Advancements in Fast Epitaxial High-Temperature Brazing of Single-Crystalline Nickel-Base Superalloys

2009 ◽  
Author(s):  
Britta Laux ◽  
Sebastian Piegert ◽  
Joachim Ro¨sler
Keyword(s):  
High Temperature ◽  
Gas Turbines ◽  
Base Material ◽  
Secondary Phases ◽  
Single Crystalline ◽  
Thermodynamic Simulations ◽  
Nickel Base Superalloys ◽  
Stray Grains ◽  
Nickel Base ◽  
Nickel Manganese

High temperature diffusion brazing is a very important technology for filling cracks in components from single-crystalline nickel-base superalloys as used in aircraft engines and stationary gas turbines: alloys, which are similar to the base material, are enhanced by a fast diffusing melting-point depressant (MPD) like boron or silicon, which causes solidification by diffusing into the base material. Generally, epitaxial solidification of single-crystalline materials can be achieved by use of conventional braze alloys, however, very long hold times are necessary to provide a complete diffusion of the MPD out of the braze gap. If the temperature is lowered before diffusion is completed, brittle secondary phases precipitate, which serve as nucleation sites for stray grains and, therefore, lead to deteriorating mechanical properties. It was demonstrated in earlier works that nickel-manganese-based braze alloys are appropriate systems for the braze repair of particularly wide gaps in the range of more than 200 μm, which allow a significant shortening of the required hold times. This is caused by the complete solubility of manganese in nickel: epitaxial solidification can be controlled by cooling in addition to diffusion. In this work, it will be shown that the nickel-manganese-based systems can be enhanced by chromium and aluminium, which is with regard to high-temperature applications a very important aspect. Furthermore, it will be demonstrated that silicon, which could be identified as appropriate secondary MPD in recent works, can be replaced by titanium, as this element has additionally a γ′ stabilizing effect. Several braze alloys containing nickel, manganese, chromium, aluminium and titanium will be presented. Previously, the influence of the above mentioned elements on the nickel-manganese-based systems will be visualized by thermodynamic simulations. Afterwards, different compositions in combination with a heat treatment, which is typical for nickel-base superalloys, will be discussed: a microstructure, which is very similar to that within the base material can be presented.

Advanced Braze Alloys for Fast Epitaxial High-Temperature Brazing of Single-Crystalline Nickel-Base Superalloys

2009 ◽  
Vol 132 (3) ◽  
Author(s):  
Britta Laux ◽  
Sebastian Piegert ◽  
Joachim Rösler
Keyword(s):  
High Temperature ◽  
Gas Turbines ◽  
Base Material ◽  
Secondary Phases ◽  
Single Crystalline ◽  
Thermodynamic Simulations ◽  
Nickel Base Superalloys ◽  
Stray Grains ◽  
Nickel Base ◽  
Nickel Manganese

High-temperature diffusion brazing is a very important technology for filling cracks in components from single-crystalline nickel-base superalloys as used in aircraft engines and stationary gas turbines: Alloys, which are similar to the base material, are enhanced by a fast diffusing melting-point depressant (MPD) like boron or silicon, which causes solidification by diffusing into the base material. Generally, epitaxial solidification of single-crystalline materials can be achieved by use of conventional braze alloys; however, very long hold times are necessary to provide a complete diffusion of the MPD out of the braze gap. If the temperature is lowered before diffusion is completed, brittle secondary phases precipitate, which serve as nucleation sites for stray grains and, therefore, lead to deteriorating mechanical properties. It was demonstrated in earlier works that nickel-manganese-based braze alloys are appropriate systems for the braze repair of particularly wide gaps in the range of more than 200 μm, which allow a significant shortening of the required hold times. This is caused by the complete solubility of manganese in nickel: Epitaxial solidification can be controlled by cooling in addition to diffusion. In this work, it will be shown that the nickel-manganese-based systems can be enhanced by chromium and aluminum, which is with regard to high-temperature applications, a very important aspect. Furthermore, it will be demonstrated that silicon, which could be identified as appropriate secondary MPD in recent works, can be replaced by titanium as this element has additionally a γ′ stabilizing effect. Several braze alloys containing nickel, manganese, chromium, aluminum, and titanium will be presented. Previously, the influence of the above mentioned elements on the nickel-manganese-based systems will be visualized by thermodynamic simulations. Afterward, different compositions in combination with a heat treatment, which is typical for nickel-base superalloys, will be discussed: A microstructure, which is very similar to that within the base material, can be presented.

