This thesis is devoted to the numerical and experimental investigation of residual stress and deformation in polycrystalline metallic alloys at different scales. The emphasis in the current study is placed on establishing the connection between the simulation of deformation by the Finite Element (FE) method and experimental characterisation by synchrotron X-Ray Diffraction (XRD). Of particular importance is the interpretation of modelling results and their validation by careful comparison with experimental data. The concept of eigenstrain was used extensively throughout the report to study the residual elastic strain distributions and their sources. A pseudo-thermal strain FE procedure was used systematically to simulate the residual stress states in samples and engineering components of different shape and dimensionality. The case of 1-D strain variation was considered using the example of a plastically bent bar. The direct and inverse problems of eigenstrain analysis were solved, and validated experimentally by the use of XRD and EDM slitting methods. A novel 2-D discrete inverse eigenstrain algorithm was proposed and implemented to reconstruct the residual stress distribution in a worn rail head. The link between the residual stress and deformation history was studied via thermo-mechanical modelling of the Linear Friction Welding (LFW) process. To advance the understanding of polycrystalline deformation behaviour across the scales, a crystal plasticity model was employed to simulate the elastic-plastic deformation behaviour of Ti-6Al-4V alloy. A post-processor was developed to extract the average elastic strains for orientation-specific grain groups and to compare them with XRD data. A “peak constructor” post-processor was developed that utilised the knowledge of both the elastic strain and dislocation density. In a further development step, a strain gradient crystal plasticity formulation was adopted to account for the local dislocation evolution. Intra-granular deformation analysis was carried out and micro-beam Laue experimental diffraction technique was used for validation. Thus, local lattice arrangement was studied at the microscopic, intragranular scale. Special attention was paid to the phenomenon of Laue spot “streaking”, indicative of the local lattice misorientation caused by dislocation activity during deformation. The results presented in this thesis contributed to the fundamental understanding of the residual stress and deformation in polycrystalline metallic alloys and lead to more than 20 publications in peer-reviewed journals and conference proceedings, which are listed in the Appendix.

Die Hydrierung von Zintl-Phasen führt zur Bildung von Einlagerungshydriden, die ausschließlich von Kationen koordiniert sind, zu polyanionischen Hydriden, bei denen Wasserstoff kovalent an das stärker elektronegative Element bindet, oder zu einer Kombination von beiden Motiven. Es wurde eine Reihe neuer Verbindungen dargestellt und mittels Laborröntgen-, Synchrotron- und Neutronenpulverbeugung strukturell charakterisiert. Die meisten Beispiele werden durch die Hydrierung von Zintl-Phasen im CrB- oder FeB-Strukturtyp erhalten. Die beiden Typen sind strukturell eng verwandt. Sie sind durch das Auftreten von polyanionischen Zickzackketten gekennzeichnet. Die Einlagerungshydride LnTtH (Ln = La, Nd, Tt = Si, Ge, Sn) sind Oxidationsprodukte der formal metallischen Zintl-Phasen LnTt = Ln3+ Tt2- e- . Wasserstoff besetzt dabei Ln-Tetraederlücken. Die Produkte treten als gefüllter FeB- (P -Phase, LaGeH-Strukturtyp) oder als gefüllter CrB-Strukturtyp (C -Phase, NiZrH-Strukturtyp) auf. Die Hydrierung der elektronenpräzisen Zintl-Phasen AeTt (Ae = Sr, Ba, Tt = Ge, Sn, CrB-Strukturtyp) führt zu wasserstoffarmen (AeTtHy , y < 1) und wasserstoffreichen (AeTtHy , 1 < y ≤ 2) Phasen. Erstere weisen partiell gefüllte Ae4-Lücken auf. In Phasen mit kleinem y (< 0.4) wird der Wasserstoff statistisch über die Lücken verteilt (α-Phasen). Etwas höhere Gehalte führen zu partieller (β-SrGeHy , 0.47 < y < 0.75) oder vollständiger (β-BaGeH0.5 ) Ordnung. Die wasserstoffreichen Phasen AeTtHy , 1 < y ≤ 2 (γ-Phasen), zeigen