Fraction Of Special Boundaries Research Articles

Microstructural characterization of interfaces between cold sprayed copper and electrodeposited copper corrosion barrier coatings for used nuclear fuel containers

Copper coatings on steel, manufactured by a novel combination of two different manufacturing technologies, electrodeposition and cold spraying, are employed as a corrosion barrier in the current design of used fuel containers (UFCs) for the long-term storage of Canada's used nuclear fuel. This study examines such copper coatings on a prototype container section, with a particular focus on the interface region where copper materials fabricated by the two processes converge. Distinct microstructures for the electrodeposited and cold sprayed copper layers were observed. An unexpected recrystallized layer on top of electrodeposited copper was identified for the first time. Local annealing at 350 °C and 600 °C for one hour resulted in more homogeneous microstructures and Vickers hardness profiles among the copper layers, which is favorable for this application by reducing processing related heterogeneity in the interface region. More homogenized structures with high fractions of special grain boundaries in this region are expected to provide enhanced mechanical and corrosion properties.

Characterizing grain boundary network length features through a harmonic representation

When modeling and characterizing grain boundary networks (GBNs), there are situations where local descriptors such as triple junction fractions (TJFs) and special boundary fractions are identical between two microstructures, but the performance or properties between the two are distinct. These differences are caused by higher length-scale features that cannot be identified using local structural descriptors. Spectral graph theory (SGT) has been used previously to encode network length features, but did not enable direct quantitative comparisons between the structures that cause property differences. In this paper, we derive a harmonic representation of diffusion on GBNs based on SGT. This method enables direct quantitative comparisons between GBNs for microstructures with different morphologies, and identifies network length features responsible for structural and performance differences, which local descriptors cannot explain. We show an interpretation of the eigenmodes generated by this method that explains long-range structural causes of certain property differences. We apply this method to a large library of microstructures, and identify structural classes through clustering. We show that equal proportioned TJF and J1 dominated microstructures are the most sensitive to network length differences because of boundary configurations, while J2-J3 dominated structures are the least sensitive. This method also identifies network length features that result in anomalous percolation/non-percolation compared to predictions based on local correlations alone.

A novel surface grain boundary engineering approach to improving corrosion resistance of a high-N and Ni-free austenitic stainless steel

Grain boundary engineering (GBE) can effectively improve the corrosion resistance of materials, but the traditional thermal-mechanical process still exhibits some limitations. In the present work, a novel surface spinning strengthening (3 S) technology followed by heat treatment was applied to modify the microstructure near the surface (∼ 400 μm) of a high-N Ni-free austenitic stainless steel. Under an optimal condition of annealing at 1323 K for 60 min after 3 S, the fraction of special boundaries mainly involving Σ3 boundaries in GBE layer was significantly improved from 48.3 % to 69.1 %, thus achieving excellent resistances to intergranular corrosion and stress corrosion cracking.

Roles of the grain-boundary characteristics and distributions on hydrogen embrittlement in face-centered cubic medium-entropy VxCr1-xCoNi alloys

The issue of hydrogen embrittlement (HE) in face-centered (FCC) structured alloys is significant for H storage and transportation application due to unanticipated damage beyond its predicted service life. This unpredictable situation may harm human life and limit hydrogen to a reliable source of renewable energy in industrial fields. Recent research has suggested that multi-principal element alloys possess high resistance to HE. However, there has been limited exploration of how their unique properties affect the HE mechanisms. In this study, using simple model VCrCoNi alloys with analogous grain sizes, the reduction rate of ductility by hydrogen uptake was measured through a slow strain rate tensile test following electro-chemical H charging. Further, the origin of HE resistance was investigated by analyzing various factors such as hydrogen contents, fracture and deformation behaviors, and grain boundary properties using thermal desorption spectroscopy, scanning electron microscope, and electron backscatter diffraction. Despite the consistent trends of the H content, stacking fault energy, and stress with increasing V content, the resistance to HE is the highest for the alloy with an intermediate ratio of V and Cr, namely, for the V0.7Cr0.3CoNi alloy. Through the analysis of grain boundary characteristics, the high resistance is attributed to large fractions of special boundaries and special triple junctions and large twin-related domain size, which suppresses crack growth and interlinkage. The favorable grain boundary characteristics result from mechanical dynamic recovery, achieved by the competitive effects of solid-solution strengthening and stacking fault energy. Thus, the present study provides novel insights into enhancing HE resistance in FCC-structured alloys.

