Journal of Thermal Spray Technology最新文献

Overcoming difficulties associated with feeding very fine particles (typically < 5 microns) into the plasma plume has been the main motivation for development of suspension plasma spray (SPS) process for more than two decades. This approach has led to exciting advances and demonstrated the ability to obtain columnar microstructures, fine porous coatings and dense layers. While these results have led to a constantly growing interest within the research community, implementation of SPS technology at industrial scale comes with challenges. A novel technique for thermal spraying of very fine and non-flowable powders is presented as promising alternative to SPS: the cord plasma spray (CPS) which combines a specifically designed solid-shape consumable (cord) and an axially-fed plasma torch. In this approach, the cord acts as a carrier of the fine particles that are released in the spray stream while the organic binder is almost instantaneously pyrolyzed. The proof-of-concept experiments were led with the Yttria-stabilized Zirconia (YSZ) coating material and showed that this process is suitable to generate a wide range of coating microstructures relevant for the field of thermal barrier coatings (TBC) among. The advantages of this new approach are presented, as well as its perspectives and potential for industrial applications.

The present study concerns understanding the role of mechanical milling (aimed at the development of nano-crystalline structure) and spraying techniques (High Velocity Oxy-Fuel (HVOF) and Air Plasma Spray (APS)) on the microstructure and wear behavior of CoNiCrAlY coatings (in unmilled and milled state) developed on Inconel 718 substrate. The role of polishing of the deposited coating on the microstructure and wear behavior was also investigated. The coatings developed by both techniques exhibited γ (Co, Ni, Cr), γ'(Co, Ni)₃Al, and β (Co, Ni)Al phases in the microstructure. HVOF-deposited coatings showed increasing microhardness with increasing milling time (290-800 VHN), whereas APS-deposited coating showed a decreasing trend with increasing milling time (450-550 VHN). In HVOF-deposited coatings, the wear rate was found to be significantly reduced with an increase in milling time. Polishing of the coating was found to influence the wear rate. In APS-deposited coatings, the wear rate was always reduced due to polishing for both milled and unmilled samples, though it does not follow any specific trend with milling hours. In HVOF-deposited coatings, the wear rate decreased with polishing for the coatings with milled powder; however, it increased due to polishing in coatings with unmilled powder. The study demonstrates that mechanical milling does not uniformly improve hardness or wear resistance, as its influence is strongly dependent on the thermal spray technique. Likewise, polishing—commonly assumed to enhance wear behavior—may instead reduce wear performance depending on the powder state and deposition method. The contrasting wear responses observed in HVOF and APS-deposited coatings arise from the distinct microstructural evolutions introduced during milling and spraying. These outcomes collectively establish that optimizing CoNiCrAlY coating performance requires a balanced integration of powder refinement, deposition technique, and post-treatment conditions.

The key to heterogeneous structure additive manufacturing lies in the fusion of interfaces. In this paper, the forming characteristics, microstructures, and mechanical properties of Al/Mg dissimilar metals were investigated during wire-arc directed energy deposition based on the cold metal transfer (CMT) process. The results show that heat input affects the Al/Mg bimetallic structure’s geometry, porosity, and microstructures at the interface, with a specific emphasis on the intermetallic compounds (IMCs) formation, and the subsequent impact on the joint. The interface reaction zone is composed of Mg₁₇Al₁₂ + δ-Mg eutectic layer/ Mg₁₇Al₁₂ layer/ Mg₂Al₃ layer. Combined with thermodynamic calculations, the formation mechanism of compounds was clarified. The maximum compression–shear strength of the joints reached 48.45 MPa. Fracture analysis indicates that the crack propagates along the Mg₂Al₃ layer and eventually causes the joint to break. Experimental calculations also confirm that the fracture toughness value of the Mg₂Al₃ layer is only 1.26 MPa·m^1/2.

High-strength low-alloy (HSLA) steels are extensively utilized in shipbuilding and offshore structures due to their excellent strength, durability, and workability, specifically the DH-36 naval-grade variant. However, its susceptibility to cavitation erosion and corrosion, particularly in acidic and marine environments, limits its long-term performance. This study emphasizes enhancing the cavitation erosion and scratch resistance of a WC-10Co-4Cr coating on DH-36 steel by adding graphene nanoparticles (GNPs). A corrosion-resistant coating composed of WC-10Co-4Cr reinforced with 3 wt.% GNPs is applied using the high-velocity oxy-fuel (HVOF) thermal spray technique. These powders were deposited on DH-36 steel specimens that had undergone two surface treatments: sandblasting and laser surface texturing. Circular laser patterns were created using a fiber laser at two different pitch-to-diameter (p/d) ratios of 2 and 3. Cavitation erosion resistance was evaluated using ultrasonic cavitation tests by ASTM G32-16, where samples were exposed to a 3.5 wt.% NaCl solution for 600 minutes. Weight loss was measured at hourly intervals to assess erosion rates. Additionally, scratch indentation tests were performed under progressively increasing loads until coating failure, and the critical loads along with the coefficient of friction (COF) were analyzed. Results demonstrated that laser-textured surfaces, particularly those with optimized p/d ratios, significantly improved the coating’s adhesion and mechanical performance compared to sandblasted surfaces. Post-test surface damage from cavitation and scratch wear was examined using FE-SEM and XRD, confirming the superior protective performance of the graphene-reinforced WC-10Co-4Cr coating.

