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Laser cladding was used to synthesize the coatings of the AlCoCr 0.5 NiTa x Ti (N) alloys on a Ti–6Al–4 V substrate. As the Ta content increased, the alloy evolved from columnar crystals composed of dendritic face-centered cubic (FCC)/L1 2 phases and interdendritic Laves phases to a eutectic structure. The high-valence state of Ta diminished oxygen vacancies in TiO 2 , which reduced the diffusion rate, so an appropriate Ta content improved high-temperature oxidation resistance. In the cladding process, nitrogen from the protective gas was partially dissolved in the alloy and partially formed Ti 2 N, both of which act as diffusion barriers for titanium, inhibiting the formation of titanium oxide and promoting the formation of continuous single aluminum oxide, thereby improving oxidation resistance at high temperatures. • AlCoCr 0.5 NiTa x Ti(N) coating consists of FCC/L1 2 and Laves phases. • An increase in Ta content promoted the formation of eutectic structures. • These coatings, oxidized in air at 800 °C for 240 h, followed a parabolic law. • Ta reduced the oxygen vacancies in TiO 2 , thereby improving oxidation performance. • Ti 2 N and a nitrogen-rich solid solution within the coating inhibited TiO 2 formation. [ABSTRACT FROM AUTHOR]

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]

The elemental interdiffusion between the bond-coat in thermal barrier coatings and the superalloy substrate has emerged as a critical factor in the failure of turbine blades. In order to mitigate this elemental interdiffusion, a Zr/ZrN diffusion barrier was strategically designed and deposited between the NiCrAlY bond-coat and the superalloy substrate using multi-arc ion plating. The performance of the as-deposited coatings was evaluated through annealing, quenching, thermal cycle oxidation, and isothermal oxidation tests. The microstructural evolutions of the Zr/ZrN diffusion barrier and the NiCrAlY bond-coat were investigated. The Zr/ZrN diffusion barrier exhibited remarkable bonding strength and diffusion barrier effect. Importantly, the structural integrity of the diffusion barrier remained unaffected by thermal stresses during quenching and thermal oxidation tests. Additionally, twins were observed within the ZrN layer after thermal cycle oxidation tests. The application of the Zr/ZrN diffusion barrier layer substantially enhanced the oxidation resistance of NiCrAlY by preventing the depletion of Al. These results suggest that ZrN holds promise as a favorable candidate material for diffusion barriers. • A Zr/ZrN double-layer diffusion barrier was deposited between NiCrAlY and superalloy. • The diffusion barrier showed excellent bonding property under large thermal stress. • The diffusion barrier can significantly improve the oxidation resistance of NiCrAlY. • Twins have formed in ZrN after thermal cycle oxidation. • Zr/ZrN can be an auspicious diffusion barrier material. [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 suitability of refractory high entropy metal sublattice nitride (HEAN) thin films to act as diffusion barrier between Cu and Si was evaluated. For this purpose, bi-layers comprising a 150 nm thick Cu layer and a 20 nm thick layer based on (MoNbTaW)N and alloyed with either Ti, V, Cr, Mn, Zr or Hf have been deposited onto Si substrates using high power impulse magnetron sputtering. Subsequently, the bi-layers were annealed up to 950 °C in vacuum and analyzed by X-ray diffraction, confocal laser scanning microscopy and resistance measurements to check for barrier failure. Depending on the elements present in the HEAN layer, two failure modes were identified: (1) interdiffusion of Cu and Si leading to the formation of Cu 3 Si starting at 850 °C and (2) dewetting of the Cu layer starting at 900 °C. A better barrier performance could be correlated to a lower formation enthalpy of the binary nitride of metals present in the HEAN layer leading to the conclusion that more stable metal‑nitrogen bonds in the HEAN phase are beneficial for its diffusion barrier performance. • Diffusion barrier performance of refractory high entropy alloy nitride films assessed • Synthesis by high power impulse magnetron sputtering at room temperature • No barrier failure observed up to 800 °C for all films • Cu 3 Si formation at 850 °C and dewetting of Cu at 950 °C identified as failure modes [ABSTRACT FROM AUTHOR]

