Journal of Thermal Spray Technology最新文献

In recent years, the increase in gas turbine inlet temperatures has led to the problem of excessive temperatures in gas turbine blades. To address this issue, thermal barrier coatings (TBCs), internal cooling, and film cooling have been applied to the hot-side surfaces of the blades. However, it remains necessary to manage crack initiation and spalling damage of the TBC caused by thermal fatigue around the cooling holes. In this study, a thermomechanical fatigue analysis was performed on a TBC/IN738LC plate-type substrate with cooling holes using finite element analysis software. The analysis incorporated a damage-coupled inelastic constitutive equation for TBC developed by our research group. The damage and thermal stress fields around the cooling holes under cyclic loading were analyzed under thermomechanical fatigue conditions, considering both in-phase conditions—where the temperature and load patterns were synchronized—and out-of-phase conditions, where they were out of sync. Under temperature and cyclic loading conditions where the mechanical stress level around the cooling holes was lower than the thermal stress, thermal fatigue cracks were initiated at the edges of the cooling hole, notably at the 3 and 9 o’clock positions, corresponding to the loading direction, and the cracks propagated near the top coating (TC)/substrate interface. Conversely, under loading conditions where the mechanical stress exceeded the thermal stress, thermal fatigue cracks initiated at the edges of the cooling hole at 6 and 12 o’clock positions, and the cracks propagated rapidly near the TC surface. The stress level was higher in the out-of-phase condition than in the in-phase condition, and the fatigue crack initiation life was shorter. However, the differences in the temperature loading patterns had little effect on the crack initiation location.

Laser Directed Energy Deposition(L-DED) is an important method for repairing single crystal coatings. However, defects in the deposition such as premature columnar to equiaxal transition(CET) can affect the quality. An assisted external energy field can effectively reduce the defects. This paper investigated the steady-state magnetic field-assisted L-DED of GH3536 coatings onto single-crystal DD6 substrates, focusing on the effects of different magnetic field strengths on the directional growth, microstructure, and microhardness. The results showed that the assistance of magnetic field facilitates the growth of single crystals along the direction of the substrate. When the intensity was 200 mT, the electromagnetic braking effect suppressed the flow velocity of the molten pool, resulting in the height of columnar crystal grain region of 448.259 μm, which was 1.20 times observed in the absence of magnetic field, and the area of stray grains in the upper part of the coating has decreased by homogenizing the solute distribution. The thermoelectric magnetic convection effect promoted solute diffusion causing the dendrites and PDAS to appear coarsened. The microhardness has increased to an average microhardness of 340 HV_0.2 at 200 mT, which is 7. 9% higher than at no magnetic field.

In this study, a preliminary experimental investigation was conducted to assess the feasibility of using the cold spray process for the fabrication of capsules intended for hot isostatic pressing (HIP). Mild steel powder was employed as the feedstock material for cold spray deposition. Microstructural characterization and mechanical testing indicated that the as-sprayed mild steel coating exhibited inadequate properties for use as a HIP capsule material. However, subsequent heat treatment led to a substantial enhancement of the coating’s mechanical performance. Specifically, the elongation at break increased from approximately 1% to 20%, while the ultimate tensile strength improved from about 65 to 250 MPa. Finally, encapsulated HIP experiments were performed using cold-sprayed capsules. The deformation of the capsule during the HIP process was found to be insufficient to achieve full densification of the nickel-based alloy powder, likely due to the excessive thickness of the capsule walls.

This study investigates the high-temperature tribological performance of nano-CeO₂-modified multimodal Cr₃C₂-NiCr coatings (NMC) fabricated via high-velocity oxygen fuel (HVOF) spraying, in comparison with conventional Cr₃C₂-NiCr coatings (CC). Through comprehensive microstructural characterization, mechanical property evaluation, and high-temperature friction-wear tests (500-700 °C, 20-50N), the synergistic effects of multimodal architecture and CeO₂ modification were elucidated. Results demonstrate that NMC exhibits a refined multimodal architecture comprising uniformly distributed nano-, submicron-, and micron-scale Cr₃C₂ particles embedded in a NiCr matrix, achieving significantly reduced porosity (0.30 ± 0.12% vs. 1.41 ± 0.15% for CC) and enhanced microhardness (1014.9 ± 72.2 HV₀.₃ vs. 906.4 ± 47.8 HV₀.₃). These improvements are attributed to synergistic mechanisms involving nano-CeO₂-induced solid-solution strengthening, grain refinement, and hierarchical carbide dispersion, which collectively optimize interfacial bonding, minimize structural defects, and enhance load-bearing capacity. At elevated temperatures, NMC achieves a lower friction coefficient (0.49-0.72 vs. 0.55-1.25 for CC) and reduced wear rates (1.88-3.3 × 10⁻⁵ mm³/N·m vs. 4.03-5.74 × 10⁻⁵ mm³/N·m for CC), owing to the formation of adherent Cr₂O₃-rich tribofilms and suppressed decarburization via CeO₂-mediated interfacial passivation. Wear surface and debris observations indicate that CC is dominated by adhesive wear, severe third-body abrasion, and lamellar delamination, whereas NMC shows mainly adhesive/abrasive wear with more persistent Cr₂O₃-rich tribofilms. The synergistic effect of the multimodal architecture and nano-CeO₂ modification improves NMC’s high-temperature tribological performance. These findings highlight the potential of nano-modified multimodal Cr₃C₂-NiCr coatings for high-temperature tribological applications, particularly in demanding industrial environments such as continuous casting crystallizers.

In today’s increasingly competitive global marketplace, thermal spray processes are needed to support higher-value user manufacturing techniques and to satisfy continuously changing customer demands. These require thermal spray systems that are flexible enough to be produced at different scales of manufacturing batches, while still achieving high-quality coatings at a low cost. Therefore, the established and standard thermal spray processes are in the need to be upgraded to catch up with the stringent requirements of Industry 4.0. The purpose of this study is to provide a comprehensive review on the technologies of Industry 4.0 already integrated with thermal spray processes to uplift their applications through advanced digitization and automation, leading to enhanced efficiency and sustainability. To this purpose, the main current challenges facing the thermal spray family are described. Specific technologies including process control for improving the stability of the spray system, characterization for tailoring coatings to the specific requirements of various applications, modeling and simulation for enhanced replicability, analysis and optimization of the process, in situ observation for monitoring and data collection, artificial intelligence for allowing efficient and effective control and decision making and finally robotics for realizing hybrid thermal spray processes are detailed. These progressive technological aspects can play an irreplaceable role in enhancing the quality and applicability of thermal spray processes. Ultimately, the potential for incorporating these advanced technologies into thermal spray process chains is comprehensively evaluated, and the prospective trajectory of thermal spray technology’s evolution is discussed.

316L stainless steel is widely used in functional coatings due to its excellent corrosion resistance, biocompatibility, and processability. Transition metal carbide/nitride ceramics can further enhance these coatings owing to their superior mechanical properties. In this study, laser directed energy deposition was employed to fabricate five ceramic-reinforced 316L composite coatings. Microstructural and property analyses revealed that multi-element ceramic addition refined grain structure, induced lattice distortion, and promoted Nb/Mo-rich Laves phase precipitation. With 10% ceramic addition, coating hardness increased by 40% while wear volume decreased by 33.7%, alongside significantly improved corrosion resistance. These strengthening effects originate from the synergistic effect of solid solution strengthening, grain refinement, and second-phase strengthening, presenting a promising strategy for high-performance stainless steel coatings.

Graphical Abstract