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To overcome the critical issue of low density of the MoSi 2 coating prepared by slurry sintering method, a novel strategy of adding diffusion barrier (DB) at the interface was developed to achieve a high density of the coating. The effect of sintering process on the density and microstructure of the MoSi 2 coating was investigated systematically. The addition of DB promotes the formation of dense MoSi 2 coatings with a low area porosity of 0.96–3.98 %, while the value is basically over 41 % for the coatings without DB. The MoSi 2 coating with DB shows an enhanced oxidation resistance due to its dense structure as well as the reduction of the inward diffusion loss of Si by the DB during oxidation. • A novel strategy is proposed to achieve densification of MoSi 2 coating by slurry sintering. • DB can diminish chemical potential gradient to reduce Si diffusion driving force. • The addition of DB promotes the formation of dense coatings with a low area porosity. • The dense MoSi 2 coating exhibits a significantly improved oxidation resistance. • DB can effectively reduce the inward diffusion loss of Si in the coating during oxidation. [ABSTRACT FROM AUTHOR]

A MoSi 2 /NbSi 2 coating with an Al-Si-O interlayer as diffusion barrier was deposited on Nb-based alloy by firstly halide activated pack cementation (HAPC) and then hot press sintering (HPS). The multilayer structure of MoSi 2 /Al-Si-O/NbSi 2 /Nb 5 Si 3 or MoSi 2 /(Nb, Mo) 5 Si 3 /NbSi 2 /Nb 5 Si 3 was formed in the coating with or without the diffusion barrier, respectively. With the addition of diffusion barrier, elemental diffusion was suppressed markedly during formation of the MoSi 2 overlayer and during thermal exposure of the coating sample. Exposed at 1350 °C for 100 h in air, the MoSi 2 /Al-Si-O/NbSi 2 coating exhibited a weight gain about 0.10 mg/cm2 with a slow degeneration in the NbSi 2 transition layer and the thickening rate of surface oxide scale was 0.048 μm2/h, which was increased to 0.15 mg/cm2 and 0.050 μm2/h respectively for the MoSi 2 /NbSi 2 coating without the diffusion barrier. Combining with analyses of the coating formation and the microstructural evolution, mechanism of oxidation resistance and of diffusion for the two coatings were compared and built. • A dense and continuous Al-Si-O interlayer was sandwiched into the MoSi 2 /NbSi 2 coating. • The coating with the interlayer exhibited stronger resistance to corrosion and degeneration. • Interdiffusion was suppressed by the interlayer with strong stability of thermal and structure. [ABSTRACT FROM AUTHOR]

Multi-principal element alloy coatings (MPEACs) have great application potential for high-temperature diffusion barrier coatings. The sluggish diffusion and lattice distortion of this new coating material due to its own atomic size effect give the coating excellent resistance to high temperature oxidation and grain coarsening. In this study, the high-temperature oxidation properties, and microstructure evolution of quaternary, quinary, senary, and denary alloy coatings (whose lattice distortion magnitude is linearly increased) at 1100 °C were studied. The evolution of grain orientation, size, and grain boundaries of alloy coatings after high temperature exposure were analyzed by EBSD. The results showed that from quaternary to denary alloy coatings, with the rise in lattice distortion magnitude of the alloy system, the sluggish diffusion ability of the coating at high temperatures was more obvious. Specifically, the oxidative activation energy of quaternary to denary alloy coatings is 355.41, 480.96, 478.76, and 654.03 kJ/mol, respectively. A high distortion magnitude is beneficial to increase the activation energy of the alloy coating, as a result, grain growth of alloy coatings with high activation energy is significantly inhibited, and under the combined action of storage strain energy and solute dragging, the grain boundary migration rate of the coatings also declines. Finally, the denary alloy coating shows good resistance to high temperature softening. This study provides a positive reference for promoting the application of multi-principal alloys in diffusion barrier coatings. • High-temperature oxidation and microstructure evolution of quaternary, quinary, senary, and denary alloy coatings at 1100 °C were studied. • The oxidative activation energy increases linearly from quaternary to denary alloy coatings. • The grain growth of the coating gradually weakened from quaternary to denary alloy coatings. • Grain boundary migration rates are affected by the combined effects of storage strain energy and solute dragging. • The denary alloy coating shows good resistance to high-temperature softening. [ABSTRACT FROM AUTHOR]

