Abstract The precipitation of topologically close packed (TCP) phases is detrimental for the high temperature strength of high refractory Ni-based superalloys. The beneficial influence of Ru with respect to this so called instability is nowadays well accepted. In the present paper the precipitation of topologically close packed (TCP) phases is studied quantitatively in two experimental alloys (one Ru-free and one with addition of Ru) to clarify the mechanism of the Ru effect. It is confirmed that the TCP phase precipitates undergo sequential phase transformation with the tetragonal σ-phase precipitating first. Ru retards the phase transformation and leads to decreased equilibrium volume fraction of TCP phases. The results clearly indicate that Ru decreases the driving force for TCP phase precipitation. Investigations of crystallography and chemistry of the TCP/matrix interface point to an additional effect by increase of misfit strain energy.
Last. Dierk Raabe(MPG: Max Planck Society)H-Index: 134
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Two Ni-based superalloys (one Ru-free and one containing 1 at.% Ru) were comparatively studied by Atom Probe Tomography and complimentary techniques. Ru addition impedes precipitation of the σ phase at 950 °C. Ru partitions nearly equally to the γ and σ phase. Neither reverse elemental partitioning nor destabilization of the γ′ phase is detected when adding Ru. We propose an increase in the γ/σ lattice misfit caused by Ru as a major reason for impeded nucleation of the σ phase.
#1Kamil Matuszewski(FAU: University of Erlangen-Nuremberg)H-Index: 6
#2Ralf Rettig(FAU: University of Erlangen-Nuremberg)H-Index: 15
Last. Robert F. Singer(FAU: University of Erlangen-Nuremberg)H-Index: 53
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A new approach to clarify the ruthenium effect on the precipitation of topologically close packed (TCP) phases is described in the paper. It is based on focused ion beam – scanning electron microscopy (FIB – SEM) dual beam methodology as well as three-dimensional imaging. The high-temperature capabilities of nickel base superalloys can be improved by alloying with refractory elements. With excessive refractory element content or excessive exposure to high temperature, brittle TCP phases precipit...
The suppression of topologically close-packed phases (TCP) in nickel-based single-crystal superalloys by the addition of ruthenium is modeled with a fully multicomponent mesoscale precipitation model based on the numerical Kampmann-Wagnermethod using thermodynamic CALPHAD-calculations. For the application of the model in ruthenium-containing superalloys, mobility assessments of the binary systems nickel-ruthenium (NiRu) and nickel-rhenium (Ni-Re) were performed to create a new mobility database....
#1A. Heckl(FAU: University of Erlangen-Nuremberg)H-Index: 8
#2Steffen Neumeier(FAU: University of Erlangen-Nuremberg)H-Index: 29
Last. Robert F. Singer(FAU: University of Erlangen-Nuremberg)H-Index: 53
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Abstract Improvements in phase stability on the addition of Ru are well known in the field of nickel-based superalloy development. However, the key mechanism of this benefit remains unclear. A new alloy series with stepwise increased additions of Ru was used to systematically investigate the impact of Ru on yopologically close-packed (TCP) phase inhibition. In addition, the investigation was carried out on a less known type of TCP formation, the so-called discontinuous precipitation. This type o...
#1Ralf Rettig(FAU: University of Erlangen-Nuremberg)H-Index: 15
#2A. Heckl(FAU: University of Erlangen-Nuremberg)H-Index: 8
Last. Robert F. Singer(FAU: University of Erlangen-Nuremberg)H-Index: 53
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The precipitation of brittle so-called TCP-phases is critical for the application of Re-containing single crystal superalloys. In this work a fully multicomponent precipitation model is presented, which is capable of simulating the precipitation process of the TCP-phases in superalloys considering complex precipitation sequences with several metastable phases. The model is coupled to multicomponent thermodynamic CALPHAD calculations and relies on multicomponent diffusion models based on the TC-A...
#1A. Heckl(FAU: University of Erlangen-Nuremberg)H-Index: 8
#2Steffen Neumeier(FAU: University of Erlangen-Nuremberg)H-Index: 29
Last. Robert F. Singer(FAU: University of Erlangen-Nuremberg)H-Index: 53
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Abstract A new in-house designed series of Ni based superalloys with stepwise increased Re and Ru additions has been investigated, to systematically determine the influence of Re and Ru on γ/γ′-microstructure and high temperature creep properties. Improved creep resistance and thus also a higher alloy temperature capability of up to 87 K/at.% was found for additions of Re. Additions of Ru revealed a lower temperature capability improvement of up to 38 K/at.% for low Re-containing second generati...
Abstract The partitioning behaviour of alloying elements between the γ and γ ′ phase in nickel-base superalloys with systematically varied contents of rhenium and ruthenium was investigated in the temperature range between 850 °C and 1300 °C. Ruthenium promotes a reverse partitioning of rhenium to the γ ′ phase. This reverse partitioning is found over the whole temperature range up to γ ′ solvus temperature. It is caused by an increased solubility of rhenium in the γ ′ phase when ruthenium is pr...
#1A. Heckl(FAU: University of Erlangen-Nuremberg)H-Index: 8
#2Ralf Rettig(FAU: University of Erlangen-Nuremberg)H-Index: 15
Last. Robert F. Singer(FAU: University of Erlangen-Nuremberg)H-Index: 53
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The influence of Re and Ru on phase diagram, as-cast microstructure, and segregation behavior has been investigated using a series of 12 experimental nickel-base superalloys derived from the parent alloy CSMX-4. Up to 2 at. pct Re and 4 at. pct Ru were added at the expense of nickel, while all other alloying elements were kept constant. The Re is found to increase the liquidus temperature and to decrease the γ′-solvus. The Re additions also strongly increase the amount of eutectic and the tenden...
