scholarly journals Influence of σ Phase on the Allotropic Transformation of the Matrix in Co-Re-Cr-Based Alloys with Ni Addition

Metals ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 706 ◽  
Author(s):  
Kai Dörries ◽  
Debashis Mukherji ◽  
Joachim Rösler ◽  
Katharina Esleben ◽  
Bronislava Gorr ◽  
...  
Keyword(s):  
High Temperature ◽  
Gas Turbines ◽  
Allotropic Transformation ◽  
Σ Phase ◽  
Ni Addition ◽  
Alloy Hardness ◽  
The Matrix ◽  
Temperature Application ◽  
Lower Heat ◽  
The Stability

Co-Re-Cr alloys are being developed for high-temperature application in gas turbines. In these alloys, the Cr2Re3-based σ phase is stable when the Cr content is higher than 20 atomic %. The addition of Ni is being studied to partially substitute Cr, which aims to suppress σ formation without sacrificing the benefit of Cr in the oxidation resistance of the alloy. The microstructure of the alloys with varying Cr (18–23%) and Ni (8–25%) was investigated by electron microscopy in the present study, primarily to look into the stability of the σ phase and its influence on the Co matrix phase transformation. The σ phase is mainly found in two morphologies in these alloys, where at high temperature only blocky σ phase is present at grain boundaries but cellular σ is formed through a discontinuous precipitation within the grains at lower heat treatment temperatures. The presence of fine cellular σ phase influences the alloy hardness. Moreover, the σ precipitation, which depletes the matrix in Re, also influences the allotropic transformation of the Co matrix.

Relationships between the Abilities of the Forming Bond of the Precipitated Phases and their Precipitations and Phases Transition in Al-Fe-Si Alloy

2010 ◽  
Vol 152-153 ◽  
pp. 1049-1053
Author(s):  
Hua Qu ◽  
Wei Dong Liu ◽  
Chuang Liu ◽  
Gang Zhou ◽  
Xiao Lu Shen
Keyword(s):  
High Temperature ◽  
Solid Solutions ◽  
Electron Theory ◽  
Empirical Electron Theory ◽  
The Matrix ◽  
Cooling Speed ◽  
The Stability ◽  
Precipitated Phases

According to the empirical electron theory of solid and molecule, the valence election structures of the matrix  of Al-Fe-Si alloy, solid solutions of -Al-Fe and -Al-Fe-Si, precipitated phases of A13(Fe,Si), Al8Fe2Si and Al12Fe3Si and their abilities of the forming bond were calculated, then the relationships between the abilities of the forming bond of the main precipitated phases in Al-Fe-Si alloys and their precipitations and phases transition were studied in this paper. From the results we find that the ability of the forming bond of Al12Fe3Si (637.23) is small, that of Al3(Fe,Si) (670.52) is large and that of Al8Fe2Si (1038.27) is the largest; the larger the cooling speed, the more amount of the precipitated first of Al12Fe3Si, the few amount of the precipitated of Al3(Fe,Si) and Al8Fe2Si; the stability of Al12Fe3Si is smaller than that of Al3(Fe,Si) and Al8Fe2Si, and under high temperature, the phase of Al12Fe3Si can grow up and coarsen and even change into Al3(Fe,Si) and Al8Fe2Si.

Improvement of high-temperature initial oxidation behavior of HR3C austenitic heat-resistant steel using silicon modification: experimental and first-principle study

2019 ◽  
Vol 116 (4) ◽  
pp. 401
Author(s):  
Tao Gao ◽  
Jian Wang ◽  
Nan Dong ◽  
Peide Han
Keyword(s):  
High Temperature ◽  
Oxidation Resistance ◽  
Oxidation Mechanism ◽  
Optical Emission ◽  
Energy Dispersive Spectrum ◽  
X Ray Diffraction ◽  
Initial Oxidation ◽  
Temperature Oxidation ◽  
The Matrix ◽  
The Stability

A novel silicon-containing austenitic stainless steel with excellent high-temperature initial oxidation resistance was prepared by adding 2.5 wt.% Si and modifying composition of the HR3C steels. Compared with HR3C steel, the oxidation resistance property of the steels containing silicon was markedly better at 800 °C. The high temperature oxidation mechanism of the steels containing silicon was analyzed by using scanning electron microscopy (SEM) with energy-dispersive spectrum (EDS) system, X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GDOES), and first-principles calculations. The results show that the Si atom in the 22Cr-25Ni-2.5Si steel initially diffused from the matrix to the surface and then reacted with O2 to form SiO2. The SiO2 had an inhibiting effect on the diffusion of Cr from matrix resulting in maintenance of the stability of the oxidation film and improvement of the oxidation resistance as compared with the HR3C.

