In recent years, additive manufacturing (AM) has been one of the essential production techniques in the engineering community. Rapid integration of this technique drew a bead on the reliability of the microstructural and mechanical properties of engineering components. However, due to the nature of the layer-by-layer approach of AM, complex thermal gradients can cause inhomogeneous microstructure and significant residual stresses (RS). These, expectedly, can lead to a dramatic reduction in material performance. Therefore, especially for alloys like Ni-based Inconel 718 (IN718) used in critical applications, the characterization and later optimization of the DED process on material properties become essential. Nevertheless, empirical and conventional approaches are needed to improve, or new techniques should be introduced. In this regard, this study aims to understand better the evolution of the mechanical and microstructural properties of IN718 during and post-DED processes. For this purpose, an in-situ 2D neutron diffraction strain monitoring was carried out during the DED of IN718. The strain contributions originated from microstructural, thermal, and stress-based events during deposition and cooling periods at different positions concerning melt pool were investigated. Stabilization of different positions and processing regions on the sample as a function of the temperature profile, build height, and microstructural events are examined. Laboratory-scale microstructural studies were performed on wire-DED parts to observe the process parameter dependency of precipitation, composition, and morphology of microstructural constituents. Moreover, these findings were benchmarked with neutron powder diffraction measurements to relate the crystallographic behavior with macroscopic ones. Solidification under different cooling rates and heat treatments was carried out using the neutron powder diffraction technique to comprehend the precipitation dynamics and explain the microstructural events during and after the DED process. Laboratory scale and neutron diffraction tensile characterization tests were performed to observe and relate the mechanical response of wire- DED IN718 at different temperatures and microstructural conditions.:Keywords i
Abstract iii
Table of Contents v
List of Figures ix
List of Tables xvii
List of Abbreviations xix
Acknowledgments xxi
Chapter 1: Introduction 1
1.1 Residual Stress in Polycrystalline Materials 1
1.1.1 Residual Stress Determination 3
1.2 Neutron Scattering 5
1.2.1 Neutron-Matter Interaction 6
1.2.2 Strain Measurement by Neutron Diffraction 7
1.2.3 SALSA Neutron Strain Diffractometer 14
1.2.4 Neutron Powder Diffraction 16
1.2.5 D20 Neutron Powder Diffractometer 17
1.2.6 Peak Analysis in Diffraction Measurements 18
1.3 Nickel Superalloys 22
1.3.1 Physical Metallurgy of IN718 23
1.4 Metal Additive Manufacturing 33
1.4.1 Direct Energy Deposition (DED) 34
1.4.2 Process Monitoring in Metal AM 36
1.5 Context and Aim of the Study 40
Chapter 2: Materials and Experimental Methods 43
2.1 IN718 Feedstock Material 43
2.2 Fabrication Process by wire-DED Method 43
2.2.1 Post Processing of IN718 via Solution Treatment and Aging 47
2.2.2 Preparation of Tensile Specimens 48
2.3 Microstructural Characterization 49
2.3.1 Electron Microscopy Studies 49
2.3.2 Differential Scanning Calorimetry Analysis 50
2.3.3 Lattice Parameter Evolution of IN718 with Temperature 52
2.3.3.1 Data Reduction for Phase Analysis 54
2.4 Mechanical Characterization 57
2.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 57
2.4.1.1 Temperature Data Treatment and Processing Regions 61
