scholarly journals A Study of the Effects of Alloying Additions on TCP Phase Formation in 4th Generation Nickel-Base Single-Crystal Superalloys

2011 ◽  
Vol 278 ◽  
pp. 54-59 ◽  
Author(s):  
H.T. Pang ◽  
R.A. Hobbs ◽  
Howard J. Stone ◽  
Catherine M.F. Rae
Keyword(s):  
Single Crystal ◽  
Detailed Analysis ◽  
Phase Formation ◽  
Environmental Performance ◽  
Elevated Temperatures ◽  
Turbine Blades ◽  
Alloying Additions ◽  
Tcp Phases ◽  
Tcp Phase ◽  
Nickel Base

The demand for higher engine operating temperatures to improve aeroengine efficiency has meant that increasing levels of alloying additions are being added to single-crystal nickel-base superalloys for turbine blades applications. Whilst better mechanical and environmental performance may be obtained with these alloying additions, they also destabilise the alloys forming topologically closed-packed (TCP) phases. In this study, the formation of TCP phases has been studied in a series of four alloys designated LDSX1-4 which have a systematic variation in the levels of Co, Mo and W. The alloys were exposed to elevated temperatures between 900-1100°C for up to 1000 hours. This was followed by detailed analysis of the microstructures in the SEM. Identification of the TCP phases in selected alloys was also carried out. The effects of each alloying addition on TCP phase formation is discussed in light of these results.

scholarly journals Modeling of Precipitation Kinetics of TCP-Phases in Single Crystal Nickel-Base Superalloys

2011 ◽  
Vol 278 ◽  
pp. 180-185 ◽  
Author(s):  
Ralf Rettig ◽  
Astrid Heckl ◽  
Robert F. Singer
Keyword(s):  
Single Crystal ◽  
Multicomponent Diffusion ◽  
Interface Energy ◽  
Precipitation Process ◽  
Precipitation Model ◽  
Mobility Database ◽  
Tcp Phases ◽  
Tcp Phase ◽  
Nickel Base ◽  
Kinetics Of

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-API interface of the software DICTRA. The required mobility database has been newly developed and covers all relevant alloying elements of the Ni-base superalloys including rhenium (Re) and ruthenium (Ru). It is well known that adding Ru strongly reduces TCP-phase precipitation. Based on the developed precipitation model, possible mechanisms are investigated to explain this effect and it is concluded that Ru mostly influences the nucleation rate by a combined influence on interface energy, “reverse partitioning” and γ’-phase fraction.

Alloy Phase Stability Requirements in Single Crystal Superalloys

1990 ◽  
Vol 186 ◽  
Author(s):  
David N. Duhl
Keyword(s):  
Single Crystal ◽  
Phase Stability ◽  
Elevated Temperatures ◽  
Engine Performance ◽  
Two Phase ◽  
Gamma Prime ◽  
Tcp Phases ◽  
Nickel Base ◽  
Alloy Properties ◽  
Electron Vacancy

AbstractAlloy phase stability is a critical parameter in the design and implementation of nickel-base superalloys. To achieve the high temperature properties required of single crystal superalloys for application in gas turbine machinery, these alloys must have a stable gamma plus gamma prime microstructure for long periods of time at elevated temperatures. Significant deviation from this stable two phase microstructure, due to the precipitation of other phases, results in the loss of critical alloy properties which can have a deleterious impact on engine performance.Empirical methods based on the electron vacancy concept, commonly employed to predict and prevent the formation of undesirable topologically close packed (TCP) phases such as sigma or mu in polycrystalline nickelbase superalloys, are also used with single crystal superalloys. These undesirable phases result in the loss of alloy properties primarily as a result of the depletion of refractory strengthening elements from the superalloy matrix. The consequence of the formation of undesirable TCP phases on alloy properties and subsequent single crystal component behavior is reviewed.

