Presence Of Grain Boundaries Research Articles

Influence of M <sub>23</sub>C <sub>6</sub> Carbides on the Heterogeneous Strain Development in Annealed 420 Stainless Steel

Understanding the local strain enhancement resulting from different microstructure features in metal alloys is crucial in many engineering processes as it plays an important role in the work hardening and in other processes such as recrystallization and damage. Isolating the contribution of precipitates to the development of heterogeneous strain can be challenging due to the presence of grain boundaries or other microstructure features that might cause ambiguous interpretation. In this work a statistical analysis of local strains measured by electron back scatter diffraction and crystal plasticity based simulations are combined to determine the effect of M23 C6 carbides on the deformation of an annealed AISI 420 steel. Results suggest that carbides provide a more effective hardening at low plastic strain by a predominant long-range interaction mechanism than that of a pure ferritic microstructure. Carbides influence local strain by elastic incompatibilities with the ferritic matrix and also the spatial interactions between ferrite grains. The development of strain observed near ferrite grain boundaries is enhanced by the presence of carbides. However, this effect is mitigated at regions with high density of carbides and ferrite grain boundaries. Generation of artificial microstructures with controlled distribution of precipitates emerges as a powerful tool for the understanding of heterogeneous strains development.

Thermoelectric properties of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite

Nanoparticles of Zn0.85Al0.15Te and Pb0.98Na0.02Te were used as the starting materials to prepare p-type Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite. The resulting powder was densified, sintered at 380 °C for 24 h in an evacuated and encapsulated ampoule and its thermoelectric transport property was characterized between 300 K and 600 K. At 300 K, the electrical resistivity of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite is 4.2 mΩ-cm; exhibits nonmetal-like behavior from 300 K to 375 K and degenerate behavior beyond 375 K. The temperature dependence of the electrical conductivity shows deviation from the normal power law (1/Tδ, δ ≈ 1.84–2.27 for lead chalcogenides), suggesting a sharp drop in mobility in 425 K–600 K which is ascribed to defects, grain boundaries, and potential energy fluctuation due to atomic disorders. The maximum thermopower of Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te is 400 μVK-1 at 600 K. Assuming acoustic phonon scattering is the dominant mechanism, we calculate the reduced Fermi energy and Lorenz numbers and compare them with other materials. As-calculated Lorenz numbers is used to estimate the lattice thermal conductivity, which is 11% lower than the total thermal conductivity at 300 K. The lattice thermal conductivity varies as κL ~ T-0.46 proving the presence of grain boundary scattering, dislocations, and alloy scattering. The maximum power factor (P.F.) of 17.7 μWcm-1K-2 is observed at 400 K. Finally, the Pb0.833Na0.017(Zn0.85Al0.15)0.15Te-Te composite exhibits a dimensionless figure-of-merit (zT) of 1.08 at 600 K, demonstrating the material from the current study can compete with many high performing PbTe-based materials.

Cyclic martensitic transformations and damage evolution in shape memory zirconia: Single crystals vs polycrystals

AbstractIn zirconia‐based shape memory ceramics (SMCs), cracking during the martensitic transformation can be avoided in structures that reduce the relative presence of grain boundaries where high levels of transformation mismatch stress develop. This approach has been well established in single crystals, but only for sample sizes below about 5 microns. In this paper, we extend the strategy of eliminating grain boundaries to bulk specimen scales by fabricating mm‐scale single crystal SMCs via cold crucible induction melting. For 1.5 and 2.0 mol% Y2O3‐ZrO2, we study the cyclic martensitic transformation of both single crystal and polycrystal structures. Whereas single crystals have very repeatable transformation behavior in terms of hysteresis and strain amplitude, polycrystals degrade dramatically as they accumulate cracking damage with repeated cycling. As the polycrystal evolves from a pellet to granular packing of loose single crystals/grains, the energy dissipation converges with that of the single‐crystal structure, and the energy spent on cracking throughout that process is captured by calorimetry analysis. These results verify that grain boundaries play a key role in damage evolution during martensitic transformation and that microstructural control can extend the size‐scale of viable single crystal or oligocrystal SMCs from the micro‐ to the millimeter scale.