The transition layer prepared on the cemented carbide surface through double glow plasma surface alloying (DGPSA) is believed to be an effective strategy to improve the adhesion between the diamond and cemented carbide. In this work, to fully reveal and understand the behavior of double glow discharge plasma, DGPSA processes were studied using optical emission spectroscopy (OES), and the effect of the as-prepared TiMoTa transition layer on the diamond growth mechanism and adhesion property was analyzed. The microstructure, composition, and adhesion properties of TiMoTa transition layers and diamond coating were analyzed using SEM, TEM, XPS, XRD, and Rockwell C indentation. The results indicated that the intensity of the plasmas (Ti, Mo, and Ta) remained stable with the deposition time with the increase of deposition temperature, the electron temperature remained in the range of 1 × 104–1.4 × 104 K during the deposition process. OES results showed that the TiMoTa transition layer with a high deposition rate and high performance can be prepared by selecting the appropriate deposition temperature and time through DGPSA technique. The TiMoTa transition interlayers with nanocrystalline structure can effectively restrain the out-diffusion of Co and the in-diffusion of C, thereby effectively improving the adhesion between diamond and cemented carbide. Hence, the TiMoTa transition layer prepared through DGPSA technique offers an effective way to develop a good adhesion diamond coating on WC-Co substrate. • TiMoTa interlayers were prepared by double glow plasma surface alloying technique. • The deposition of TiMoTa interlayer was in situ investigated by OES. • The TiMoTa interlayer can serve as effective cobalt and carbon diffusion barrier. • Plasma is composed of Ti, Mo, Ta, and W atoms, monovalent Ar ions, and Ti ions. • TiMoTa is an optimal interlayer material for enhancing the adhesion of diamond. [ABSTRACT FROM AUTHOR]

TaN and TiB 2 ceramic coatings on steel were tested as barriers to protect steel against molten aluminum by sessile drop experiments. Coatings tested were deposited by PVD using conventional DC-MS (Direct Current Magnetron Sputtering) and HiPIMS (High-Power Impulse Magnetron Sputtering) techniques. The evolution of contact angle and contact radius of the molten aluminum drop was recorded at 800 °C for H13 tool steel bare and coated samples. The influence of the thickness and microstructure of the coatings was investigated by XRD, SEM/EDS to elucidate the mechanism of the wetting process. Spreading rate of aluminum on coated samples was between 10 and 50 times slower than on bare steel samples. Coated samples showed reactive wettability with a reaction-controlled spreading stage observed as a constant spreading rate after an initial transient stage. The spreading mechanism of the molten metal on coated samples is a two-step mechanism: (i) molten metal infiltration through the coatings and (ii) fracture of the coating after the formation of Fe-Al intermetallic compounds that leads to an increased volume of the metallic substrate. The quantification of both steps proves that the coating's thickness plays a key role in the reactive wettability kinetics. Results show that HiPIMS deposited TaN coatings could be a promising candidate to protect steels against molten aluminum attack. • TaN and TiB 2 coated AISI H13 steel show reactive wettability with molten aluminum. • Wetting proceeds via a two-step mechanism: infiltration and fracture of the coating. • TaN HiPIMS coatings show better resistance than TaN DC-MS. • Results show that the thicker the coating, the slower the spreading rate. [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]

