<p>There has been a long-standing need in the marketplace for the economic production of small lots of components that have complex geometry. A potential solution is additive manufacturing (AM). AM is a manufacturing process that adds material bottom-up. It has the distinct advantages of low preparation cost and high geometric creation capability. Components fabricated via AM are now being selectively used for less-demanding applications in motor vehicles, consumer products, medical products, aerospace devices, and even some military projects.</p><p><br></p> <p>For engineering applications, high value-added components require consistency in the fatigue properties. However, components fabricated by AM have large variation in the fatigue properties compared to those by conventional manufacturing processes. To alleviate unpredictable catastrophic failures of components, it is essential to study and predict fatigue life. Previous study reported that fatigue crack initiation process accounts for a large portion of fatigue life, especially for low loading amplitude and high cycle fatigue. However, this major portion of fatigue life prediction is mostly ignored by main stream researchers working on fatigue modeling. For industrial applications, engineers often specify a lower stress condition to obtain a higher safety factor. Under these circumstances, fatigue crack initiation becomes even more important, so it is essential to further study of crack initiation.</p><p><br></p> <p>The objective of this research is to develop a fatigue crack initiation model for metal components produced by AM. To improve life prediction accuracy, the model must incorporate the effect of different microstructures, which are typically produced by AM due to a large number of repetitive cycles of re-heating and re-cooling processes. To fulfill this objective, the tasks are separated into three studies: (1) developing a temperature model to simulate temperature history, (2) modeling the component’s microstructure for the potential crack initiation zone, and (3) developing a fatigue crack initiation model for life estimation. A summary of each task is provided in the following.</p> <p>First, the role of temperature model is to understand the mechanism that leads to the variation of microstructures. The existing temperature models are computationally expensive to obtain an accurate prediction of the temperature history due to repetitive heating and cooling. The main reason is that these models considered entire boundary conditions of all the material points. In this section, we proposed and employed the concept of effective computation zone, which can save the computational time significantly for AM process. </p><p><br></p> <p>Second, it is critical to include the effect of microstructure in the fatigue life model since the microstructure variation at different locations within the real AM component is large. The grain size variation is modeled by using representative volume element, which is defined as a volume of heterogeneous material that is sufficiently large to be statistically representative of the real component’s microstructure. Regarding phase transformation, a continuous cooling transformation (CCT) diagram is a useful tool that can be used with a thermal model for microstructure design and manufacturing process control. However, traditional CCT diagrams are developed based on slow and monotonic cooling processes such as furnace cooling and air cooling, which are greatly different from the repetitive heating and cooling processes in AM. In this study, a new general methodology is presented to create CCT diagrams for materials fabricated by AM. We showed that the effect of the segmented duration within the critical temperature range, which induced precipitate formation, could be cumulative. </p><p><br></p> <p>Third, the existing fatigue crack initiation life model has poor accuracy. One of the reasons for the poor accuracy is the coefficients change due to the variation in microstructure is not accounted for. In this section, a semi-empirical fatigue crack initiation model is presented. The important coefficients include maximum persistent slipband width, energy efficiency coefficient, resolved shear stress and plastic slip rate per cycle. These coefficients are modeled and determined as a function of microstructure, which can improve the accuracy of life estimation.</p><p><br></p> <p>The contribution of this study is to provide a new engineering tool for designing the melting AM process based on scientific research. With this tool, the fundamental mechanism contributing to a large variation of the fatigue life of the metal components made by AM process can be understood, attributed, predicted and improved. The seemly ‘stochastic’ nature of fatigue life of the AM components can be changed to be more deterministic and predictable. This approach represents a major advance in fatigue research on AM materials. The model developed is considered as a tool for research, design, and control for laser-based AM process applications. </p>

The presence of the compressive or tensile thermal residual stresses in layers of a ceramic laminate induced due to different volume change of each layer´s material during the cooling from the sintering temperature can considerably affect resistivity of ceramics against contact damage. Within this work 2D parametric FEM models were created, in order to study the effect of the surface layer thickness, residual stress values and indenting body dimension on the initiation and propagation of the cone crack in the surface layer of the laminate. For the analysis of the critical conditions for the crack initiation, the coupled stress-energy criterion was used and for the determination of the direction of crack propagation we used the maximum tangential stress criterion. The results show that compressive thermal stresses in the surface layer increase the critical force for the crack initiation, shorten the crack distance from the contact area and shorten the occurred crack itself. Moreover, the compressive stresses enlarge the angle of the crack declination during the propagation process which cause an earlier crack arrest. The tensile thermal stresses have exactly the opposite effect. Results of simulations were compared to experimental results but due to lack of available measurements, the verification is partially limited.

