Accuracy of composition measurement using X-ray spectroscopy in precipitate-strengthened alloys: Application to Ni-base superalloys (original) (raw)
Related papers
Ultramicroscopy, 2014
Energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope (STEM) has been used to demonstrate the presence of size-dependent compositional variation for L1 2 -structured Ni 3 Al-type gamma-prime (γ 0 ) precipitates within a commercial RR1000 Ni-based superalloy. This semiquantitative elemental analysis has been achieved using electrochemical extraction of the γ 0 precipitates from the γ matrix. The applicability of this approach to size-dependent compositional analysis of precipitates was confirmed by a comparison of the size distribution for the extracted precipitates with those present in traditional electropolished foil specimens in the size range 20-250 nm. By applying suitable thickness-dependent absorption-corrections we have demonstrated that the composition of γ 0 precipitates in our material depends on the size of the precipitate in the range of 5 nm to 3 μm. In particular, the Al content was observed to increase in smaller γ 0 precipitates while Ti and Ta contents are constant for all sizes of precipitate. Hf was observed to be present only in the largest precipitates. This type of local compositional information provides invaluable input to assess the accuracy of microstructural modelling for these complex alloys and provides new evidence supporting the importance of anti-site diffusion.
Journal of Materials Processing Technology, 2013
The Scheil equation was used to model the solidification path, microsegregation of alloying elements in the interdendritic regions, solidification temperature ranges, and to predict the formation of secondary structures and the castability behavior of as-cast superalloys. 4 experimental alloys with pre-specified ␥-Ti,Nb,Al,Mo composition containing different Nb, Ti and Al contents were designed using vacuum induction melting furnace. The produced as-cast superalloys were characterized using optical and scanning electron microscopy equipped with energy dispersive X-ray spectrometer and TG-DSC analysis. The experiments showed logic conformity to the modeling results. The model and experiment confirmed the highest segregation behavior for Ti and Nb. All the experimental superalloys indicated the remarkable tendency to form secondary eutectic structures at the last stages of solidification. Superalloy with chemical composition of ␥-3.5%Mo,1.8%Al,4%Ti,2.9%Nb showed the shorter solidification temperature range and the best castability.
Scripta Materialia, 2007
Differential thermal analyses along with microstructural characterization has been used to study the solidification path in the Ni-based superalloy CMSX 10 K. It was found that solidification initiates with freezing of primary c dendrites, continues with a peritectic reaction resulting in nucleation and growth of c 0 particles in the interdendritic liquid, and terminates with the precipitation of fine lamellar [c-c 0 ] phases between the coarsened c 0 particles.
Chemical Physics, 2010
In this study, r Ka;b production cross-sections, K b /K a , KLM/K a and KMM/K b RAE intensity ratios of Ni and r Ka ; r K b1;2 production cross-sections, K b1,3 /K a , K b2,4 /K a , K b2,4 /K b1,3 , KLM/K a and KMM/K b RAE intensity ratios of Mo have been measured in pure metals and in superalloy specimens. The samples were excited by 59.5 keV c-rays from a 241 Am annular radioactive source. K X-rays emitted by samples were counted by an Ultra-LEGe detector with a resolution of 150 eV at 5.9 keV. The effect of alloying on the fluorescence parameters of Ni and Mo, phase structure, and corrosion behavior were investigated. The X-ray fluorescence parameters of Ni and Mo in superalloys indicate significant differences with respect to the pure metals. These differences are attributed to the reorganization of valence shell electrons and/or charge transfer phenomena in superalloys.
Nucleation and Growth of Precipitates in a Ni-based Superalloy
Materials Science Forum, 2001
The precipitation sequence at 700 °C of the Ni 3 (Ti,Al)-type ordered γ' phase in the commercial nickelbased superalloy Inconel X-750 was investigated using Coincidence Doppler Broadening (CDB) technique. The results obtained are discussed in terms of positron annihilation in two well-defined states: one corresponding to the matrix (γ phase) and a second related to the γ' precipitates. Between these two aging stages, CDB distributions corresponding to selected intermediate aging treatments could be presented exactly, within the experimental scatter, as a linear combination of the γ and γ' signatures.
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.