Twin-Related Grain Boundary Engineering and Its Influence on Mechanical Properties of Face-Centered Cubic Metals: A Review

On the basis of reiterating the concept of grain boundary engineering (GBE), the recent progress in the theoretical models and mechanisms of twin-related GBE optimization and its effect on the mechanical properties is systematically summarized in this review. First, several important GBE-quantifying parameters are introduced, e.g., the fraction of special grain boundaries (GBs), the distribution of triple-junctions, and the ratio of twin-related domain size to grain size. Subsequently, some theoretical models for the GBE optimization in face-centered cubic (FCC) metals are sketched, with a focus on the model of “twin cluster growth” by summarizing the in-situ and quasi-in-situ observations on the evolution of grain boundary character distribution during the thermal-mechanical process. Finally, some case studies are presented on the applications of twin-related GBE in improving the various mechanical properties of FCC metals, involving room-temperature tensile ductility, high-temperature strength-ductility match, creep resistance, and fatigue properties. It has been well recognized that the mechanical properties of FCC materials could be obviously improved by a GBE treatment, especially at high temperatures or under high cyclic loads; under these circumstances, the materials are prone to intergranular cracking. In short, GBE has tremendous potential for improving the mechanical properties of FCC metallic materials, and it is a feasible method for designing high-performance metallic materials.

Coupling effect of torsion and electric pulse treatment on grain boundary regulation and plasticizing of nickel wire

Thermomechanical process (TMP) for grain boundary (GB) regulation is conducted on pure nickel wires to study the coupling effect of torsion and electric pulse treatment (EPT) on GB characteristics, recrystallization behavior and plasticity. The results show that high fraction of SBs, refined grains and high elongation can be achieved. The increase of most EPT parameters is able to increase the special boundary fraction and grain size. With the rising of current density, the elongation of samples with different torsional cycles tends to be uniform. Both microstructure characterization and theoretical calculation manifest that only Joule thermal effect is insufficient to stimulate recrystallization while athermal effect contributes more in accelerating recrystallization and refining grains. The electron wind force enhances the stored energy difference among deformed grains and thus reduces the critical nucleation radius, which evidently improves the nucleation rate. The interfaces between nuclei and matrixes are mostly Σ3 boundaries. Subsequently, the rapid decline of driving force suppresses nuclei growth and eventually the material retains fine grains and a high fraction of special boundaries. Σ3 boundaries are conducive to material plasticizing because they can relieve nearby stress concentration by transforming into random boundaries during plastic deformation. Dislocation pile-up is much slighter on Σ3 boundaries than random boundaries.

Effect of grain boundary constitution on corrosion behaviour in cobalt-carbon nanotube composite coatings

Corrosion behavior and micro-texture of electrodeposited cobalt coatings containing different volume fractions of carbon nanotubes (CNTs) were investigated and correlated. For lower CNT volume fractions, a compact and smoother coating morphology were observed. The morphology however, became coarser for higher CNT volume fractions. Corrosion properties of the coatings were determined using the electrochemical impedance spectroscopy and Tafel polarization techniques. Pristine cobalt coating showed corrosion potential (Ecorr), corrosion current density (icorr), and polarization resistance (Rp) values of -0.574 V, 21.48µA/cm2 and 2071 ohms.cm2 respectively. With the incorporation of CNTs, the coating corrosion resistance increased up to Co-CNT3 coating (produced by 20mg/L of CNT dispersion). Co-CNT3 coating showed Ecorr, icorr and Rp values of -0.521V, 5.33µA/cm2 and 3525 ohms.cm2 respectively. However, for higher volume fractions of CNTs, the coating corrosion resistance dropped to values lower than pristine cobalt coating. For Co-CNT6 coating (produced from 80 mg/L of CNT dispersion) the Ecorr, icorr and Rp values were -0.581V, 23.45µA/cm2 and 1409 ohms.cm2 respectively. Micro-texture analysis was conducted for pristine Co and Co-CNT3 coatings to investigate the correlation between the observed corrosion behavior and coating micro-texture. Both the coatings showed strong {211¯0} texture along the coating growth direction. When compared to printine Co coating, the Co-CNT3 coating showed lesser fraction of high angle grain boundaries as well as higher fraction of low energy special boundaries like STGBs (32°/ [211¯0], 62°/ [211¯0] angle axis pair) leading to better corrosion resistance performance for Co-CNT3 coatings.