Specified topic of the thesis is a multilevel evaluation of brittleness of selected building composites. The work deals with the opinions of fracture parameters of test specimens of lightweight and ordinary concrete. Specimens further differed fibres content in concrete mixtures, their type and length. The work is divided into two parts, theoretical and practical. The theoretical part conceives composite materials and introduction to fracture mechanics. The practical part describes the different steps for fracture-mechanical parameters evaluation using StiCrack and Excel Visual Basic software. The main part of the work is to evaluate the brittleness of different test specimens, taking into account the type of concrete mix and type of fibres.

In der vorliegenden Arbeit wurden Untersuchungen zum Initiierungs- und Ausbreitungsverhalten kurzer Ermüdungsrisse in einem austenitischen sowie einem austenitisch-ferritischen Edelstahl durchgeführt. Dazu erfolgten zyklische Verformungsexperimente sowohl ex situ als auch in situ im Rasterelektronenmikroskop. Die Auswertung der Experimente erfolgte im Rasterelektronenmikroskop sowohl abbildend in verschiedenen Modi als auch über Rückstreuelektronenbeugungsmessungen. Bezüglich der Rissinitiierung wurde eine Häufigkeitsverteilung der Rissinitiierungsorte für beide Stähle erstellt. Die dabei ermittelte stark unterschiedliche Häufigkeit für die transkristalline Rissinitiierung in der austenitischen Phase konnte mit der unterschiedlichen Textur und Mikrostruktur der beiden Stähle in Zusammenwirken mit den elastischen Eigenschaften der beiden Phasen erklärt werden. Für die Rissausbreitung wurde gezeigt, dass eine Korrelation zwischen der Risslänge und der Rissausbreitungsrate besteht, aus der hervorgeht, dass die Übergangsrisslänge zwischen den Bereichen der mikrostrukturell und mechanisch kurzen Risse etwa einen Korndurchmesser beträgt. Anhand der in situ Messung der (plastischen) Rissöffnung und -scherung wurden die Unterschiede im Rissausbreitungsverhalten in den verschiedenen Phasen herausgearbeitet. Für die austenitische Phase ergibt sich dabei ein öffnungsdominierter und für die ferritische Phase ein scherungsdominierter Mechanismus. Die im Ferrit auftretenden zwei unterschiedlichen Ausprägungen der Oberflächenrisspfade („rau“ und „glatt“) konnten mit der Orientierung der jeweils risstragenden Körner korreliert werden. In Zusammenwirken mit der beobachteten Systematik der Anordnung der Gleitspuren um kurze Risse im Ferrit sowie einer Analyse der Spannungsverteilung um die Rissspitze wurde ein Modell des Rissausbreitungsmechanismus\' erstellt sowie die bisher in der Literatur vorherrschende These des Einfachgleitens widerlegt. Schließlich konnte die Barrierenwirkung von Korn- und Phasengrenzen sowohl anhand der Messung der Rissausbreitungsrate als auch der plastischen Rissöffnung bzw. -scherung gezeigt und daraus Rückschlüsse auf die Ausdehnung der plastischen Zone vor der Rissspitze gezogen werden. Gleichzeitig wurde dabei die Korrelation zwischen Rissausbreitungsrate und plastischer Rissöffnung bzw. -scherung nachgewiesen.