Abstract The zirconia (ZrO 2) as a precursor layer for the diffusion barrier coating (DBC) was deposited by electron beam physical vapor deposition (EB-PVD) between the René N5 superalloy substrate and NiCrAl coating. The high temperature exposure for the N5/ZrO 2 /NiCrAl system was carried out at 1000 °C for 5 h, 100 h and 200 h in atmosphere to investigate the structure evolution of the ZrO 2 precursor layer and the elements interdiffusion of the system compared with the N5/NiCrAl system. The results showed that a sandwich structural DBC (α-Al 2 O 3 /rich-Zr/α-Al 2 O 3) was formed through redox reaction between zirconia and aluminum under high temperature, leading to the transformation of N5/ZrO 2 /NiCrAl system into the N5/DBC/NiCrAl system. It was found that the sandwiched DBC could effectively suppress the interdiffusion of elements compared to the N5/NiCrAl system. Highlights • René N5-type superalloy was used as the substrate. • ZrO 2 was used as a precursor layer of diffusion barrier coating (DBC). • A sandwich structural DBC was formed at high temperature. • The DBC was located between the superalloy substrate and a NiCrAlY bond coat. • The sandwiched DBC could effectively suppress the interdiffusion of elements. [ABSTRACT FROM AUTHOR]

Fuel clad chemical interaction (FCCI) is a pervasive issue for metallic nuclear fuels. FCCI can damage cladding, reduce thermal efficiency, and compromise the structural integrity of the fuel rod. In this study, we evaluated the FCCI mitigation capabilities of electrophoretically-deposited Zr nanoparticle coatings on ferritic-martensitic stainless-steel cladding (HT9). Zr was deposited on the internal surface of 6 mm outer diameter cladding using electrophoretic deposition (EPD). Thickness varied among samples with similar EPD conditions. A uniformly coated sample was selected and sent to the Argonne Tandem Linac Accelerator System (ATLAS) to simulate the coating's behavior under irradiation conditions. The coating prevented FCCI in diffusion couple studies. Results of this study confirm that Zr could potentially make an effective FCCI barrier in metallic fuel rods but the deposition process needs improvement. • Demonstrated zirconium coating in nuclear cladding with nanoparticle electrophoresis • Diffusion analysis shows coatings help prevent uranium diffusion. • Electrophoretic deposition fabricates non-line-of-sight coating. • Adhesion of zirconium nanoparticle coatings improves under ion irradiation. [ABSTRACT FROM AUTHOR]

The cyclic and early isothermal oxidation behaviors at 1050 °C of the NiCoCrAlY, Pt-modified NiCoCrAlY and Pt-modified NiCoCrAlY with Re-based diffusion barrier (DB) have been evaluated. The atomic immigration and electron location function (ELF) at the Ni-Re interface were simulated by density function theory (DFT) calculations. After isothermal oxidation for 1 h, island NiCoCrAlY particles with extremely poor Al were observed in the oxide scale of normal NiCoCrAlY coating, and then the oxide scale transformed into a double-layer structure after oxidation for 20 h. The initial "island-oxide" scale model was proposed to illustrate the oxidation mechanisms for normal NiCoCrAlY coating. The oxide scale of Pt-modified NiCoCrAlY coating was single-layer Al 2 O 3 with rapid coverage at the surface, because the modification of Pt changed the initial oxidation mechanism by promoting the uphill diffusion of Al. The Re-based DB reduced the thickness of the secondary reaction zone (SRZ) by inhibiting the element interdiffusion between the NiCoCrAlY coating and the substrate, thus the Pt-modified NiCoCrAlY with Re-based DB exhibited the lowest interdiffusion extent. Interestingly, the thermal stability of Re-based DB in NiCoCrAlY coating system was poorer than that in NiCrAlY system. The DFT simulation shows that the incorporation of Co made the energy difference more negative, which confirmed that Co promoted the diffusion of Re in the NiCoCrAlY coating, thus accelerating the degradation of Re-based DB. • A model of "island-oxide" scale on NiCoCrAlY coating in initial oxidation is proposed. • A novel Pt-modified NiCoCrAlY coating with Re-based DB layer is fabricated. • Pt modification changes initial oxidation mechanism and increases adhesion of oxide scale. • Co promoted the diffusion of Re and accelerated the degradation of Re-based DB. [ABSTRACT FROM AUTHOR]

