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Thermal barrier coatings (TBCs) are widely used to protect high-temperature components against harsh environments, such as extremely high temperatures. In this work, a second generation Ni-based single crystal superalloy (DD6) was treated in two ways: (1) via simple surface sandblasting under different pressures with no additional coating, and (2) through simple surface sandblasting under different pressures and then by applying NiCoCrAlYHf (HY5) coatings. The effects of pre-treatment (sandblasting) and the HY5 coating on the surface recrystallization of the alloy were thoroughly investigated. According to the results, both sandblasting pressure and the presence or absence of a coating significantly influence surface recrystallization. In particular, the critical sandblasting pressure for recrystallization increased the maximum recrystallization depth in both the coated and uncoated samples. Meanwhile, the recrystallization depth of the alloy with a coating was reduced compared to that without a coating. In addition, the number of recrystallized cells in the coated alloy was decreased, which indicated that the HY5 coating effectively reduced the degree of recrystallization.

The high processing efficiency and quality are constant pursuits for modern manufacturing industry. This paper investigated the ablation efficiency and quality of ultrashort pulsed laser ablation of DD6 single crystal alloy based on experiments and theoretical analysis. The experimental results showed that the ablation rate increases with the increase of laser fluence and with the decrease of scanning speed and scanning width, while the ablation efficiency decreases with the increase of laser fluence. A relatively flat and low melted zone ablation surface could be obtained by employing a low laser fluence and high scanning speed. The influence of laser parameters on the ablation diameter, equivalent energy density, and heat accumulation effect was analyzed based on the theory of laser ablation and heat conduction. The theoretical analysis revealed the material removal transforms from plasma or vaporization removal to melt ejection with the pulse energy increases and the scanning speed decreases, which can explain the formation mechanism of surface morphology very well. In addition, the scanning strategy of high efficiency and quality was proposed based on the theoretical analysis and experimental results.

The particles in high-temperature and high-speed airflow in the battlefield environment will form sliding friction and wear on the aeroengine turbine blades, thus reducing the service performance of the blades. However, few studies has been reported on the tribological properties of Ni-based single crystal alloy. Accordingly, the tribological properties of Ni-based single crystal alloys with different contents of Re (0 wt%, 1.5 wt%, 2.5 wt%, 3.5 wt%, 4.5 wt% and 5.5 wt%) are investigated by tribological experiments and molecular dynamics simulations in this paper. The results of tribological experiments show that Ni-based single crystal alloy without Re exhibits the characteristics of abrasive wear and adhesive wear, while the wear state is significantly improved after adding Re element. In particular, the worn surface of Ni-based single crystal alloy containing 5.5% Re (NSCA5) is the smoothest and only a few minor defects are observed. In addition, the micro-tribological characteristics of Ni-based single crystal alloy are analyzed by molecular dynamics simulations, the results show that Re atoms can inhibit the dislocation movement and reduce the system potential energy, which enhance the stability and hardness of Ni-based single crystal alloy, thereby the wear resistance of the material are improved.

The deformation and damage mechanisms of a single crystal nickel-based superalloy containing 6.0%Re/5.0%Ru were studied through creep performance tests at 800 °C/860–880 MPa, microstructure and morphology observation, and dislocation configuration analyzation. It was found that, during the creep process at the intermediate temperature, the γ′ phase does not form a raft-like structure. After a creep fracture, the distortion degree of the cubic γ′ phase becomes greater when the observation region is closer to the fracture. The alloy has a long creep life at 800 °C, and the dislocation slipping or climbing in the γ matrix is the deformation mechanism at the early and middle creep stages. At the later creep stage, the γ′ phase is sheared by dislocations. Because of the low stacking-fault energy of the alloy, the superdislocation shearing into the γ′ phase can decompose on the 111 plane to form a (1/3) partial dislocation and stacking-fault configuration or cross-slip to the 100 plane to form the Kear–Wilsdorf (K-W) lock, which greatly improves the creep resistance of the alloy. At the later creep stage, the primary/secondary slip systems in the alloy are activated alternately, resulting in micro-cracks at the intersection of the two slip systems. As the creep progresses, the initiated cracks spread and propagate in the γ matrix phase along a direction normal to the stress axis and connect with each other until creep fracture occurs. This is the fracture mechanism of the alloy during creep at the medium temperature.