A Life Prediction Model for Single-Crystal Nickel-Base Alloys Under Low-Cycle Fatigue

2020 ◽  
Author(s):  
Firat Irmak ◽  
Navindra Wijeyeratne ◽  
Taejun Yun ◽  
Ali Gordon
Keyword(s):  
Single Crystal ◽  
Gas Turbine ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Turbine Blades ◽  
Deformation Model ◽  
Cycle Fatigue ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Prediction Approach

Abstract In the development and assessment of critical gas turbine components, simulations have a crucial role. An accurate life prediction approach is needed to estimate lifespan of these components. Nickel base superalloys remain the material of choice for gas turbine blades in the energy industry. These blades are required to withstand both fatigue and creep at extreme temperatures during their usage time. Nickel-base superalloys present an excellent heat resistance at high temperatures. Presence of chromium in the chemical composition makes these alloys highly resistant to corrosion, which is critical for turbine blades. This study presents a flexible approach to combine creep and fatigue damages for a single crystal Nickel-base superalloy. Stress and strain states are used to compute life calculations, which makes this approach applicable for component level. The cumulative damage approach is utilized in this study, where dominant damage modes are capturing primary microstructural mechanism associated with failure. The total damage is divided into two distinctive modules: fatigue and creep. Flexibility is imparted to the model through its ability to emphasize the dominant damage mechanism which may vary among alloys. Fatigue module is governed by a modified version of Coffin-Manson and Basquin model, which captures the orientation dependence of the candidate material. Additionally, Robinson’s creep rupture model is applied to predict creep damage in this study. A novel crystal visco-plasticity (CVP) model is used to simulate deformation of the alloy under several different types of loading. This model has capability to illustrate the temperature-, rate-, orientation-, and history-dependence of the material. A user defined material (usermat) is created to be used in ANSYS APDL 19.0, where the CVP model is applied by User Programmable Feature (UPF). This deformation model is constructed of a flow rule and internal state variables, where the kinematic hardening phenomena is captured by back stress. Octahedral, cubic and cross slip systems are included to perform simulations in different orientations. An implicit integration process that uses Newton-Raphson iteration scheme is utilized to calculate the desired solutions. Several tensile, low-cycle fatigue (LCF) and creep experiments were conducted to inform modeling parameters for the life prediction and the CVP models.

scholarly journals The Microstructure, Mechanical Properties and Coatability of Diffusion Brazed CMSX-4 Single Crystal

1996 ◽  
Author(s):  
Warren M. Miglietti ◽  
Ros C. Pennefather
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Elevated Temperatures ◽  
Aluminide Coating ◽  
Turbine Blades ◽  
Stress Rupture ◽  
Directionally Solidified ◽  
Diffusion Brazing ◽  
Brazed Joints ◽  
Boride Phases

Diffusion brazing is a joining process utilized both in the manufacture and repair of turbine blades and vanes. CMSX-4 is an investment cast, single crystal, Ni-based superalloy used for turbine blading and vanes, and has enhanced mechanical properties at elevated temperatures when compared to equiaxed, directionally solidified and first generation single crystal superalloys. The objective of this work was to develop a diffusion brazing procedure to achieve reliable joints in the manufacture of a hollow turbine blade (for a prototype engine in South Africa), and to verify the coatability of the diffusion brazed joints. Two commercially available brazing filler metals of composition Ni-15Cr-3.5B and Ni-7Cr-3Fe-4.5Si-3.2B-0.06C and a proprietary (wide gap) braze were utilized. With the aim of eliminating brittle centre-line boride phases, the effects of temperature and time on the joint microstructure were studied. Once the metallurgy of the joint was understood, tensile and stress rupture tests were undertaken, the latter being one of the severest tests to evaluate joint strength. The results demonstrated that the diffusion brazed joints could satisfy the specified stress rupture criterion of a minimum of 40 hrs life at 925 °C and 200 MPa. After mechanical property evaluations, an investigation into the effects of a low temperature high activity (LTHA) pack aluminide coating and a high temperature low activity (HTLA) pack aluminide coating on the braze joints was undertaken. The results showed that diffusion brazed joints could be readily coated.

Influence of an Aluminide Coating on the TMF Life of a Single Crystal Nickel-Base Superalloy

1998 ◽  
Author(s):  
Ernst E. Affeldt
Keyword(s):  
Single Crystal ◽  
Aluminide Coating ◽  
Turbine Blades ◽  
Temperature Cycling ◽  
Nickel Base Superalloy ◽  
Test Results ◽  
Bending Tests ◽  
Quantitative Correlation ◽  
Nickel Based Superalloy ◽  
Nickel Base

TMF tests were conducted with bare and aluminide coated single crystal nickel-based superalloy specimens. Temperature cycling was between 400°C and 1100°C with a phase shift (135°) which is typical for damaged locations on turbine blades. Stress response is characterized by a constant range and the formation of a tensile mean stress as a result of relaxation in the high temperature part of the cycle which is in compression. Bare specimens showed crack initiation from typical oxide hillocks. Coated specimens showed life reduction with respect to the bare ones caused by brittle cracking of the coating in the low temperature part of the cycle. Isothermal bending tests of coated specimens confirmed the low ductility of the coating at tempeatures below 600°C but quantitative correlation with the TMF test results failed.

