Search Results (37)

The service environment of the turbine blade–disk dovetail joint structure in aero-engines is complex. Uncertainties in material properties and geometry, as well as the failure correlations among multiple locations or components, make reliability assessment challenging. First, a probabilistic life modeling method based on linear heteroscedastic regression is proposed, and the Manson–Coffin probabilistic life models of DD6 and FGH96 alloys at 650 °C are established. Then, the Copula function is introduced to characterize the failure dependence structure, and the effectiveness of the method is verified through numerical examples. Fatigue-critical locations of the dovetail are identified, and a Kriging surrogate model is established to obtain the probabilistic stress distribution at the critical locations. Subsequently, the Copula method is employed to conduct reliability analysis of dovetail structures. The results show that the reliability of multiple dovetails considering correlation lies between that of a single dovetail and that under the assumption of complete independence. Moreover, the life of the entire disk dovetail structure is significantly influenced by the number of dovetails and the required reliability level. Finally, the study is extended to the blade–disk dovetail multi-component system. The results indicate that when correlation is considered, the reliability of both components decreases, and the overall structural life is dominated by the dovetail component with the lower life. The analytical method proposed in this paper provides theoretical support and engineering reference for the reliability design and life assessment of aero-engine rotor structures. Full article

Using the seeding method, nickel-based single-crystal superalloy DD6 specimens with different growth orientations were prepared in a liquid metal cooling (LMC) directional solidification furnace. Subsequent standard heat treatment was carried out, and the influence of growth orientation on the microstructure of the (001) crystal plane of the alloy after heat treatment was investigated. Results show that with the increase in growth orientation deviation angle from the <001> orientation, the area fraction of residual eutectic content is reduced, the average size and volume of pore and γ′ strengthening phase increase, and the cubicity of the γ′ strengthening phase decreases. The growth orientation does not significantly affect the morphology of residual eutectic content or the morphology of the strengthening phase of the γ′ in the dendrite cores and interdendrite regions. However, the size uniformity of the γ′ strengthening phase in dendrite cores and the width of the γ matrix channels decrease as the growth orientation deviation angle increases. Full article

This study investigates the influence of solidification conditions on the high-cycle fatigue (HCF) behavior of a second-generation DD6 single-crystal superalloy. Single-crystal bars with a [001] orientation were prepared using the high-rate solidification (HRS) and liquid-metal cooling (LMC) techniques under various pouring temperatures. The HCF performance of the heat-treated alloy was subsequently evaluated at 800 °C using rotary bending fatigue tests. The results demonstrate that increasing the pouring temperature effectively reduced the content and size of microporosity in the HRS alloys. At an identical pouring temperature, the LMC alloy exhibited a significant reduction in microporosity, with its content and maximum pore size being only 44.4% and 45.8% of those in the HRS alloy, respectively. Consequently, the HCF performance was enhanced with increasing pouring temperature for the HRS alloys. The LMC alloy outperformed its HRS counterpart processed at the same temperature, showing a 9.4% increase in the conditional fatigue limit (at 10⁷ cycles). Microporosity was identified as the dominant site for HCF crack initiation at 800 °C. The role of γ/γ′ eutectic in crack initiation diminished or even vanished as the solidification conditions were optimized. Fractographic analysis revealed that the HCF fracture mechanism was quasi-cleavage, independent of the solidification conditions. Under a typical stress amplitude of 550 MPa, the deformation mechanism was characterized by the slip of a/2<011> dislocations within the γ matrix channels, which was also unaffected by the solidification conditions. In conclusion, optimizing solidification conditions, such as by increasing the pouring temperature or employing the LMC process, enhances the HCF performance of the DD6 alloy primarily by refining microporosity, which in turn prolongs the fatigue crack initiation life. Full article