This doctoral thesis deals with the determination of the influence of plasma electrolytic oxidation (PEO) on fatigue behaviour of extruded AZ61 magnesium alloy in air and in the 3.5% NaCl solution. The coatings were formed in the silicate-phosphate electrolyte under pulsed current conditions at a frequency of 50 Hz. The influence of current density on coating formation was examined under current densities of 70, 130 and 200 mA cm-2 for different durations up to a maximum of 1800 s. 8 g dm-3 of KF were added to the electrolyte to study the influence of fluoride ions in plasma electrolytic oxidation. It is shown that fluoride ions inhibit localised oxidation in the initial stage of the process, associated with the secondary particles based on Al–Mn. The presence of fluoride also modified the sparking characteristics, decreased the rate of coating growth and changed the morphologies of the coatings. The influence of fluoride on the coating hardness, and the corrosion resistance of the alloy during exposure to salt spray, was negligible. Based on previous optimised PEO conditions, coatings formed under a current density of 130 mA cm-2 for 300 s in the electrolyte containing KF were chosen for fatigue testing. The high-cycle fatigue tests were carried out on cylindrical samples under a force controlled sinusoidal tension-tension cycle with asymmetry parameter R=0. The experimental data were fitted with Kohout & Věchet function. The fatigue limit of uncoated alloy in air for 107 cycles was determined at 145.4 MPa and the combination of PEO coating with chloride ions caused a reduction of ~55 %. Attention was paid to the fatigue crack initiation in different conditions of cyclic loading. The fracture surfaces underwent detailed fractography analysis including secondary crack observation on the gauge length. The contribution of Al–Mn particles were confirmed on the uncoated alloy in air and the presence of chloride ions were observed as another influential contributor to local corrosion attack. The cyclic loading caused spalling of the outer layer, and the multiple initiation was observed on PEO coated alloy, caused by cracks in the coating and stress transferring to the alloy.

This master thesis project was performed in collaboration with Scania CV AB, Engine Materials group. The purpose with the project was to investigate different ceramic TBC (Thermal Barrier Coating) thermal insulation properties inside the combustion chamber. Experimental testing was performed with a Single-Cylinder engine with TBC deposited on selected components. A dummy-valve was developed and manufactured specifically for this test in order to enable a water cooling system and to ease the testing procedure. The dummy-valve consists of a headlock, socket, valve poppet and valve shaft. Additionally, a copper ring is mounted between the cylinder head and the valve poppet to seal the system from combustion gases. Thermocouples attached to the modified valve poppet and valve shaft measured the temperature during engine test to calculate the heat flux. The TBCs consisted of three different materials: 7-8% yttrium-stabilized zirconia (8YSZ), gadolinium zirconia and lanthanum zirconia. The 8YSZ TBC was tested as standard, but also with microstructural modifications. Modifications such as pre-induced segmented cracks, nanostructured zones and sealed porosity were used. The results indicated that the heat flux of 8YSZ-standard, 8YSZ-nano and 8YSZ-segmented cracks was in level with the steel reference. In the case of 8YSZ-sealed porosity the heat flux was measured higher than the steel reference. Since 8YSZ-standard and 8YSZ-sealed porosity are deposited with the same powder it is believed that the high heat flux is caused by radiative heat transfer. The remaining samples have had some microstructural changes during engine testing. 8YSZ-nano had undergone sintering and its nanostructured zones became fewer and almost gone after engine testing leading to less heat barrier in the top coat of the TBC. However, for 8YSZ-segmented cracks and gadolinium zirconia lower heat flux was measured due to the appearance of horizontal cracks. These cracks are believed to act as internal barriers as they are orientated perpendicular to the heat flow. During long-time (5 hour) engine tests the 8YSZ-standard exhibited the same phenomena: a decrease in heat flux due to propagation of horizontal cracks. One-dimensional heat flux was not achieved and the main reason for that was caused by heating and cooling of the shafts outer surface. However, the dummy-valve system has proven to be a quick, easy and stable to perform tests with a Single-Cylinder engine. Both water-cooling and long-time engine tests were conducted with minor issues. The dummy-valve has been further developed for future tests. Changes to the valve shaft are the most remarkable: smaller diameter to reduce heat transfer and smaller pockets to ensure better thermocouple positioning. Another issue was gas leakage from the combustion chamber through the copper ring and valve poppet joint. The copper ring will be designed with a 1 mm thick track to improve sealing, hence better attachment to the valve poppet.

