Titanium and its alloys are widely used in applications ranging from aeroengines and offshore equipment to biomedical implants and sporting goods, owing to their high ratio of strength to density, excellent corrosion resistance, and biomedical compatibility. Among the titanium alloys used in aerospace, Ti-6Al-4V (an α+β alloy) is the most widely used, in applications in which the temperature may reach 350°C, at which point it retains good fatigue and fracture properties as well as moderate tensile strength and ductility. These alloy properties are dependent on variables such as crystalline structure, alloy chemistry, manufacturing techniques and environmental conditions during service. These variables influence the microstructure and mechanical properties of titanium alloys. With regard to the alloy chemistry and operating environment, the focus of the present work is to understand the influence of boron and hydrogen on the microstructure and selected mechanical properties of cast Ti-6Al-4V. The addition of boron to cast Ti-6Al-4V (0.06 and 0.11 wt% in this work) refines the coarse “as cast” microstructure, which is evaluated quantitatively using FoveaPro image analysis software. Compression testing was performed using a Gleeble 1500 instrument, by applying a 10% strain at different strain rates (0.001, 0.1 and 1 s-1) for temperatures in the range 25-1100°C. The tests were performed to evaluate the effect of boron on the mechanical properties of the alloy. It was observed that there is an increase in the compressive strength, predominantly at room temperature, of cast Ti-6Al-4V after the addition of boron. Metallographic evaluation showed that this increase in strength is a likely result of reductions in both the prior β grain and α colony dimensions, which is caused by boron addition. Studies in a hydrogen environment at 150 bar showed that cast Ti-6Al-4V exhibited lower yield strength and lower ultimate tensile strength in comparison with those properties measured in an air environment. No significant change in the ductility was observed. It was also noted that in a high strain range (≈2%) the low cycle fatigue (LCF) life was significantly reduced in hydrogen compared with air. Microstructural and fractographic characterization techniques were used to establish the role of hydrogen on the deformation mechanism by analysing the crack propagation path through the microstructure. It is seen that cracks tend to propagate along the interface between prior β grain boundaries and/or along the α colony boundaries

The work presented aims to find microstructure and mechanical properties after remelting of aluman-16 alloy by using high pressure die casting (HPDC). Alloy has been casted with specific composition. The alumna-16 alloy has been casted in 2 different composition of different Si content of 0.22% and 0.062%. This work describes a method for creating samples for tensile tests through experimental techniques on standard samples. Microstructural analysis utilizing scheil simulation and fracture analysis have also been undertaken. The results have been compared by using received data to available data. The difference between the two alloys was noted in the microstructure study, where the two Fe-rich intermetallic Al8Fe2Si and Al9Fe2Si2 were not visible in the ThermoCalc software. Elongation percentage was found to decrease with remelting and to increase when Si weight percentage increased. / Not applicable

No description available.

No description available.

No description available.