The outstanding mechanical properties of nickel-based alloys are predominantly governed by the characteristics of their nano-precipitation. Traditional optimization approaches, however, have focused almost exclusively on average precipitation size, neglecting the non-uniform size distribution induced by the temperature gradient during the actual preparation process. This oversight leads to inaccurate optimization parameters, hindering the reliable design and broader engineering application of these alloys. This study investigates the coupling effect of average size and deviation on the mechanical behavior of nickel-based superalloys by experiment and simulation. The characterization of prepared nickel-based alloys confirms the spatial non-uniform distribution of the precipitation size and calibrates dislocation dynamics (DD) simulation inputs. When the precipitation size exhibits no deviation, conventional strengthening models align with simulation results, confirming the accuracy of the simulations. Under high size deviation, however, significant discrepancies arise between traditional models and simulation outcomes, indicating that conventional models fail to account for the effect of size deviation. This is because size deviation leads to spatial heterogeneity in precipitate distribution, which is difficult to describe using a unified theoretical framework. Machine learning (ML)-augmented analysis of the extensive DD dataset reveals a previously unrecognized synergistic effect governed by precipitation size heterogeneity. Surprisingly, contrary to the conventional preference for a uniform size distribution, we find that an appropriate size deviation increases the number of precipitates that effectively pin dislocations in three-dimensional space, thereby enhancing strength at a constant volume fraction. Our combined experimentally calibrated DD/ML approach identifies an optimal range of size variation that maximizes strengthening potential. These results provide a new strategy and an effective pathway for performance optimization of nickel-based alloys. Full article

This study establishes a robust small-angle neutron scattering (SANS) methodology for the quantitative characterization of γ matrix channel widths in the nickel-based single-crystal superalloy DD10. By combining SANS with TEM analyses and modeling the one-dimensional SANS data via a polydisperse lamellar model, we accurately determined the channel width distribution across macroscopic sample volumes. In the virgin state, the mean channel widths were nearly isotropic, measuring 17.8 ± 0.1 nm along [002] and 20.5 ± 0.1 nm along [020]. After standard heat treatment (solution and two-step aging), significant anisotropic coarsening was observed, with widths increasing to 36.8 ± 0.2 nm along [002] and 28.0 ± 0.1 nm along [020], indicating stress-free rafting. Elemental mapping revealed substantial redistribution of key alloying elements: Al content in γ′ precipitates increased by 2.6 at.%, while Cr in the γ channels rose by 5.9 at.%. These quantitative results demonstrate that SANS provides reliable, bulk-statistical insights into nanoscale channel geometry, highlighting its critical role in influencing elemental diffusion kinetics and microstructural evolution during thermal exposure. Full article

Nickel-based superalloys are widely utilized in critical hot-end components, such as aeroengine turbine blades, owing to their exceptional high-temperature strength, creep resistance, and oxidation resistance. During service, these components are frequently subjected to complex localized loading, leading to non-uniform plastic deformation and microstructure evolution within the material. Combining nanoindentation experiments with the crystal plasticity finite element method (CPFEM), this study systematically investigates the effects of loading rate and crystal orientation on the elastoplastic deformation of DD6 alloy under spherical indenter loading. The results indicate that the maximum indentation depth increases and hardness decreases with prolonged loading time, exhibiting a significant strain rate strengthening effect. The CPFEM model incorporating dislocation density effectively simulates the nonlinear characteristics of the nanoindentation process and elucidates the evolution of dislocation density and slip system strength with indentation depth. At low loading rates, both dislocation density and slip system strength increase with loading time. Significant differences in mechanical behavior are observed across different crystal orientations, which correspond to the extent of lattice rotation during texture evolution. For the [111] orientation, crystal rotation is concentrated and highly regular, while the [001] orientation shows uniform texture evolution. This demonstrates that anisotropy governs the deformation mechanism through differential slip system activation and texture evolution. Full article

Image processing has been widely adopted as an effective technology for analyzing weld forming quality which is greatly affected by the welding process parameters. In this paper, an L₂₅(5³) orthogonal experiment is designed to investigate the effects of welding process parameters on the weld forming quality in laser welding of aluminum alloy. The weld characteristics including the weld width (WW), weld penetration (PD), weld area (WA) and weld porosity (WP) under the conditions of the different welding process parameters consisting of the laser power (LP), welding speed (WS) and defocus distance (DD) are extracted from the laser welding experiment based on image processing. The effectiveness of the weld characteristics extraction method is verified by comparing the extracted results with the measured results. It is found that the WW, PD and WA are all significantly influenced by the LP among the three welding process parameters while the influences of the three process parameters on the WP are insignificant. The DD has a significant influence on the PD and the WS has a significant influence on the WA. The corresponding significance of influence is lower than the significance of influence of LP. The analysis results are conducive to the optimization of laser welding process parameters and improvement of welding quality. Full article