Ces travaux ont pour objectif l'identification et la compréhension de l'effet de la corrosion aqueuse sur la durée de vie en fatigue à grand nombre de cycles (HCF) d'un acier inoxydable martensitique utilisé dans des applications aéronautiques. Tout d'abord, l'effet géométrique des défauts de corrosion sur la limite de fatigue à 10^7 cycles à l'air a été étudié avec quatre tailles différentes de piqûres de corrosion. A partir de ces résultats, une nouvelle approche volumique non locale de modélisation numérique a été proposée pour prendre en compte une géométrie réelle d'un défaut de corrosion issu des analyses en microtomographie X. Ensuite, les phénomènes de couplage chargement cyclique/corrosion ont été identifiés par des essais de fatigue à grande durée de vie (entre 10^5 et 10^7 cycles) dans une solution aqueuse à 0,1 M NaCl (à pH = 6) pour deux rapports de charge (R = -1 et 0,1). Le comportement électrochimique du film passif a été étudié in situ au cours des essais de fatigue-corrosion par le suivi du potentiel libre de corrosion et des mesures d'impédance électrochimique. Les observations des mécanismes d'amorçage de fissures et des mesures électrochimiques in-situ ont permis d'identifier un scénario d'amorçage de fissures de fatigue. Ce scénario implique des processus de rupture locale du film passif (induite par le chargement cyclique) et de corrosion assistée par le chargement cyclique. Finalement un modèle analytiquede prévision de la durée de vie en fatigue dans un milieu aqueux corrosif a été proposé à partir des résultats expérimentaux. / This study addresses the effects of corrosion on the high cycle fatigue (HCF)strength of a martensitic stainless steel used in aeronautic applications. First, the geometry of corrosion pits on the fatigue strength in air at 10^7 cycles were studied with four different pit sizes. A new non-local fatigue criterion was proposed to simulate real shapes of pits as identified by X-ray microtomography. Corrosion fatigue synergy phenomena was studied by HCF tests (between 10^5 and 10^7 cycles) in a 0.1 M NaCl aqueous solution (pH = 6) with two load ratios (R = -1 and 0.1). Next, the electrochemical behavior of the passive film was investigated during in situ corrosion fatigue tests by free potential measurements and electrochemical impedance spectroscopy (EIS). Based on fractography analysis and electrochemical test results, corrosion fatigue crack initiation mechanisms were investigated. A scenario of fatigue crack initiation was proposed based on physical evidence. This scenario implied combined processes of local passive film rupture (induced by the cyclic loading), stress-assisted corrosion and enhanced pitting development. Local passive film ruptures were the main cause of the corrosion fatigue crack initiation. Finally, a analytical model for corrosion fatigue crack initiation was proposed based.

The purpose of dissertation is the analysis of the calculation of fracture parameters using Double-K fracture model for quasi-brittle specimens with the stress concentrator loaded by three-point bending or wedge splitting. To calculation of these parameters was used the developed DKFM_BUT software in Microsoft Excel application with using of Visual Basic programming language. Furthermore, the adequate shape functions and compliance functions were introduced for the selected wedge splitting test configurations. Main part of this dissertation is the series of comprehensively implemented and evaluated fracture experiments on specimens from advanced building materials, while the attention was paid to the analysis of experimental data. Finally, the selected results obtained using mentioned software support were presented and discussed.