Zirconium alloy has been used as fuel cladding in LWR for a long time. However, during the loss-of-coolant accident, the zirconium alloy cladding will be exposed to steam environment at 1200 °C, and the damage to the cladding is inestimable. Therefore, in this study, Cr and Cr Si coating were prepared on the surface of Zr-4 alloy by magnetron sputtering, and their steam oxidation behaviors at 1200 °C were investigated. The Cr-coated Zr-4 revealed an α-Zr(O) layer with ZrO 2 particles at the interface after oxidation at 1200 °C. However, the Cr Si coated Zr-4 exhibited excellent oxidation resistance due to the introduction of Si atoms. During oxidation, the diffusion barrier of Zr 2 Si layer with Zr Si ionic bonds was formed in situ because of the inward diffusion of Si atoms, which effectively inhibited the inter-diffusion of Zr and Cr. The aggregation of ZrO 2 at the grain boundaries of the coating was prevented, which cut off the short-circuit path of oxygen diffusion inward. Moreover, the first principles calculation was employed to compare the adsorption energies of the external Zr atoms by Zr 2 Si and ZrCr 2 diffusion layers. The adsorption energy of the in situ formed Zr 2 Si layer for Zr atoms is higher than that of the ZrCr 2 layer, which is evidence of the barrier effect of the Zr 2 Si layer. Thus, the Cr Si coated Zr-4 in this work showed a high prospective in the practical applications. • The Cr Si coating exhibits excellent oxidation resistance compared with Cr coating; • Si atoms diffuse inward to the coating/substrate interface at high temperatures; • A Zr 2 Si layer is formed to reduce the outward diffusion rate of Zr atoms; • The Zr 2 Si layer exhibits high adsorption energy for Zr atoms; [ABSTRACT FROM AUTHOR]

(Ni,Pt)Al coating with varying thicknesses of α-W-based diffusion barrier (DB) were prepared by adding various thicknesses of Ni W plating layer. The oxidation performance of the DB-contained coatings was compared to that of the normal (Ni,Pt)Al coating at 1100 °C. With the thicker of DB, the inter-diffusion of Ni, Al as well as the refractory elements was more effectively inhibited. Moreover, better oxidation resistance was observed on (Ni,Pt)Al coating with a thicker DB, exhibiting a lower oxidation rate, flatter surface rumpling extent and slower phase degradation rate. The effects of DB on the inter-diffusion behaviour and oxidation performance of the (Ni,Pt)Al coating are discussed, and the degradation mechanism of the DB is proposed. • (Ni,Pt)Al coatings with varying thicknesses of in situ formed α-W-based diffusion barrier (DB) are prepared. • (Ni,Pt)Al coatings with thicker DB exhibit better oxidation resistance. • Less inter-diffusion occurs for thicker DB-contained (Ni,Pt)Al coatings. • The DB gets degenerating when the intermittent channels between α-W become wide enough. [ABSTRACT FROM AUTHOR]

The reactivity of Al 0.66 Ti 0.33 N, Al 0.31 Ti 0.62 Si 0.07 N, Al 0.60 Cr 0.40 N, and Al 0.38 Cr 0.54 Si 0.07 N cathodic arc-coated hardmetal tools with Inconel 718 has been evaluated by using diffusion couple experiments at 900 °C and 1100 °C. As expected, a strong reaction occurs at these temperatures between Inconel 718 and uncoated hardmetal samples leading to the formation of η phases; mainly M 12 C and M 6 C carbides. PVD coatings act as diffusion barriers limiting the presence of such reactions as long as they maintain their structure in contact with Inconel 718 at high temperatures. Diffusion couple experiments confirm that Cr-containing coatings are significantly more unstable than Al 0.66 Ti 0.33 N or Al 0.31 Ti 0.62 Si 0.07 N materials, thus leading to notable differences in cutting performance. The relation between diffusion couple results and drill wear mechanisms in drilling Inconel 718 with different coating materials are also analysed. The best results are obtained either with Al 0.66 Ti 0.33 N or Al 0.31 Ti 0.62 Si 0.07 N coated drills, where the coating remains longer time at the cutting edge leading to more efficient protection, especially at the drill corner. • Relation between diffusion couples and drill wear. • Interaction between Cr-, Al- and Ti-based coatings with Inconel 718 • Drill wear mechanisms in drilling of Inconel 718 for different tool coating materials. [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]