Effects of Grain Boundary Engineering on the Microstructure and Corrosion Fatigue Properties of 316L Austenitic Stainless Steel

Grain boundary engineering (GBE) treatment was performed through thermomechanical processing (TMP) to optimize the grain boundary character distribution (GBCD) of 316L austenitic stainless steel. The effects of TMP on the GBCD and corrosion fatigue properties in high-temperature and high-pressure water were investigated. The results indicated that a high fraction (about 74%) of special boundaries as well as the interrupted network of random high-angle grain boundaries were obtained through 5% strain followed by annealing at 1,273 K for 90 min. The Σ9 and Σ27 boundaries were generated by the reaction of special boundaries. The highest corrosion fatigue life for 3,187 cycles was obtained when the TMP parameters of the 316L ASS were of 5% strain, annealing temperature of 1,273 K, and annealing time of 45 min. The low-energy special boundaries had strong intergranular corrosion resistance, but the strength of these boundaries was not enough to resist the propagation of transgranular fatigue cracks.

Recrystallization behavior and grain boundary character evolution in Co-Cr alloy from selective laser melting to heat treatment

Co-Cr alloy fabricated by selective laser melting was used to investigate the recrystallization behavior and grain boundary character evolution from As-SLM to isothermal annealed at 1200 °C for 5 min to 60 min. The As-SLM Co-Cr alloy has a prominent residual strain, high densities of dislocations and stacking faults, and solute segregation along the subgrain boundaries. The driving force for recrystallization of As-SLM Co-Cr alloy is mainly provided by phase transformation rather than crystal defects, which also offer plenty of routeways for both low- and high-angle grain boundary diffusion. In addition, the stacking faults in As-SLM Co-Cr alloy can generate morphologically complex twins by extending and gliding. The obtained optimal Co-Cr alloy has a large fraction (more than 80%) of special boundaries (Σ3, Σ9, and Σ27) after complete recrystallization, which enables high designing freedom and near-net-shape production towards additive manufacturing (AM) compatible grain boundary engineering (GBE) processing strategy.

Effects of Unidirection/Bidirection Torsional Thermomechanical Processes on Grain Boundary Characteristics and Plasticity of Pure Nickel.

The “torsion and annealing” grain boundary modification of pure nickel wires with different diameters was carried out in this paper. The effects of torsional cycles as well as unidirectional/bidirectional torsion methods on grain boundary characteristic distribution and plasticity were investigated. The fraction of special boundaries, grain boundary characteristic distributions and grain orientations of samples with different torsion parameters were detected by electron backscatter diffraction. Hardness measurement was conducted to characterize the plasticity. Then, the relationship between micro grain boundary characteristics and macro plasticity was explored. It was found that the special boundaries, especially Σ3 boundaries, are increased after torsion and annealing and effectively broke the random boundary network. The bidirectional torsion with small torsional circulation unit was the most conducive way to improve the fraction of special boundaries. The experiments also showed that there was a good linear correlation between the fraction of special boundaries and hardness. The plasticization mechanism was that plenty of grains with Σ3 boundaries, [001] orientations and small Taylor factor were generated in the thermomechanical processes. Meanwhile, the special boundaries broke the random boundary network. Therefore, the material was able to achieve greater plastic deformation. Moreover, the mechanism of torsion and annealing on the plasticity of pure nickel was illustrated, which provides theoretical guidance for the pre-plasticization of nickel workpieces.

Grain boundary evolution during low-strain grain boundary engineering achieved by strain-induced boundary migration in pure copper

Grain boundary engineering (GBE) approaches involving small deformation and annealing to modify grain boundary networks have been widely used to improve grain boundary-related properties of polycrystalline materials. However, most GBE approaches are designed by trial-and-error method since the mechanism of GBE is unclear. An important issue still under debate is whether GBE is achieved by strain induced boundary migration (SIBM) or recrystallization. Also, the evolution of grain boundary structure during GBE process is unclear. a series of strains and annealing treatments covering SIBM and recrystallization were applied to pure copper in the current study. The result indicates that SIBM is more effective in the optimization of grain boundary character distribution compared with recrystallization. Then a quasi in-situ heating electron backscatter diffraction method was employed to the 10% compression/500 °C annealing copper to study the microstructural evolution during SIBM. SIBM was observed to be activated consecutively at high residual stress regions and then sweep into surrounding deformed areas until almost the whole material was covered by SIBM. The major procedure of SIBM involves the formation of numerous new Σ3 boundaries behind the migrating grain boundary front to enhance the fraction of special boundaries and the introduction of low energy segments to interrupt the connectivity of random high-angle boundary networks. A schematic model is proposed to understand the SIBM controlled GBE process. Our results provide the underlying insights needed to guide the design of GBE routes and parameters.