Die vorliegende Arbeit beschäftigt sich mit der Herstellung von CrNi-Stahl/Aluminium-Mischverbunden mit dem Ziel der Verbesserung der mechanischen Eigenschaften und der Erhöhung der Lebensdauer der Lötverbindungen. Da sich die Eigenschaften der Fügepartner stark unterscheiden, ist ein geeignetes Fügeverfahren erforderlich. Die wesentliche Herausforderung besteht in der Vermeidung der Bildung von dicken intermetallischen Schichten in der Reaktionszone, welche die mechanischen Eigenschaften der resultierenden Lötverbindungen verschlechtern. Dementsprechend wird ausgehend vom Stand der Technik ein Konzept zur vollständigen Untersuchung der Mikrostruktur-Eigenschafts-Beziehungen der Mischverbunde erarbeitet und umgesetzt. Die Mischverbunde werden durch Induktionslöten hergestellt, was einen lokalen Wärmeeintrag in die Fügestelle ermöglicht. Dadurch können Lötverbindungen mit dünnen Reaktionszonen erzeugt werden. Das Potenzial der Lötverbindungen wird anhand von Zugscher- und Ermüdungsversuchen aufgezeigt, die mit den Ergebnissen der Mikrostrukturanalyse und der fraktografischen Bewertung korreliert werden.:Abkürzungen und Formelzeichen iii Abkürzungen iii Formelzeichen iv Abbildungsverzeichnis v Tabellenverzeichnis xi 1 Einleitung und Motivation 1 2 Stand der Technik 2 2.1 Anwendungen von Stahl/Aluminium-Mischverbunden 2 2.2 Stoffschlüssiges Fügen von Stahl/Aluminium-Mischverbunden 3 2.2.1 Schweißen von Stahl/Aluminium-Mischverbunden 3 2.2.2 Löten von Stahl/Aluminium-Mischverbunden 8 2.2.2.1 Grundlagen 8 2.2.2.2 Verfahren und Lotwerkstoffe 10 2.3 Besonderheiten bei Stahl/Aluminium-Mischverbunden 15 2.3.1 Intermetallische Fe-Al-Verbindungen in der Reaktionszone 15 2.3.2 Kontrolle der Bildung und des Wachstums der Reaktionszone 20 2.3.3 Problematik bei mechanischer Charakterisierung der Mischverbunde 23 3 Folgerungen und Zielstellung 27 4 Experimentelle Durchführung 29 4.1 Grund- und Lotwerkstoffe 29 4.2 Benetzungs- und Lötversuche 31 4.3 Mikrostrukturelle Charakterisierung 34 4.3.1 Mikrostrukturanalyse 34 4.3.2 Mikrohärtemessung und Nanoindentation 35 4.3.3 Thermische Auslagerung 37 4.4 Mechanische Charakterisierung 39 4.4.1 Zugscher- und Warmzugscherversuche 39 4.4.2 Ermüdungsversuche 40 5 Ergebnisse 43 5.1 Benetzungsverhalten 43 5.2 Mikrostrukturelle Untersuchungen 45 5.2.1 Mikrostruktur der Lötverbindungen und Bildung der Reaktionszone 45 5.2.2 Mechanische Charakteristika der Gefügebestandteile 55 5.3 Festigkeitsuntersuchungen 59 5.3.1 Quasistatische Untersuchungen gelöteter Mischverbunde 59 5.3.2 Ermüdungsverhalten gelöteter Mischverbunde 69 5.4 Korrelation zwischen Reaktionszonendicke und Festigkeit 81 6 Diskussion der Ergebnisse 88 7 Zusammenfassung und Ausblick 92 8 Anlagen 93 8.1 Übersicht der Benetzungsproben auf Stahl X5CrNi18-10 93 8.2 Übersicht der Benetzungsproben auf AlMn1Cu 94 8.3 Beispiel der Ergebnisse der EDX-Analyse 95 8.4 Härteverlauf über die Reaktionszone 96 8.5 EBSD-Analyse der Lötverbindung 97 8.6 Mikrozugversuche 98 8.7 TEM-Untersuchungen der hergestellten Lötverbindungen 99 9 Literaturverzeichnis 102 10 Normenverzeichnis 112 11 Publikationen 113 / This thesis deals with the production of aluminum/stainless steel mixed joints in order to improve the mechanical properties and to extend the lifetime of the joints. Because of the different physical properties of the joining partners, a suitable joining technique is necessary. In comparison to welding, brazing offers significant advantages due to the lower liquidus temperature of the used brazing fillers. The main challenge is to prevent the formation of thick intermetallic layers in the reaction zone. These layers deteriorate the mechanical properties of the resulting joints predominantly. Correspondingly, a concept for the complete investigation of the microstructure-property relationships of the brazed joints is investigated. The joints are produced by induction