Coatings

Bi₂Te₃-based thin films for micro-thermoelectric devices must carry metal contacts and withstand device processing. A roughness amplitude alone, the usual surface metric, distinguishes neither protrusions from depressions nor film from substrate features. We examined pressure-gradient-sputtered (Bi₂Te₃)_x(Sb₂Te₃)_1−x films at five compositions on polished alumina by stylus profilometry, white-light interferometry, electron microscopy, and instrumented indentation. Among the thinnest films, protrusions dominate only at x = 0.48 and give a positive skewness (+2.03) and the largest areal roughness (442 nm). At approximately 2 µm thickness, the film at this composition has faceted grains (0.2–0.5 µm), coarser than those at x = 0.00 and 0.24. In the other four thinnest films, sparse depressions 4–11 µm wide give a negative skewness (−3.10 to −10.42). At x = 1.00, two depressions reach below the level of the adjacent bare substrate and thus replicate its defects; elsewhere, they stay within the film thickness. Indentation separates hard Sb-rich films (x = 0.00 and 0.24; hardness 1.76–1.89 GPa; creep 5.1%–8.2%) from soft Bi-rich films (x = 0.73 and 1.00; hardness 0.80–0.99 GPa; creep 20.0%–23.4%). The film at x = 0.24 is also the smoothest (areal roughness 4.2 nm). A stylus profile across the film edge identifies depressions below the bare-substrate level as substrate-derived.

Many special components such as catapult guide rail, turret base, flight deck, bomb sales, etc., suffer from continuous salt fog corrosion with irregular and intermittent heavy load wear in the marine environment, which leads to serious damage to equipment. This kind of wear–corrosion allows the accumulation of corrosion products, which is different from continuous coupled wear and corrosion. However, the corrosion problems for these components are serious, and how the corrosion products, after wear, influence the corrosion is not well known. In the present work, a newly developed FeCr₃₅Ni₂₀Mn₁₀B₈Mo₅Al_1.8Si_1.5 (FAA) coating was chosen to evaluate the effect of wear on the corrosion behavior in seawater. The corrosion behaviors of the high-velocity oxygen fuel (HVOF)-sprayed FAA coating were investigated after wear under different loads by PDP and EIS; the corrosion products in the wear trace were analyzed with SEM, EDS, and XRD. The results indicate that the HVOF FAA coating has a dense structure with a porosity of 3.12 ± 0.25%, an amorphous content of 85.5 ± 4.3%, a bonding strength above 38.9 ± 6.7 MPa, and a hardness of 655 ± 48 HV_0.2. Under low-to-medium intensity pre-wear, the wear-induced formation of a dense oxidation layer effectively enhances the corrosion resistance, resulting in the corrosion rate of 0.307 μA/cm² being a bit higher than that of the as-sprayed FAA coating (0.260 μA/cm²). Conversely, under high-intensity wear, mechanical force tears down the surface protective layer, resulting in a substantial degradation in the anti-corrosion barrier. The sample subjected to 30N and 300 mm/s exhibits a corrosion current density of 1.67 μA/cm².

Although 3D printing enables the flexible manufacturing of ceramic components, the fabrication of complex, large-span ceramic structures usually requires additional supports, leading to high production costs, low efficiency, and increased defect rates. Herein, an ultraviolet (UV)-based in situ photocuring-assisted direct ink writing (DIW) method was developed for shaping alumina-filled photocurable slurries into preceramic composites, which were subsequently debound and sintered into alumina ceramics. The effects of the slurry composition and processing parameters on curing depth and printing accuracy were systematically investigated, and the mechanical properties of the cured and sintered samples were compared. The results showed that the curing depth decreased with increasing photoinitiator and alumina powder content but increased with prolonged UV irradiation time. Due to the increase in viscosity with the increase in alumina content, the flowability of the slurry before solidification decreases, and the printing accuracy increases. The cured composites exhibited good mechanical integrity. After debinding and sintering, the bending modulus and bending strength increased from approximately 125 MPa and 5 MPa for the cured composites to about 200 GPa and 38 MPa for the sintered ceramics, respectively. The linear shrinkage of the sintered sample was around 20%. Using the optimized slurry, various unsupported structures—including discs, solid rectangles, triangular frames, L-shaped brackets, and a 12.5 cm high vase—were successfully printed without any supports. All printed structures exhibited good continuity and integrity, demonstrating the proposed method as a promising route toward the low-cost and efficient manufacturing of alumina ceramic components.