Self‐healing of TiSiN/Ag coatings induced by Ag Zhu, Yebiao; Dong, Minpeng; Zhao, Xiaoran ...
Journal of the American Ceramic Society,
December 2019, 2019-12-00, 20191201, Letnik:
102, Številka:
12
Journal Article
Recenzirano
Ceramic coatings often suffer from the formation and expansion of microcracks, which leads to a failure of the protective function. In this work, we observed self‐healing of the microcracks in the ...TiSiN/Ag multilayer coating upon heating. This behavior can be attributed to diffusion of the Ag atoms to the cracks in the multilayer coating, while similar cracks in the TiSiN monolayer coating remain unchanged after the same treatment. Furthermore, the TiSiN/Ag coating with healed cracks possesses similar electrochemical corrosion and biofouling properties to the as‐deposited one, suggesting that TiSiN/Ag is a promising system in marine engineering applications. The mechanism of self‐healing was explained by kinetic simulations based on ab initio molecular dynamics and the diffusion activation energies of Ag in irregular ceramic structures have been calculated. The here adopted theoretical method also provides a new pathway for exploring new coating systems with a potential self‐healing function.
TiC-based cermets have inadequate corrosion resistance despite wide use in high-performance applications. Rare earth dopants like Nd2O3 and Yb2O3 aim to improve cermet properties, but their impacts ...on corrosion are unclear. This work prepared 0.7 wt% Nd2O3- and Yb2O3-doped TiC cermets via vacuum sintering. Experimental results revealed that Nd2O3 doping enhances corrosion resistance by promoting α-FeOOH in corrosion products, while Yb2O3 doping has little effect. First-principles calculations confirmed that Nd promotes α-FeOOH formation. By elucidating contrasting dopant impacts on corrosion, this study provides new insights to guide optimization of rare earth-containing cermet compositions for superior corrosion resistance.
A ternary carbide Dy3Si2C2 coating was fabricated on the surface of SiC through a molten salt technique. Using the Dy3Si2C2 coating as the joining interlayer, seamless joining of SiC ceramic was ...achieved at temperature as low as 1500 °C. Phase diagram calculation indicates that seamless joining was achieved by the formation of liquid phase at the interface between Dy3Si2C2 and SiC, which was squeezed out under pressure and continuously consumed by the joining interlayer. This work implies the great potential of the family of ternary rare-earth metal carbide Re3Si2C2 (Re = Y, La-Nd) as the sacrificial interlayer for high-quality SiC joining.
Metastable transition metal aluminum nitride (TMAlN, TM = Ti, V) thin films are today deposited utilizing ionized vapor phase condensation techniques where variations in ion flux and ion energy cause ...compressive film stress, in turn affecting Al solubility. While the metastable phase formation of TiAlN has been modeled, the influence of film stresses on phase formation has so far been overlooked. Using combinatorial deposition via magnetron sputtering, thermodynamic modeling and density functional theory calculations, we investigated the phase formation of V1−xAlxN and Ti1−xAlxN thin films at various substrate temperatures and deposition rates. Ab initio calculations indicate that the maximum solid solubility of Al in face-centered cubic (fcc) V1−xAlxN or fcc-Ti1−xAlxN shows a linear trend as a function of the magnitude of compressive stress. Here, we consider the influence of film stresses on the metastable phase formation of fcc-V1−xAlxN and fcc-Ti1−xAlxN for the first time. Specifically, experimental data from a single combinatorial deposition is utilized to predict the stress-dependent formation of metastable phases based on thermodynamic and ab initio data. Explicit consideration of stress extends the Al solubility limit to higher values for both Ti1-xAlxN and V1-xAlxN thin films, previously unobtainable by energetics, but accessible experimentally. These predictions are experimentally verified and thus provide guidance for experimental efforts with the goal of increasing the Al concentration in fcc-TMAlN thin films.