Influence of surfactant polarity on the evolution of micro-texture, grain boundary constitution and corrosion behavior of electrodeposited Zn coatings

Corrosion behavior, morphology and micro-texture of Zn coatings, electrodeposited from electrolyte bath without and with surfactants of different polarity, were investigated and correlated. Polarization resistance (Rp) value which is directly proportional to the corrosion resistance behavior, was determined from the electrochemical impedance spectroscopy technique. Rp value was highest for the coating with Cetyltrimethylammonium bromide [CTAB (cationic surfactant)], followed by coatings with Sodium lauryl sulphate [SLS (anionic surfactant)], and Triton X-100 (non-ionic surfactant) surfactant. Surfactant-free coating showed the lowest Rp value, indicating lowest corrosion resistance. Surfactant-free coating and coating with SLS showed large-sized columnar grains, whereas coatings with CTAB and Triton X-100 contained smaller-sized grains throughout the coating thickness. XRD and EBSD suggested low energy near basal micro-texture on the coating surface with SLS as surfactant. Whereas other coatings with CTAB and Triton X-100 showed higher energy micro-texture. SLS containing coatings and surfactant-free coatings exhibited higher percentage (greater than 60%) of high angle grain boundaries (HAGBs). Zn coatings with CTAB showed lower fraction of HAGBs followed by coatings with Triton X-100. With similar micro-texture and grain boundary constitutions, in coatings electrodeposited using CTAB and Triton X-100, higher corrosion resistance in the case of CTAB was due to more compact and relatively less defective surface morphology. Between the coatings, produced without surfactant and using SLS surfactant, both of which exhibited similar columnar grains and percentage of high angle grain boundaries, the higher corrosion resistance in the case of SLS surfactant coating was due to near basal micro-texture along coating growth direction and high fraction of low energy special boundaries (90°/211¯0 angle/axis pair).

Effect of increased length fraction of Ʃ3n special boundaries on OAIC response of cold rolled Ni-based alloy 718 thin sheets

Among the well-established Ni-based superalloys, alloy 718 is one of the most widely used in the industry. However, its application is limited up to 650°C due to the occurrence of the oxidation assisted intergranular cracking (OAIC) phenomenon. As a general rule, an increased fraction of special boundaries (3 < Ʃ<29) along the grain boundary network, in replacement of the high energy random high angle boundaries (RHABs), is usually associated with enhanced resistance to several intergranular failure mechanisms. In the present investigation, thin sheets of alloy 718 were subjected to three different thermomechanical processing (TMP) routes, in order to manipulate the grain boundary character distribution (GBCD), aiming to achieve an increased fraction of low-Ʃ special boundaries and, consequently, to reduce the alloy's OAIC susceptibility. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were used to characterize the different microstructures and GBCD resulting from TMP. Thin sheet specimens underwent hot tensile tests at 650 °C under secondary vacuum at a strain rate of 3.2 × 10−4 s−1. Fractography analyses were performed to quantify the fraction of brittle areas on the fracture surface. The results indicate that the sample processed through iterative steps of cold rolling and solution annealing, followed by a double aging heat treatment, resulted in a microstructure resistant to OAIC, with 100% of ductile fracture. Such good resistance to OAIC was attributed to the higher percentage of special Ʃ3n boundaries, as well as to the best configuration of grain boundaries network, presenting increased fraction of special triple junctions 3CSL and 2CSL as well as a favorable triple junction ratio (TJR).