Inspired by diffusion barriers, (Cr,Al)ON coatings are developed as oxidation protection for gamma titanium aluminide alloys (γ-TiAl), offering oxidation resistance for applications at elevated temperatures, such as turbines. In this study, (Cr,Al)N and (Cr,Al)ON coatings were deposited by means of high speed physical vapor deposition (HS-PVD) technology, basing on hollow cathode discharge (HCD) and gas flow sputtering. Using argon as plasma gas and transport medium, the HS-PVD combines the advantages of thermal spraying and physical vapor deposition, which provides very high deposition rates. The objectives of this study were to synthesize thick PVD (Cr,Al)ON coatings and to understand how various process parameters influence coating morphology, deposition rate and phase composition. Keeping other parameters constant, the argon gas flow was varied between Q Ar = 6000 sccm and Q Ar = 12,000 sccm, different N 2 :O 2 gas flow mixtures from 1:2 to 4:1 were introduced into the coating chamber and the bias voltage was adjusted between U B = − 25 V and U B = − 150 V. A special target configuration was applied for synthesizing coatings with different Cr:Al ratios within one coating cycle. The atomic Cr:Al ratio was varied between 25/75 and 75/25. The results showed that thick s > 35 μm (Cr,Al)ON coatings can be synthesized very efficiently at a deposition rate ds/dt ≈ 20 μm/h. Strong influences of argon gas flow and bias voltage on the deposition rate were revealed. Furthermore, stable plasma processes were observed, even at high oxygen flows Q O2 = 600 sccm, which would lead to target poisoning in conventional PVD processes. In this way, the HS-PVD technology reveals a high potential for the deposition of high temperature oxidation protective coatings and extends the application range of conventional PVD technology significantly. [ABSTRACT FROM AUTHOR]

This work deals with a double-layer coating for the corrosion protection of stainless steel (SS) structures used in molten fluoride salt reactors for energy production. It aims to mitigate the dissolution of chromium from stainless steel structures into the molten salts. On 304SS substrates, three coating layers consisting of NiCoCrAlY, Ni(O), and the nickel layer on the top were deposited by cold spraying. The Ni(O) coating was made by using a powder containing active oxygen and prepared by mechanical-alloyed pure Ni powders in ambient atmosphere. The Al 2 O 3 diffusion barrier was evolved by annealing the cold-sprayed coating system in argon at temperatures ranging from 800 to 1000 °C at the interface between NiCoCrAlY and Ni(O) layers. During the annealing, the Al 2 O 3 layer formed with a growth following a parabolic law, resulting from the reaction of the oxygen in the Ni (O) layer with the aluminium in the NiCoCrAlY layer. The coating test conducted at 900 °C for 100 h in argon showed that the Al 2 O 3 layer changed little during annealing and could effectively prevent the diffusion of Fe and Cr from the SS substrate to the upper Ni layer. [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]