2.4.1.2 Neutron Data Acquisition and Analysis 64
2.4.2 Residual Stress Mapping of Samples for Mechanical Characterization 69
2.4.3 Macro-scale Tensile Characterization at Room and High Temperatures 71
2.4.4 Neutron Diffraction Tensile Characterization Testing 72
2.4.4.1 Neutron Data Processing Procedure 77
Chapter 3: Results and Discussion 79
3.1 Microstructural Characterization of Feedstock Wire 79
3.1.1 Metallography of IN718 Feedstock Wire 79
3.1.2 Simulation of Phase Precipitations in IN718 80
3.1.3 Thermal Stability of IN718 Feedstock Wire 82
3.1.3.1 Differential Scanning Calorimetry 82
3.1.3.2 Lattice Parameter Evolution during Melting & Solidification 83
3.1.4 Discussion 91
3.2 Microstructure of IN718 wire-DED Parts 94
3.2.1 IN718-DED Cylindrical Walls 94
3.2.2 IN718 -DED Prisms 103
3.2.3 Discussion 108
3.3 Heat Treatments of IN718 Wire-DED Parts 112
3.3.1 Time and Temperature Impact into Laves Phase Dissolution 112
3.3.2 Lattice Parameter Evolution of IN718 during Solution and Aging Treatments 115
3.3.3 Discussion 118
3.4 Mechanical Characterization of IN718 wire-DED 122
3.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 122
3.4.1.1 Bragg Angle Evolution 122
3.4.1.2 Evolution of Bragg Angle Position in MP Processing Region 123
3.4.1.3 Evolution of Bragg Angle Position in the NMP Processing Region 126
3.4.1.4 Evolution of Bragg Angle Position in FF Processing Region 129
3.4.2 Discussion 131
3.4.2.1 Comparison of Equilibrium State of IN718 through In-situ and Ex-situ Investigations 135
3.4.3 Reference (d0) Approaches for Strain Calculations 136
3.4.3.1 Stable processing regime reference 136
3.4.3.2 Neutron powder diffraction reference 137
3.4.4 Evolution of Strain Contributions during IN718 wire-DED by Using Stable Reference (d0) Approach 140
3.4.4.1 Strain Evolution in MP Processing Region 141
3.4.4.2 Strain Evolution in NMP Processing Region 143
3.4.4.3 Strain Evolution in FF Processing Region 145
3.4.5 Evolution of Strain Contributions during IN718 wire-DED by Using Neutron Powder Diffraction Reference d0 Approach 148
3.4.6 Discussion 151
3.4.7 Tensile Characterization 153
3.4.7.1 Macro-scale Tensile Behavior 153
3.4.7.2 Residual Stress State in In-situ Tensile Test Specimens 155
3.4.7.3 Lattice-scale Tensile Behavior 158
3.4.8 Discussion 169
3.4.8.1 Residual Stress State prior to Tensile Test Characterization 169
3.4.8.2 Macro-scale Tensile Behavior of IN718 at Room and High Temperatures 169
3.4.8.3 Lattice-dependent Behavior As-built and Direct-aged Condition as a function of Applied Stresses 175
Chapter 4: Summary Discussion 182
4.1 Microstructural Considerations 182
4.1.1 Comparison of Materials and Extrapolation of Properties 182
4.2 Thermal Stability of IN718 Feedstock Wire and DED Parts 183
4.2.1 Matrix, Phase Precipitation, and CTE Evolution as a Function of Temperature 183
4.2.2 Heat Treatments of IN718 DED materials 184
4.3 Fabrication and Neutron Strain Monitoring Considerations 185
4.3.1 Temperature Gradients and Regions of Interest 185
4.3.2 In-situ Neutron Monitoring of Bragg Angle Evolution of γ-matrix 185
4.3.3 2D Strain Evolution 186
4.4 Tensile Mechanical Behaviour at Room and High-Temperature Considerations 189
4.4.1 Macro-scale Characterization 189
4.4.2 Lattice-scale Neutron Diffraction Characterization 189
Chapter 5: Conclusions 191