Two models with a wax module tree structure were employed for directional solidification simulation. An experimental alloy of a second-generation nickel-based single-crystal superalloy, DD5, was set for this investigation. The temperature gradient value of the conventional model at 80 mm and 160 mm was less than 3.8 K/mm, and the temperature gradient value of the new model structure at the same height could reach more than 5.0 K/mm. The paste–liquid interface paste zone of the new model structure in the directional solidification process was narrower. The solidification interface was more stable than that of the conventional model. The declination angle between the primary dendrite and the principal stress axis was smaller, and the average crystal orientation was about 6.0°. Under the new model, the integrity of the single crystal of the edge plate was good, and no heterocrystalline defects were formed. At the sharp corner of the end face of the edge plate, the solidified dendrites grew staggered, which hindered the effective contraction of other parts of the edge plate and produced micro-looseness. The whole simulation was in line with the test results. Full article

Oxide-dispersion-strengthened (ODS) alloys generally exhibit extraordinary service performance under severe conditions through the formation of ultrafine nano oxides. Y₂Ti₂O₇ has been characterized as the major strengthening oxide in Fe-based ODS alloys. First-principles energetic analyses were performed to investigate the structural, elastic and interface properties of Y₂Ti₂O₇ in either Fe-based or Ni-based ODS alloys. Y₂Ti₂O₇ has comparable elastic constants to bcc-Fe and fcc-Ni and similar elastic deformation compatibility in Y₂Ti₂O₇-strengthened Fe-based and Ni-based ODS alloys is therefore expected. The Ni/oxide interface has generally better thermostability than Fe/oxide across the whole range of the concerned oxygen chemical potential. Further interface bonding and adhesion calculations revealed that Y₂Ti₂O₇ can enhance the bonding strength of Ni/Y₂Ti₂O₇ through d-d orbital interaction between the interfacial YTi layer and Ni layer, while the interface bonding between the Fe layer and YTi layer is weakened compared to the metal matrix. First-principles calculations suggest that Y₂Ti₂O₇ can be a candidate for strengthening nano-oxides in either Fe-based or Ni-based ODS alloys with well-behaved mechanical properties for fourth-generation fission reactors and further experimental validations are encouraged. Full article

The failure mechanism of a thermal barrier coatings (TBCs) system is investigated using cyclic thermo-mechanical loading with a thermal gradient. Hollow circular cylindrical specimens are employed, consisting of a nickel-based single-crystal alloy DD6 coated with a NiCoCrAlYHf bond coat via arc-ion plating and a surface electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia topcoat. The experimental setup allows for a surface temperature of 1130 °C and a substrate temperature of 1070 °C, while a tensile mechanical load of 200 MPa is employed to simulate the centrifugal stress in the middle of the high-pressure turbine blade. The comparison between TBCs with and without mechanical loading implies that the coupled thermo-mechanical load significantly promotes coating spallation since the superposition of mechanical strain enhances the local tensile stress at the peak region of the topcoat/thermally grown oxides (TGOs) interface. A subsequent interfacial morphology analysis demonstrates that the topcoat/TGO interface exhibited a degradation in the direction parallel to the mechanical loading axis. For all the specimens, TGO comprises a duplex structure, consisting of outer spinel and inner α-Al₂O₃. Full article

Different ageing treatments have been developed to achieve targeted properties in aluminum alloys through altering microstructures. However, there is a lack of understanding regarding the effect of ageing treatments on the formability of these alloys. In this study, we employed crystal plasticity finite element (CPFE) modeling, in conjunction with the Marciniak-Kuczynski (M-K) approach, to investigate the effects of ageing treatments on the mechanical properties and formability of AA6061 aluminum alloy. The as-received sheet was in the T6 heat treatment state, which was subjected to artificial ageing and pre-ageing, respectively, to achieve two age-hardened alloys with modified precipitation states. The microstructures and crystallographic textures of the three alloys were measured using the electron backscattering diffraction (EBSD) technique, and uniaxial tensile tests were performed along the rolling direction (RD), transverse direction (TD), and diagonal direction (DD, 45° to the RD) for each alloy. The forming limit curve (FLC) of the as-received alloy was determined using the Nakazima test. The dependence of mechanical strength, tensile ductility, and work-hardening behavior on the ageing treatments was clarified. Then, the tensile test results were utilized to calibrate the modeling parameters used in the CPFE model, whereas the FLC predictability of the developed model was validated with the experimental one. In the formability analysis, the effects of the ageing treatment on the FLC exhibit a notable dependency on loading paths, and the pre-aged alloy exhibits better formability than the other two at the plane strain tension state, thanks to its high work-hardening levels. In addition, the deformed textures along the different loading paths and the effects of the initial texture on the FLC are also discussed. Full article