The present work focuses on the preparation of amorphous Si–B–C–N coatings to protect γ -TiAl intermetallic alloys against oxidation above 750 °C that otherwise leads to surface degradation and embrittlement. The film fabrication process included the deposition of an amorphous Si interlayer at a temperature of 700 °C to promote adhesion. Subsequently, Si–B–C–N coatings were prepared by pulsed dc and rf magnetron co-sputtering from Si and B 4 C targets in Ar + N 2 gas mixtures. Specifically, we studied the oxidation behavior of the coatings and the evolution of the microstructure, composition, and mechanical properties upon an isothermal oxidation test performed in laboratory air at 800 °C for 100 h. We found that an optimized Si 40 B 5 C 2 N 47 (at.%) coating protects the γ -TiAl alloy substrate against oxidation by a combination of several effects: a) Interdiffusion of Si and Ti results in the formation of Ti x Si y phases on the film-substrate interface promoting adhesion of the coating, b) Diffusion of Ti to the surface is effectively inhibited and no fast-growing TiO 2 is formed at the outer surface, and c) Stable amorphous structure of Si–B–C–N coatings hinders inward oxidation of O. Investigation of the oxidation kinetics at 800 °C up to 1000 h proved that Si–B–C–N coating serves as an efficient oxidation barrier demonstrated by the significantly reduced mass gain and the parabolic oxidation rate constant (1.05 × 10−13 g2·cm−4·s−1) compared to the uncoated γ -TiAl alloy (5.65 × 10−13 g2·cm−4·s−1). • Si–B–C–N coatings were deposited on the γ -TiAl alloy by pulsed dc and rf magnetron sputtering. • A continuous Si interlayer promotes coating adhesion and inhibits outward Ti diffusion. • Si–B–C–N coatings possess stable composition and amorphous structure during oxidation at 800 °C. • The stable amorphous structure of the Si–B–C–N coatings acts as an efficient oxidation barrier. • Si–B–C–N coatings exhibit significantly reduced mass gain and oxidation rate compared to the γ -TiAl alloy. [ABSTRACT FROM AUTHOR]

Nickel aluminide diffusion coatings act like an aluminium reservoir to form protective alumina scales at high temperatures. However, interdiffusion phenomena play a critical role in the metallurgical integrity of these coatings. This work explores a new type of self-healing coating for high temperature oxidation applications. Micro-reservoirs consisting of an aluminium-rich intermetallic core (Al 3 Ni 2) and an aluminium oxide shell are embedded in a nickel aluminide matrix (NiAl). This new type of coating has been synthesized by an electrochemical chemical route to trap the micro-reservoirs in an electrodeposited nickel matrix followed by aluminization via a slurry route. Under high temperature oxidation conditions, the micro-reservoirs allow to form a diffusion barrier and to release Al into the coating matrix. These two simultaneous phenomena make it possible to maintain a sufficient amount of aluminium and ensure the unique formation of α-alumina at the surface of the coatings, hence to possibly increase the lifespan of the aluminium diffusion coatings. [Display omitted] • Successful synthesis of a self-regenerating aluminide coating • Coating made of preoxidized Al-rich NixAly reservoirs in a nickel aluminide matrix • Reservoirs trapped in a Ni electrodeposit that is subsequently aluminized by slurry • Distribution of reservoirs in high energy areas of the coatings • Loss of Al by interdiffusion reduced to 6 % vs. 30 % in the absence of the reservoirs [ABSTRACT FROM AUTHOR]

This paper studied the effects of internal oxide contents on the high temperature oxidation and β-phase depletion behaviour of high velocity oxygen fuel (HVOF) thermally sprayed CoNiCrAlY coatings. Two oxygen-to-kerosene ratios were employed in the HVOF thermal spraying process to generate different internal oxide contents in the as-deposited CoNiCrAlY coatings. The isothermal oxidation behaviour of the as-deposited CoNiCrAlY coatings were examined in air at 1100 °C. The as-deposited HVOF CoNiCrAlY coatings before and after oxidation were characterised by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It was shown that the high oxygen-to-kerosene ratio caused significant oxidation of in-flight particles, resulting in a large volume fraction of the internal oxides in the as-deposited CoNiCrAlY coatings. Furthermore, it was found that the CoNiCrAlY coating with a higher content of internal oxides exhibited larger mass gain and significant β-phase depletion during oxidation. This is likely due to that the Al in the coating was initially consumed during the spraying process and the discrete internal oxide stringers were not effective diffusion barriers. • Two CoNiCrAlY coatings were prepared at different oxygen-to-kerosene ratios. • The internal oxides were found to be Al-rich oxides by EDS analysis. • High mass gain was found in the coating with high internal oxide content. • Rapid β-phase depletion occurred in the coating with high internal oxide content. [ABSTRACT FROM AUTHOR]