Materials Characterization, 2021
Modern engineering alloys have bespoke microstructures, where features such as precipitates are used to control properties. In many Ni-based alloys, carbo-nitride precipitates are introduced to strength and improve performance. These precipitates can be distributed throughout the microstructure and niobium rich carbides are often found at grain boundaries. In this work, we used combined energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD) to characterise the population of these precipitates. Processing of the EDS signal is used to label the Mo-rich precipitates, and their size and location are measured from maps using a circular Hough transform. This label map is combined with the grain boundary network (from EBSD analysis). Statistical analysis, using ANOVA testing, reveals differences in chemistry between carbides found in Ni-rich matrix grain interiors, on random high angle boundaries and on special boundaries (Σ3 and Σ9). These results are compared between wrought and power metallurgy product forms. These distributions are discussed in the context of their performance within demanding environments, such as reactor core internals.
SAXS and XAFS Characterization of Precipitates in a High-Performance Cu–Ni–Si Alloy
MATERIALS TRANSACTIONS, 2007
Analyses of small-angle X-ray scattering (SAXS) and X-ray absorption fine structure (XAFS) were performed for characterizing precipitates formed in a Cu-3.1 at %Ni-1.4 at%Si alloy, the strength and electrical conductivity of which were improved by aging. SAXS profiles and XAFS spectra of samples aged at 720 K for different periods of time after a solution treatment were measured. SAXS profiles of samples, which were aged after the solution treatment and subsequently cold rolled, were also measured to investigate the effect of dislocations on precipitation. The results of SAXS measurements showed that nanometer-size precipitates formed in the alloy samples during isothermal aging at 720 K. The precipitates in the samples without cold rolling were coarsened in a single modal size distribution with increasing aging time. In contrast, the precipitates formed in the cold-rolled samples appeared to be coarsened in a multi-modal size distribution with increasing aging time. This aging characteristic of the cold-rolled samples is presumably attributable to their good electrical conductivity. The results of XAFS measurements at the Ni K-edge showed that nickel was substituted for copper in the face-centered cubic (fcc) copper matrix and that the local structure around nickel was changed by isothermal aging. With increasing aging time, extended X-ray absorption fine structure (EXAFS) functions at the Ni K-edge of the samples were found to be changed, which implies that nickel atoms were precipitated as nickel-silicon clusters or intermediate compounds in the fcc copper matrix. In addition, X-ray absorption near edge structure (XANES) spectra at the Ni K-edge indicated that the electronic structure of nickel in the samples was influenced by silicon during aging. [
Acta Materialia, 1998
AbstractÐDiraction pro®les of single crystal Ni-based superalloy samples with dierent microstructures were measured in situ up to the complete solutionizing of the g' phase, using a high resolution triple crystal diractometer and high energy synchrotron radiation (150 keV, l = 0.08 A Ê ). A comparison between an undeformed sample and creep-deformed specimens with various resultant microstructures evidenced a relation between the lattice parameter distribution, the g' precipitate microstructure and the sign of the connectivity. It was shown that a deformation induces a change in the relative volume cell of g and g' phases. Moreover, the high resolution of the experimental set-up allows in many cases the g' phase volume fraction to be measured with a good accuracy. # 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.
Metallurgical and Materials Transactions A
We prepared 41 different superalloy compositions by an arc melting, casting, and heat treatment process. Alloy solid solution strengthening elements were added in graded amounts, and we measured the solidus, liquidus, and c¢-solvus temperatures of the samples by DSC. The c¢-phase fraction increased as the W, Mo, and Re contents were increased, and W showed the most pronounced effect. Ru decreased the c¢-phase fraction. Melting temperatures (i.e., solidus and liquidus) were increased by addition of Re, W, and Ru (the effect increased in that order). Addition of Mo decreased the melting temperature. W was effective as a strengthening element because it acted as a solid solution strengthener and increased the fraction of fine c¢-precipitates, thus improving precipitation strengthening. Experimentally determined values were compared with calculated values based on the CALPHAD software tools Thermo-Calc (databases: TTNI8 and TCNI6) and MatCalc (database ME-NI). The ME-NI database, which was specially adapted to the present investigation, showed good agreement. TTNI8 also showed good results. The TCNI6 database is suitable for computational design of complex nickel-based superalloys. However, a large deviation remained between the experiment results and calculations based on this database. It also erroneously predicted c¢-phase separations and failed to describe the Ru-effect on transition temperatures.