Room temperature synthesis of perovskite (MAPbI3) single crystal by anti-solvent assisted inverse temperature crystallization method

Hybrid organic-inorganic lead halide perovskites have shown excellent photovoltaic performance due to their remarkable unique optoelectronic properties in their polycrystalline thin film; however their performance is limited due to the presence of grain boundaries. It is noted that perovskite single crystals have larger domains and hence significantly low trap density with higher diffusion length. In the present manuscript, we report the anti-solvent modified inverse-temperature-crystallization (ITC) approach to synthesis perovskite (MAPbI3) single crystals (1 cm in size) of superior opto-electronic quality at room temperature (30 °C/RT). To accomplish this first we have developed an understanding on the role of various growth parameters such as temperatures and precursor compositions (amount of anti-solvent and solution molarity) during crystal growth via ITC process in attaining the suitable condition for crystal. Careful control over the amount of anti-solvent and solution molarity helps in realizing the crystal growth even at very high temperatures (140 °C) as well as at room temperature. Specifically, the quality of RT crystals was compared with control (60 °C) crystals and high temperature (140 °C/HT) crystals using XRD, vis-NIR absorbance, photoluminescence (PL) and scanning electron microscope (SEM) analysis. The RT single crystals are compared with the control and HT single crystal.

Crystalline versus Amorphous Donor-Acceptor Blends: Influence of Layer Morphology on the Charge-Transfer Density of States

Organic small molecule solar cells are used as a test bed to investigate the influence of film morphology on the density of charge-transfer (CT) states. CT states are considered as precursors for charge generation and their energy as the upper limit for the open-circuit voltage in organic donor-acceptor solar cells. In this study the influence of morphology for two perylene donors [crystalline diindenoperylene (DIP) versus amorphous tetraphenyldibenzoperiflanthene (DBP)] with almost identical ionization energy is investigated. As acceptor material, the fullerene ${\mathrm{C}}_{60}$ is used. By combining device measurements with optical and low-energy ultraviolet photoelectron spectroscopy, a comprehensive picture is obtained that describes how morphology and the connected density of states (DOS) affect device performance and the spectroscopic signature of CT states. Especially for the crystalline donor material DIP, strong exponential tail states reaching far into the gap are observed, which can be related to the presence of grain boundaries. A voltage-dependent filling of these states is identified as the origin of a blue shift of electroluminescence spectra with increasing applied voltage. Different approaches are compared to study the influence of static and dynamic disorder in the description of CT emission and absorption spectra of organic solar cells. Despite the fact that both donors yield almost identical CT energy (and, thus, the same open-circuit voltage) the Stokes shift between photocurrent and electroluminescence spectra and, concomitantly, the width of the CT DOS varies by more than a factor of 2. We discuss this observation in terms of the donor-acceptor reorganization energy as well as an additional line broadening by static disorder. Remarkably, the more crystalline donor DIP shows a significant deviation from a Marcus-type description, while this is not the case for the amorphous DBP. This highlights the importance of film morphology in organic solar cells.

Efficient CH3NH3PbI3-x(SeCN)x perovskite solar cells with improved crystallization and defect passivation

The presence of grain boundaries and defects in perovskite films can be detrimental to performance of perovskite solar cells (PSCs), such as leading to nonradiative recombination and environmental instability. Additive engineering is a key tactic to control crystal growth and passivate defects of perovskite film. In this work, lead-free alkali metal additive of potassium selenocyanate (KSeCN) was firstly added in precursor solution to prepare a novel perovskite of CH3NH3PbI3-x(SeCN)x. The SeCN− is substitute for I− to enhance structure stability, simultaneously facilitate nucleation, meanwhile, effectively increase crystalline grain size and passivate the defects. Finally, the power conversion efficiency of planar perovskite solar cells boosts from 14.34% to 18.41%, and the hysteresis reduces from 21% to 1.5%, nearly negligible. Our findings provide an avenue for crystalline regulation and defects passivation to further improve the performance of perovskite solar cells and propose a promising CH3NH3PbI3-x(SeCN)x-based perovskite.