Bibliography 196 / In den letzten Jahren hat sich die additive Fertigung (AM) zu einer der wichtigsten Produktionstechniken in der Ingenieurwelt entwickelt. Die schnelle Integration dieser Technik hat die Zuverlässigkeit der mikrostrukturellen und mechanischen Eigenschaften von technischen Komponenten deutlich verbessert. Aufgrund des schichtweisen Ansatzes der AM können jedoch komplexe thermische Gradienten eine inhomogene Mikrostruktur und erhebliche Eigenspannungen (RS) verursachen. Diese können erwartungsgemäß zu einer dramatischen Verringerung der Materialleistung führen. Daher sind insbesondere bei Legierungen wie Inconel 718 (IN718) auf Ni-Basis, die in kritischen Anwendungen eingesetzt werden, die Charakterisierung und spätere Optimierung des DED-Prozesses auf die Materialeigenschaften von entscheidender Bedeutung. Dennoch müssen empirische und konventionelle Ansätze verbessert werden, oder es sollten neue Techniken eingeführt werden. In diesem Zusammenhang zielt diese Studie darauf ab, die Entwicklung der mechanischen und mikrostrukturellen Eigenschaften von IN718 während und nach dem DED-Prozess besser zu verstehen. Zu diesem Zweck wurde während des DED-Prozesses von IN718 eine in-situ 2D-Neutronenbeugungsmessung der Dehnung durchgeführt. Die Dehnungsbeiträge, die von mikrostrukturellen, thermischen und spannungsbasierten Ereignissen während der Abscheidungs- und Abkühlungsperioden an verschiedenen Positionen des Schmelzbades herrühren, wurden untersucht. Die Stabilisierung verschiedener Positionen und Verarbeitungsbereiche auf der Probe als Funktion des Temperaturprofils, der Aufschmelzhöhe und der mikrostrukturellen Ereignisse wurde untersucht. Im Labormaßstab wurden mikrostrukturelle Studien an Draht-DED-Teilen durchgeführt, um die Abhängigkeit der Prozessparameter von der Ausscheidung, Zusammensetzung und Morphologie der mikrostrukturellen Bestandteile zu beobachten. Darüber hinaus wurden diese Ergebnisse mit Neutronenpulverbeugungsmessungen verglichen, um das kristallographische Verhalten mit dem makroskopischen Verhalten in Beziehung zu setzen. Die Erstarrung unter verschiedenen Abkühlungsraten und Wärmebehandlungen wurde mit Hilfe der Neutronenpulverbeugungstechnik durchgeführt, um die Ausscheidungsdynamik zu verstehen und die mikrostrukturellen Ereignisse während und nach dem DED-Prozess zu erklären. Es wurden Zugversuche im Labormaßstab und mit Neutronenbeugung durchgeführt, um die mechanische Reaktion von IN718 bei verschiedenen Temperaturen und Mikrostrukturbedingungen zu beobachten und in Beziehung zu setzen.:Keywords i
Abstract iii
Table of Contents v
List of Figures ix
List of Tables xvii
List of Abbreviations xix
Acknowledgments xxi
Chapter 1: Introduction 1
1.1 Residual Stress in Polycrystalline Materials 1
1.1.1 Residual Stress Determination 3
1.2 Neutron Scattering 5
1.2.1 Neutron-Matter Interaction 6
1.2.2 Strain Measurement by Neutron Diffraction 7
1.2.3 SALSA Neutron Strain Diffractometer 14
1.2.4 Neutron Powder Diffraction 16
1.2.5 D20 Neutron Powder Diffractometer 17
1.2.6 Peak Analysis in Diffraction Measurements 18
1.3 Nickel Superalloys 22
1.3.1 Physical Metallurgy of IN718 23
1.4 Metal Additive Manufacturing 33
1.4.1 Direct Energy Deposition (DED) 34
1.4.2 Process Monitoring in Metal AM 36
1.5 Context and Aim of the Study 40
Chapter 2: Materials and Experimental Methods 43
2.1 IN718 Feedstock Material 43
2.2 Fabrication Process by wire-DED Method 43
2.2.1 Post Processing of IN718 via Solution Treatment and Aging 47
2.2.2 Preparation of Tensile Specimens 48
2.3 Microstructural Characterization 49
2.3.1 Electron Microscopy Studies 49
2.3.2 Differential Scanning Calorimetry Analysis 50
2.3.3 Lattice Parameter Evolution of IN718 with Temperature 52
2.3.3.1 Data Reduction for Phase Analysis 54
2.4 Mechanical Characterization 57
2.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 57
2.4.1.1 Temperature Data Treatment and Processing Regions 61
