Journal of Thermal Spray Technology最新文献

Wear-induced failure represents the predominant degradation mechanism in brake disks. Laser cladding technology provides a rapid and environmentally sustainable approach to enhance wear resistance. In this study, extreme-high-speed laser cladding (EHLA) was employed to fabricate a 316L steel matrix composite coating containing 16% TiC (comprising a 316L transition layer and a wear-resistant layer of 316L steel reinforced with 16 wt.% TiC particles) on gray cast iron (GCI) brake disks. The microstructure and mechanical properties were systematically characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), Vickers microhardness testing, and pin-on-disk tribometry. Phase analysis confirmed the predominant presence of TiC carbides and γ-Fe in the coating. Microhardness measurements revealed a 1.41-fold enhancement in the wear-resistant layer (318.2 HV_0.3) compared to the substrate (225.6 HV_0.3). Tribological evaluations under room temperature (RT) and elevated (300 °C) temperatures demonstrated distinct friction behavior: The substrate exhibited a friction coefficient (COF) increase from 0.282 to 0.498 (1.77-fold rise) with temperature elevation, while the coating showed a more moderate COF increase from 0.241 to 0.331 (1.37-fold rise), demonstrating superior thermal stability. Wear mass loss measurements further confirmed the coating's enhanced performance: At RT, the substrate and coating exhibited mass losses of 3.6 mg and 2 mg, respectively, while at 300 °C, these values increased to 9.6 and 6 mg. In both temperature conditions, the coating demonstrated 44.4-37.5% lower wear mass loss than the substrate. These results conclusively validate the coating's exceptional wear resistance and temperature-adaptive performance.

Stainless steel–tungsten carbide (WC) composite layers were fabricated via laser metal deposition (LMD) and then treated by low-temperature plasma nitriding at 425 °C to improve wear and corrosion resistance. This thermochemical process resulted in the formation of nitrogen-supersaturated expanded austenite (S-phase) and chromium nitride (CrN) phases. To investigate the effects of alloying elements on the nitrided layers, a combination of experimental characterization, statistical analysis, and computational simulation was used. Ordinary least squares (OLS) analysis indicated that chromium might negatively influence nitrided layer thickness (regression coefficient = –0.40, p < 0.01), possibly due to its strong affinity for nitrogen. This trend was further supported by Monte Carlo simulations and density functional theory (DFT) calculations. Among the alloying elements studied, tungsten showed a potential positive correlation with surface hardness, increasing it by 21.85 HV per 1 wt.% increment. This effect may be attributed to the formation of eutectic carbides from the interaction between WC particles and stainless steel during LMD, which may contribute to hardening the nitrogen-enriched matrix. Anodic polarization testing suggested a possible positive correlation between the ferrite-to-austenite phase ratio in the as-deposited layers and the corrosion current density (p < 0.01, R² = 0.71). These results provide preliminary insights suggesting that controlling both the chromium content and ferrite phase ratio might be important for optimizing nitrided layer formation and improving corrosion resistance. Additionally, the formation of eutectic carbides could enhance surface hardness in the nitrided WC composite layers.

This work reports the effect of powder heat treatment on the tensile properties and microstructure of cold-sprayed AA7075. High-quality, cold-sprayed AA7075 material can be produced with a range of powder microstructures, but the tensile properties when using powders produced by gas atomization are suboptimal. Two types of heat treatment, overaging and solution treatment, were used to modify the intermetallic content of the starting powders. Cold spray deposits using as-atomized, overaged, and solution-treated powders were produced using high-pressure cold spray with helium as the spray gas. The microstructure and nanostructure of the starting powders and the resultant deposits were characterized using a combination of SEM and STEM imaging and diffraction techniques. The powder heat treatment increased the ductility in both cases, with overaging doubling the ductility of the as-atomized material. The solution-treated powder produced a deposit with the same yield strength as the as-atomized material and with a 30% increase in ductility. Fractography demonstrated a difference in the overload fracture mechanism between the three specimen types, which STEM imaging reveals results from differences in microstructure and particle bonding at the interface between individual particles.

Doping active elements into the adhesive layer effectively inhibits the formation of brittle phases, such as spinel, and enhances the coating's high-temperature oxidation resistance. In this study, a NiCoCrAlY-nano-HfO₂ coating was fabricated using laser cladding technology. The effect of nano-HfO₂ doping on the oxidation behavior of NiCoCrAlY coatings was investigated at 1100 °C. The results show that nano-HfO₂ doping improves the hardness of the cladding layer. Initially, at high temperatures, nano-HfO₂ doping promotes the selective oxidation of the alumina film. During oxidation, hafnium oxide diffuses into the vicinity of the oxide film, promoting the formation of an oxide pinning structure, which improves the exfoliation resistance of the oxide film. Additionally, the large size and low solubility of HfO₂ result in its distribution at the interface between the two phases, inhibiting Al diffusion, limiting oxide film growth, delaying the formation of the spinel phase in the oxide film, reducing the growth rate of the thermally grown oxide (TGO), and enhancing the high-temperature oxidation resistance of the coating.