Steady Characteristics of High-Speed Micro-Gas Journal Bearings With Different Gaseous Lubricants and Extreme Temperature Difference

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Xueqing Zhang ◽  
Qinghua Chen ◽  
Juanfang Liu
Keyword(s):  
High Temperature ◽  
Temperature Difference ◽  
Gas Turbines ◽  
High Speed ◽  
Load Capacity ◽  
Axial Direction ◽  
Operating Conditions ◽  
Thermal Creep ◽  
Large Temperature ◽  
The Stability

High-speed micro-gas journal bearing is one of the essential components of micro-gas turbines. As for the operating conditions of bearings, the high-speed, high-temperature, ultra-high temperature difference along the axial direction and the species of gaseous lubricants are extremely essential to be taken into account, and the effects of these factors are examined in this paper. The first-order modified Reynolds equation including the thermal creep, which results from the extremely large temperature gradient along the axial direction, is first derived and coupled with the simplified energy equation to investigate the steady hydrodynamic characteristics of the micro-gas bearings. Under the isothermal condition, it is found that CO2 can not only improve the stability of bearings but also generate a relatively higher load capacity by some comparisons. Thus, CO2 is chosen as the lubricant to further explore the influence of thermal creep. As the rotation speed and eccentricity ratio change, the thermal creep hardly has any effect on the gas film pressure. However, the shorter bearing length can augment the thermal creep. Compared with the cases without the thermal creep, the thermal creep could remarkably destroy the stability of gas bearing, but it might slightly enhance the load capacity.

Development of a Tool for Temperature Estimation From Microstructural Condition of a Nicoraly+Re Coating Applied on the Surface of Gas Turbine Hot Components

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
Alessio Costa ◽  
Vacchieri Erica ◽  
Emma Barbareschi ◽  
Paola Guarnone ◽  
Alessandra Bonadei ◽  
...  
Keyword(s):  
Phase Composition ◽  
High Temperature ◽  
Gas Turbines ◽  
Residual Life ◽  
Intermetallic Phase ◽  
Service Temperature ◽  
Temperature Oxidation ◽  
Σ Phase ◽  
Temperature Range ◽  
Different Temperatures

The hot gas path components of gas turbines have to withstand to severe conditions in terms of high temperature oxidation, hot corrosion, and creep-fatigue phenomena. The evaluation of components residual life is an important matter for gas turbines producers and the estimation of service temperatures is a key tool for this evaluation. The most diffused methods to estimate service temperatures of gas turbines blades and vanes in Ni based superalloys are related to the microstructural evolution of the dispersed intermetallic phase γ′, Ni3Al. The aim of this work has been the determination of a tool to estimate service temperature on the basis of the microstructural evolutions of a NiCoCrAlY+Re coating. In order to obtain a deep characterization of the coating after exposure at different durations and temperatures, an extensive experimental test program has been planned. Samples of Ni based superalloys, covered by the investigated coating, have been aged in chamber furnaces in the temperature range 700 °C–1000 °C with durations up to 20,000 h. The microstructure of this coating is characterized by β phase, NiAl, which is the Al reservoir, embedded in the matrix, that is constituted by γ′ phase at low temperature and by γ phase over 900 °C. Moreover, electron back scattered diffraction and X-ray diffraction measurements on samples have revealed three classes of secondary phases: the first one has been identified as σ-Cr2Re3, the second one as Cr carbide-Cr23C6 and the third one as α-Cr. σ phase is very abundant at the lower temperatures while it disappears after long exposures at temperatures higher than 900 °C. The σ phase composition is different at different temperatures and the Re content in particular increases with the temperature. Starting from the σ phase composition determined at different temperatures, a tool has been constructed that relates the service temperature to the Re content in the same phase. The new tool has been applied to the analyses of different components. The results of the new method have been compared to those ones obtained with the method based on γ′ features, developed in the past through huge experimental campaigns. The agreement between the two methods is generally good, they can be used in a complementary way due to the fact that the γ′ one seems to be more suitable for high temperature ranges (T > 900 °C) where it gives a reliable estimation, while the σ method is more suitable in the temperature range 700 °C–900 °C.