2.4.1.2 Neutron Data Acquisition and Analysis 64
2.4.2 Residual Stress Mapping of Samples for Mechanical Characterization 69
2.4.3 Macro-scale Tensile Characterization at Room and High Temperatures 71
2.4.4 Neutron Diffraction Tensile Characterization Testing 72
2.4.4.1 Neutron Data Processing Procedure 77
Chapter 3: Results and Discussion 79
3.1 Microstructural Characterization of Feedstock Wire 79
3.1.1 Metallography of IN718 Feedstock Wire 79
3.1.2 Simulation of Phase Precipitations in IN718 80
3.1.3 Thermal Stability of IN718 Feedstock Wire 82
3.1.3.1 Differential Scanning Calorimetry 82
3.1.3.2 Lattice Parameter Evolution during Melting & Solidification 83
3.1.4 Discussion 91
3.2 Microstructure of IN718 wire-DED Parts 94
3.2.1 IN718-DED Cylindrical Walls 94
3.2.2 IN718 -DED Prisms 103
3.2.3 Discussion 108
3.3 Heat Treatments of IN718 Wire-DED Parts 112
3.3.1 Time and Temperature Impact into Laves Phase Dissolution 112
3.3.2 Lattice Parameter Evolution of IN718 during Solution and Aging Treatments 115
3.3.3 Discussion 118
3.4 Mechanical Characterization of IN718 wire-DED 122
3.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 122
3.4.1.1 Bragg Angle Evolution 122
3.4.1.2 Evolution of Bragg Angle Position in MP Processing Region 123
3.4.1.3 Evolution of Bragg Angle Position in the NMP Processing Region 126
3.4.1.4 Evolution of Bragg Angle Position in FF Processing Region 129
3.4.2 Discussion 131
3.4.2.1 Comparison of Equilibrium State of IN718 through In-situ and Ex-situ Investigations 135
3.4.3 Reference (d0) Approaches for Strain Calculations 136
3.4.3.1 Stable processing regime reference 136
3.4.3.2 Neutron powder diffraction reference 137
3.4.4 Evolution of Strain Contributions during IN718 wire-DED by Using Stable Reference (d0) Approach 140
3.4.4.1 Strain Evolution in MP Processing Region 141
3.4.4.2 Strain Evolution in NMP Processing Region 143
3.4.4.3 Strain Evolution in FF Processing Region 145
3.4.5 Evolution of Strain Contributions during IN718 wire-DED by Using Neutron Powder Diffraction Reference d0 Approach 148
3.4.6 Discussion 151
3.4.7 Tensile Characterization 153
3.4.7.1 Macro-scale Tensile Behavior 153
3.4.7.2 Residual Stress State in In-situ Tensile Test Specimens 155
3.4.7.3 Lattice-scale Tensile Behavior 158
3.4.8 Discussion 169
3.4.8.1 Residual Stress State prior to Tensile Test Characterization 169
3.4.8.2 Macro-scale Tensile Behavior of IN718 at Room and High Temperatures 169
3.4.8.3 Lattice-dependent Behavior As-built and Direct-aged Condition as a function of Applied Stresses 175
Chapter 4: Summary Discussion 182
4.1 Microstructural Considerations 182
4.1.1 Comparison of Materials and Extrapolation of Properties 182
4.2 Thermal Stability of IN718 Feedstock Wire and DED Parts 183
4.2.1 Matrix, Phase Precipitation, and CTE Evolution as a Function of Temperature 183
4.2.2 Heat Treatments of IN718 DED materials 184
4.3 Fabrication and Neutron Strain Monitoring Considerations 185
4.3.1 Temperature Gradients and Regions of Interest 185
4.3.2 In-situ Neutron Monitoring of Bragg Angle Evolution of γ-matrix 185
4.3.3 2D Strain Evolution 186
4.4 Tensile Mechanical Behaviour at Room and High-Temperature Considerations 189
4.4.1 Macro-scale Characterization 189
4.4.2 Lattice-scale Neutron Diffraction Characterization 189
Chapter 5: Conclusions 191
Bibliography 196
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:83853 |
| Date | 28 February 2023 |
| Creators | Ozcan, Burak |
| Contributors | Leyens, Christoph, Cabeza, Sandra, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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