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Detailed electron microscopy investigations were performed to evaluate the effects of PtIr on the growth structure and oxidation resistance of the CrWN coating. The undoped CrWN coating showed an obviously coherent growth and a rough growth texture with a roughness value of 13.80 nm. The doped PtIr atoms induced a prominent structural modification on the CrWN coating and effectively inhibited the coherent growth, leading to a smoother texture and a reduced roughness value of 4.75 nm. The CrWN coating exhibited a loose texture that permitted the internal diffusion of oxygen and degraded its oxidation resistance and roughness, but these doped PtIr atoms had high chemical inertness, which enabled them to act as oxygen diffusion barriers, consequently improving the oxidation resistance and coarsening resistance of the CrWN–PtIr coating. [ABSTRACT FROM AUTHOR]

High-temperature elemental inter-diffusion is an important cause of failure for high-temperature antioxidant coatings on tantalum substrate, yet little research has been reported on improving this phenomenon. A new MoSi 2 composite coating with TaB 2 diffusion barrier was prepared on a tantalum substrate surface by three steps of embedding/slurry sintering/embedding to solve the failure of silicide coating on tantalum substrate due to elemental diffusion under a high-temperature oxidation environment. The composite silicide coating showed excellent oxidation resistance at 1700 ℃, and the protection time was more than 14 h before failure. This may be due to the prevention of diffusion of Si atoms at the initial stage by the TaB 2 with many B atoms in a solid solution. The Mo 5 SiB 2 layer with a low diffusion coefficient will be formed with the slow release of B atoms. The diffusion of Si atoms is further hindered by the formation of a new diffusion barrier between the TaB 2 phase and the main layer, and thus slowing down the depletion of Si elements in the main coating. In addition, the coating successfully passed 1021 thermal cycles from room temperature to 1700 ℃, which may be because of the alleviation of thermal mismatch between the ceramic coating body and the tantalum substrate by a diffusion layer thus reducing the cracking trend of coating. [Display omitted] • A new type of tantalum-based MoSi 2 coating with a TaB 2 diffusion barrier was designed. • The coating showed excellent oxidation resistance at 1700 °C for 14 h. • The cycle thermal shock test life of the coating at room temperature to 1700 ℃ could reach 1021 times. [ABSTRACT FROM AUTHOR]

Owing to the diffusion of Si elements towards the metal substrate and the "pesting" behavior caused by volatilization of MoO 3 , magnetron-sputtered MoSi 2 coating is highly susceptible to failure and unable to protect the metal substrate from oxidation. In this work, therefore, an MoSi 2 (N) interlayer was sputtered on Mo substrates as the diffusion barrier, followed by deposition of Si-doped MoSi 2 (i.e., MoSi 2 (Si)) layer to suppress the "pesting" behavior. The as-deposited coatings were annealed subsequently at 1000 °C in an Ar atmosphere to obtain a stable structure. To evaluate the oxidation resistance, the annealed coating was heated in a muffle furnace in air at 700 °C, 1000 °C and 1200 °C for different durations. The coating structure, surface morphology, cross section and chemical composition were examined by X-ray diffraction, field emission scanning electron microscopy, and energy dispersive spectroscopy. The results showed the MoSi 2 (N) interlayer was amorphous and kept the most stable thermal stability at Ar/N 2 flow rate of 20/20 sccm. It effectively blocked the downward diffusion of Si. Free state Si elements only diffused towards the coating surface. "Pesting" pores in the MoSi 2 (Si) layer were repaired by the growth of SiO 2 layer via the preferential oxidation of Si. The mechanism for the enhanced oxidation resistance was explained through a model. • Amorphous MoSi 2 (N) interlayer is an effective diffusion barrier. • MoSi 2 (N) interlayer blocks diffusion of Si elements in MoSi 2 (Si) coating to enhance oxidation resistance of Mo substrate. • "Pesting" pores are repaired by growth of SiO 2 layer via oxidation of Si. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • W-11.2Cr-1.7 Zr presents the optimal oxidation resistance. • The addition of Zr can improve the high temperature oxidation resistance. • The power law is suitable to exactly describe the oxidation curves. Abstract W-Cr-Zr systems with different compositions were oxidized in a mixed gas (Ar + 20 vol.% O 2) atmosphere at 1000 °C. The power law which was used to describe the oxidation behaviour, indicates that W-11.2wt.%Cr-1.7wt.%Zr has an excellent oxidation behaviour. As analysed from the ten-hour exposure, W-Cr-Zr thin film oxidation shows a self-passivating stage followed by a linear oxidation stage. Furthermore, a study on the addition of zirconium indicates that zirconia particles act as diffusion barriers for the chromium cation diffusion and another function as the nucleation sites for the formation of the initial oxide scale. [ABSTRACT FROM AUTHOR]