The duplex coating system consisted of electroplated Re-Ni as the diffusion barrier layer and the thermally sprayed NiCoCrAlY coating deposited. The adhesion strength and thermal shock resistance of the NiCoCrAlY coatings with and without the diffusion barrier were evaluated. Thermal shock resistance was investigated by quenching the coated samples in cold water from the temperature of 1100 °C. Also, the capability of Re-Ni as the diffusion barrier layer was investigated by isothermal oxidation at 1100 °C. The results showed that application of the thin interlayer of Re-Ni as a diffusion barrier beneath the NiCoCrAlY coating could slightly decrease the thermal shock and the adhesion strength of the NiCoCrAlY coating. The thermal expansion coefficient mismatch between the Re-Ni diffusion barrier and the NiCoCrAlY coating and the reduction of the substrate surface roughness due to Re-Ni deposition were the two main mechanisms limiting the lifetime of the NiCoCrAlY coating. But with significant improvement in oxidation resistance, these limitations could be compensated. [ABSTRACT FROM AUTHOR]

A platinum:silicon carbide thermocouple has been developed to measure the surface temperature of ceramic matrix composites (CMC) with high resolution. Platinum was deposited by rf sputtering onto a SiC-SiC CMC substrates coated with a dielectric, such that the SiC-SiC CMC was one thermoelement and the platinum film was another thermoelement comprising the Pt:SiC(CMC) thermocouple. The purpose of the dielectric was to electrically isolate the platinum leads from the SiC-SiC CMC. The thermoelectric output, hysteresis and drift of the Pt:SiC(CMC) thermocouples were measured at temperatures ranging from 600 °C to 1000 °C. The thermoelectric powers generated by the Pt:SiC thermocouples were an order in magnitude greater than conventional Pt:Pd or Type K thermocouples. Thermoelectric powers as large as 250 μV/K were reported for these thermocouples, as compared to thermoelectric powers of 10 μV/K reported for Pt:Pd and Type K thermocouples. The results presented within show that the Pt:SiC(CMC) thermocouples exhibit excellent stability at high temperatures, relatively low drift rates, and little hysteresis during thermal cycling. However, the Pt:SiC junctions were prone to oxidation effects as well as the formation of platinum silicides at high temperature, which can compromise the junction and lead to excessive drift. Therefore, a number of diffusion barrier coatings were applied to the Pt:SiC junctions in an attempt to improve stability and lower drift in this promising new class of thermocouples. [ABSTRACT FROM AUTHOR]

In this study, Cr 2 N and (Cr,W) 2 N coatings were deposited on Crofer 22 APU ferritic stainless steel as protective coatings by using cathodic arc evaporation. Oxidation kinetics of the Cr 2 N- and (Cr,W) 2 N-coated samples were evaluated through isothermal tests in an atmospheric furnace at 800 °C for 1000 h. The results showed that (Cr,W) 2 N comprised Cr 2 N and W 2 N and possessed a fine-grained columnar structure. The average grain sizes of Cr 2 N and W 2 N were 7.2 and 5.0 nm, respectively, and that of the deposited Cr 2 N coating was 12.7 nm. After oxidation at 800 °C for 1000 h, both the Cr 2 N and (Cr,W) 2 N coatings had bilayer scales comprising Cr 2 O 3 and (Mn,Cr) 3 O 4 . The Cr 2 N and (Cr,W) 2 N coatings exhibited similar oxidation curves and a two stages of oxidation mechanism. The main reason for the occurrence of the dominant oxidation mechanism transfer is the growth of Cr 2 O 3 and (Mn,Cr) 3 O 4 spinel. Moreover, the doping of W benefited the formation of a χ phase to precipitate at the oxide/coating interface, which acted as a diffusion barrier retarding the reaction rate between Cr and O. [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]

