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.

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.

SURFACE SEGREGATION STUDIES OF SOFC CATHODES: COMBINING SOFT X-RAYS AND ELECTROCHEMICAL IMPEDENCE SPECTROSCOPY

2009 ◽  
Vol 1217 ◽  
Author(s):  
Lincoln Miara ◽  
Louis Piper ◽  
Jacob Nathan Davis ◽  
Laxmikant Saraf ◽  
Tiffany Kaspar ◽  
...  
Keyword(s):  
Single Crystal ◽  
Surface Segregation ◽  
Elevated Temperatures ◽  
Electrochemical Impedance ◽  
Lanthanum Manganite ◽  
X Rays ◽  
Two Phase ◽  
X Ray ◽  
Cation Migration ◽  
X Ray Absorption

AbstractA system to grow heteroepitaxial thin-films of solid oxide fuel cell (SOFC) cathodes on single crystal substrates was developed. The cathode composition investigated was 20% strontium-doped lanthanum manganite (LSM) grown by pulsed laser deposition (PLD) on single crystal (111) yttria-stabilized zirconia (YSZ) substrates. By combining electrochemical impedance spectroscopy (EIS) with x-ray photoemission spectroscopy (XPS) and x-ray absorption spectroscopy XAS measurements, we conclude that electrically driven cation migration away from the two-phase gas-cathode interface results in improved electrochemical performance. Our results provide support to the premise that the removal of surface passivating phases containing Sr2+ and Mn2+, which readily form at elevated temperatures even in O2 atmospheric pressures, is responsible for the improved cathodic performance upon application of a bias.

Effect of Precipitation Aging Temperatures on Reheat Treated Microstructures and its Phase Stability after Long-Term Exposure in Cast Nickel Base Superalloy, Grade Inconel 738

2017 ◽  
Vol 891 ◽  
pp. 433-437 ◽  
Author(s):  
Nattapol Kontikame ◽  
Sureerat Polsilapa ◽  
Panyawat Wangyao
Keyword(s):  
Phase Stability ◽  
Power Plants ◽  
Turbine Blades ◽  
Research Work ◽  
Nickel Base Superalloy ◽  
Gamma Prime ◽  
Treatment Conditions ◽  
Nickel Base ◽  
Base Superalloy

This research work has an aim to investigate the effect of precipitation aging temperatures of 845°C, 865°C, 885°C and 905°C for 24 hours after solutioning treatment at temperature of 1145°C for 4 hours on final microstructure of cast nickel base superalloy, grade Inconel 738, which is used as a material for turbine blades in land base gas turbine engines to generate electricity in power plants. Further interesting is also extended to study and evaluate the phase stability of precipitated gamma prime particles after long-term heating at tempeatures of 900°C and 1000°C for 200 hours of all received final microstructures after various reheat treatment conditions. From all obtained results, it was found that the higher precipitation aging temperatures provided the more coarsening size of both coarse and fine gamma prime particles. Furthermore, after long-term exposure at high temperatures, this resulted in an increasing of both area density and size of gamma prime particles.

Gamma prime coarsening in a nickel base single crystal superalloy

2014 ◽  
Vol 128 ◽  
pp. 388-391 ◽  
Author(s):  
S. Tang ◽  
Z. Zheng ◽  
L.K. Ning
Keyword(s):  
Single Crystal ◽  
Single Crystal Superalloy ◽  
Gamma Prime ◽  
Nickel Base

SANS Investigation of γ´ Precipitate Morphology Evolution in Creep Exposed Single Crystal Ni Base Superalloy

2010 ◽  
Vol 636-637 ◽  
pp. 1475-1482
Author(s):  
Jozef Zrník ◽  
Pavel Strunz ◽  
Maurizio Maldini ◽  
Vadim Davydov
Keyword(s):  
Single Crystal ◽  
Constant Load ◽  
Scattering Method ◽  
Creep Tests ◽  
Precipitate Morphology ◽  
Gamma Prime ◽  
Directional Coarsening ◽  
Structure Degradation ◽  
Temperature Ranges ◽  
Nickel Base

The creep degraded nickel base single crystal superalloy CMSX-4 of two axial orientations [001] and [111] was investigated with aim to assess the structure degradation. Constant load creep tests were conducted in the stress/temperature ranges of 250–780 MPa/750 – 50°C resulting in rupture time variation from 50 to 4000 hours. A combination of scanning electron microscopy (SEM) and non-destructive small-angle neutron scattering method (SANS) was used to investigate the directional coarsening (rafting) of the gamma prime (γ') precipitates in relation to the stress and temperature applied as well as to the initial crystallographic orientation of the specimens. The SANS results are discussed in terms of the correlation with the raft development, the axial orientation of specimen, the creep parameters and the mechanical properties.

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.

scholarly journals Verification of a Commercial CALPHAD Database for Re and Ru Containing Nickel-Base Superalloys

2009 ◽  
Vol 289-292 ◽  
pp. 101-108 ◽  
Author(s):  
Ralf Rettig ◽  
Astrid Heckl ◽  
Steffen Neumeier ◽  
Florian Pyczak ◽  
Matthias Göken ◽  
...  
Keyword(s):  
High Temperature ◽  
Melting Point ◽  
Single Crystal ◽  
Weight Percent ◽  
Incipient Melting ◽  
High Temperature Properties ◽  
First Approximation ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Alloy Properties

The addition of rhenium and ruthenium to single crystal nickel-base superalloys improves the high-temperature properties of the alloys. In this work the applicability of the database TTNi7 (ThermoTech Ltd, UK) for developing 4th generation single crystal superalloys containing rhenium (Re) and ruthenium (Ru) was investigated. We systematically compared experimentally determined alloy properties to the predictions of ThermoCalc with the database TTNi7. The investigated properties were liquidus, solidus and ´ solvus temperature as well as incipient melting point and segregation. Calculations were based on thermodynamic principles with the assumption of either equilibrium or Scheil-Gulliver conditions, i.e. no diffusion in the solid and complete diffusion in the liquid. Furthermore the composition of the  and the  phase of a Re- and Ru-containing superalloy was measured and compared to calculations. Our results show that the database is capable of simulating general trends of 4th generation superalloys up to 6 weight percent (wt.-%) Re and 6 wt.-% Ru. The present work shows that Scheil-Gulliver calculations can only be used as a first approximation for nickel-base superalloys.

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