Highlights • Nanostructured YSZ top coat slightly reduced double layered TGO growth rate and weight gain of TBCs. • Y was slightly incorporated in the Al 2 O 3 (TGO) layer of HVOF NiCoCrAlTaY coating as Y containing small oxide precipitates. • The segregation of Ta-enriched oxides (TaO x) at the middle of TGO layer led to the formation of some cavities. • TaO x formation in TBCs including MCrAlTaY bond coats can be prevented by presence of Al 2 O 3 film including fine Al-Y oxides. Abstract In this research, the effects of thin Al 2 O 3 diffusion barrier layer (including Y-containing small oxide precipitates) and nanostructured YSZ top coat on the high temperature oxidation behavior of HVOF NiCoCrAlTaY/APS YSZ coatings were examined by using isothermal oxidation tests at 1100 °C. Nanostructured YSZ top coat could slightly reduce the double layered TGO growth rate and weight gain of thermal barrier coating systems. However, Al 2 O 3 diffusion barrier layer (consisting of Y-containing small oxide precipitates) could substantially decline the oxidation rate and Ta movement (Ta-enriched oxides formation) in the NiCoCrAlTaY/Al 2 O 3 /nanostructured YSZ coating at 1100 °C. [ABSTRACT FROM AUTHOR]

The cold spray process has been investigated for the deposition of FeCrAl coatings on optimized ZIRLO™ fuel cladding tubes in order to enhance oxidation resistance at high temperatures (>1000 °C) that would be encountered in loss of coolant accident (LOCA) scenarios. The FeCrAl alloy provides excellent oxidation resistance, however Fe forms a eutectic with Zr at temperatures as low as 928 °C resulting in massive inter-diffusion and associated melting. Therefore, a Mo interlayer coating was developed also using the cold spray process to serve as a diffusion barrier between the Fe-based coating and the Zr-alloy substrate. To achieve a combination of desired properties for the dual-layered coating-substrate, an optimization study of spray parameters such as propellant gas pre-heat temperature, helical spray speed, and the number of spray passes was conducted. This parametric study was aimed at achieving dense coatings with desired thickness and coverage of the substrate, and good adhesion of the Mo interlayer coating with subsequent top FeCrAl coating and the Zr-alloy substrate. The optimal FeCrAl-Mo coating protected the Zr-alloy cladding tubes from oxidation at high temperatures of 1200 °C, while at the same time preventing diffusion-induced eutectic melting in the substrate. [ABSTRACT FROM AUTHOR]

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe 2 Al 5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr 2 O 3 + SiO 2) and Al 2 O 3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe 2 Al 5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer. • Effect of Cr layer on the oxidation resistance of AlSi alloy coating was investigated. • The Cr diffusion triggered the growth of the (Al 2 O 3 + SiO 2) and Al 2 O 3 barrier layer. • This oxide barrier layer effectively suppressed severe inerdiffusion of Fe and Al. • The sufficient upward diffusion of Cr induced a significant self-healing effect. • The AlSi alloy coating with a Cr layer showed an improved oxidation resistance. [ABSTRACT FROM AUTHOR]