The goal of this research is to aid the development of large-scale additive manufacturing of jointless underbody hulls for the Army Ground Vehicle Systems by 1) generating an improved mechanical and metallurgical database and 2) understanding the Additive Friction Stir Deposition (AFSD) process. AFSD is a solid-state additive manufacturing process that is a high strain rate and a hot working process that deforms material onto a substrate and builds a component layer by layer. This unique, solid-state additive manufacturing process has the potential for scalability into ground vehicle applications on the extra large-scale due to its solid-state nature. Two different aluminum alloys were investigated: Al-Mg-Si (6061) and Al-Zn-Mg-Cu (7075). AFSD builds were evaluated in the transverse or through layer direction (Z) and the 6061 material was also evaluated in the longitudinal direction (X). Uniaxial tensile testing was performed to generate mechanical property data while fractography, and metallography were used to better understand the metallurgical implications of this process. This research determined that the refinement of the grain size caused by the AFSD process had little or no strengthening effect on the mechanical properties of either alloy. Instead, the as-deposited condition in both alloys were soft with good ductility due to the dissolution of the strengthening particles. After heat treatment, the elongation and fracture mode of the 6061 alloy was dependent on the layer direction. Failure often initiated at interfaces and affected the materials' elastic-plastic behavior. For the 7075 alloy, the strength and failure mechanism of the material were affected by the presence of the graphite lubricant used during processing. The use of graphite increased the variability of the mechanical properties results and caused premature failure in numerous samples. In both alloys, the heat treatment caused grain coarsening to varying degrees which can affect the mechanical behavior. From these results, it was found that a precipitation strengthening heat treatment is required for material deposited with AFSD to achieve the minimum mechanical property standards for a forging. Recommendations and future work include 1) investigating the effect of residual stresses on AFSD components, 2) determining the fatigue properties of AFSD materials, 3) continuing to increase the database of mechanical properties for AFSD materials, and 4) developing additional lubricants for the AFSD process. / Master of Science / The results of this research will be used to help generate design requirements for large-scale additively manufactured parts such as underbody tank hulls. This research generated and expanded on the mechanical and metallurgical understanding of solid-state additively manufactured aluminum. The solid-state additive process used was Additive Friction Stir Deposition. Like its name, this process uses a rotating tool head to apply friction to a solid bar of aluminum that then generates heat which makes the metal soft enough to stir and deposit into a layer. Another layer is then deposited on top and repeated layer by layer until the final part is completed. Other metal additive manufacturing processes that involve melting and then rapidly cooling the material degrade the quality of the metal material. The first part of this research investigated the mechanical properties in different layer directions either pulling along the build direction or against the layers. The results showed that a heat treatment was required to improve the strength of the aluminum to meet current standards of quality. However, the ability of the aluminum to elongate depended on the orientation of the layers. The second part of this research investigated the effect that a graphite lubricant used on the aluminum feedstock to help prevent the material from sticking in the tool head affected the mechanical properties. The results show that the graphite lubricant did not dissolve or disappear into the metal and caused a reduction in the elongation of the aluminum. Recommendations for extra large-scale metal additive manufacturing are to design parts to apply the highest stress along the layer direction and to eliminate the use of the graphite lubricant.

Self-healing is an inherent property of living organisms, which poses a significant challenge for materials science. In recent years, self-repair mechanisms observed in plants have been recognized as promising models for the development of bio-inspired self-healing materials. The potential of biomimetic approaches to develop self-healing materials has been widely studied in the literature. In the field of composite materials, the concept of self-healing composites refers to the design of materials capable of autonomously restoring lost mechanical properties. The advantages of self-healing composites are numerous, including reduced maintenance and repair costs, and improved service life, leading to enhanced sustainability. Two types of self-healing composites have been extensively studied: extrinsic and intrinsic. This PhD Thesis focuses on investigating the intrinsic self-healing mechanism within polymer composites, which involves the ability of polymer matrices to heal micro-damage, such as cracks, under external stimuli. This Thesis aims to develop a thermoplastic matrix possessing self-healing properties using polyamide 6 (PA6), which is the most commonly utilized thermoplastic