sowohl die Strukturmotive von Einlagerungs- als auch von polyanionischen Hydriden. SrSiH1.6 und BaSiH1.9 als literaturbekannte Verbindungen wurden das erste mal strukturell charakterisiert. Die homologe Reihe konnte um SrGeH1.2 , BaGeH1.6 und BaSnH1.3 erweitert werden. Die Ae4 -Tetraeder sind in diesen Phasen vollständig mit Hydridionen besetzt. Zusätzlicher Wasserstoff bindet kovalent an die Polyanionen. Außerdem verknüpfen sich die Zickzackketten z. T. senkrecht zur Kettenrichtung. Es wurden insgesamt drei Strukturtypen differenziert, die alle strukturell eng verwandt sind. Das führt zu Problemen bei der Strukturbestimmung aus Pulverdaten. Der kovalente Charakter der Bindung wurde durch Festkörperkernresonanzspektroskopie und Dichtefunktionaltheorierechnungen charakterisiert. Typische Tetrel-Wasserstoff-Bindungslängen sind 155(2) pm (Si-H), 163(2) pm (Ge-H) und 186(1) pm (Sn-H). In situ -Neutron, Röntgen- und Synchrotronpulverbeugung wurden angewandt um Reaktionsabläufe aufzuklären. Beim Heizen unter Wasserstoffdruck treten im AeTt-H2 -System (Ae = Sr, Ba, Tt = Ge, Sn) verschiedene reversible Reaktionen zwischen den γ-, β- und α-Phasen auf, bevor ein irreversibler Zersetzungsschritt in die binären Hydride AeH2 und die Tt-reichen Zintl-Phasen AeTt2 beobachtet wird. Ein In situ Beugungsexperiment der Reaktion von NdGa mit Wasserstoff zeigt direkt die Bildung von NdGaH1+x (isostrukturell zu γ-AeTtHy ), das eine Zusammensetzung von mindestens x = 0.17 bis 0.80 aufweist. Die Ga-H Abstände sind lang (ca. 200 pm) und darum keine klassischen 2-Elektronen-2-Zentrenbindungen. In situ Beugung an den Reaktionen von KSi und CsSi mit Wasserstoff konnte gezeigt werden, dass die Hydride KSiH3 und CsSiH3 in einem Schritt gebildet werden. Diese Phasen weisen SiH3--Anionien auf, die isoelektronisch zu PH3 sind. Weiteres Heizen unter Wasserstoffdruck führt zur Zersetzung in KH und K8Si46 oder zur Rückbildung von CsSi. Außerdem wurde eine Reihe weiterer Verbindungen auf die Reaktivität gegenüber Wasserstoff untersucht. Die Phasen AeTt2 , AGe und ASixGe1-x (A = K, Rb, Cs) bilden keine Hydride unter den untersuchten Bedingungen (mindestens 5 MPa H2, 700 K). Die Gallide CaGa, Sr8Ga7 und Ba8Ga7 weisen Reaktivität gegenüber Wasserstoff auf. Diese Beispiele zersetzen sich in binäres Hydrid und die galliumreichen Phasen Ca3Ga8, SrGa4 und BaGa4 . In situ Laborröntgenbeugung der Reaktion von CaGa mit Wasserstoff führt zur Bildung einer neuen, kristallinen Phase. Bildung und Zersetzung laufen in einem sehr schmalen Temperaturfenster ab. Die neue Phase konnte noch nicht charakterisiert werden. / The hydrogenation of Zintl phases leads to interstitial hydrides that are coordinated exclusively by cations, polyanionic hydrides that exhibit a covalent bond to the more electronegative element, or a combination of both motifs. A series of new compounds is prepared and structurally characterised by laboratory X-ray, synchrotron and neutron powder diffraction. Most examples can be derived via hydrogenation of CrB- or FeB-type Zintl phases. These structure types are closely related and characterised by polyanionic zigzag chains. The interstitial hydrides LnTtH (Ln = La, Nd, Tt = Si, Ge, Sn) are oxidation products of the formally metallic Zintl phases LnTt = Ln3+ Tt2- e- . Hydrogen occupies tetrahedral Ln4-voids. The products occur as a filled FeB-type phase (P-phase, LaGeH-structure type) or a filled CrB-type phase (C-phase, ZrNiH-structure type). The hydrogenation of electron-precise Zintl phases AeTt (Ae = Sr, Ba, Tt = Ge, Sn, CrB-structure type) leads to hydrogen-poor (AeTtHy , y < 1) and hydrogen-rich phases (AeTtHy , 1 < y ≤ 2). The first show partially hydrogen-filled Ae4-voids. For low contents y < 0.4, hydrogen is statistically distributed over the voids (α-phases). Slightly increased hydrogen contents lead to partial (β-SrGeHy , 0.47 ≤ y ≤ 0.75) or full ordering (β-BaGeH0.5 ). The hydrogen-rich phases AeTtHy, 1 < y ≤ 2 (γ-phases), combine interstitial and polyanionic hydride motifs. The literature-known phases SrSiH1.6 and BaSiH1.9 could be structurally characterised for the first time. The homologue series was