To investigate the effect of γ/γʹ interface on the nano-deformation of the workpiece during nanoindentation of nickel-based single crystal alloys, a two-phase model of γ phase doped with Cr and Co elements was simulated using a molecular dynamics approach with controlling the indenter displacement. It is found that: in the early stage of loading, the load increases gradually with the increase of loading depth; when the indenter is close to the interface, the load is affected by the interface and changes abruptly, generating a great value; after the indenter breaks through the interface, the load fluctuates and becomes larger. More Stair-rod dislocations and Hirth dislocations are generated at the interface, and these dislocations, together with some dislocation nodes, strengthen the matrix dislocations to enhance the deformation resistance of the workpiece. In addition, atomic displacement, strain transfer, and defect development are discontinuous during the movement of the γ phase to the γʹ phase. In particular, the displaced atom morphology in the γʹ phase evolves from triangular to filleted corner, reflecting the inhibitory effect of the boundary on the development of the plastic deformation region. Graphical abstract

The deformation characteristics of a single-crystal nickel-based alloy containing Re during creep at room temperature were studied by means of creep property tests, microstructure observations and contrast analysis of the dislocation configuration. The results show that during the deformation of the alloy at room temperature, the original cubic γ ′ phase transforms into a rhombus shape along the direction of maximum shearing stress, and its deformation feature is that the dislocation slips in the matrix and shears the γ ′ phase. The superdislocation shear into the γ ′ phase can cross slip from the 111 plane to the 100 plane, forming a K-W lock, and can also be decomposed at the 111 plane. The dislocation configurations of (1/2) partial dislocation plus antiphase boundary (APB) and (1/3) partial dislocation plus SISF can effectively inhibit the slip and cross-slip of the dislocation and improve the deformation resistance of the alloy. At the later stage of creep, under the action of shear stress, the initial slip system is activated first to distort the γ and γ ′ phases, and then the secondary slip system is activated and shears the primary slip system, resulting in a large stress concentration at the delivery point and the initiation of cracks in this area. With the alternating activation of the primary slip system and secondary slip system during creep, the initiation and expansion of cracks continue. Damage and fracture mechanisms occur in alloys during room temperature creep.

In this paper, we investigate the creep-deformation behavior of Fe-Cr-Ni single-crystal alloys, a crucial factor in the longevity and safety of materials in high-temperature applications. Using molecular-dynamics (MD) simulations, we generate the creep-strain data on the creep behavior of Fe-Cr-Ni single-crystal alloy. To predict creep curves under various temperatures and stress conditions, we employ random forest (RF) and convolutional neural network (CNN) models. These models are trained, tested, and validated on creep data at 300 K, 750 K, 950 K, and 1150 K, achieving deviations within 20% of simulation values. The RF model demonstrates strong predictive capabilities, with correlation coefficients of 0.96, 0.96, 0.94, and 0.98 at the respective temperatures. In contrast, the CNN model shows correlation coefficients of 0.92, 0.99, 0.99, and 0.99. The results of this investigation show that both models are capable of accurately predicting creep behavior. As compared to the CNN model, which performs better at higher temperatures and with larger datasets, the RF model works better at lower temperatures and with smaller datasets. These results enhance our understanding of creep properties and improve predictive modeling under varying conditions.

