Influence of rhenium and ruthenium on the local mechanical properties of the γ and γ ′ phases in nickel-base superalloys (original) (raw)
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Materials Science and Engineering: A, 2004
Three commercial single-crystalline nickel-base superalloys CMSX-6, CMSX-4 and CMSX-10 which have an increasing amount of rhenium and tungsten were investigated and the micromechanical properties such as hardness and modulus of elasticity of the individual phases were tested in a nanoindenting atomic force microscope. The hardness of the matrix phase increases with the concentration of refractory elements, whereas only a small change in the hardness of the precipitates was found. The hardness ratio of precipitate and matrix decreases significantly with increasing rhenium content in the initial condition and after heat treatment. In the initial condition the hardness ratio ranges from 1.31 for CMSX-10 to 1.41 for CMSX-4 and 1.67 for CMSX-6. Moreover, the modulus of elasticity increases with the concentration of refractory elements.
Materials Science and Engineering: A, 2011
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 ␥/␥-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 generation alloys. However, in third and fourth generation alloys with higher Re-contents, no significant influence of Ru on creep rupture strength was observed. The creep properties are discussed with respect to the ␥-volume fraction, ␥size and ␥-coarsening rate, as well as the ␥/␥-lattice misfit and the ␥/␥ partitioning coefficient of the different Re and Ru containing alloys. The presented data shows, that these microstructure parameters are strongly influenced by additions of Re, but only marginally by additions of Ru. A further influence on creep rupture strength is given by the solid solution hardening of the ␥-matrix, which is discussed based on solid solution hardener concentrations either experimentally derived or calculated from ThermoCalc data.
Effects of Re on microstructure evolution of nickel-based single crystal superalloys
Applied Physics A, 2020
The high temperature creep and long-term aging tests of the second-generation (DD6) and the third-generation (DD9) single crystal superalloys with different Re contents were carried out. The effects of Re, dislocations, TCP phases and their interaction on creep properties and microstructure evolution were researched. The third-generation single crystal superalloy has the more compact and uniform two-phase structure and the better creep properties. The rafting rate in dendrite is higher than that in interdendrite. The γ' phases connect into a stripline, the γ phases on the strip line are truncated, and the TCP phase is precipitated along the stripline. The element Re carries out the pipe diffusion and the vacancy diffusion at the high temperature. The TCP phase precipitates in the region with many dislocations and vacancies. Re hinders the movement of dislocations and promote the precipitation of TCP phases. The movement of dislocations promotes the diffusion of Re and the precipitation of TCP phases. TCP phases promote the diffusion of elements and accelerate the rafting of γ' phases.
Applied Physics Letters, 2008
The partitioning behavior and sublattice site preference of Re or Ru in the Ni 3 Al ͑L1 2 ͒ ␥Јprecipitates of model Ni-Al-Cr alloys are investigated by atom-probe tomography ͑APT͒ and first-principles calculations. Rhenium and Ru are experimentally observed to partition to the ␥͑fcc͒-phase, which is consistent with the smaller values of the ␥-matrix Re and Ru substitutional formation energies determined by first-principles calculations. APT measurements of the ␥Ј-precipitate composition indicate that Re and Ru occupy the Al sublattice sites of the Ni 3 Al ͑L1 2 ͒ phase. The preferential site substitution of Re and Ru at Al sublattice sites is confirmed by first-principles calculations.
2014
The influences of ruthenium and surface orientation on creep behavior of aluminized Ni-base single crystal superalloys were investigated by comparing two different types of NKH superalloys. The aluminized coated specimens were then subjected to creep rupture tests at a temperature of 900 1C and a stress of 392 MPa. The coating treatment resulted in a significant decrease in creep rupture lives for both superalloys. The diffusion zones between the coating and substrate led to changes in microstructure, which diminished the creep behavior of the aluminized superalloys. Because of the interdiffusion of Ru, Al and Ni, the solubility of some of the refractory elements, such as W, Re. Mo, Co and Cr decreased in the diffusion zone; the precipitation of topologically close-packed (TCP) phases was thus inevitable. In the present study, the addition of Ru increased the degree of Re and Cr supersaturation in the γ matrix. Consequently, the addition of Ru indirectly promoted the precipitation of TCP phases in aluminized Ni-base single crystal superalloys. Furthermore, the growth of TCP precipitates was greatly influenced by the specific surface orientations of the Ni-base single crystal superalloys. In conclusion, the {110} specimens showed shorter creep rupture life than the {100} specimens, this was due to the difference in the crystallographic geometry of {111}〈101〉 slip system and TCP precipitates between the two side-surface orientations of the specimens.