Diffusion Brazing of Single Crystalline Nickel Base Superalloys Using Boron Free Nickel Base Braze Alloys

2008 ◽  
Vol 273-276 ◽  
pp. 294-299 ◽  
Author(s):  
Paul Heinz ◽  
Andreas Volek ◽  
Robert F. Singer ◽  
Markus Dinkel ◽  
Florian Pyczak ◽  
...  
Keyword(s):  
Melting Point ◽  
Liquid Phase ◽  
Gas Turbines ◽  
Transient Liquid Phase ◽  
Base Material ◽  
Transient Liquid Phase Bonding ◽  
Single Crystalline ◽  
Nickel Base Superalloys ◽  
Nickel Base ◽  
Diffusion Behaviour

Brazing is a well established repair technique for high temperature components in both industrial gas turbines and aero engines. Conventional nickel base braze alloys contain boron or silicon as melting point depressing elements. The major benefit of boron and silicon compared to other melting point depressants is its large effect on the melting point and its high diffusion coefficient in nickel base superalloys. However these elements promote precipitation of undesired brittle phases during the brazing process. To avoid these phases, transient liquid phase bonding in combination with boron and silicon free brazing alloys will be examined in this work. The influence of the brazing temperature on solidification and diffusion behaviour during transient liquid phase bonding for a single crystalline first generation and a second generation superalloy will be reported. Our experiments show that isothermal solidification without precipitation of brittle phases in the braze joint or the base material can be achieved. The brazed joint consists of fine γ/γ´ microstructure. EBSD measurements demonstrated that the single crystalline orientation of the base material was maintained throughout the joint. Electron probe micro analysis is used to characterize the diffusion behaviour. Solidification velocity will be compared with the theory of transient liquid phase bonding established by Tuah-Poku [1].

Fast Epitaxial High Temperature Brazing of Single Crystalline Nickel Based Superalloys

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Britta Laux ◽  
Sebastian Piegert ◽  
Joachim Rösler
Keyword(s):  
High Temperature ◽  
Phase Formation ◽  
Melting Behavior ◽  
Maximum Width ◽  
Single Crystalline ◽  
Manganese Alloys ◽  
Thermodynamic Simulations ◽  
Thermocalc Software ◽  
Nickel Manganese ◽  
Short Times

A new high temperature brazing technology for the repair of turbine components made of single crystalline nickel based superalloys has been developed. It allows the repair of single crystalline parts by producing an epitaxially grown braze gap within very short times. In contrast to commonly used brazing technologies, the process is not diffusion based but works with consolute systems, particularly nickel-manganese alloys. Brazing experiments with 300 μm wide parallel braze gaps, as well as V-shaped gaps with a maximum width of 250 μm, were conducted. Furthermore, thermodynamic simulations, with the help of THERMOCALC software, Version TCR, were carried out to identify compositions with a suitable melting behavior and phase formation. With the new alloys complete, epitaxial bridging of both gap shapes has been achieved within brazing times as short as 10 min.

scholarly journals Mechanical Properties of New Ni-Mn-Based Braze Alloys for the Fast Epitaxial Braze Repair of Single-Crystalline Ni-Base Superalloys

2011 ◽  
Vol 278 ◽  
pp. 479-484
Author(s):  
Britta Laux ◽  
Joachim Rösler
Keyword(s):  
Base Material ◽  
Repair Process ◽  
Isothermal Solidification ◽  
High Temperature Strength ◽  
Secondary Phases ◽  
Single Crystalline ◽  
Nucleation Sites ◽  
Diffusion Controlled ◽  
Wide Gap ◽  
Stray Grains