polymer in the production of thermoplastic composites. As there is a lack of systematic investigation on this particular research topic in the scientific literature, various combinations of PA6 and thermoplastic healing agents, along with different types of compatibilizers, were employed. The optimized matrix has been used for the manufacture of both short and long-carbon fiber composites. This PhD Thesis not only focuses on the production of thermoplastic self-healing composites but also investigates thermosetting intrinsic self-healing composites. Two distinct systems are examined, and in both cases, thermoplastic healing agents has been applied by depositing them on top of the fiber fabrics. A crucial aspect of this PhD Thesis is the fractography analysis, which enables an understanding of the reasons behind the failure of several healing mechanisms and the factors contributing to the success of other healing mechanisms. The PhD Thesis is divided into eight Chapters. Chapter I highlights the aim of this work together with the outline of the Thesis. Chapter II provides a brief introduction and the theoretical background of self-healing composites. Chapter III details all the experimental techniques utilized for the characterization of the polymer blends and for the characterization of the prepared composites. All the obtained results are thoroughly reported in Chapters IV-VIII. Chapter IV presents the results of PA6 with the combination of two different healing agents, i.e., Polycaprolactone (PCL) and Cyclic olefinic copolymer (COC) and it is subdivided into four different parts. The first investigated system was PA6/PCL and the latter was melt compounded with PA6 in different amounts. PCL caused a decrease in the mechanical properties of PA6, due to its immiscibility and low mechanical properties. Nevertheless, acceptable fracture toughness values in quasi-static mode were obtained. Samples were thermally mended at 80 and 100 °C, and the healing efficiency (HE) was assessed by comparing the fracture toughness of virgin and repaired samples both in quasi-static and in impact mode. The blend with a PCL content of 30 wt% showed limited HE values (up to 6%) in quasi-static mode, while interesting HE values (53%) were detected under impact conditions. This discrepancy was explained through microstructural analysis and correlated to a different fracture morphology. In fact, under quasi-static mode, the PA6 matrix was severely plasticized, while under impact a brittle fracture surface was obtained favoring thus the flow of PCL during the thermal healing process. The second investigated system was PA6/COC and the latter was melt compounded with PA6 in different amounts. From scanning electron microscope micrographs, it was possible to highlight the immiscibility and the lack of interfacial adhesion between the constituents. The HE of the system was evaluated by comparing the fracture toughness of the produced blends, both in quasi-static and impact mode, before and after the healing process performed at 140°C by applying a pressure of 0.5 MPa. Through the addition of 30 wt% of COC, the fracture toughness of the virgin samples slightly decreased, passing from 2.3 MPa·m1/2 of neat PA6 to 2.1 MPa·m1/2. However, the presence of the 30 wt% of COC homogeneously distributed within the PA6 matrix led to a HE of 11% in quasi-static mode and 35% in impact mode. From the analysis of these preliminary systems, it was decided that the best matrix/healing agent combination with the highest potential was the one reported by PA6/COC system. At this aim, since the lack of interfacial adhesion between the two different constituents severely decreased the healing performances of the system, different types of compatibilizers were selected in order to enhance the interphase between PA6 and COC. Three different types of compatibilizers were selected, i.e., poly(ethylene)-graft-maleic anhydride (PE-g-MAH), polyolefin elastomer-graft-maleic anhydride (POE-g-MAH), and ethylene glycidyl methacrylate (E-GMA), and thoroughly investigated in the third subchapter. The dynamic rheological analysis revealed that E-GMA played a crucial role in reducing interfacial tension and promoting PA6 chain entanglement with COC domains. Mechanical tests showed that PE-g-MAH and POE-g-MAH compatibilizers enhanced elongation at break, while E-GMA had a milder effect. A thermal healing process at 140 °C for 1 h was carried out on specimens broken in fracture toughness tests, performed under quasi-static and impact conditions, and HE was evaluated as the ratio of critical stress intensity factors of healed and virgin samples. All the compatibilizers increased HE, especially E-GMA, achieving 29% and 68% in quasi-static and impact conditions, respectively. SEM images of specimens tested in quasi-static conditions showed that all the compatibilizers induced PA6 plasticization and crack corrugation, thus hindering COC flow in the crack zone. Conversely, under impact conditions, E-GMA led to the formation of brittle fractures with planar surfaces, promoting COC flow and thus higher HE values. This study demonstrated that compatibilizers, loading mode, and fracture surface morphologies strongly influenced self-healing performance. From this study, it was evident that the best compatibilizer, in terms of HE performance, was E-GMA. For these reasons, it was decided to perform a fine-tuning of both the E-GMA content in the PA6/COC matrix and