Reasons for the enhanced phase stability of Ru-containing nickel-based superalloys
Acta Materialia, 2011
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 of TCP phase formation offers two major advantages compared with commonly investigated TCP plates in dendritic regions. First, the microstructure is much coarser than fine TCP plates, allowing reliable and less time consuming investigations. Second, discontinuous precipitation transforms the supersaturated and unstable c/c 0 microstructure in a condition close to equilibrium, permitting a meaningful insight into the stable alloy constitution. The experimental results for alloy phase stability dependence on Ru are evaluated with respect to all possible effects of TCP phase inhibition by Ru. Furthermore, experimental evidence for increased Re solubility in the c matrix was found on addition of Ru, which is not seen in corresponding ThermoCalc calculations. This finding is probably the dominant reason for the increased TCP phase capability of Ru-containing alloys. A ternary phase diagram model has been developed to describe the new approach.
Phases Micromechanical Properties of Ni-base Superalloy Measured by Nanoindentation
Materials Science, 2012
This investigation describes the changes in the phase's micromechanical properties as a result of alloying elements moving at interdiffusion. The induction of the interdiffusion between different phases of a Ni-based single crystal superalloy still is a challenging issue in this field of the materials science. For this we used novel technique -hard cyclic viscoplastic deformation at room temperature. The chemical compositions of the phases were determined by the cumulative bulk deformation. For detailed knowledge of this material behavior during life time the micromechanical properties of phases were investigated by nanoindentation and the results were analyzed by scanning electron microscope and the corresponding chemical content was investigated by X-ray microanalysis.
Influence of Chemistry on the Tensile Yield Strength of Nickel-Based Single Crystal Superalloys
Advanced Materials Research, 2011
The tensile yield strength of AM1 and MC-NG single crystal superalloys with a γ’ precipitate size close to 300 nm were compared within the 20-1050°C temperature range. The room temperature yield strength of the fourth generation MC-NG superalloy is about 200 MPa less than that of the AM1 first generation one. Inversely, at higher temperatures (T > 800°C), the tensile strength of MC-NG is higher than that of AM1. These results are discussed by taking into account the elementary deformation mechanisms and the respective strengths of the γ and γ’ phases. Experiments on a modified MC-NG alloy show that reinforcing the γ’ phase by increasing the contents of Ti and Ta is an efficient way to recover a higher tensile strength at low temperatures. Rhenium addition and increase of the γ’ solvus temperature are suggested to be beneficial for the high temperature tensile strength. Data published on various other single crystals are in agreement with these hypotheses.
Transactions of Nonferrous Metals Society of China - TRANS NONFERROUS METAL SOC CH, 2011
Based on a 5% (mass fraction) Re-containing single crystal nickel-based superalloy with 3% (mass fraction) Cr, the microstructural variation with Cr addition was investigated. The experimental results show that segregation of alloying elements was enhanced in as-cast microstructure with Cr addition; and the volume fraction of eutectic is increased. However, the solidus and liquidus temperatures are remarkably reduced. With the increase of Cr content, the average γ′ size and volume fraction are decreased in the fully heat treated microstructure. X-ray diffraction results indicate that γ/γ′ lattice misfit becomes more negative. According to the energy dispersive spectroscopy (EDS) results, Cr is mainly distributed in the γ matrix; and more γ-forming elements, such as Re and W, enter the γ matrix, while the γ/γ′ partition ratio of Cr is inversely decreased.
Microstructure of Nickel-Based Superalloys
physica status solidi (b), 1969
Contents 1. Introduction 2. Constituents of nickel-based superalloys 2.1 The gamma phase (y) 2.2 The gamma-prime phase (y') 2.3 Carbide phases in Ni-based superalloys 2. 4 Minor phases in Ni-based superalloys 2.5 Prediction and control of t.c.p. phase formation in Ni-based superalloys 2.6 Wrought and cast microstructures 2.7 Phase instability during extended high-temperature exposure 3. Conclusion References ' 0.05 4.