A gradient NiCoCrAlY coating with a Re -base diffusion barrier (RG-NiCoCrAlY) was prepared by sequential treatments of Ni Re coelectrodeposition, arc ion plating and chemical vapor aluminization. For comparison, normal NiCoCrAlY and simply aluminized NiCoCrAlY coatings (G-NiCoCrAlY) were also prepared to assess their cyclic oxidation behavior at 1050 °C. The results indicated that the oxide scale formed on the normal NiCoCrAlY coating peeled off after 400 cycles, while the G-NiCoCrAlY and RG-NiCoCrAlY coatings developed and maintained continuously dense alumina scale after oxidation for 600 cycles, confirming the benefits of increasing the Al content in NiCoCrAlY. In contrast to G-NiCoCrAlY, the presence of Re -base diffusion barrier mitigated element interdiffusion, which not only reserved Al in the coating but also reduced the outward diffusion of refractory elements from the substrate, thus was capable of minimizing precipitation of topologically close-packed phase (TCP) in single-crystal superalloy. Instead of outward diffusion, refractory elements were dissolved in the diffusion barrier and became fixed. Undoubtedly, the best anti-cycling performance was achieved by the RG-NiCoCrAlY coating. The mechanisms of the effect of the Re -base diffusion barrier on oxide scale growth and elemental interdiffusion, which influence the overall oxidation behavior of the NiCoCrAlY coating, are discussed. • An Al-gradient NiCoCrAlY coating with Re -base DB is prepared on single crystal superalloy. • RG-NiCoCrAlY exhibits best oxidation resistance by the higher Al content and the Re-base DB. • Re-base DB prevents inward diffusion of Al and outward diffusion of refractory elements. • SRZ formation and TCP precipitation are alleviated by the Re-base DB [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]

Mo 2 N skin layers were formed on columnar-structural Mo films by simple NH 3 plasma nitridation. The plasma-nitrided Mo (n-Mo) films contained the (111) preferred phase of γ–Mo 2 N phase and (112) preferred phase of β-Mo 2 N. The thickness of n-Mo films slightly increased without structural morphology change compared to that of pure-Mo films, and seldom changed after selenization. The electrical properties of the n-Mo films changed slightly compared to the Mo films after nitridation and the resistivity of the n-Mo films exhibited a slight increase after selenization. N-element was found widely along the z-axis of n-Mo films, and the concentration of N decreased gradually from the surface to bottom of Mo films. These results imply that the diffusion of N element occurred simultaneously along the lattice and grain boundaries (GB), which followed B-kinetics of Harrison's classification (GB width ≪ nitridation depth ≪ grain size). The n-Mo films exhibited the strong chemical stability under Se-environment, and the method developed in this study was an easy and effective technique for forming a Mo 2 N skin layer. Therefore, it is expected that this method can not only extend the process margin for selenization, but also reduce the resistive components in solar cell devices. [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]

MCrAlY (M denotes Ni and/or Co) coatings are widely used on the turbine blades to protect the aeroengine at high temperature. However, the interdiffusion between coating/substrate and the coefficient of thermal expansion (CTE) mismatch between protective oxides layer/coating are the main factors that limit the service lifetime of MCrAlY coatings. In this work, a Ni+CrAlYSiHfN/AlN nanocomposite duplex coating system was designed to improve the weakness of conventional MCrAlY coatings. The nanocomposite coating system exhibited a low oxidation rate in the 1000 °C isothermal oxidation test and the oxidation rate constant of the coating system was 6.33 ∗ 10 − 13 g 2 cm − 4 s − 1 at the first 20 h, and then the TGO grew at a low constant of 1.49 ∗ 10 − 13 g 2 cm − 4 s − 1 until 200 h. Besides, the AlN diffusion barrier effectively inhibited the interdiffusion between coating/substrate. The evolution of coating microstructures and thermal growth oxides (TGO) at high temperature were studied with the aid of transmission electron microscopy. [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]