A novel Cr barrier layer was designed for suppressing the interdiffusion of an AlSi alloy coating on stainless steel. Without a Cr barrier layer, the same coating experienced a severe element interdiffusion upon exposure to high-temperature air. The rapid upward movement of the Fe atoms induced the formation of the (FeAl + Fe 2 Al 5) alloy compounds and eventually led to severe volume shrinkage and the ultimate fracture of coating. The significant downward diffusion of the (Al + Si) atoms not only triggered numerous pores but also induced the accumulation of the FeAl alloy compound in the substrate resulting in extreme interfacial cracking. In contrast, a diffusion barrier layer comprising (Cr 2 O 3 + SiO 2) and Al 2 O 3 was formed in the coating with a Cr layer during high-temperature exposure, effectively preventing the rapid elemental interdiffusion. Moreover, it inhibited the formation of the (FeAl + Fe 2 Al 5) alloy compounds in the coating as well as prevented the accumulation of the FeAl in the substrate. The obvious upward diffusion of Cr atoms further healed these pores induced by the downward diffusion of (Al + Si) atoms. The strong barrier capability of this composite oxide layer and the healing effect of Cr diffusion eventually led to an improved oxidation resistance of the Cr-coated layer. • Effect of Cr layer on the oxidation resistance of AlSi alloy coating was investigated. • The Cr diffusion triggered the growth of the (Al 2 O 3 + SiO 2) and Al 2 O 3 barrier layer. • This oxide barrier layer effectively suppressed severe inerdiffusion of Fe and Al. • The sufficient upward diffusion of Cr induced a significant self-healing effect. • The AlSi alloy coating with a Cr layer showed an improved oxidation resistance. [ABSTRACT FROM AUTHOR]

To obtain long-term oxidation protection for C/C composites at high temperatures, a dense Si-Cr-W multiphase ceramic coating was prepared on the surface of SiC coated C/C composites by a combined method of slurry brushing, heat treatment and liquid silicon infiltration, which drastically enhanced the oxidation resistance of SiC coated C/C composites at 1773 K and 1973 K in air. The microstructure evolution, phase composition and oxidation behavior of the multiphase coating were analyzed before and after oxidation. Results display that the Si-Cr-W coating with a thickness of ~ 115 µm possessed a dense and uniform multiphase mosaic structure (WSi 2 , CrSi 2 , Cr 5 Si 3 , SiC and Si). The mass loss of the coated sample was only 1.08 mg/cm2 after oxidation for 325 h at 1773 K in air owing to the formation of the compact compound glass layer (SiO 2 , Cr 2 O 3 and WO 3) acted as an oxygen diffusion barrier. The coating can effectively protect C/C substrate from oxidation for 76 h at 1973 K in air, demonstrating its outstanding high-temperature oxidation protective ability. • A dense Si-Cr-W multiphase ceramic coating was prepared on the surface of SiC coated C/C composites. • The Si-Cr-W coating with a thickness of ~ 115 µm possessed a dense and uniform multiphase mosaic structure. • The coating can effectively protect C/C substrate from oxidation for 76 h at 1973 K in air. [ABSTRACT FROM AUTHOR]

A multilayer coating, which consisted of a Cr-Si co-deposited layer as the diffusion barrier, a plasma sprayed NiCrAlY middle layer, and an aluminized top layer, was developed. During the aluminizing treatment, Cr in the NiCrAlY layer was released as the γ/γ′ structure of this layer transformed to the β phase. The released Cr was inhibited by the inner Cr-Si layer to diffuse into the substrate, and a Cr layer eventually formed over the Cr-Si layer. The Cr layer impeded the inward diffusion of Al due to the low solubility of Al in the Cr layer so that more Al atoms remain in the coating and contributed to the oxidation resistance of the coating. The multilayer coating exhibited better oxidation and spallation resistance than coatings without a Cr-Si layer, at least at 1050 °C for up to 1000 h. [ABSTRACT FROM AUTHOR]