On interface conditions on a material singular surface

The presence of grain boundaries significantly influences the overall mechanical behavior of materials with an underlying crystalline microstructure. They act as an obstacle against the movement of dislocations and, thus, significantly contribute to size effects as for example the Hall–Petch effect. Hence, the thermodynamically consistent modeling of the behavior of the plastic slip at a grain boundary is of utmost interest. To this end, balance equations at a grain boundary are derived from an extended energy balance by means of invariance considerations. The grain boundary is considered as a material singular surface with own internal and kinetic energy as well as energy supply. Consequently, the balances at the grain boundary depend on its mean curvature. The framework presented is applied to a small strain slip gradient crystal plasticity theory, regarding single slip. Accounting for the derived balance equations, thermodynamically consistent flow rules for the plastic slip at the grain boundary are obtained by exploitation of the Coleman–Noll procedure. In this context, a classification of flow rules for the plastic slip at the grain boundary is provided. Finally, the distribution of the plastic slip is presented regarding a three-phase laminate material with two elastoplastic phases and one elastic phase. The two elastoplastic phases represent the grains of a bicrystal. A grain boundary effect is discussed which is based on a variation of the internal length scale in one of the two elastoplastic phases.

Controlled Fragmentation of Single-Atom-Thick Polycrystalline Graphene

Summary Controlling the fragmentation of atomically thin and brittle materials is of critical importance for both fundamental interest and technical purposes in fracture mechanics. However, the fragmentation of graphene is often random and uncontrollable because of the presence of grain boundaries and numerous defects. Here, by harnessing the strong localized strain during the necking process of thermoplastic polymers, we introduce a simple yet controllable method to tear apart a monolayer polycrystalline graphene (MPG) sheet into ordered graphene ribbons. More importantly, we show that the presence of active edges helps the graphene ribbons in exhibiting a field-effect characteristic pH response and improves the introduction of dopants. Furthermore, we demonstrate an optically transparent (∼98%), ultrathin (∼70 ± 15 nm), and skin-conformal pressure sensor for real-time tactile sensing. We believe that our results lead to further understanding of the fracture mechanics of graphene and offer unique advantages for practical applications, such as flexible electronics, chemical sensing, and biosensing.

Multilayer Metal‐Oxide Memristive Device with Stabilized Resistive Switching

AbstractVariability of resistive switching is a key problem for application of memristive devices in emerging information‐computing systems. Achieving a stable switching between the nonlinear resistive states is an important task on the way to implementation of large memristive cross‐bar arrays and solving the related sneak‐path‐current problem. A promising approach is the fabrication of memristive structures with appropriate interfaces by combining the materials of electrodes with certain oxygen affinity and different dielectric layers. In the present work, such approach allows the demonstration of stabilized resistive switching in a multilayer device structure based on ZrO2(Y) and Ta2O5 films. It is established for the large‐area devices that the switching is stabilized after several hundreds of cycles. A possible scenario of the stabilization is proposed taking into account experimental data on the presence of grain boundaries in ZrO2(Y) as the preferred sites for nucleation of filaments, self‐organization of Ta nanocrystals as the electric field concentrators in Ta2O5 film, as well as oxygen exchange between oxide layers and interface with bottom TiN electrode. The robust resistive switching between nonlinear states is implemented in microscale cross‐point devices without numerous cycling before stabilization promising for the fabrication of programmable memristive weights in passively integrated cross‐bar arrays.

Unveiling Defect-Mediated Charge-Carrier Recombination at the Nanometer Scale in Polycrystalline Solar Cells.

Solar cells made of polycrystalline thin-films can outperform their single-crystalline counterparts despite the presence of grain boundaries (GBs). To unveil the influence of GBs, high spatial resolution characterization techniques are needed to measure local properties in their vicinity. However, results obtained using single technique may provide limited aspects about the GB effect. Here, we employ two techniques, near-field scanning photocurrent microscopy (NSPM) and scanning transmission electron microscope based cathodoluminescence spectroscopy (STEM-CL), to characterize CdTe solar cells at the nanoscale. The signal contrast from the grain interiors (GIs) to the GBs, for high-efficiency cells where CdTe is deposited at a high substrate temperature (500 °C) and treated by CdCl2, is found reverse from one technique to another. NSPM reveals increased photocurrents at the GBs, while STEM-CL shows reduced CL intensity and energy redshifts of the spectral peak at the GBs. The results are attributed to the increased nonradiative recombination and the band bending mediated by the surface defects and the shallow-level defects at GBs, respectively. We discuss the advantages of sample geometry for room-temperature STEM-CL and present numerical simulations as well as analytical models to extract the ratio of GB recombination velocity to minority carrier diffusivity that can be used for evaluating the GB effect in other polycrystalline solar cells.