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FeCrAl alloy coatings are widely used for their excellent oxidation resistance at high temperatures, but they can suffer from rapid material degradation due to breakaway oxidation of the coating. ...Composition manipulation is an essential way to prompt the oxidation resistance of the coatings. In this study, we prepared Fe-13Cr-7Al (at.%) alloy coatings with varying Mo contents (Mo = 0, 1.5, 3, 6 at.%) by magnetron sputtering and investigated their oxidation behaviors at 550 °C. The surface and cross-sectional morphologies of the coatings before and after oxidation were examined using electron microscopy. The results showed that the crystalline grain and particle size of the coatings decreased significantly with the increase of Mo content, leading to a notable increase of grain boundaries and further enhancing element diffusion during the oxidation tests. As a result, a protective and stable oxide scale rapidly grew on the surface of FeCrAlMo coatings during oxidation. Moreover, FeCrAlMo coatings demonstrated improved secondary protection mechanisms with increasing Mo contents. This was attributed to the formation of an internal oxidation layer of a spinel barrier (M3O4, M = Fe, Cr, Al, Mo) beneath the outer oxidation layer. The spinel barrier impeded inward diffusion of oxygen ions and outward diffusion of metal cations, resulting in enhanced oxidation resistance of the spinel-type oxide. The thermodynamic calculations were used to evaluate the oxidation mechanisms of the coatings. These results provide a deeper understanding of the effect of Mo addition on the oxidation behavior and underlying protection mechanisms of FeCrAl coatings, and can be beneficial for designing and developing materials for use in oxidation environments.
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•Mo-containing FeCrAl coatings exhibited low oxidation depth with great secondary oxidation protection.•Mo refines grain & provides diffusion paths, leading to form a protective layer quickly.•Mo dissolves in M3O4 oxide layer, which forms the spinel phase and reduces the growth rate of Fe-oxide.•Thermodynamic calculations show Mo stabilizes the M3O4 oxide layer by reducing Gibbs free energy.
Rare earth (RE) oxides are typically used as dopants to improve the toughness of cermet materials. However, their effect on the cermet microstructure remains to be clarified. Towards this end, we ...used a vacuum sintering method to prepare the TiC-based cermets with different La2O3 contents (0.3 wt.% and 0.5 wt.%) and studied the cermet microstructures evolution by coupling experimental approaches and thermodynamic calculations. With the addition of La2O3, the ceramic phase in TiC-based cermets formed the black core-grey rim structure, where the undissolved La2O3 appeared at the edges of grey rims. In addition, an unanticipated solid-solution of La in the ceramic phase was observed, which helped to refine the particle size of the black cores and reduce the porosity of cermets. Correspondingly, the toughness and density were increased as a result of the well-developed grey rims around the black cores and the improved wettability between the ceramic and metallic phases. Thermodynamic calculations further unveiled that the solid-solution of La was inclined to occur in the ceramic phase rather than the metallic phase, while the incorporation of a trace amount of La could enlarge the temperature range of liquid-phase sintering, facilitating the formation of grey rims following an iterative dissolution and precipitation process. Thus, the current work has described the effect of La on the microstructure and mechanical properties of TiC-based cermets, which may help guide the future developments of RE-containing cermets.
Elemental modification of traditional cemented carbides could impart better service properties for offshore drilling applications. The WC-Co-Al cemented carbides that weaken the galvanic corrosion ...effect and expand the immunity were designed based on calculated phase diagram and Pourbaix diagram, with experiments performed to demonstrate their corrosion resistance. As the Al content increased to 0.8 wt%, the corrosion current density decreased by two orders of magnitude and the charge transfer resistance doubled, with a less-damaged binder phase, indicating an improved corrosion resistance. Furthermore, the corrosion products of WC, Al, and Co were WO3, Al2O3, Co3O4, and a small amount of Co(OH)2, respectively, showing a very good agreement between experiments and the calculated Pourbaix diagram. Therefore, the here adopted comparative theoretical and experimental research strategy enables the efficient design of corrosion-resistant cemented carbides.
•Phase diagram and Pourbaix diagram guided corrosion-resistant materials design.•Improved corrosion resistance attained on WC-Co-Al cemented carbides.•Corrosion behavior and micro-mechanism elucidated for WC-Co-Al cemented carbides.
The Y3Si2C2 coating on the surface of the silicon carbide powders can play as an important additive to improve the sintering process of silicon carbide ceramics. A detailed thermodynamic description ...for the Y-Si-C system is desired to study the sintering and densification mechanisms. Coupling the first-principles calculations and CALPHAD approach, we have thermodynamically investigated the Y-Si-C with its binary sub-systems. The presently obtained thermodynamic parameters can reasonably reproduce the available experimental data. With the theoretical analysis, we have successfully elaborated the thermal behaviors of the Y3Si2C2 coating during the sintering process. Similar work on other SiC based systems may provide a solid thermodynamic basis for the development of other sintering aids in ceramics.
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A method to estimate the activation energy for surface diffusion during magnetron sputtering based on experimental metastable phase formation data has been developed. The so obtained ...activation energies are consistent with diffusion activation barriers determined by ab initio calculations. The here adopted comparative experimental and theoretical research strategy enables the efficient acquisition of activation energy data and constitutes an improved description of surface diffusion processes of metastable materials during magnetron sputtering.