Grain boundary character and stress corrosion cracking behavior of Co-Cr alloy fabricated by selective laser melting

In this work, we used the selective laser melting (SLM) fabricated Co-Cr alloy with prominent residual strain, extremely non-equilibrium microstructures, and low stacking fault energy as a precursor to fabricate materials with the optimal grain boundary character distribution. The grain boundary engineering (GBE) of the Co-Cr alloy was achieved by a simple heat treatment of the SLM-fabricated Co-Cr alloy. The obtained GBE Co-Cr alloy exhibited 81.47% of special grain boundaries (Σ3n n = 1, 2, 3)), while it substantially disrupted the connectivity of the random high-angle boundaries, successfully reducing the propensity of intergranular degradation. Slow strain rate tests (SSRTs) showed that the GBE Co-Cr alloy possessed lower stress corrosion cracking (SCC) susceptibility and higher ductility in the corrosive environment (0.9% NaCl solution) than in the air. The high fraction of special boundaries, coupled with the stress-induced martensitic transformation (SIMT) in the GBE Co-Cr alloy yielded these results, which unique and rarely simultaneously satisfied for common structural materials. The current “SLM induced GBE strategy” offers a novel approach towards customized GBE materials with high SCC resistance and ductility in the corrosive environment, shedding new light on developing high-performance structural materials.

Low temperature electrogalvanization: Texture and corrosion behavior

Electrogalvanization at room temperature using aqueous bath is extensively used for protection of steel in highly corrosive environments. Here, it is shown that low temperature galvanization conducted at ~2 °C using aqueous electrolyte bath produces Zn coating which exhibits significantly lower corrosion current density (icorr) value when compared to the icorr values of coatings deposited at room temperature (~28 °C) and high temperature (~60 °C) when these coatings are exposed to a corrosive environment (3.5 wt% NaCl solution). The icorr values for coatings deposited at 2 °C, 28 °C and 60 °C were 8.94 µA/cm2, 24 µA/cm2 and 182 µA/cm2 respectively. Micro-texture analysis revealed that the texture (grain orientation and grain boundary constitution) of the coatings is also highly sensitive to the deposition temperature. Higher corrosion resistance observed in case of 2 °C deposited coatings was due to factors such as growth of grains oriented with relatively inert basal plane on the coating surface which retards the transgranular corrosion and presence of higher fraction of low energy special boundaries (such as low angle grain boundaries, coincidence site lattices and symmetrical tilt grain boundaries) which retards the intergranular corrosion significantly.

The influence of the processing route on the fragmentation of (Nb,Ti)C stringers and its role on mechanical properties and hydrogen embrittlement of nickel based alloy 718

The nickel-base superalloy 718 is a precipitation hardened alloy widely used in the nuclear fuel assembly of pressurized water reactors (PWR). However, the alloy can experience failure due to hydrogen embrittlement (HE). The processing route can influence the microstructure of the material and, therefore, the HE degree. In particular, the size and distribution of the (Nb,Ti)C particles can be affected by the processing. In this regard, the objective of this work was to analyze the influence of cold and hot deformation processing routes on the development of the microstructure, and the consequences on mechanical properties and hydrogen embrittlement. Tensile samples were hydrogenated through gaseous charging and compared to non-hydrogenated samples. Characterization was performed via scanning and transmission electron microscopies, as well as electron backscattered diffraction. The processing was effective to promote significant variations in average grain size and length fraction of special Σ3n boundaries, as well as reduction of average (Nb,Ti)C particle size, being these changes more intense for the cold-rolled route. For the mechanical properties, on one side, the cold-rolled route presented the highest increase in ductility for non-hydrogenated samples, while, on the other side, had the highest degree of embrittlement under hydrogen. This dual behavior was attributed to the interaction of hydrogen with the (Nb,Ti)C particles and stringers and its ensuing influence on the fracture processes.

Pitting behavior of friction stir repair-welded 304L stainless steel in 3.5% NaCl solution at room temperature: role of grain and defect structures