Massive Vacancy Concentration Yields Strong Room-Temperature Ferromagnetism in Two-Dimensional ZnO.

Two-dimensional (2D) ZnO nanosheets with highly concentrated Zn vacancies (VZn) of up to approximately 33% were synthesized by ionic layer epitaxy at the water-toluene interface. This high cation vacancy concentration is unprecedented for ZnO and may provide unique opportunities to realize exotic properties not attainable in the conventional bulk form. After annealing, the nanosheets showed characteristic magnetic hysteresis with saturation magnetization of 57.2 emu/g at 5 K and 50.9 emu/g at room temperature. This value is 1 order of magnitude higher than other ZnO nanostructures and comparable to the conventional ferrimagnetic Fe3O4. Density functional theory calculations, with the support of experimental results, suggest that a high concentration of VZn (approximately one-third of the Zn sites) can form spontaneously during synthesis when stabilized by H ions, and the formation of VZn could be further facilitated by the presence of grain boundaries. It is essential to remove the H for the nanosheets to show ferromagnetism. The mechanisms identified for the origin of the high magnetism in ZnO nanosheets presents an intriguing example of a kinetically stabilized, non-equilibrium, highly defective 2D nanomaterial with a significantly enhanced physical property.

FeMnNiAl Iron-Based Shape Memory Alloy: Promises and Challenges

Among all shape memory alloys, the iron-based FeMnNiAl has emerged as one of the most promising compositions with a huge superelasticity temperature window (> 400 °C). In this article, we first point to the high local transformation strains (> 10%) and high transformation stress levels (500–700 MPa) that result in a large work output. When subjected to either tensile or compressive loading, the transformation stress exhibits very small temperature dependence (Clausius–Clapeyron slope less than 0.2 MPa/°C in compression and 0.5 MPa/°C in tension) and an extremely small adiabatic temperature rise (less than 1 °C) during transformation. The complexity in transformation behavior associated with the presence of grain boundaries (GBs) is discussed. In particular, the work provides insight in the localization occurring at GBs due to transformation front–GB interactions and the potential cracking that can degrade fatigue performance. Overall, this work provides a deeper insight into the deformation response, advantages, and drawbacks of FeMnNiAl SMA. The comprehensive handling of various aspects of this alloy system paves the way for the development of future iron-based shape memory alloys.

Parallel point defect identification in molecular dynamics simulations without post-processing: A compute and dump style for LAMMPS

Two classes for the molecular dynamics program LAMMPS – one compute style and one dump style – are presented that are designed to identify, count, and output point defects in cascade damage and related molecular dynamics simulations. The calculations are done in parallel across multiple MPI processes, and can be done at the same time as the original simulation. This drastically reduces storage requirements by eliminating the need to post-process every atom in the system. Non-cubic lattices, free surfaces, and large voids can be eliminated from the output by suitable choices of the reference lattice. The classes are derived from LAMMPS’s Dump and Compute classes, and pose no additional overhead to LAMMPS if they are not used. PROGRAM SUMMARYProgram Title: Compute style “frenkel” and dump style “frenkel”Program Files doi:http://dx.doi.org/10.17632/p39kb4fshj.1Licensing provisions: GPLv2Programming language: C++Nature of problem: Identify and count point defects (interstitials and vacancies) in metals created by high-energy cascade damage, in parallel, without post-processing, relative to an arbitrary defect-free crystal lattice.Solution method: Defects are identified and counted in parallel, across an arbitrary number of processors, through LAMMPS’s domain decomposition techniques [1]. Defects are counted according to the occupancy of the Wigner–Seitz cell of each lattice site, but can be visualized by either Wigner–Seitz cell occupancy or by Lindemann sphere analysis. Results are then shared across all processes by message-passing.Restrictions: This implementation is likely restricted to orthorhombic domains. It is also inadvisable to use this software in the presence of grain boundaries. It is possible (with care) to use it with free surfaces.[1] S. Plimpton, Fast Parallel Algorithms for Short-Range Molecular Dynamics, J. Comput. Phys. 117 (1) (1995) 1–19. doi: https://doi.org/10.1006/jcph.1995.1039.