Development of a Tool for Temperature Estimation From Microstructural Condition of a NiCoCrAlY+Re Coating Applied on the Surface of Gas Turbine Hot Components

2013 ◽  
Author(s):  
Alessio Costa ◽  
Erica Vacchieri ◽  
Emma Barbareschi ◽  
Paola Guarnone ◽  
Alessandra Bonadei ◽  
...  
Keyword(s):  
Phase Composition ◽  
High Temperature ◽  
Gas Turbines ◽  
Residual Life ◽  
Intermetallic Phase ◽  
Service Temperature ◽  
Temperature Oxidation ◽  
Σ Phase ◽  
Temperature Range ◽  
Different Temperatures

The hot gas path components of gas turbines have to withstand to severe conditions in terms of high temperature oxidation, hot corrosion and creep-fatigue phenomena. The evaluation of components residual life is an important matter for gas turbines producers and the estimation of service temperatures is a key tool for this evaluation. The most diffused methods to estimate service temperatures of gas turbines blades and vanes in Ni based superalloys are related to the microstructural evolution of the dispersed intermetallic phase γ′, Ni3Al. The aim of this work has been the determination of a tool to estimate service temperature on the basis of the microstructural evolutions of a NiCoCrAlY+Re coating. In order to obtain a deep characterisation of the coating after exposure at different durations and temperatures, an extensive experimental test program has been planned. Samples of Ni based superalloys, covered by the investigated coating, have been aged in chamber furnaces in the temperature range 700°C – 1000°C with durations up to 20000 hours. The microstructure of this coating is characterised by β phase, NiAl, which is the Al reservoir, embedded in the matrix, that is constituted by γ′ phase at low temperature and by γ phase over 900°C. Moreover, electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) measurements on samples have revealed three classes of secondary phases: the first one has been identified as σ-Cr2Re3, the second one as Cr carbide-Cr23C6 and the third one as α-Cr. σ phase is very abundant at the lower temperatures while it disappears after long exposures at temperatures higher than 900°C. The σ phase composition is different at different temperatures and the Re content in particular increases with the temperature. Starting from the σ phase composition determined at different temperatures, a tool has been constructed that relates the service temperature to the Re content in the same phase. The new tool has been applied to the analyses of different components. The results of the new method have been compared to those ones obtained with the method based on γ′ features, developed in the past through huge experimental campaigns. The agreement between the two methods is generally good, they can be used in a complementary way due to the fact that the γ′ one seems to be more suitable for high temperature ranges (T>900°C) where it gives a reliable estimation, while the sigma method is more suitable in the temperature range 700°C – 900°C.

Effect of Improved ThO2 Particle Dispersion in Nickel on High-Temperature Strength

1970 ◽  
Vol 28 ◽  
pp. 444-445
Author(s):  
E. R. Kimmel ◽  
H. L. Anthony ◽  
W. Scheithauer
Keyword(s):  
High Temperature ◽  
Metal Matrix ◽  
Oxide Particle ◽  
Oxide Phase ◽  
Dislocation Motion ◽  
Particle Dispersion ◽  
High Temperature Strength ◽  
Strengthening Effect ◽  
Oxide Particles ◽  
The Stability

The strengthening effect at high temperature produced by a dispersed oxide phase in a metal matrix is seemingly dependent on at least two major contributors: oxide particle size and spatial distribution, and stability of the worked microstructure. These two are strongly interrelated. The stability of the microstructure is produced by polygonization of the worked structure forming low angle cell boundaries which become anchored by the dispersed oxide particles. The effect of the particles on strength is therefore twofold, in that they stabilize the worked microstructure and also hinder dislocation motion during loading.

Effect of High Temperature on Wear Behavior of Stir Cast Aluminium/Boron Carbide Composites

2020 ◽  
Vol 22 (4) ◽  
pp. 1031-1046
Author(s):  
X. Canute ◽  
M. C. Majumder
Keyword(s):  
High Temperature ◽  
Wear Rate ◽  
Boron Carbide ◽  
Wear Behavior ◽  
Base Alloy ◽  
Weight Fraction ◽  
Sliding Velocity ◽  
Wear Properties ◽  
High Temperature Wear ◽  
The Matrix

AbstractThe need for development of high temperature wear resistant composite materials with superior mechanical properties and tribological properties is increasing significantly. The high temperature wear properties of aluminium boron carbide composites was evaluated in this investigation. The effect of load, sliding velocity, temperature and reinforcement percentage on wear rate was determined by the pin heating method using pin heating arrangement. The size and structure of base alloy particles change considerably with an increase of boron carbide particles. The wettability and interface bonding between the matrix and reinforcement enhanced by the addition of potassium flurotitanate. ANOVA technique was used to study the effect of input parameters on wear rate. The investigation reveals that the load had higher significance than sliding velocity, temperature and weight fraction. The pin surface was studied with a high-resolution scanning electron microscope. Regression analysis revealed an extensive association between control parameters and response. The developed composites can be used in the production of automobile parts requiring high wear, frictional and thermal resistance.

Spring and piston system for high temperature application

1997 ◽  
Author(s):  
R. Spivey ◽  
S. Breeding ◽  
J. Andrews ◽  
D. Stefanescu ◽  
S. Sen ◽  
...  
Keyword(s):  
High Temperature ◽  
High Temperature Application ◽  
Piston System ◽  
Temperature Application
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