To solve the issue of elemental interdiffusion between protective coating and superalloy substrate during high-temperature service, an AlCoCrNiMo high-entropy alloy (HEA) diffusion barrier was deposited by direct current magnetron sputtering between NiAlHf protective coating and Ni-based single crystal superalloy (René N5). The interdiffusion behavior and high-temperature oxidation resistance of the coating system were investigated via isothermal oxidation at 1373 K. After long-term oxidation at 1373 K, no interdiffusion zone (IDZ), secondary reaction zone (SRZ) and rod/needle-like topologically close-packed (TCP) precipitates were observed in the coating system with HEA diffusion barrier. Besides, the NiAlHf coating exhibited an improved oxidation resistance with the addition of HEA diffusion barrier. The results indicate that the HEA diffusion barrier can suppress the interdiffusion of alloying elements between substrate and coating effectively, which is attributed to the sluggish diffusion effect of HEA and the in-suit formed alumina layers at the substrate/HEA and HEA/NiAlHf interfaces during high-temperature oxidation. Moreover, it was found that the Co element in HEA layer also plays an important role in suppressing the formation of SRZ and TCP precipitates in the superalloy. [Display omitted] • An AlCoCrNiMo high-entropy alloy is adopted as the diffusion barrier. • Diffusion barrier effectively retards the elemental interdiffusion at 1373 K. • NiAlHf coating with diffusion barrier shows an improved oxidation resistance. • Co element plays an important role in suppressing the formation of precipitates. [ABSTRACT FROM AUTHOR]

• A coating-free method is used to improve the Cu oxidation resistance under melting. • Pb addition in-situ converts to a reticular structure as protective films. • Pb films locally consume the oxygen and impede oxygen diffusion to the Cu matrix. • Lower contact resistance and temperature rise are achieved after repeated melting. Copper is readily oxidizable in the air, especially at high temperatures. The existing anti-oxidation methods are mainly based on coatings that cannot survive in the harsh environment of repeated melting. This work introduces the in-situ formation of protective films along grain boundaries to improve the oxidation resistance under repeated melting. The Pb is more favorable oxidized than Cu and applied as the protective materials. Under repeated melting, the Pb dissolves in liquid Cu, then precipitates a reticular structure that wrapping up Cu grains and absorbing local oxygens. The formed PbO acts as a diffusion barrier to oxygen. The low-voltage contact test showed the Cu-Pb composite provides better oxidation resistance with a decreased contact resistance and temperature rise compared with pure Cu samples after 5,000 times arcing. [ABSTRACT FROM AUTHOR]

CoCrAlYTaSi coatings with different Al 2 O 3 mass fractions were fabricated on Ti–6Al–4V alloy using a laser cladding (LC). The effects of Al 2 O 3 mass fractions on the microstructure, oxidation resistance and friction–wear performance of obtained coatings were investigated, and the wear mechanisms were also discussed. The results show that the hardness of CoCrAlYTaSi coating increases with the increase of Al 2 O 3 mass fractions, the dendritic structure with the Al 2 O 3 mass fraction of 15% is compactly refined. The diffusion barrier layer of Al 2 O 3 contains Y oxide precipitate, which reduces the oxidation rate and the movement of Ta. The total mass gain per unit area of CoCrAlYTaSi coating with the Al 2 O 3 mass fractions of 15, 30 and 45% is 33.96, 29.82, and 26.27 mg •cm−2, respectively, the oxidation resistance with the Al 2 O 3 mass fraction of 15% is the best among the three kinds of coatings. The average coefficients of friction (COFs) of CoCrAlYTaSi coatings with the Al 2 O 3 mass fractions of 0, 15, 30 and 45% are 1.12, 0.17, 0.23, and 0.35, respectively, and the corresponding wear rates of are 1.59 × 10−4, 1.02 × 10−4, 0.54 × 10−4, and 0.3 × 10−4 mm3 N−1•m−1, respectively, the wear mechanism is abrasive wear and micro–cutting. • The dendritic structure of CoCrAlYTaSi coating decreased with the increase of Al 2 O 3 mass fractions. • The hardness of CoCrAlYTaSi coatings increased with the increase of Al 2 O 3 mass fractions. • The total mass gains per unit area of CoCrAlYTaSi coatings decreased with the increase of Al 2 O 3 mass fractions. • The Al 2 O 3 mass fractions affect the average COFs and wear rates of CoCrAlYTaSi coatings. [ABSTRACT FROM AUTHOR]