Defect segregation facilitates oxygen transport at fluorite UO2 grain boundaries.

An important challenge for modelling transport in materials for energy applications is that in most applications they are polycrystalline, and hence it is critical to understand the properties in the presence of grain boundaries. Moreover, most grain boundaries are not pristine stoichiometric interfaces and hence dopants are likely to play a significant role. In this paper, we describe our recent work on using atomistic molecular dynamics simulations to model the effect of doped grain boundaries on oxygen transport of fluorite structured UO2. UO2, much like other fluorite grain boundaries, are found to be sinks for oxygen vacancy segregation relative to the grain interior, thus facilitating oxygen transport. Fission products further enhance diffusivity via strong interactions between the impurities and oxygen defects. Doping produces a striking structural alteration in the Σ5 class of grain boundaries that enhances oxygen diffusivity even further. This article is part of a discussion meeting issue 'Energy materials for a low carbon future'.

Aligned Proton‐Conducting Graphene Sheets via Block Copolymer Supramolecular Assembly and Their Application for Highly Transparent Moisture‐Sensing Conductive Coating

AbstractHere, we have demonstrated a well‐defined strategy to prepare highly sulphonated reduced graphene oxide (S‐rGO) sheets via non‐covalent modification of rGO with water soluble rod‐coil conjugated block copolymer poly(3‐hexylthiophene)‐block‐poly(4‐styrenesulfonic acid) (P3HT‐b‐PSSA) carrying a long PSSA block. S‐rGO sheets are highly water soluble and its aqueous solution can be used to fabricate highly transparent conductive thin film coating on versatile smooth substrate surfaces like glass, indium tin oxide (ITO), quartz and flexible PET. The successful anchoring of sulfonic acid group on rGO surface via non‐covalent modification by P3HT‐b‐PSSA was confirmed and analyzed by FTIR and XRD study. The bulk morphology of S‐rGO reveals sheet like morphology where individual sheets are aligned with each other in a parallel arrangement through intercalation of PSSA chains driven by block copolymer self‐ assembly. AFM image of the thin film also supports nice parallel alignment of S‐rGO sheets of average thickness ∼100 nm on substrate surface. S‐rGO sample shows very high water uptake (∼91% in comparison to its initial weight) and proton conductivity 0.5 S/cm after water vapor exposure for 1 hour. Such high proton conductivity is due to the synergy of alignment of graphene sheets with a continuous network of proton conducting nanochannels created by block copolymer microphase separation on the rGO surface. Nyquist plot with two semicircles suggested the presence of grain boundaries in the sample. I−V measurement of transparent thin film device fabricated from S‐rGO sheets shows linear behavior with systematic increase of current on increasing water vapor exposure time. The block copolymer device shows well correlated, systematic and reversible resistance change with relative humidity (RH) confirming its efficient sensing capability towards moisture. We believe that high proton conductivity and interesting, reversible moisture sensitive electrical property of this material will be useful in fabricating transparent and flexible moisture sensors, flexible electronics, moisture induced energy storage, fuel cell, biological applications and others.

Investigations on induced residual stresses, mechanical and metallurgical properties of CO2 laser beam and pulse current gas tungsten arc welded SMO 254

This research article focuses on the joining of SMO 254 stainless steel by autogenous CO2 Laser beam welding and pulsed current gas tungsten arc welding (PCGTAW) with ERNiCrMo3 filler. The studies proved that full penetration could be achieved on the weld joint of a 5 mm thick plate with a reduced heat input of 120 J/mm in the laser welding while in the case of PCGTAW it was 3032 J/mm. An attempt is made to do a comparative evaluation of the microstructure changes which have occurred owing to welding and thereby the mechanical properties. The studies revealed the lack of deleterious phases in both welding techniques. Presence of grain boundary thickening near the fusion zone and elemental segregation was observed in PCGTAW joints. The residual stress measurements by X-ray diffraction method were executed over the cross-section of the two different weldments. An attempt is made to represent the stresses variation along the weld region, heat affected zone and the base metal graphically. The tensile test validated that in every case the rupture ensued at the base metal and the higher weldment hardness than base metal proves the soundness of the joint.

