The paper summarizes the current development of high-velocity oxygen–fuel coupled physical vapor deposition (HVOF-PVD) duplex coatings as protective candidates. Following a detailed historical overview of HVOF and PVD technologies, the fabrication methods for duplex protective coatings are presented. The duplex coating superimposes the synergistic advantages of coatings deposited by HVOF and PVD, where the traditional weaknesses of each technique are modified to a great certain extent. Subsequently, the relation between structural characteristics of the duplex coatings and their mechanical, tribological, and corrosive behavior is described in detail. It is demonstrated that the duplex coatings show more excellent overall performance than coatings deposited by both HVOF and PVD separately. Finally, we summarize the protective performance and promising potential of HVOF-PVD duplex coating for applications as well as the research prospects of challenges in future.

To explore the Co/Cr ratio impact on the high-velocity oxygen fuel (HVOF)-sprayed WC-Co-Cr coatings microstructure and performances, three kinds of WC-Co-Cr coatings, namely WC-4Co-10Cr, WC-7Co-7Cr, and WC-10Co-4Cr, were prepared by using a high-velocity oxygen fuel (HVOF) spraying process. The three coatings’ phase composition, microstructure, basic mechanical properties, abrasive wear, and corrosion resistance were investigated. The results show that all three WC-Co-Cr coatings comprise the main phase WC, minor W₂C, and amorphous W-Co-Cr phase, besides the WC-4Co-10Cr coating containing a small amount of Cr_xC_y phase. In addition, WC-7Co-7Cr coating exhibited the highest hardness and abrasive wear resistance, followed by WC-10Co-4Cr and WC-4Co-10Cr coatings. The corrosion resistance as a hierarchy was found to be WC-10Co-4Cr > WC-7Co-7Cr > WC-4Co-10Cr.

A plasma electrolytic oxidation (PEO) coating fabricated on AZ31 Mg alloy was sealed with polymeric sealant. The sealant penetrated into the PEO coating and filled the micropores and microcracks of the coating. The effect of the sealant treatment on the sliding wear behavior of the PEO coating was investigated by systematically varying the axial wear loads applied onto the unsealed and sealed PEO coatings. The results of the sliding wear tests revealed that the polymeric sealing treatment enhanced the wear resistance of the Mg-based PEO coating by reducing the wear rate and by improving the load-bearing capacity.

It is of significant theoretical and practical value to study the deposition process and deformation behavior of cold-sprayed particles to find the deposition mechanism of cold-sprayed coatings, further improve the coating performance, and expand its application scope. However, observing the deposition process and particle behavior through experiments is difficult due to the brief deposition duration of cold spray particles. Numerical simulation offers a means to slow the deposition process and predict the critical velocity, deformation behavior, bonding mechanism, and residual stress of cold-sprayed particles. This paper uses finite element analysis software, including ANSYS LS Dynamic-2022 R1 and ABAQUS-6.14, alongside various prevalent finite element methods for numerically simulating cold spray particle deposition. These methods involve the Lagrange, Euler, arbitrary Lagrange-Euler (ALE), and Smoothed Particle Hydrodynamics (SPH) to investigate the cold spray particle deposition process. The recent literature primarily summarizes the simulation outcomes achieved by applying these methodologies for simulating the deposition process and deformation characteristics of different particles under varying cold spraying conditions. In addition, the reliability of these simulation results is analyzed by comparing the consistency between the simulation results of single-particle and multi-particle and the actual experimental results. On this basis, these methods’ advantages, disadvantages, and applicability are comprehensively analyzed, and the future simulation research work of particle deposition process and deformation behavior of cold spraying prospects is discussed. Future research is expected to provide a more in-depth study of the micro-mechanisms, such as the evolution of the inter-particle and internal organization of the particles, near the actual situation.

Plasma-sprayed yttria-stabilized zirconia (YSZ) coatings are critical to enhancing the performance of thermal barrier coatings in gas turbines and aero-engines; however, their service life is significantly constrained by microstructural evolution and multi-mechanism coupling effects. Focusing on plasma spraying process routes (atmospheric plasma spraying, APS; suspension plasma spraying/solution precursor plasma spraying, SPS/SPPS; low-pressure plasma spraying, LPPS) and key process parameters as primary input variables, this review systematically analyzes their regulatory roles in microstructural characteristics such as porosity and crack density. Available studies indicate that distinct process routes give rise to pronounced structural differences: the porosity of APS coatings is 10%–20%, that of SPS/SPPS coatings is 15%–30%, and that of LPPS coatings is 1%–8%. After thermal exposure above 1100 °C, the porosity decreases to 6%–12%, 8%–18%, and 0.5%–3%, respectively, while the thermal conductivity increases to a maximum of approximately 2.5 W·m⁻¹·K⁻¹ and the Young’s modulus rises to 60–220 GPa. Further analysis reveals that mechanisms such as sintering densification, phase destabilization, thermally grown oxide (TGO) interfacial stress accumulation, and calcium–magnesium–alumino-silicate (CMAS) infiltration exert coupled amplification effects through microstructural evolution, thereby accelerating coating failure. On this basis, emerging regulation strategies are evaluated: the CMAS penetration depth of high-entropy oxides at 1300 °C for 5 h is only about 1/7 that of conventional YSZ, the thermal cycling life of self-healing coatings is enhanced by up to 4.2 times, and the crack density is reduced by approximately 35%. Finally, it is proposed that a quantitative prediction model integrating “structural parameters–evolution kinetics–service life” should be established, and that anti-sintering design, gradient structures, and functionalized systems be combined to enable the transition of YSZ coatings from empirical optimization to predictable design.

This study successfully achieved the in situ synthesis of carbon nanotubes (CNTs) on aluminum powder substrates through rotating chemical vapor deposition (R-CVD) using nickel-based catalysts with acetylene as the carbon source. Through systematic parameter optimization, we elucidated the effects of catalyst loading, synthesis temperature, reaction duration, reactor rotation speed, and carrier gas ratio on the morphology, crystallinity, and yield of CNTs. Comprehensive characterization employing transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray diffraction (XRD) demonstrated that R-CVD enables low-temperature synthesis (480 °C) of CNTs with enhanced crystallinity, improved yield, and uniform distribution, exhibiting superior performance compared to conventional CVD methods. Our analysis revealed two concurrent growth mechanisms on aluminum substrates: the tip-growth and base-growth modes, wherein the proportion of the base-growth mechanism exhibited significant temperature dependence. The present work establishes an innovative strategy for the low-temperature fabrication of high-performance CNT-based composite materials.