Additive manufacturing, particularly selective laser melting, presents exciting possibilities for fabricating components from high-temperature nickel-based superalloys. Controlling microstructural features and minimizing defects in fabricated specimens are critical challenges. This study explores the influence of process parameters on microstructure and defect formation in directionally solidified nickel-based superalloy specimens. We conducted a comprehensive analysis of selective laser melting process variables, including interdendritic spacing, crystallization times, and volumetric energy density. Electron backscatter diffraction analysis was employed to assess the feasibility of obtaining a directional structure in single-crystal nickel-based heat-resistant alloy specimens using selective laser melting. The study shows a significant correlation between reduced interdendritic spacing and increased defect formation. Longer crystallization times and higher volumetric energy density lead to decreased defect volumes and sizes. Electron backscatter diffraction analysis confirms the maintenance of preferential growth direction across subsequent layers. Our research underscores the importance of optimizing selective laser melting parameters, balancing refractory elements in alloy composition, and adopting strategies for enhancing crystallization times to minimize structural defects. This comprehensive approach ensures both heat resistance and minimal defects, facilitating the production of high-quality components. These findings contribute to advancing selective laser melting applications in critical industries like aerospace and power generation, where heat-resistant materials are paramount.

The purpose of this study was to investigate the friction and wear behavior of single crystal superalloys at elevated temperatures. Pin-on-plate experiments were conducted using a custom-built high-temperature fretting/wear apparatus. Measurements were performed on two single crystal Ni-based alloys and Waspaloy ® (used as a baseline material). The coefficient of friction for the single crystal materials (i.e., during running-in and steady state) was lower compared to the Waspaloy ® . In addition, the experiments showed that the friction coefficient of the single crystal is dependent on the crystallographic plane; the friction coefficient was lower for the tests on the {100} plane compared to the {111} plane. The wear behavior was aligned with the friction behavior, where the single crystal Ni-based alloys showed slightly higher wear resistance compared to the Waspaloy ® . Ex situ analysis by means of FIB/SEM and XPS analysis revealed the formation of Co-base metal oxide layer on the surface of the single crystal alloy. Similarly, a Co-base oxide layer is observed on the counterface providing a self-mated oxide-on-oxide contact and thus lower friction and wear compared to the Waspaloy ® .

Thermal barrier coatings (TBCs) and air film-cooling technology have been extensively utilized in nickel-based, single-crystal turbine blades to enhance their heat resistance. However, structural complexity and material property mismatches between layers can affect residual stresses and potentially lead to coating failure. In this study, a three-dimensional finite element model with atmospheric plasma-spraying thermal barrier coatings (APS-TBCs) deposited on air-cooled, nickel-based, single-crystal blades was established to investigate residual stress character under centrifugal load, considering the effect of temperature, crystal orientation deviation angle, oxide layer thickness, and the number of cycles. The results show that when the centrifugal load is increased from 300 MPa to 700 MPa, the absolute value of the residual stress at the crest of the interface between Top Coat (TC) and Thermally Grown Oxide (TGO) increases by only 8.5%, whereas in the region of compressive to tensile stress conversion, residual stress decreases by 100.9%. As the crystal orientation deviation angle increases, the absolute value of the residual compressive stress increases and the absolute value of the residual tensile stress decreases, but the performance is more special in the valley region, where the absolute value of the residual stress increases with the increase in the deviation angle. Special attention is required, as the increase in temperature leads to a rise in the absolute value of residual stress. For example, at the trough of the TC–TGO interface, when the temperature increases from 910 °C to 1100 °C, the residual stress increases by 9.8%. The effect of the number of cycles on residual stress is relatively weak. For instance, at the wave crest of the TC–TGO interface, the residual stress differs by only 0.6 MPa between one cycle and three cycles. The effect of oxide layer thickness on residual stress in the TBCs after a single cycle is nonlinear. When the oxide layer thickness is 0, 4, and 7 μm, the residual stress undergoes a transition between tensile and compressive directions at different locations. The exploration of these results has yielded some valuable laws that can provide a reference for the study of the damage mechanism of TBCs, as well as a guide for the optimization of nickel-based turbine blades in the manufacturing and use processes.