also a tuning of the temperature of the healing process. The experimental results of this investigation are reported in the fourth subchapter. From the capillary rheometer analysis, it was possible to assess that the addition of E-GMA improved both the melt strength (MS) and the breaking stretching ratio (BSR). The enhancement of these parameters reflected better processability and an improved capability of forming film by the optimized blend. From the performed fracture toughness tests, both in quasi-static mode and impact mode, it was possible to obtain, utilizing analysis of variance (ANOVA) statistics, the optimum E-GMA content, and healing temperature. The HE values in quasi-static mode at a healing temperature of 160 °C passed from 12 % for the non-compatibilized blend up to 38 % for the blend containing 5 wt% E-GMA. Passing to the performance in impact mode, the HE values at a healing temperature of 160 °C pass from 57 % for the non-compatibilized blend up to 82 % for the blend containing 5 wt% E-GMA. The differences in these two HE values for quasi-static conditions and impact mode were investigated through field emission scanning electron microscopy and it was noticed that the specimens tested in quasi-static mode showed severe plasticized fractured surfaces. On the other hand, the specimens tested in impact mode reported brittle fractured surfaces. The differences between the severely plasticized surfaces and the brittle surfaces explained the difference between the HE values of the two different tests. Severely plasticized surfaces hindered the flow of the healing agent during the thermal mending process, while the brittle surfaces allowed a better distribution of the healing agent during the thermal mending process. In conclusion, from the performed analysis, it was possible to obtain an optimized thermoplastic self-healing matrix to be used in structural composite applications. Chapter V presents the results of both short and long-carbon fiber composites produced by using the optimized self-healing thermoplastic blend detected in Chapter IV. The first investigated system was composed of short carbon fiber composite with self-healing properties. All the prepared compositions were produced in collaboration with the University of Pisa by means of a semi-industrial extruder, followed by an injection molding machine. Thanks to the remarkably high quality of the prepared specimens, the thermal mending capability was assessed through Charpy impact testing and plane-strain fracture toughness tests. The HE values of the self-healing composites were remarkable, and the system was successfully proven with HE values of approximately 10 % in quasi-static mode and approximately 50 % in Charpy impact tests. From the fractography analysis, it was possible to assess that the healing agent was capable of flowing in the crack plane but since, in both tests, a catastrophic rupture took place, the fiber integrity was thus lost. Thus, it was decided to perform fatigue testing and implement a statistical method found in the literature. In particular, a damage criterion was adopted to predict the fatigue life of these materials. Through the presented statistical approach, the Wöhler curves for both reinforced systems, i.e., the neat containing only PA6 and short carbon fibers and the self-healing short carbon fiber composites, were produced. Through the damaging/healing process, it was possible to highlight that the mending process was able to improve the fatigue life of the self-healing composites by approximately 77 %. The obtained results highlighted the potential of the self-healing composites in prolonging the fatigue life and therefore enhancing the working life of structural components. From the presented results it was highlighted that the prepared self-healing thermoplastic blend was capable of effectively repairing micro-damages and not catastrophic damages. The second investigated system was composed of long carbon fiber composites with self-healing properties prepared starting from the thermoplastic blend developed in Chapter IV. Long carbon fiber composites are prepared through film stacking and hot pressing process, the thermoplastic thin films were produced in collaboration with Professor Pietro Russo from the University of Naples by using an extruder equipped with a calender. A thorough analysis of the thermal and mechanical properties of these laminates highlighted the repair capabilities of PA6 and self-healing blend long carbon fiber laminates. The optical microscope revealed matrix-rich and fiber-rich regions, which could potentially undermine the mechanical integrity of the laminates due to incomplete impregnation of the carbon fiber by the matrices. However, pycnometer analysis confirmed that the void percentage within the composites remained acceptable for structural applications. The evaluation of the interlaminar shear strength (ILSS) through short beam shear (SBS) tests highlighted that there was no difference between the two different laminates. Through the thermal mending process, it was possible to demonstrate that the neat laminates were not able, as expected, to recover their mechanical properties. On the other hand, the self-healing laminates were capable of restoring the mechanical properties with a healing efficiency value of 104 %. From the analysis of the fracture surfaces, before and after the thermal mending process, it was possible to understand the reason