Direct-current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) were used to deposit understoichiometric Ti 1-x Al x B 2-y diboride coatings by sputtering from a segmented TiB 2 -AlB 2 target using Ar and Kr as sputtering gas. For films with a fixed Al/(Ti + Al) ratio of x = 0.1 (Ti 0.9 Al 0.1 B 2-y), the B content was varied with y ∈ (0.1, 0.6 and 0.7). For films with a fixed y = 0.7 (Ti 1-x Al x B 1.3), the Al content was varied with x ∈ (0.1, 0.4 and 0.7). Evaluation of the mechanical properties of the Ti 1-x Al x B 1.3 samples showed a reduction in both hardness and elastic modulus with increasing Al concentration, while the Ti 0.9 Al 0.1 B 2-y samples showed a hardness increase with decreasing B content. Thus, Ti 0.9 Al 0.1 B 1.3 films exhibited a superior hardness of 46.2 ± 1.1 GPa and an elastic modulus of 523 ± 7 GPa, compared to the values for Ti 0.9 Al 0.1 B 1.4 and Ti 0.9 Al 0.1 B 1.9 , showing a hardness of 44 ± 1 GPa and 36 ± 1 GPa, and an elastic modulus of 569 ± 7 GPa and 493 ± 6 GPa, respectively. The oxidation behavior of the mechanically most promising Ti 0.9 Al 0.1 B 2-y sample series was investigated through air-annealing at 600 °C for durations from 1 h to 10 h. All films formed a mixed non-conformal Al 2 O 3 -TiO 2 oxide scale which acts as an inward and outward diffusion barrier, significantly reducing the oxidation rate compared to TiB z films, which form an oxide scale consisting of porous TiO 2. The thinnest oxide scale after 10 h was found in the B-deficient samples, Ti 0.9 Al 0.1 B 1.3 and Ti 0.9 Al 0.1 B 1.4 , at ~200 nm, which is significantly below that for Ti 0.9 Al 0.1 B 1.9 at 320 nm. The enhanced oxidation resistance of highly understoichiometric films is due to the elimination of the B-rich tissue phase that is present at the grain boundaries for higher B content, where the latter has been shown to enhance the rate of oxidation in borides. [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]

Surface-modified Zr alloys by protective coatings are being developed as the most viable near-term accident tolerant fuel (ATF) claddings. Herein, an amorphous FeCrAlMoSiY coating was deposited on Zr alloys by magnetron sputtering. The key performance of specimens in terms of ion irradiation, autoclave corrosion, and high-temperature steam oxidation were studied using X-ray diffractometer (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM). We found that the surface of the irradiated coating became more compact with a lower surface roughness than the as-deposited coating. Meanwhile, the hardness and indentation modulus decreased slightly after irradiation. After 30 days autoclave corrosion, a continuous spinel FeCr 2 O 4 scale was formed on the surface, and the residual coating had the same composition and ~76% in thickness of that of the as-deposited coating. During the 1200 °C steam oxidation of that corroded sample, the protective α-Al 2 O 3 scale was formed underneath the FeCr 2 O 4 layer, along with the formation of a diffusion barrier at the coating-substrate interface. These findings highlight the potential of the FeCrAlMoSiY coating considered as a protective coating for ATF claddings. • An amorphous FeCrAlMoSiY coating was deposited. • Irradiation-induced smoother surface and decreased hardness. • High corrosion resistance in 345 °C and 16.5 MPa autoclave. • Corroded specimens retain excellent oxidation resistance in 1200 °C steam. [ABSTRACT FROM AUTHOR]