The performance of Haynes 282 and its weld in supercritical CO2

The supercritical carbon dioxide Brayton cycle is being considered as a replacement of the steam Rankine cycle due to the potential for higher operational efficiency and lower capital cost. Higher temperature and pressure conditions allow for higher efficiencies, leading to a demand for materials with high strength at these elevated temperatures. Haynes 282® has been found to have good high temperature strength and corrosion resistance, but the mechanical and weld performance in CO2 has not been studied. This work addresses that gap in knowledge by testing the mechanical properties of both base and gas tungsten arc welded samples before and after exposure to either supercritical carbon dioxide at 750 °C, 20 MPa or argon at 750 °C, 0.12 MPa for 1000 h. Both exposures resulted in a small increase in yield strength and a loss in ductility in welded and base material, with the fusion line exhibiting the most severe loss of ductility. Corrosion analysis revealed attack at a maximum of 20 μm for both base and fusion zones, with no impact of a depth-dependent effect in the fracture surfaces. Bulk analysis revealed the presence of grain boundary carbides – intermittent in base material and constant in the fusion zone – which created a region devoid of γ’ strengthening precipitates. This morphology, as well as all observed mechanical effects, was caused by the thermal aging of 282. Corrosion in CO2 was not mechanically detrimental to 282 at 750 °C, 20 MPa after 1000 h for the sample size and orientation used in this study.

First Principles Investigation of Grain Boundary Effects in Perovskite-Type Lithium Lanthanum Titanate Solid Electrolyte

Lithium lanthanum titanate (LLTO) is considered a particularly promising candidate for use as an electrolyte in all-solid-state lithium ion batteries due its good electrochemical stability and high ionic conductivity. However, measured values for the ionic conductivity of LLTO fall far below theoretical predictions, an incongruity which has been attributed to the presence of grain boundaries. Furthermore, recent experimental work has shown that lithium dendrite growth occurs along the grain boundaries in LLTO. While experimental studies have been able to reveal the detailed microstructure of polycrystalline LLTO, but little effort has been made to identify the fundamental mechanisms at work within the grain boundaries which lead to to suppressed ionic conductivity and Li dendrite growth. Using ab-initio calculations, we examine the electronic character of LLTO grain boundaries and investigate the impact of the defect states on ion transport and dendrite formation. Based on a fundamental understanding of the atomic and electronic character of LLTO grain boundaries, material design approaches are proposed to mitigate the impact of grain boundary behavior and improve the viability of LLTO as a practical solid electrolyte. This work was supported by the International Energy Joint R&D Program (No. 20168510011350) of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Ministry of Knowledge Economy, Korean government. This work is also supported by the L&F Co.’s World Class 300 Project of the Korea Institute of Advancement of Technology (KIAT) funded by the Ministry of Trade, industry and Energy (No.S2483103).

Effects of buried grain boundaries in multilayer MoS2

Two-dimensional transition metal dichalcogenides have been the focus of intense research for their potential application in novel electronic and optoelectronic devices. However, growth of large area two-dimensional transition metal dichalcogenides invariably leads to the formation of grain boundaries that can significantly degrade electrical transport by forming large electrostatic barriers. It is therefore critical to understand their effect on the electronic properties of two-dimensional semiconductors. Using MoS2 as an example material, we are able to probe grain boundaries in top and buried layers using conductive atomic force microscopy. We find that the electrical radius of the grain boundary extends approximately 2 nm from the core into the pristine material. The presence of grain boundaries affects electrical conductivity not just within its own layer, but also in the surrounding layers. Therefore, electrical grain size is always smaller than the physical size, and decreases with increasing thickness of the MoS2. These results signify that the number of layers in synthetically grown 2D materials must ideally be limited for device applications.

Enhanced laser weldability of an aerospace superalloy by thermal treatment

ABSTRACTWeldability improvement of the Inconel 738 alloy, subjected to different pre-weld heat treatments and, thermomechanical fatigue of the unwelded and welded alloy is investigated. A new pre-weld heat treatment is found to significantly reduce the susceptibility of the extremely difficult-to-weld alloy to weld cracking. The heat treatment also produces welded material with enhanced resistance to thermomechanical fatigue failure at high mechanical strain ranges, in comparison to the unwelded alloy. Furthermore, by comparing polycrystalline and single crystal materials, without altering the chemistry/microstructure of the superalloy, the presence of grain boundaries in the alloy is found to aid damage mechanisms during in-phase thermomechanical fatigue.