behind the high value of healing efficiency. SBS tests induced mainly micro damages in the matrix and delamination. The damages were totally recovered upon the thermal mending process since there were no cracks or evident delamination on the observed specimens. In conclusion, this Chapter substantiated the efficacy of the developed thermoplastic self-healing blend in producing intrinsic self-healing composites. The self-healing laminates, with their superior tensile properties and robust self-healing performance, highlighted their potential for advanced applications in structural components with enhanced working life. Chapter VI reports the two different studies conducted on intrinsic self-healing thermosetting composites. The first investigated system was focused on the self-healing behavior of carbon fiber (CF) reinforced composites by depositing jet-spun COC meshes on dry carbon fiber plies before lamination with epoxy resin (EP). Three different laminates were prepared, including neat EP/CF and two composites with 4 wt.% and 8 wt.% in the form of a jet-spun COC network. The introduction of COC mesh reduced flexural stress by 26% and interlaminar shear strength by 50%. Mode I interlaminar fracture toughness was evaluated and specimens were mended at 110 °C by resistive heating generated by an electrical current flowing within the samples. The laminates containing 8 wt% COC reported a healing efficiency, evaluated as the ratio between the GIC and the maximum load of virgin and healed samples, of 9.4% and 33.7%, respectively. Fractography analysis highlighted the poor adhesion between the COC mesh and EP matrix, and several COC microfibers were trapped inside the epoxy matrix, hindering their diffusion inside the crack zone, which limited the healing capability of the prepared laminates. The second investigated system was based on the intrinsic-extrinsic self-healing laminates in which different healing agents were directly 3D printed on top of the fiber fabrics. Different amounts of thermoplastic healing agents were deposited through a specifically designed 3D printed process on top of fiber fabrics and with different percentages of covered area. Through vacuum assisted resin transfer molding (VARTM) process it was possible to produce, two reference laminates containing only carbon fibers and glass fibers, and laminates containing polyamide 11 (PA11), thermoplastic polyurethane (TPU) and PA11 with carbon nanotubes (PA11CNT). All the samples were labeled according to the following code “XX_YY_ZZ”, where “XX” stands for the selected reinforcements (CF or GF), “YY” stands for the thermoplastic polymer utilized, and “ZZ” stands for the percentage of the covered area by the thermoplastic polymers. A complete characterization of the thermal and mechanical properties was performed to assess the effect of the thermoplastic insertion on the physical properties of the composites. From the measurement of mode I fracture toughness, it was possible to assess the extremely positive effect of the healing agent on the GIC values. CF_PA11 laminates were demonstrated to be the best systems thanks to the toughening effect generated in the thermoplastic enriched plane. The fracture toughness was 674% higher with respect to the neat reference laminates in the case of the CF_PA11_36 system (GIC = 1641 J/m2). This exceptional result was attributable to the enhanced adhesion of the deposited thermoplastic pattern within the midplane laminae, while the large data scattering is related to the concomitant delamination processes induced in the adjacent planes. The same trend was recorded also for the CF_PA11_24 and the CF_PA11_12 laminates with a fracture toughness increase of 516 % and 359 %, respectively. On the other hand, for the TPU and PA11+CNTs laminates, the fracture toughness was marginally affected due to the possible degradation of TPU and the lack of interfacial adhesion of the PA11+CNTs thermoplastic healing agent with the GF. The specimens used for the determination of the mode I fracture toughness were healed at a temperature of 210 °C allowing the flow of the introduced healing agent in the crack plane thus restoring the loss of mechanical properties. The healing efficiency was successfully determined by calculating the variation of the fracture toughness upon the thermally activated healing cycles. In the considered analysis, the best systems were proved to be the CF_PA11_36 and the GF_PA11_CNTs laminates with a healing efficiency of 74%. Nevertheless, the best system was the one presenting the PA11 thermoplastic healing agent due to the much higher virgin fracture toughness value. Since the best system was the one composed of CF_PA11 laminates, several healing cycles were performed in order to assess the healing efficiency also for subsequent damage/healing processes. By evaluating the healing efficiency through the fracture toughness, it was possible to assess recovery of almost 50% after the three subsequent healing cycles for the CF_PA11_36 system. In conclusion, the results reported in this Chapter demonstrated that CF/epoxy laminates enriched with the 36% covered area pattern of PA11_20C were the best system in terms of both healing efficiency and fracture toughness. Chapter VII reported the final conclusion of the PhD Thesis and the general evaluation of the performances of the produced systems. Chapter VIII reported a summary of all the side activities performed during the PhD program.