Having been deposited on 304 stainless steel (SS304) substrates by RF reactive co-sputtering, 1 μm-thick Ti-Cr-N films were annealed at 400 °C and 700 °C. Accordingly, nitride phases of TiN and CrN, and as a result of the lost capability as an oxygen diffusion barrier, oxide phases of Fe 2 O 3 , Cr 2 O 3 , and TiO 2 formed after the annealing process at 700 °C. For short-term immersion (1 h), the corrosion testing illustrated that the film annealed at 400 °C shows greater corrosion resistance than the other films and SS304. For long-term immersion (30 days), all the films demonstrated greater corrosion resistance than SS304, with the as-deposited film delivering the best performance. It was found that protective passivation layer formation, porosity closures, and surface characteristics such as pits, trenches, grooves, cracks, and protuberances govern the corrosion behavior differences. The surface micrographs imply that pitting corrosion and superficial filiform corrosion are among the underlying mechanisms affecting the surfaces. Finally, given the concerns about the capability of SS304 to release toxic elements such as chromium, it was determined that not only can Ti-Cr-N films increase the corrosion resistance of SS304 but also they can reduce the release of chromium by almost 67% in the long-term exposure. [Display omitted] • 1 μm thick Ti-Cr-N films were deposited by RF reactive co-sputtering. • The GIXRD shows TiN, CrN, Fe 2 O 3 , Cr 2 O 3 , and TiO 2 phases after annealing at 700 °C. • Surface features/porosity closures/passivation layers govern the corrosion behavior. • Pitting corrosion and superficial filiform corrosion affect the corroded surfaces. • Ti-Cr-N films can reduce the SS304's release of the potentially toxic Cr by 67%. [ABSTRACT FROM AUTHOR]

Abstract: A CeO2 dispersed δ-Ni2Al3 was formed by partially aluminizing an electrodeposited Ni film containing CeO2. The aluminide/Ni–CeO2 coating system itself quickly formed a CeO2-rich diffusion barrier between aluminide and Ni during annealing in vacuum at 1000°C. A model for the formation of the diffusion barrier was proposed, based on the characterization of the evolution with time of the phase compositions of the aluminide at the interface. [Copyright &y& Elsevier]

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]

An oxidation or nitridation treatment was performed on the interfacial layer (IL) with optimal oxidation state in order to form an oxygen diffusion barrier for Ge nMOSFET. Through the analysis of X-ray photoelectron spectroscopy and electrical characterization of Ge nMOSFET, the reaction mechanism and physical model were studied in details. The fewer interface traps and lower subthreshold swing can be achieved by forming oxygen diffusion barrier in an optimal IL with remote NH 3 plasma. As compared to devices with oxidation treatments, that improvement can be attributed to the nitrogen passivation and alloy-like interface formation. The proposed oxygen diffusion barrier with remote NH 3 plasma treatment on IL is a promising technique to improve the interface properties effectively without influencing equivalent oxide thickness for high performance Ge nMOSFET. • An interfacial layer buffer formation method is proposed. • An oxygen diffusion barrier can be formed by remote plasma treatment. • A n-channel Ge transistor can be enhanced by NH 3 plasma. • Reaction mechanism about oxygen diffusion is explained by material analysis. [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]

Abstract: Chromium, zirconium, niobium and tantalum nitrides layers have been sputtered onto WC–12 wt.% Co substrates as diffusion barriers and buffer layers for improving performances of diamond surface coating. X-ray diffraction shows under specific reactive sputtering conditions, only MN (M=Cr, Zr, Nb, Ta) type phase exits. Their electric resistivity has been measured on samples deposited onto silica under the same conditions and related to those published. Surface and transverse scanning electron microscopy shows a dense columnar morphology. Thermo chemical computing proves the stability of those nitrides against Co, hydrogen and methane up to 1150 K (877 °C). A computed diagram of nitrogen partial pressure is given for their carburization with methane showing the highest stability for ZrN and TaN. Diamond deposition for 5 h up to 1153 K (880 °C) highlights a different behaviour for each of those materials. Auger Electron Spectroscopy (AES) profiles show a massive diffusion of cobalt through the decomposed CrN layer, a transformation of TaN and NbN into carbide without diffusion of cobalt while ZrN is outstandingly well preserved. [Copyright &y& Elsevier]