brazing, which takes place in a short process time and allows a local heat input into the joint. Therefore, joints with a thin intermetallic layer in the reaction zone can be manufactured. The potential of the joints is demonstrated using monotonic tensile shear tests as well as fatigue tests. The achieved results are correlated with the results of the microstructural and fractographic analysis.:Abkürzungen und Formelzeichen iii Abkürzungen iii Formelzeichen iv Abbildungsverzeichnis v Tabellenverzeichnis xi 1 Einleitung und Motivation 1 2 Stand der Technik 2 2.1 Anwendungen von Stahl/Aluminium-Mischverbunden 2 2.2 Stoffschlüssiges Fügen von Stahl/Aluminium-Mischverbunden 3 2.2.1 Schweißen von Stahl/Aluminium-Mischverbunden 3 2.2.2 Löten von Stahl/Aluminium-Mischverbunden 8 2.2.2.1 Grundlagen 8 2.2.2.2 Verfahren und Lotwerkstoffe 10 2.3 Besonderheiten bei Stahl/Aluminium-Mischverbunden 15 2.3.1 Intermetallische Fe-Al-Verbindungen in der Reaktionszone 15 2.3.2 Kontrolle der Bildung und des Wachstums der Reaktionszone 20 2.3.3 Problematik bei mechanischer Charakterisierung der Mischverbunde 23 3 Folgerungen und Zielstellung 27 4 Experimentelle Durchführung 29 4.1 Grund- und Lotwerkstoffe 29 4.2 Benetzungs- und Lötversuche 31 4.3 Mikrostrukturelle Charakterisierung 34 4.3.1 Mikrostrukturanalyse 34 4.3.2 Mikrohärtemessung und Nanoindentation 35 4.3.3 Thermische Auslagerung 37 4.4 Mechanische Charakterisierung 39 4.4.1 Zugscher- und Warmzugscherversuche 39 4.4.2 Ermüdungsversuche 40 5 Ergebnisse 43 5.1 Benetzungsverhalten 43 5.2 Mikrostrukturelle Untersuchungen 45 5.2.1 Mikrostruktur der Lötverbindungen und Bildung der Reaktionszone 45 5.2.2 Mechanische Charakteristika der Gefügebestandteile 55 5.3 Festigkeitsuntersuchungen 59 5.3.1 Quasistatische Untersuchungen gelöteter Mischverbunde 59 5.3.2 Ermüdungsverhalten gelöteter Mischverbunde 69 5.4 Korrelation zwischen Reaktionszonendicke und Festigkeit 81 6 Diskussion der Ergebnisse 88 7 Zusammenfassung und Ausblick 92 8 Anlagen 93 8.1 Übersicht der Benetzungsproben auf Stahl X5CrNi18-10 93 8.2 Übersicht der Benetzungsproben auf AlMn1Cu 94 8.3 Beispiel der Ergebnisse der EDX-Analyse 95 8.4 Härteverlauf über die Reaktionszone 96 8.5 EBSD-Analyse der Lötverbindung 97 8.6 Mikrozugversuche 98 8.7 TEM-Untersuchungen der hergestellten Lötverbindungen 99 9 Literaturverzeichnis 102 10 Normenverzeichnis 112 11 Publikationen 113

<p dir="ltr">In structural metallic components, a material’s lifecycle begins with the processing route, to produce a desired structure, which dictates the in-service performance. The variability of microstructural features as a consequence of the processing route has a direct influence on the properties and performance of a material. In order to correlate the influence processing conditions have on material performance, large test matrices are required which tend to be time consuming and expensive. An alternative route to avoid such large test matrices is to incorporate physics-based process modeling and lifing paradigms to better understand the performance of structural materials. By linking microstructural information to the material’s lifecycle, the processing path can be modified without the need to repeat large-scale testing requirements. Additionally, when a materials system is accurately modeled throughout its lifecycle, the performance predictions can be leveraged to improve the design of materials and components.