[pt] A utilização de materiais de construção civil a base de cimento reforçado com fibras vem aumentando rapidamente nos últimos anos. No Brasil um vasto programa experimental para avaliar o comportamento mecânico desses materiais através de ensaios de flexão monotônicos e de compressão, vem sendo desenvolvidos na PUC/RIO desde 1979. Este trabalho procura dar continuidade a essa linha de pesquisa, sendo o primeiro a estudar o comportamento em fadiga de compósitos cimentícios reforçados com polpa de bambu, através de curvas de vida-fadiga S-N e da cinética de crescimento de trincas. As curvas S-N foram levantadas para compósitos entalhados e não entalhados, contendo 6% em massa de polpa em relação a massa de cimento. Essas curvas foram modeladas, com base nas propriedades mecânicas básicas levantadas nos ensaios de compressão e flexão. Com o objetivo de verificar a aplicabilidade da lei de Paris à cinética de crescimento de trincas de fadiga nesses compósitos, foi levantada a relação entre o comprimento da trinca a e o número de ciclos N durante a propagação estável da mesma, adotando-se teores de reforço de 6 e 14% em relação a massa de cimento. Finalmente as superfícies de fratura foram avaliadas por meio de microscópio eletrônico de varredura. / [en] The use of fiber reinforced cementious composites as construction materials in civil engineering has rapidly grown in the last few years. In Brasil, a large experimental program for evaluating the mechanical behavior of these materials has been developed in PUC-RIO since 1979. The present study has the purpose of evaluating the fatigue behavior of cementitious composites by means of determining the S-N curves for notched and unnotched specimens. The fatigue curves were modeled using basic mechanical properties determined by means of compression and slow bend tests. With the purpose of verifying the applicability of Paris law to the fatigue crack growth kinetics, the crack length was determined as a function of the number of cycles N during stable crack propagation, for composites containing 6% and 14% weight percentage of bamboo pulp relative to the weight of cement. Finally, the fracture surface was analyzed by means of scanning electron microscopy.

Compósitos de matriz metálica (CMM) reforçados com dois tipos de particulado cerâmico foram produzidos por meio do processo ARB (Accumulative Roll Bonding) a fim de estudar os efeitos destes no que diz respeito às propriedades mecânicas e microestruturais. ARB é um processo de deformação plástica severa aplicada originalmente a uma pilha de lâminas metálicas, a qual é laminada, seccionada em duas metades, as quais são empilhadas e novamente laminadas, e assim por diante, desenvolvido com o propósito de reduzir o tamanho de grão e aumentar a resistência mecânica do produto final. O processo é econômico e capaz de produzir de folhas ultrafinas a placas espessas, sem que haja restrição de quantidade. Confeccionou-se CMM de alumínio reforçados com partículas de carbeto de silício (Al+SiCp) e alumina (e Al+Al2O3p) com granulometria média de 40µm, as quais foram caracterizadas microestruturalmente e ensaiadas em tração até a falha, cuja análise foi conduzida via microscopia eletrônica de varredura. Ambas as amostras obtiveram ganho em sua resistência mecânica, comparadas ao alumínio monolítico (sem adição de partículas de reforço) e alumínio recozido. Foram ensaiados em tração corpos de prova com e sem presença de entalhe, sendo que as peças entalhadas apresentaram comportamento esperado de aumento de resistência mecânica e baixo alongamento e fratura de aspecto frágil. De acordo com análise feita por fratografia houve boa ancoragem e dispersão das partículas de reforço na matriz. / Metal matrix composite (CMM) reinforced with two types of ceramic particles have been produced through the process ARB (Accumulative Roll Bonding) in order to study their effect as regards the mechanical and microstructural properties. ARB is a severe plastic deformation process originally applied to a stack of metal sheets, which is laminated, sectioned into two halves, which are stacked and rolled again, and so on, developed with the purpose of reducing the grain size and increase the mechanical strength of the final product. The process is economical and capable of