The Microstructure Evolution of a Nickel-Base Single Crystal Superalloy after Long-Term Aging

2015 ◽  
Vol 1088 ◽  
pp. 217-220 ◽  
Author(s):  
Yu Xian Jia
Keyword(s):  
Single Crystal ◽  
Exposure Time ◽  
Microstructure Evolution ◽  
Ageing Time ◽  
Thermal Exposure ◽  
Single Crystal Superalloy ◽  
Phase Precipitation ◽  
Tcp Phase ◽  
Nickel Base

Microstructure evolution of a nickel-base single crystal superalloy during thermal exposure at 982°C was investigated. The SEM studies revealed that the size of γ' phase increased and some of which linked together with the elongation of the exposure time. There is acicular phase precipitation after the long-term ageing treatment. The TCP phase is not increased by the increment of ageing time after reaching a certain amount. There are skeleton shape carbides precipitate after 100h and 300h. The amount of precipitated carbides decreases by the elongation of ageing time.

A Life Prediction Model for Nickel-Base Single Crystal Superalloy DD3

2004 ◽  
Vol 261-263 ◽  
pp. 1123-1128 ◽  
Author(s):  
T. Li ◽  
Zhu Feng Yue
Keyword(s):  
Prediction Model ◽  
Single Crystal ◽  
Thermal Fatigue ◽  
Life Prediction ◽  
Hold Time ◽  
Turbine Blades ◽  
Single Crystal Superalloy ◽  
Main Factors ◽  
Nickel Base ◽  
Life Prediction Model

The possibility of the life prediction model for nickel-base single crystal blades has been studied. The fatigue-creep (FC) and thermal fatigue-creep (TMFC) as well as creep experiments have been carried out with different hold time of DD3. The hold time and the frequency as well as the temperature range are the main factors influencing on the life. An emphasis has been put on the micro mechanism of the rupture of creep, FC and TMFC. Two main factors are the voiding and degeneration of the material for the creep, FC and TMFC experiments. There are voids in the fracture surfaces, and size of the voids is dependent on the loading condition. Generally, the rupture mechanism is the same for creep, FC and TMFC. If the loading can be simplified to the working conditions of the turbine blades, i.e. the hold time is at the top temperature and maximum stress, a linear life model is satisfactory to the life prediction of nickel-base single crystal superalloy from the experimental study in this paper. The temperature and the stress level of the nickel-base single crystal (SC)blades are not uniform. To predict the life of SC blades, one should consider the cycles of the temperature and stress as well as the oxidation simultaneously. In the past 30 years, there are many works on the mechanical behavior and description, such as the inelastic constitutive relationships, plastic, fracture, isothermal creep and fatigue and thermal fatigue as well as oxidation[1-3]. There are also special software (program) to analyze the deformation and life of nickel-base single crystal structures, such as blades. In order to apply to the engineering more conveniently, there should be a life prediction model for the blades. The model should not be too complex, but take more influential factors as possible into consideration.

Microstructure Development of an Electroplating Coated Nickel-Base SC Superalloy in Oxidation Processes—Simulation Results

2021 ◽  
Author(s):  
Kang Yuan ◽  
Zhaoran Zheng
Keyword(s):  
Kinetic Model ◽  
Single Crystal ◽  
Diffusion Zone ◽  
Microstructure Development ◽  
Diffusion Kinetic ◽  
Oxidation Processes ◽  
Secondary Reaction Zone ◽  
Tcp Phases ◽  
Simulation Results ◽  
Nickel Base

Abstract In this paper; a diffusion kinetic model was applied to simulate the microstructure development in a MCrAlY-superalloy system at high temperatures. Both simulation and experimental results showed that γ+γ’ microstructure was obtained in the coatings due to Al depletion after oxidation. With the help of the modelling; the mechanism of the formation of the diffusion zones in the single crystal (SC) superalloy can be also analyzed. The results revealed that the inward diffusion of Al from coating affected the depth of secondary reaction zone (SRZ) with the precipitation of TCP phases while the depth of inter-diffusion zone (IDZ) was decided by the inward diffusion of Cr.

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