Deposition Of Thick Coatings Research Articles

An Approach to Synthesize Thick α‐ and γ‐Al2O3 Coatings by High‐Speed Physical Vapor Deposition

Crystalline α‐ and γ‐Al2O3 exhibit in many applications high wear resistance, chemical resistance, and hot hardness, making them interesting materials for production engineering. To synthesize α‐Al2O3 with high coating thickness of s ≥ 10 μm, chemical vapor deposition at temperatures T > 1000 °C is well established. However, there are almost no studies dealing with the synthesis of thick α‐Al2O3 by physical vapor deposition (PVD) at high temperatures T > 700 °C. High‐temperature deposition of thick coatings can be realized by means of the dense hollow cathode plasma, combined with the transport function of the plasma gas in high‐speed (HS) PVD. Herein, crystalline α‐ and γ‐Al2O3 films are deposited on cemented carbides at substrate temperatures T s ≈ 570 °C and T s ≈ 780 °C by HS‐PVD. These coatings exhibit a thickness up to s = 20 μm. Moreover, phase analysis presents α‐phases in coatings synthesized at substrate temperature of T s ≈ 780 °C with significant higher hardness than films by T s ≈ 570 °C. These release the potential of HS‐PVD to synthesize α‐Al2O3 coatings with high thickness. Thereby, a higher thickness of these coatings is beneficial for the wear protection of turning and die casting tools.

REVIEW OF APPLICATION AND RESEARCH BASED ON COLD SPRAY COATING MATERIALS

Cold spray technology is an advanced spray technology, and its technical principle is the same as that of additive manufacturing technology. Cold spraying technology combines multiple advantages in the spraying field: not only can the deposition of thick coatings be achieved, but the coatings prepared by this technology have the characteristics of high density, low oxygen content, good mechanical properties of the coating surface, and high deposition efficiency. Cold spraying technology can prepare corrosion-resistant coatings, high-temperature resistant coatings, wear-resistant coatings, conductive coatings, anti-oxidation coatings, and other functional coatings. After decades of development and exploration, cold spraying technology is preparing metal coatings. The application is very wide and the process is mature; the same cold spray technology can also prepare non-metallic coatings. Mainly to immerse repair and protect the surface of metal alloy parts and a small part of non-metal parts, so that these parts have better mechanical properties and mechanical behavior. This article mainly reviews the application of cold spray technology in the field of spray materials and summarizes the existing conventional metal series, rare metal series and non-metal material, conventional non-ferrous metals: copper, titanium, aluminum and nickel. Metal materials are currently widely used in the field of cold spraying. Among them, titanium-based metals restrict their applications due to their own properties; rare metals: tungsten, tantalum, and niobium-based metal materials. The application of rare metals in cold spraying is still in its infancy stage; non-metallic materials: polymer materials and ceramic powder materials, non-metallic materials have the characteristics of surface modification and strengthening technology, but also have low oxygen content, low thermal stress, high density, good bonding strength, in the deposition process and the substrate will not change the advantages of physical organization structure. Finally, the existing problems of rare metal materials and non-metal materials are raised.

Deposition of a nanocomposite (Ti, Al, Si)N coating with high thickness by high‐speed physical vapor deposition

AbstractNanocomposite coatings such as (Ti, Al, Si)N have been demonstrated as promising candidates for the use as protection against solid particle erosion for compressor blades. Typically, nanocomposite (Ti, Al, Si)N coatings are deposited by different physical vapor deposition (PVD) techniques. However, the relatively low coating thickness up to a few micrometers due to low deposition rates leads to a limited lifetime of the coatings under erosive particle bombardment. In this study, the deposition of a nanocomposite (Ti, Al, Si)N coating was performed by a hollow cathode gas flow sputtering method, the high‐speed physical vapor deposition, which enables the high‐rate deposition of thick coatings. Morphology and microstructure of the coating were investigated via scanning electron microscopy and transmission electron microscopy, respectively. Tribological characterization by impact tests and erosion tests demonstrates that the nanocomposite (Ti, Al, Si)N coated sample reveals a promising resistance against impact loads and the solid particle erosion. Summarily, nanocomposite (Ti, Al, Si)N coatings deposited by the high‐speed physical vapor deposition provide a high potential for the erosion protection of compressor blades.

Electrophoretic deposition of thick titania coatings at constant voltage by controlling current density

AbstractKinetics of electrophoretic deposition (EPD) process usually slows down with time due to the reduction in effective electric field (Eeff) across the suspension. So, normally the deposition of thick coatings or 3‐D objects by EPD is not possible at low voltages. The suspensions of nanometer (NT) and micrometer (MT)‐sized titania particles were prepared in isopropanol, using triethanolamine (TEA) plus acetic acid (AA) as the charging additives. Eeff is directly proportional to the current density. It was found that depending on the composition of suspensions, the current density and so Eeff decrease, remain constant or increase during EPD from them. Current density increased during EPD from NT suspensions with 0.33 (AA≥1.33 mL/L), 0.66 (AA≥2 mL/L) and 1.33 mL/L (AA≥6.66 mL/L) TEA. However, it did not increase any of the MT suspensions, but remained nearly constant for those with 0.33 and 0.66 mL/L TEA plus AA>1.33 mL/L and AA>2 mL/L, respectively. Current density increased or remained constant during EPD from the suspensions in which majority of H+TEA ions are adsorbed on the particles surface and the zeta potential of particles is below the critical value in them (NT≈70 mV and MT≈60 mV). Deposition rate increased continuously during EPD from the suspensions in which current density increased for them.