producing ultrafine sheets to thicker plates without much restriction. Were fabricated CMM of the aluminum reinforced with particles of silicon carbide (Al + SiCp) and alumina (and Al + Al2O3p) with an average particle size of 40μm, which are characterized microstructurally and tested in tension until failure, whose analysis was conducted via scanning electron microscopy. Both samples were successful in its mechanical strength compared to the monolithic aluminum (without addition of reinforcing particles) and annealed aluminum. They were tested for tensile specimens with and without the presence of notch, and the carved pieces showed strength-enhancing behavior and low elongation and frail fracture. According to analysis by fractography was good anchoring and reinforcement particles dispersed in the matrix.

Turbine engine blades are subjected to extreme conditions characterized by significant and simultaneous excursions in both stress and temperature. These conditions promote thermo-mechanical fatigue (TMF) crack growth which can significantly reduce component design life beyond that which would be predicted from isothermal/constant load amplitude results. A thorough understanding of the thermo-mechanical fatigue crack behavior in single crystal superalloys is crucial to accurately evaluate component life to ensure reliable operations without blade fracture through the use of "retirement for cause" (RFC). This research was conducted on PWA1484, a single crystal superalloy used by Pratt & Whitney for turbine blades. Initially, an isothermal constant amplitude fatigue crack growth rate database was developed, filling a void that currently exists in published literature. Through additional experimental testing, fractography, and modeling, the effects of temperature interactions, load interactions, oxidation and secondary crystallographic orientation on the fatigue crack growth rate and the underlying mechanisms responsible were determined. As is typical in published literature, an R Ratio of 0.7 displays faster crack growth when compared to R = 0.1. The effect of temperature on crack growth rate becomes more pronounced as the crack driving force increases. In addition secondary orientation and R Ratio effects on crack growth rate were shown to increase with increasing temperature. Temperature interaction testing between 649°C and 982°C showed that for both R = 0.1 and 0.7, retardation is present at larger alternating cycle blocks and acceleration is present at smaller alternating cycle blocks. This transition from acceleration to retardation occurs between 10 and 20 alternating cycles for R = 0.1 and around 20 alternating cycles for R = 0.7. Load interaction testing showed that when the crack driving force is near KIC the overload size greatly influences whether acceleration or retardation will occur at 982°C. Semi-realistic spectrum testing demonstrated the extreme sensitivity that relative loading levels play on fatigue crack growth life while also calling into question the importance of dwell times. A crack trajectory modeling approach using blade primary and secondary orientations was used to determine whether crack propagation will occur on crystallographic planes or normal to the applied load. Crack plane determination using a scanning electron microscope enabled verification of the crack trajectory modeling approach. The isothermal constant amplitude fatigue crack growth results fills a much needed void in currently available data. While the temperature and load interaction fatigue crack growth results reveal the acceleration and retardation that is present in cracks growing in single crystal turbine blade materials under TMF conditions. This research also provides a deeper understanding of the failure and deformation mechanisms responsible for crack growth during thermo-mechanical fatigue. The crack path trajectory modeling will help enable "Retirement for Cause" to be used for critical turbine engine components, a drastic improvement over the standard "safe-life" calculations while also reducing the risk of catastrophic failure due to "chunk liberation" as a function of time. Leveraging off this work there exists the possibility of developing a "local approach" to define a crack growth forcing function in single crystal superalloys.