Diffusion brazing is a widely-used technology for the repair of cracks in hot section turbine components, mostly fabricated from single-crystalline Ni-based superalloys. Typically, braze alloys with a composition similar to the base material, enhanced by fast diffusing melting point depressants like B are used. If single-crystalline (SX) components are repaired, an epitaxial healing can be achieved, however, the filling of wide cracks in the range of 100-300 μm is difficult, since the process is completely diffusion controlled which means that wide cracks require very long hold times. If the temperature is lowered before a complete isothermal solidification has been awaited, the poor solubility of B in Ni leads to the precipitation of borides, serving as nucleation sites for stray grains. Thus, especially for the repair of wide cracks, new Ni-Mn-based braze alloys were developed which allow a very fast epitaxial healing. As B is replaced by Mn, the repair process can be significantly shortened since the epitaxial solidification is no longer diffusion controlled but can be enforced by cooling. This is due to the fact that Ni and Mn are almost completely miscible which means that the precipitation of secondary phases during solidification is eliminated. The Ni-Mn-based braze alloys were enhanced by Al, Cr and Ti to provide a sufficient high temperature strength and an appropriate oxidation behavior. Furthermore, heat treatment cycles have been developed producing a γ / γ’-microstructure very similar to the base material. In this work, results from mechanical testing of wide-gap samples which were filled with the new braze alloys are presented and discussed.

Fast Epitaxial High Temperature Brazing of Single Crystalline Nickel Based Superalloys

2008 ◽  
Author(s):  
Britta Laux ◽  
Sebastian Piegert ◽  
Joachim Ro¨sler
Keyword(s):  
High Temperature ◽  
Phase Formation ◽  
Melting Behavior ◽  
Maximum Width ◽  
Single Crystalline ◽  
Manganese Alloys ◽  
Thermodynamic Simulations ◽  
Thermocalc Software ◽  
Nickel Manganese ◽  
Short Times

A new high temperature brazing technology for the repair of turbine components made of single crystalline nickel based superalloys has been developed. It allows the repair of single crystalline parts by producing an epitaxially grown braze gap within very short times. In contrast to commonly used brazing technologies the process is not diffusion based but works with consolute systems, particularly nickel-manganese alloys. Brazing experiments with 300 μm wide parallel braze gaps as well as V-shaped gaps with a maximum width of 250 μm were conducted. Furthermore, thermodynamic simulations with the help of ThermoCalc software, Version TCR were carried out to identify compositions with a suitable melting behavior and phase formation. With the new alloys complete epitaxial bridging of both gap shapes has been achieved within brazing times as short as ten minutes.

Nickel Base Superalloys Single Crystal Growth Technology for Large Size Buckets in Heavy Duty Gas Turbines

1991 ◽  
Author(s):  
Akira Yoshinari ◽  
Katsumi Iijima ◽  
Hideyo Kodama ◽  
Kimio Kano ◽  
Hiroyuki Matsuzaki
Keyword(s):  
Crystal Growth ◽  
High Temperature ◽  
Single Crystal ◽  
Gas Turbines ◽  
Single Crystal Growth ◽  
High Temperature Strength ◽  
Cross Sectional ◽  
High Temperature Mechanical Properties ◽  
Nickel Base Superalloys ◽  
Nickel Base

A larger size bucket with superior high temperature strength is required for future land based gas turbines. From the viewpoint of high temperature mechanical properties, single crystal alloys are rather promising. To grow larger sized single crystals of nickel base superalloys, a two stage heating and bypass process in which single crystal growth paths are incorporated into large cross sectional positions such as platforms has been developed. It results in successful single crystal growth of alloys for buckets with a total length of 170mm and large lateral cross section. Characteristics of single crystal buckets made by the bypass process and properties of an alumina mold prepared for a single crystal casting are described herein.

UNITEMP HX

Alloy Digest ◽  
1964 ◽  
Vol 13 (5) ◽  
Keyword(s):  
Fracture Toughness ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
Base Material ◽  
Heat Treating ◽  
Operating Conditions ◽  
High Temperature Strength ◽  
Temperature Performance ◽  
Nickel Base

Abstract Unitemp-HX is a nickel-base material recommended for high temperature applications. It has outstanding oxidation resistance at high temperatures under most operating conditions, and good high-temperature strength. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness and creep. It also includes information on low and high temperature performance, and corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: Ni-91. Producer or source: Universal Cyclops Steel Corporation.

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