In this study, the effect of adding different contents of yttrium (Y) during vacuum induction melting in Al₂O₃ and Y₂O₃ crucibles on the purification of DD5 alloys was investigated. The results show that the Y₂O₃ crucible exhibited great crucible stability and an excellent desulfurization effect when melting a Y-containing DD5 alloy. The S content of the alloy was reduced from 5.03 ppm to 1.36 ppm with the addition of 0.50 wt.% Y. Element Y combined with free S in the melt to form the YS phase, which was removed from the condensate shell and slag during the vacuum induction melting (VIM) process. Meanwhile, when the alloy was melted in the Y₂O₃ crucible with 0.50 wt.% Y addition, there was a reduction in S content from 2.77 ppm to 1.36 ppm compared to the Al₂O₃ crucible. Additionally, the loss of Y decreased from 0.12 wt.% to 0.05 wt.%. Full article

In addition to cold drawing, the process of annealing is also essential in the preparation of Mg-4.7 wt%Gd (G4.7) alloy wires. The effect of annealing treatment on the recrystallized microstructure and texture of cold-drawn G4.7 wires was investigated. The results demonstrate that the uniformity and regularity of the recrystallized grains, as well as the annealing texture, impact the follow-up cold drawing performance. When the as-drawn G4.7 wires were annealed at 375 °C, the recrystallized grains were refined, accompanied by uniformity and regularity. Accordingly, the G4.7 wire had a good subsequent drawing deformability, with a maximum accumulative true strain (ATS) of 144%. Additionally, the evolution of the microstructure was consistent with the evolution of the texture. While annealing at a lower temperature (325 °C), the {0002} basal texture of the G4.7 wire was weak, forming the main texture component <10$\overline{1}$0>//DD (the drawing direction). With the increase in temperature, the basal texture was gradually strengthened and the texture component transformed from <10$\overline{1}$0>//DD to a recrystallized texture based on <11$\overline{2}$0>//DD. Even under high-temperature annealing, the G4.7 wire was still affected by the cold-drawn deformation texture and could not fully recover to the as-extruded texture, thus causing a decrease in the subsequent drawing performance. Full article

In this study, the effects of kaolin and TiO₂ additions on the interaction between DD6 alloys and Al₂O₃ shells were investigated at 1550 and 1600 °C, respectively. Through the use of optical microscopy and scanning electron microscopy, the phase composition and microstructure of the shells and the alloys were studied, and the interaction mechanism was clarified. The results indicate that the shells adding kaolin and TiO₂ had a relatively weak interaction with the alloys at 1550 °C, and no significant sand adhesion could be observed. As the contact temperature was increased to 1600 °C, the alloy melt could permeate into the shells, resulting in the generation of a thick sand adhesion layer. The thicknesses of the attached layers in the alloys, which contacted the shell with kaolin and TiO₂, were 120 and 220 μm, respectively. No significant chemical products could be detected in the interaction layer, meaning that only physical dissolution of the shell refractory occurred. This study provides an experimental foundation for improving shell performance and offers valuable references for further research in related fields. Full article

The geometric accuracy and surface quality of thin-film cooling holes have a significant impact on the cooling efficiency and fatigue life of aeroengine turbine blades. In this paper, we conducted experimental research on the processing of nickel-based single-crystal high-temperature alloy DD6 flat plates using different femtosecond laser processes. Our focus was on analyzing the effects of various laser parameters on the geometric accuracy results of microholes and the quality of the surfaces and inner walls of these holes. The results demonstrate that femtosecond laser processing has great influence on the geometrical accuracy and surface quality results of film cooling holes. Notably, the average laser power, focus position, and feed volume exert a significant influence on the geometric accuracy results of microholes. For instance, a higher laser power can damage the microhole wall, thereby leading to the formation of tiny holes and cracks. Additionally, microholes exhibit optimal roundness and taper values when using a zero defocus volume. Moreover, increasing the feed distance results in enhanced entrance and exit roundness, whereas scanning speed has a negligible impact on microhole roundness. Full article