Cr 2 AlC coating has potential applications as high temperature protective coating. However, inevitable interdiffusion at coating/substrate interface promotes Al depletion and deteriorates its oxidation resistance. In the present work, the oxidation behavior of a triple-layered Cr 2 AlC coating, with (Cr,Al) 2 O 3 inner layer, amorphous intermediate layer and crystalline Cr 2 AlC outer layer, was investigated at 900 and 1000 °C in air. The effect of the (Cr,Al) 2 O 3 inner layer as diffusion barrier was evaluated during the oxidation process. It is showed that the triple-layered Cr 2 AlC coating could effectively improve the oxidation resistance of the M38G alloy substrate, due to the Cr 2 AlC outer layer. The (Cr,Al) 2 O 3 inner layer could prohibit internal nitridation and retard interdiffusion at the coating/substrate interface, improving oxidation resistance of the triple-layered Cr 2 AlC coating. Furthermore, cracking of the triple-layered Cr 2 AlC coating was found after oxidation at 900 and 1000 °C, due to the thermal stress and internal stress introduced by intermediate amorphous layer crystallization during oxidation. • The triple-layered coating improves the oxidation resistance of the M38G alloy effectively. • The (Cr,Al) 2 O 3 inner layer prohibits inter diffusion and internal nitridation during oxidation. • Thermal stress and stress due to amorphous layer crystallization lead to cracking of the coating. [ABSTRACT FROM AUTHOR]

We present a first-principles study of pressure- and temperature-dependent diffusion barriers and coefficients for vacancy-mediated and interstitial V impurity and Ti self-diffusion in TiN. The thus obtained diffusion coefficients were fitted with an Arrhenius-type relation yielding pre-exponential coefficients and activation energies. Our results suggest that (i) V diffuses faster than Ti, (ii) vacancy-mediated mechanism is dominating over the interstitial one, and (iii) impact of pressure is much weaker than the impact of temperature. • V diffusion in TiN for knowledge-based design of novel tribological coatings • Pressure decreases diffusion rate, the effect is weaker than impact of temperature. • Vanadium impurities diffuse faster than titanium matrix atoms. • Interstitial diffusion leads to much smaller mass transport than vacancy-mediated. [ABSTRACT FROM AUTHOR]

An effective diffusion barrier between the superalloy and aluminide coating would reduce coating degradation by lowering the rate of Al loss to the substrate by interdiffusion, and by inhibiting diffusion of substrate elements (such as Cr, Re, Ta, W) into the coating, which degrade its corrosion and oxidation resistance. In this preliminary study, sputtered Hf–Ni and Hf–Pt were evaluated as potential high-temperature diffusion barrier layers beneath NiAl or NiPtAl coatings.A Ni3Hf-type layer formed during aluminizing of Ni–Hf thin films, and appeared to result in reduced β-NiAl depletion during oxidation testing at 1150 °C. Some Hf-containing simple aluminide coatings also showed very good oxidation resistance. However, the Ni–Hf phase disrupted coating microstructure and displayed limited high-temperature stability. Heat treatment of Hf and Pt thin films formed a compound similar to HfPt3-type, which subsequently dissolved during aluminizing. [Copyright &y& Elsevier]

The micro-arc oxidation (MAO) coating with different nanoparticles (Al 2 O 3 , MoS 2 , CeO 2 , and graphene oxide (GO)) was prepared on zirconium (Zr) alloy. The surface morphology, cross-section morphology, element composition, and phase structure of different composite MAO coating were investigated. Results show the composite MAO coating consists of ZrO 2 and nanoparticle, along with all the coating present a typical porous structure. The composite MAO coating is comprised of an outer porous layer and inner dense layer, and most of the nanoparticle is gathered to the outer layer. The electrochemical results demonstrate that composite MAO coating presents better corrosion protection to Zr alloy, and the MAO coating with Al 2 O 3 shows the best corrosion resistance. Because the Al 2 O 3 nanoparticle can stabilize the t-ZrO 2 during MAO process and has a denser inner layer. Meanwhile, the nanoparticles in the coating can play the part of a barrier to the diffusion pathway of corrosion medium and restrain aggressive corrosion medium entering the Zr alloy. The fretting corrosion test shows that the MAO coating with GO has the lowest wear volume, and it has the highest material loss volume ratio of corrosion induced by wear. Because GO in MAO coating can reduce the friction by small shear force between the layers. • The formation mechanism of MAO coating with different nanoparticles was proposed. • Role of nanoparticles on the corrosion behavior of MAO coating was inveatigeted. • MAO coating with GO shows the highest material loss ratio of corrosion induced by wear. [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]