Last. Sammy Tin(IIT: Illinois Institute of Technology)H-Index: 27
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Ruthenium (Ru) suppresses the precipitation of deleterious topologically close-packed (TCP) phases in high refractory content single-crystal Ni-base superalloys. The effectiveness of Ru as a TCP suppressant appears to be the net effect of its limited solubility in the TCP phase, a lower density of structural growth ledges for atomic attachment at the TCP/matrix interface, and destabilization of the γ′ phase at elevated temperatures. These characteristics combine to limit the growth rates of prec...
Abstract null null Generally, Ru can inhibit the precipitation of TCP phase in most single crystal superalloys. However, in this study, we found that the inhibition is related to the location in the exposed specimen relative to the specimen surface: Ru inhibits the precipitation of TCP phase inside the sample but promotes it in the near surface region. The promotion of the TCP phase was proven to be related to oxidation. Microstructural analysis suggested that Ru degrades the oxidation resistanc...
#10Xue Liu(HIT: Harbin Institute of Technology)H-Index: 2
Abstract null null The phase equilibria of the Cr-Re-Ru ternary system at 1100 °C and 1200 °C have been experimentally investigated using electron probe microanalyzer and X-ray diffraction. The σ1-Cr2Re3 and σ2-Cr2Ru phases with the same D8b crystal structure do not form a continuous intermetallic compound phase at 1100 °C and 1200 °C in the Cr-Re-Ru ternary system confirmed by experimental results. According to the experimental results in this work, the Cr-Re-Ru ternary system has been assessed...
Abstract null null Microstructural degradation after thermal exposure of a 5% Re-containing single crystal (SX) superalloys has been studied. The alloy was subjected to thermal exposure at temperature of 1100 °C for periods of 100, 500, and 1000 h. The microstructure of the alloy was degraded after long-term thermal exposure, mainly in γ' coarsening, the precipitation topologically close packed (TCP) phases. Moreover, the stress-rupture properties of the samples before and after long-term therma...
Abstract A long-term test run followed by room-temperature fatigue test was performed for the first-stage high-pressure turbine blades of an aero-engine. The investigation showed the appearance of cracks at the trailing edge of the blade coated with AlSiY. The failure mechanism was investigated by macroscopic observation, fracture analysis, metallographic analysis, hardness testing and structural evolution analysis by electron backscatter diffraction(EBSD), kernel average misorientation (KAM) an...
Last. Kedian Wang(Xi'an Jiaotong University)H-Index: 20
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Abstract The hot corrosion behavior of a Ni-based single-crystal (SC) superalloy treated by laser shock peening (LSP) against 75 wt.% Na2SO4+25 wt.% NaCl molten salts at 750 °C was studied. The results showed that LSP improved the hot corrosion resistance of the SC superalloy. This was attributed to significantly different LSP-induced dislocation structures in γ/γ′ phases, which promoted the formation of protective layered oxide films that inhibited the inward diffusion of corrosive media. In ad...
Abstract Single crystal Ni-based superalloys are the typical structural materials for high-pressure turbine blades, and their microstructure is critical in determining their mechanical properties. The withdrawal rate is a key parameter affecting the microstructure during the single crystal growth process. In the present work the effect of the withdrawal rate on the microstructure of a third-generation single crystal superalloy containing 6.8 wt% Re has been investigated, and the creep resistanc...
#1Shuyang Qin(USTB: University of Science and Technology Beijing)H-Index: 2
#2Longge Yan(USTB: University of Science and Technology Beijing)H-Index: 1
Last. Xinfang Zhang(USTB: University of Science and Technology Beijing)H-Index: 13
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Abstract This work investigates the reverse thermodynamic dissolution of the topologically closed-packed (TCP) phases in the deteriorated nickel-based superalloy using the pulsed electric current. The mechanical properties cannot be restored directly by the conventional heat treatment because the dissolution temperature (1130 oC) of the TCP phases is higher than the initial solvation temperature (950 oC) of the γ′ phase. Here it was found that the TCP phases can be selectively dissolved under th...
#1Huajin Yan(CUMT: China University of Mining and Technology)H-Index: 2
#2Sugui Tian(SUT: Shenyang University of Technology)H-Index: 17
Last. Shunke Zhang(Guida: Guizhou University)H-Index: 2
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Abstract By means of creep property measurement and microstructure observation, combined with finite element analysis (FEA), the creep and damage of a 4.5%Re and 3%Ru single crystal nickel-based alloy at high temperature were investigated. The results show that the creep life of the single crystal alloy at 1100 °C/140 MPa is 476 h. The deformation feature of alloy during steady state creep is dislocation slipping in γ phase and climbing over γ′ rafts. The various stress distributions are display...
#1Jian Liu(Jiangxi University of Science and Technology)
#2Chenyang Zhou(Jiangxi University of Science and Technology)
Last. Hang Wang(Jiangxi University of Science and Technology)H-Index: 1
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Abstract The Ru–X (X = Al, Hf, Mo, Ti) systems were re-optimized by means of the CALPHAD method according to the experimental phase equilibria and thermochemical data, as well as updated Gibbs energy function of “GBCCRU” in SGTE Pure 5 database. The substitutional solution model was applied to the phases liquid, fcc_A1, bcc_A2 and hcp_A3. Besides, the phases Al6Ru, Al13Ru4, Al5Ru2, Al2Ru and Al3Ru2 in the Ru–Al system were modeled as stoichiometric compounds and the phase Mo5Ru3 (σ) in the Ru–Mo...
