of cast polycrystalline Inconel 738LC (IN738LC) under different heat treatment conditions was investigated. The cast microstructure of this alloy consists of austenitic ␥ matrix, ␥ precipitates, MC carbide and ␥/␥ eutectic. The microstructure of the conventional solution treatment, 1120 • C/2 h/accelerated air cooling (AAC), contains a bimodal ␥ precipitate. Solution treatment at several temperatures of 1120, 1180, and 1220 • C for 1.5 h as well as 1180 • C/1.5 h + 1220 • C/2 h has been carried out under argon atmosphere. Accelerated air cooling (AAC) and water quenching (WQ) were applied after solution treatment. Moreover, aging treatment at 845 • C was carried out for all solutioning conditions followed by WQ. Solution treatment at 1180 • C/1.5 h + 1220 • C/2 h gives the best homogeneity for different alloying elements and a uniform size for the fine ␥ precipitates. AAC increases the volume fraction and tends to agglomerate ␥ precipitates compared to WQ.
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Materials Science and Engineering: A, 2014
The microstructure of thermally aged nickel-based 718Plus superalloy is investigated using transmission electron microscopy (TEM). Solution annealing at 980 1C for 30 min is followed by either the standard quenching to room temperature or quenching directly to 788 1C, before isothermal aging at 788 1C for four hours. Micro-hardness and yield strength are measured to compare the effects of the two variations. The size and phase fraction of γ 0 precipitates are measured using dark-field TEM and related to the hardness and yield strength through a theoretical model based on coherency and antiphase boundary effects. A population of very small sub-precipitates is observed and the larger γ 0 precipitates are investigated in detail using high resolution scanning TEM to reveal information about the chemical ordering.
The Effect of Cooling Rate on Selected Structural Parameters of Advanced Cast Ni – Base Superalloys
Quality Production Improvement
The Nibase superalloys are used in aircraft industry for production of aero engine most stressed parts, as are turbine blades or turbine discs. The most stressing factor at Nibase superalloys loading or working conditions are high temperature range of 700°C up to 850°C and, of course, centrifugal forces, and small vibrations, which produce bending of turbine blades inserted into turbine discs. All these factors cause various forms of microstructure degradation closely connected with decreasing of mechanical properties and shortening of working life as well. From this reason a dendrite arm spacing, carbides size and distribution, morphology, number and value of -phase are very important structural characteristics for blade lifetime prediction as well as aero engine its self. In this article are used methods of quantitative metallography for evaluation of structural characteristics mentioned above on experimental materials-Ni base superalloys ŽS6K and Inconel IN 738. The high temperature effect represented here by heat treatment at 800°C for 10 hours, and cooling rate, here represented by three various cooling mediums as water, air, and oil, on structural characteristics and application of quantitative methods evaluation with using of SEM are presented in this paper.
Relation between the microstructure and microchemistry in Ni-based superalloy
Surface and Interface Analysis, 2012
Ni-based superalloys with biphasic structure (g + g′) are widely used for high-temperature applications, such as disks and blades of gas turbines and aeronautical engines. For these applications, the stability at high temperature is of utmost importance, in particular the coarsening and the morphological changes of g′ may be seriously detrimental for in-service components. Evolution of g′ particles strongly depends on the composition difference between disordered matrix and particles. The present work is devoted to the investigation of the g′ morphology and the microchemistry in single crystal CM186LC superalloy in as-received condition and after creep. The study was carried out by scanning electron microscopy and atomic force microscopy, standard X-ray photoelectron spectroscopy and scanning photoemission microscopy (SPEM) at the ELETTRA synchrotron facility in Trieste. The difference in the chemical composition of two phases, g and g′, was revealed from the SPEM images and their spectral analysis. The structural evolution, taking place during creep and leading to rafting, seems to be determined not only by the external applied stress but also by W diffusion from g to g′ phase.