extended to SrGeH1.2, BaGeH1.6 and BaSnH1.3 . Tetrahedral Ae4-voids are totally filled with hydride anions. The additional hydrogen binds to the polyanions. Furthermore, some of the zigzag chains are interconnected perpendicular to the chain direction. Three different structure types exhibiting a close structural relationship were identified. This leads to difficulties in structure determination from powder diffraction. The covalent character of the bond is characterised by solid-state nuclear magnetic resonance and density functional theory calculations. Typical tetrel-hydrogen bond lengths are 155(2) pm (Si-H), 163(2) pm (Ge-H) and 186(1) pm (Sn-H). In situ neutron, X-ray and synchrotron powder diffraction were used to elucidate reaction schemes. The AeTt-H2 systems (Ae = Sr, Ba, Tt = Ge, Sn) show several reversible reaction steps between γ-, β- and α-phases upon heating under hydrogen pressure. Finally, an irreversible decomposition into the binary hydrides AeH2 and Tt-rich Zintl phases AeTt2 occurs. In situ diffraction of the reaction of NdGa with hydrogen leads directly to NdGaH1+x (isostructural to γ-AeTtHy ) which shows a large compositional range from at least x = 0.17 to 0.80. Ga-H distances are long (about 200 pm) and, thus, not classical 2-electron-2-center bonds. In situ diffraction of the reactions of KSi and CsSi with hydrogen show a one step formation of the corresponding hydrides KSiH3 and CsSiH3 . They exhibit SiH3--anions which are isoelectronic to PH3 . Further heating under hydrogen pressure leads to decomposition into KH and K8Si46 or reformation of CsSi, respectively. Finally, further compounds were tested for reactivity towards hydrogen. The phases AeTt2 (Ae = Ca, Sr, Ba, Tt = Si, Ge), AGe and ASixGe1-x (A = K, Rb, Cs) do not form corresponding hydrides under the investigated conditions (at least 5 MPa H2, 700 K). The gallides CaGa, Sr8Ga7 and Ba8Ga7 show reactivity towards hydrogen. They decompose into binary hydride and the gallium-rich phases Ca3 Ga8 , SrGa4 or BaGa4. Furthermore, laboratory in situ diffraction of the reaction of CaGa with hydrogen indicates the formation of a new, crystalline phase. Formation and decomposition occur in a relative small temperature window. The new phase could not be characterised, yet.

Many Zintl phases exhibiting a CrB type structure form hydrides. Systematic studies of AeTtHx (Ae = Ca, Sr, Ba; Tt = Si, Ge, Sn), LnTtHx (Ln = La, Nd; Tt = Si, Ge, Sn), and LnGaHx (Ln = Nd, Gd) showed the vast structural diversity of these systems. Hydrogenation reactions on REGa (RE = Y, La, Tm) and RESi (RE = Y, Er, Tm) were performed in steel autoclaves under hydrogen pressure up to 5 MPa and temperatures up to 773 K. The products were analyzed by X-ray and neutron powder diffraction. RESi (RE = Y, Er, Tm) form hydrides in the C-LaGeD type. LaGaD1.66 is isostructural to NdGaD1.66 and shows similar electronic features. Ga-D distances (1.987(13) Å and 2.396(9) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. In TmGaD0.93(2) with a distorted CrB type structure deuterium atoms exclusively occupy tetrahedral voids. Theoretical calculations on density functional theory (DFT) level confirm experimental results and suggest metallic properties for the hydrides.

L'étude de l'influence de traitements d'halogenation sur les propriétés structurales et supraconductrices des cuprates de structure de type T,T' ou T* a permis de mettre en évidence: la restauration après fluoration de la supraconductivite dans le cas de l'oxyde La1,875Ba0,125CuO4 de structure de type T. Celle-ci s'accompagne de la modification de la transition structurale orthorhombique (MTO) quadratique (LTT) ; l'apparition d' un comportement supraconducteur après traitement sous chlore de l' oxyde LaSm0,8Sr0,2CuO4 de structure de type T*. La fluoration de cet oxyde conduit a la formation de deux phases isotypes. Leurs propriétés structurales et supraconductrices ont été étudiées a l'aide de diverses techniques: diffraction X et neutronique, EXAFS, susceptibilité magnétique, conductivité électrique et thermique, pouvoir thermoelectrique...

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