Modern High Temperature Brazing Processes for Turbine and Vane Repair

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1 Modern High Temperature Brazing Processes for Turbine and Vane Repair Von der Fakultät für Maschinenbau der Technischen Universität zu Braunschweig zur Erlangung der Würde eines Doktor-Ingenieurs (Dr.-Ing.) genehmigte Dissertation von Sebastian Piegert aus Karl-Marx-Stadt (heute Chemnitz) eingereicht am: 30. September 2010 mündliche Prüfung am: 14. Januar 2011 Referenten: Prof. Dr. rer. nat. Joachim Rösler Prof. Dr.-Ing. Klaus Dilger Priv.-Doz. Dr. rer. nat. Martin 2011

2 Introduction and Objective Theoretical Background and Kinetics Phase Transformations and Driving Force Kinetics Diffusion Mechanisms of Diffusion Diffusion Lattice Imperfections Diffusion in Ordered Lattices 2g Diffusion in Multiphase Binary Systems - Moving Interface Problems Atomic Nucleation Morphological Instability of the Solid-Liquid Interface Solidification Microstructure Microstructure and High Temperatures Precipitation (Ostwald-Ripening) High Temperature Strength and Deformation Strengthening Mechanisms Creep Fatigue 66

3 Environment 3.1. High Temperature Applications of and Microstructure Heat Treatment 3.3. for Hot f and Thermal Repair of Turbine and Mechanisms and Symptoms Repair and High Temperature Brazing General Aspects of High Temperature Brazing 4.2. Braze Alloys Melting Point Depressants Elements 125 Conventional High Temperature Brazing ' Heat Microstructure Diffusion Brazing Heat Treatment ' Microstructure Theory of Diffusion Brazing for a Binary Systems Theory for Ternary Alloy Systems Defects in Braze Joints Mechanical Tensile Properties Creep Properties LCF Properties Applications 156 Application Techniques of Braze Materials Fields of Application - Conventional Brazing Methods Fields of Application - Brazing 10

4 5. Simulation Methods and Experimental Proceeding Modelling of and Kinetics Thermodynamics Kinetics - DICTRA Sample for Imaging and Electron Related Methods Light Microscopic Methods Scanning Electron Microscopic Methods Imaging Methods Energy and Wavelength Dispersive X-Ray Electron Backscatter Diffraction - EBSD X-Ray Diffraction Methods Mechanical Testing, Tensile Tests Short-Term Creep-Rupture Tests Low Fatigue Tests Conventional Brazing: A Parameter Study Objective and Test Matrix Prerequisites: Base and Braze Alloys Thermodynamic Properties Brazing Heat Treatment Characterisation of the Repair Systems Thermodynamic Properties Morphology and Composition of Phases Identification of Crystallographic Properties Discussion and Properties of Brazed Joints Microstructure of Brazed Joints Thermodynamic Properties Mechanical Properties Fractography Summary and Conclusions Solidification Mechanisms, Diffusion and Resulting Microstructure of Brazed Joints Mechanical Properties of Brazed Joints Final Conclusions and Outlook 266

5 A Brazing for Solidified 7.1. Approach and Preliminary Approach Braze Alloy Alloy Systems 7.2. Braze Alloy ' ' Theoretical Approach <.f \\ dow for Ternary Bra/.e Alloys Experimental Validation 7.3. Experimental Validation Feasibility Study on Parallel Caps Variation of Brazing Parameters 7.4. Modelling of Temperature Driven Epitaxial Solidification General Description of Experimental Braze Alloys Temperature Gradient and Gap Width Dependence of Braze Joint Characteristics Discussion and Summary Experimental and Theoretical Results Proof of Concept Sensitivity towards Brazing Parameters Conclusions and Outlook Conclusions Outlook 8. Comprehensive Summary 8.1. Conventional Braze Alloy A Novel High Temperature Brazing Method Outlook 355 A. Phase Diagrams 359 B. Mechanical Testing 371 Tensile Tests,. 371 B.2. Creep Tests. 373