</p><p dir="ltr">Ni-based superalloys are a material class widely used in many critical aerospace components exposed to coupling thermal and mechanical loads due to their increased resistance to creep, corrosion, oxidation, and strength characteristics at elevated temperatures. Many Ni-based superalloys undergo high-temperature forging to produce a desired microstructure, targeting specific strength and fatigue properties in order to perform under thermo-mechanical loads. When in-service, these alloys tend to fail as a consequence of thermo-mechanical fatigue (TMF) from either inclusion- or matrix- driven failure. In order to produce safer, cheaper and more efficient critical aerospace components, the micromechanical deformation and damage mechanisms throughout a Ni-based superalloy’s lifecycle must be understood. This research utilizes process modeling as a tool to understand the damage and deformation of inclusions in a Ni-200 matrix throughout radial forging as a means to optimize the processing conditions for improved fatigue performance. In addition, microstructural sensitive performance modeling for a Ni-based superalloy is leveraged to understand the influence TMF has on damage mechanisms.</p><p dir="ltr">The radial forging processing route requires both high temperatures and large plastic deformation. During this process, non-metallic inclusions (NMIs) can debond from the metallic matrix and break apart, resulting in a linear array of smaller inclusions, known as stringers. The evolution of NMIs into stringers can result in matrix load shedding, localized plasticity, and stress concentrations near the matrix-NMI interface. Due to these factors, stringers can be detrimental to the fatigue life of the final forged component. By performing a finite element model of the forging process with cohesive zones to simulate material debonding, this research contributes to the understanding of processing induced deformation and damage sequences on the onset of stringer formation for Alumina NMIs in a Ni-200 matrix. Through a parametric study, the interactions of forging temperature, strain rate, strain per pass, and interfacial decohesion on the NMI damage evolution metrics are studied, specifically NMI particle separation, rotation, and cavity formation. The parametric study provides a linkage between the various processing conditions parameters influence on detrimental NMI morphology related to material performance.</p><p dir="ltr">The microstructural characteristics of Ni-based superalloys, as a consequence of a particular processing route, creates a variability in TMF performance. The micromechanical failure mechanisms associated with TMF are dependent on various loading parameters, such as temperature, strain range, and strain-temperature phasing. Insights on the complexities of micromechanical TMF damage are studied via a temperature-dependent, dislocation density-based crystal plasticity finite element (CPFE) model with uncertainty quantification. The capabilities of the model’s temperature dependency are examined via direct instantiation and comparison to a high-energy X-ray diffraction microscopy (HEDM) experiment under coupled thermal and mechanical loads. Unique loading states throughout the experiment are investigated with both CPFE predictions and HEDM results to study early indicators of TMF damage mechanisms at the grain scale. The mesoscale validation of the CPFE model to HEDM experimental data provides capabilities for a well-informed TMF performance paradigm under various strain-temperature phase profiles. </p><p dir="ltr">A material’s TMF performance is highly dependent on the temperature-load phase profile as a consequence of path-dependent thermo-mechanical plasticity. To investigate the relationship between microstructural damage and TMF phasing effects, the aforementioned CPFE model investigates in-phase (IP) TMF, out-of-phase (OP) TMF, and iso-thermal (ISO) loading profiles. A microstructural sensitive performance modeling framework with capabilities to isolate phasing (IP, OP, and ISO) effects is presented to locate fatigue damage in a set of statistically equivalent microstructures (SEMs). Location specific plasticity, and grain interactions are studied under the various phasing profiles providing a connection between microstructural material damage and TMF performance.</p>