Al-rich NiAl–Cr(Mo) intermetallic compound alloy with a higher fraction of β-NiAl phase has attracted increasing attention due to the enhanced hardness and wear resistance. However, the increasing cracking sensitivity becomes the major drawback for additive manufacturing techniques like laser-directed energy deposition (L-DED). In this study, single-track samples of Al-rich NiAl–Cr(Mo) compound alloy (23Ni–52Al–22Cr–2Mo–0.09Hf, at.%) were prepared using L-DED. Laser power, scanning speed, and preheating treatment were optimized to minimize crack density and refine microstructure. Subsequently, crack characteristics, types, and formation mechanisms were systematically analyzed, and the effect of microstructural variations on microhardness was investigated. The results showed that optimizing the scanning speed and laser power reduces the crack density to 0.61 mm/mm², and preheating treatment significantly reduces the thermal stress, enabling the preparation of crack-free samples. The cracks primarily originate from the bonding interface between the molten pool and the substrate, and the eutectic phase enhances the crack resistance through branching, deflection, and bridging mechanisms. Increasing the laser power only promotes the formation of the eutectic phase, while increasing the scanning speed simultaneously increases the eutectic phase content and refines the microstructure, which are beneficial for crack resistance. Although preheating treatment has a limited impact on microstructure regulation, it significantly reduces thermal stress and inhibits crack initiation. The microhardness is positively correlated with the fineness of the microstructure and the content of the NiAl phase, and its microhardness can reach up to about 680 HV₁. This study provides process optimization guidelines for the preparation of highly brittle NiAl-based alloys using L-DED.

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The current research study underscores the potential of WC-Colmonoy-6 coatings for applications in marine, aerospace, and energy sectors, where enhanced resistance to synergistic cavitation and corrosion damage is critical. The study involves the investigation of mechanical, metallurgical, and cavitation-corrosion behavior of tungsten carbide (WC) and Colmonoy-6 based cladding developed via laser cladding on SS410 steel substrates. The developed clad exhibited a dense microstructure with minimal porosity and a uniform distribution of WC particles, as verified through FESEM, EDS, and XRD. Cavitation erosion testing revealed a significant reduction in mass loss for the cladded samples, with a 45% lower mass loss (9.29 mg) compared to the uncladded substrate (16.95 mg) under the most aggressive conditions. Salt spray testing confirmed enhanced corrosion-erosion resistance, with the laser cladded coatings showing a 28% reduction in cumulative mass loss after 168 hours exposure in 3.5% NaCl environment. Wettability analysis further demonstrated improved water contact angle by approximately 50%, reducing water retention and the risk of corrosion. Further, artificial neural network (ANN) modeling accurately predicted cavitation erosion performance, highlighting the cladded coatings' consistent behavior. Overall, the findings provide a comprehensive understanding of the optimized process parameters and microstructural attributes contributing to superior coating performance.

This study aims to research the oxidation resistance and long-term oxidation failure mechanism of AlCoCrFeNi2.1 high-entropy alloy (HEA) coating. AlCoCrFeNi2.1 coating was prepared on Ni625 substrate by atmospheric plasma spraying (APS). The oxidation behavior of the coating at 900 and 1000 °C under atmospheric conditions was discussed. The oxidation resistance of the coating was analyzed by the oxidation kinetic curve formed by the TGO layer and the oxidation weight gain of the coating as a whole. The oxidation failure process of the coating after a long time of oxidation was analyzed. The results showed that Al-depleted oxide is a priority formed at the Al-depleted boundary of the surface. The growth of Al₂O₃ will hinder the formation of Al-depleted oxides. After oxidation at 900 °C for a long time, the primary α-Al₂O₃ is gradually transformed into θ-Al₂O₃ and exists stably. The TGO layer formed on the surface of the coating is composed of stable θ-Al₂O₃. The Bcc phase of the coating gradually transforms into the Fcc phase at high temperature, accompanied by grain growth. The surface oxide layer at 1000 °C is the θ-Al₂O₃ layer and a thinner Cr₂O₃ layer. The oxidation failure of the coating is caused by the oxidation shedding of the TGO layer, which leads to increased oxidation in the coating. The coating can effectively protect the substrate at 900-1000 °C/200 h.

To meet the urgent demand of high-performance and ultra-thick thermal barrier coatings (TBCs) for key hot end components of gas turbine engines, in this work, a series of ~ 2-mm-thick yttria-stabilized zirconia (YSZ) coatings with vertical cracks were fabricated by a wide-velocity range high-energy plasma spraying technology. The effects of different process parameters on the density of vertical cracks were studied experimentally and through numerical simulation. The results suggested that the vertical crack density increased with increasing spraying power and decreasing standoff distance. When the temperature difference between the coating surface and the back of the substrate increased by approximately 95 °C, the vertical crack density increased by 1 crack/mm.

Improving the fracture toughness and wear resistance of Cr₂O₃ coating is of great significance for its application in high-end fields. Incorporating TiO₂ is an effective toughening strategy, yet its effect on wear resistance is contradictory. In this work, the effects of TiO₂ content on the microstructure, mechanical properties, and tribological properties of the plasma-sprayed Cr₂O₃–xTiO₂ composite coatings were studied. The results demonstrate that the microstructure of the composite coatings only contains the Cr₂O₃ and TiO₂ phases without an intermediate phase. The composite coatings exhibit lower porosity, higher fracture toughness, and better wear resistance compared to pure Cr₂O₃ coating. With the increase of TiO₂ content, the fracture toughness and wear resistance of composite coatings exhibit an initial increase followed by a decrease. The Cr₂O₃–15TiO₂ composite coating presents the highest fracture toughness of 6.53 MPa m^1/2 and the lowest wear rate of 0.82 × 10⁻⁶ mm³/(N m). The improvement in fracture toughness of the composite coatings is due to the reduction of porosity, crack deflection, and branching by TiO₂. Furthermore, the wear mechanism shifts from brittle fracture, fatigue wear, and oxidative wear in pure Cr₂O₃ to oxidative wear in the composite coatings. This is attributed to the enhanced toughness of composite coatings via TiO₂, reducing the crack initiation and spalling. This work provides theoretical guidance and technical support for the performance optimization of the Cr₂O₃ coating.