The repair of high-value single-crystal turbine blades is essential for both sustainability and cost efficiency, as these components are susceptible to degradation when exposed to extreme operating conditions. This study investigates and compares coatings produced using three different thermal spraying processes, cold gas spraying, high-velocity air-fuel spraying, and vacuum plasma spraying, to identify the optimal method for repair applications requiring subsequent directed recrystallization. The comparison showed that VPS coatings offer the most promising properties: They exhibit the lowest oxygen content, near-zero residual stress, and superior adhesion and successfully achieved the required 2 mm coating thickness without delamination. While CGS and HVAF were limited in achievable thickness, the resulting columnar grain structure of the VPS coating may pose a challenge for the intended directed recrystallization process.

Carbon fiber-reinforced polymer (CFRP) is used in spacecraft due to its excellent physical and mechanical properties. To improve its adaptability to the space environment, coatings are applied to its surface to alter its absorptivity–emissivity ratio. However, coatings applied directly to untreated CFRP surfaces exhibit poor bonding strength. To address this, this paper first compared and analyzed different laser surface texturing (LST) shapes, selecting the dimple pattern. Then, based on Response Surface Method, the influence of dimple LST parameters on both the texture geometry and the bonding strength of a plasma-sprayed aluminum (Al) coating on the textured CFRP surface was investigated. The results indicate that a texture spacing of 208 µm and a carbon fiber crater depth-to-diameter ratio (D/d ratio) of 0.432 constitute the optimal parameter combination. Under these parameters, the bonding strength between the textured CFRP and the supersonic plasma-sprayed Al coating reached 2.966 MPa. This represents a 420% increase compared to the non-textured sample (0.569 MPa). The study found that the mechanism for the enhanced bonding strength involves two aspects: Firstly, LST increases the specific surface area of the CFRP. Secondly, LST generates numerous inter-fiber voids and exposes significant amounts of bare carbon fibers within the CFRP. These features form anchoring points for the coating. This provides a positive foundation for the further application of CFRP in spacecraft.

The surfaces of titanium alloy/aluminum alloy friction pair serving in space are often severely worn or even stuck due to the lack of effective lubrication. Therefore, in this work, Sn11Sb6Cu coatings were prepared on Al-6061 under different cold-spraying pressures, and their wear properties in different atmospheric environments were systematically studied. The results show that the variation of cold-spraying pressure has a significant impact on the microstructure and mechanical properties of the coatings. In addition, under high-vacuum conditions, the friction coefficient and wear rate of the coating can be as low as 0.16 and 1.04 × 10⁻⁷ mm³/(N·mm), respectively, which are significantly better than those in atmosphere. The relationship between atmosphere and coating wear behavior was reasonably explained, and it was proved through EBSD and finite element analysis that excessive dislocation density and longer high-temperature duration are the driving forces for the uneven and abnormal growth of dynamic recrystallization grains during deposition. These findings offer brand-new insights into the rational preparation of Sn alloy coatings and their service in high vacuum.

As a solid-state material deposition technique with unique capabilities concerning attainable properties, cold gas spraying (CGS) is gaining increasing attraction in application fields of functional coatings, additive manufacturing, and local component repair. In the present study, CGS of grade 1 titanium was investigated in view of application as a repair method of damaged aerospace components. The current study focuses mainly on analysing residual stresses developed in the deposited material and substrate by means of the incremental hole-drilling method. This work aimed to investigate the influence of local thermal contributions on residual stresses by focusing on nozzle traverse speed and the type of substrate material. The results indicate that local residual stresses depend on the thermal mismatch between coating and substrate materials, the substrate material properties, and the nozzle traverse speeds. For instance, the residual stresses in grade 1 titanium coatings were observed to be tensile in case of coating and substrate exhibiting similar thermal properties, and compressive (thermal stress dominant) in case of coating material having significantly lower coefficient of thermal expansion than the substrate. Additionally, it was observed that the residual stresses shifted further toward the tensile residual stress regime under increased surface temperature by using decreased nozzle traverse speeds.

The lanthanum-strontium-manganite (La₀₉Sr₀₁MnO₃, LSMO) high-emissivity ceramic coatings are prepared via detonation spraying. The coatings exhibit a dense, lamellar microstructure and a thickness of 20-30 mkm. They demonstrate high thermal stability, withstanding 300 thermal cycles, and achieve an emissivity of 0.88 in the 3-7 mkm range at 450 °C. The radiance of the coated surface significantly exceeds that of bare steel, with maximum enhancement at ~ 450 °C. These results confirm the suitability of detonation-sprayed LSMO coatings for improving radiative heat transfer in high-temperature industrial applications.

Metallic glasses are widely investigated for corrosion due to their compositional homogeneity. To mitigate the deficiency of low plasticity in metallic glasses and expand their application scenarios, this study designed the novel Fe₅₂Ni₅Nb₅Cr₁₆Mo₅B₁₂Si₅ metallic glass coatings. The systematic investigation into crack and pore formation established a direct correlation between the HVAF process parameters, key coating quality indicators (compactness and amorphous phase content), and corrosion resistance, leading to the successful fabrication of dense coatings free of macroscale defects. During corrosion, the passive film formation follows a sequential process. First, Si oxidation establishes a primary film matrix. Then, the subsequent incorporation and accumulation of Cr₂O₃ within this matrix plays a critical role in densifying the passive film. This densification process is key to improving the film’s barrier property against Cl⁻. Conversely, localized pitting primarily results from the reduction of Mo⁶⁺ to Mo⁴⁺, which compromises the film’s local stability.