Stainless steel (SS) canisters used for storing spent nuclear waste are prone to chloride-induced stress corrosion cracking. Friction stir welding (FSW), being a low heat input process, can be used for repair welding of these canisters. In this study, an artificial crack was introduced on the 304L SS coupons by an electric discharge machining process. The artificial crack was repair-welded by FSW by maintaining the tool temperature a constant at two levels (725 and 825 °C). Friction stirring significantly reduced the grain size of the stirred zone (SZ) from about 47 to 2–4 μm. The fraction of low-angle grain boundaries increased in the SZ from 2 to 37–43%. On the other hand, the fraction of special grain boundaries (Σ3 and Σ9) that was ~ 50% in the base metal reduced to < 10% in the SZ. During friction stirring, the oxide layer of artificial crack was broken and aligned to form a spiral defect called lazy-S structure. All these microstructural changes affected the corrosion behavior of the FSW specimens when tested in 3.5% NaCl at room temperature using cyclic polarization, chronoamperometry, and electrochemical impedance spectroscopy. The FSW specimens showed lower polarization resistance and lower transpassive potential than those of the base metal specimens. However, the pitting protection potentials of the FSW specimens were higher than that of the base metal. The pitting behavior of the FSW specimens was influenced more by the preferential attack on the lazy-S region than by passive film breakdown. The flat band potentials of the passive film formed on the FSW specimens were more positive than that of base metal. The charge carrier density of passive film formed on the FSW specimens was higher than that of the base metal. The higher fraction of low-angle grain boundaries present in the FSW specimens could supply more number of misorientation dislocations at the metal/film interface which could form anion vacancies by a climb process leading to formation of oxide at these locations without stressing the substrate. Therefore, low-angle boundaries are considered helpful for formation of stress-free passive films that will be highly stable and enhance both pitting and stress corrosion cracking resistance.

Grain boundary engineering of AL6XN super-austenitic stainless steel: Distinctive effects of planar-slip dislocations and deformation twins

To explore the influence of deformation microstructures on the gain boundary engineering (GBE), a series of thermo-mechanical processes (TMPs) were performed on an AL6XN super-austenitic stainless steel (ASS). The deformation microstructures of cold-rolled samples and the TMPed microstructures were characterized by transmission electron microscopy and electron back-scatter diffraction, respectively. The results show that the deformation microstructures, including planar slip bands and deformation twins (DTs), play a distinctive role in the GBE treatment. Planar slip bands are in favor of the GBE treatment, since the migrating boundaries of twin related domains might generate “stacking accidents” in a sequence of closely packed atomic planes via absorbing the planar-slip dislocations, and thus derive the formation of annealing twins. In contrast, DTs are detrimental to GBE for they hinder the growth of twin related domains. Therefore, the optimal prior strain (namely cold-rolling reduction) of TMP for the GBE treatment of AL6XN super-ASS is suggested to be slightly less than the threshold strain for the appearance of DTs. The GBE-quantifying parameters are greatly improved by cold-rolling with 7% reduction and subsequently annealing at 1323 K for 12 h, and the fraction of special boundaries is increased up to 74.5%, thus effectively disrupting the connectivity of random high angle grain boundary network.

New perspectives on twinning events during strain-induced grain boundary migration (SIBM) in iteratively processed 316L stainless steel

Characterization of microstructure and grain boundary character distribution (GBCD) during iterative thermo-mechanical processing (TMP) of 316L stainless steel were done using electron backscatter diffraction (EBSD). Results from EBSD scans were analyzed in terms of the fraction of special boundaries, their deviation from ideal misorientation, connectivity of random high-angle grain boundaries, and grain size. In order to understand the efficacy of the iterative processing route leading to a well-connected twin boundary network, additional analysis was done in terms of twin-related domain statistics and triple junction distribution. Results from these analyses show that initial iteration results in a microstructure with insufficient twin boundary density, and a poor twin boundary network. Although the next iteration leads to a small increase in twin statistics, it also does not significantly improve the statistics of favorable grain boundaries and their network. However, the fourth iteration of the processing results in a large improvement in both the population and distribution of favorable grain boundaries. All the subsequent iterations were found to result in microstructural deterioration in terms of both population and network of these grain boundaries. Based on the analysis, role of underlying mechanisms such as strain-induced grain boundary migration and static recrystallization in the effective optimization of GBCD was analyzed. The present research gives important insights into these mechanisms and their control during TMP in order to achieve an engineered microstructure.

Characterization of Grain Boundary‐Engineered Aluminum–Magnesium Alloys

Herein, the effect of sputtering rate on the fraction of special grain boundaries in 5xxx series Al–Mg alloys is explored. Samples are synthesized via interrupted direct current (DC) magnetron sputtering with varying deposition rates, and the grain size and grain boundary character are evaluated with electron backscatter diffraction (EBSD). The highest sputtering rate (7 nm s−1) leads to an increase in the total number of special grain boundaries, ≈1.5× greater than that of the lower rates. Increased thermal energy and enhanced stress relaxation during film growth promote the formation of Σ3 and Σ7 boundaries.