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]

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]

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]

Ni was deposited on sintered NdFeB magnets by pulse current (PC) electro-deposition. And a better corrosion resistance of the deposits was observed. Growth direction of the Ni particles was changed to be in two dimensions, which provided the minimal defects and smooth interface, the smooth and pyknotic Ni deposits were observed. The texture of the Ni deposits by PC showed a preferred orientation along the (111) plane and a reduction in the number of extra phases, which improved the quality and corrosion resistance of the Ni deposits. In addition, the difference of the diffusion energy barrier on the different crystal surfaces results in electrochemical corrosion of the Ni deposits by first-principles calculation. These results can provide an appropriate explanation for the corrosion mechanism of Ni deposits, the theoretical corrosion model of Ni deposits was established. • The Ni deposit by pulse current got the greater corrosion resistance. • The Ni deposits by PC obtained the great morphology compared with Ni deposits by DC. • The preferred orientation on (111) is conducive to the improvement of corrosion resistance. • The diffusion energy of O on different crystal structures explained corrosion mechanism of Ni deposits. • The theoretical model the corrosion mechanism of Ni deposits was established. [ABSTRACT FROM AUTHOR]

There is a need to thermally protect titanium (Ti) alloys so that they can be used in high temperature environments, such as during hypersonic flight. In this study, a thermal barrier coating (TBC) system was developed using reactive magnetron sputtering. The coating system consists of a nickel chromium aluminum yttrium (NiCrAlY) bond coat and an yttria-stabilized zirconia (YSZ) top coat. The YSZ layer was deposited by reactive pulsed direct current (DC) magnetron sputtering a Zr-Y target in a gas mixture comprised of argon (Ar) and oxygen (O 2). The pulsed DC magnetron sputtering process used closed-loop control with the cathode voltage as the feedback signal. The YSZ coatings were deposited at different cathode voltage feedback signals. The phase structure, elemental composition, microstructure, and thickness of the YSZ coatings were examined by different means. It was found that up to 69% of the metallic deposition rate can be achieved for obtaining near stoichiometric YSZ coatings. The YSZ coatings exhibit single cubic phase structure with an Y 2 O 3 % in the range from 6.5 mol% to 8 mol%. The developed TBC consists of a 2 μm Ti adhesion layer, a 30 μm NiCrAlY bond coat, and a 40 μm YSZ top coat deposited on Ti-6Al-4 V substrate. The NiCrAlY layer exhibited a dense structure and the YSZ layer exhibited a porous columnar grain structure. The TBC showed excellent adhesion on Ti-6Al-4 V. The coated Ti-6Al-4 V was annealed from 800 °C to 1000 °C in air to evaluate the thermal protection capability of the coating. No degradation of the TBC was observed and the Ti-6Al-4 V alloy preserved fine gains and desired mechanical properties up to 900 °C. However, the coating showed horizontal cracks and degradation at the interface between the Ti-6Al-4 V substrate and the NiCrAlY bond coat at 1000 °C. It is assumed that the outward diffusion of Al from the Ti alloy led to the coating failure at the interface. This indicates that new diffusion barrier layers are needed as part of the TBC system. • Up to 69% of the metallic rate is achieved for high rate deposition of YSZ. • A YSZ/NiCrAlY based TBC was deposited on Ti-6Al-4 V using magnetron sputtering. • No degradation of the TBC occurred after thermal annealing up to 900 °C. • The coated Ti-6Al-4 V preserved fine gains and mechanical strength up to 900 °C. [ABSTRACT FROM AUTHOR]

Mo-Si-B/Al 2 O 3 composite coating was applied to Nb-Si based alloys by plasma spray-physical vapor deposition (PS-PVD) followed by spark plasma sintering (SPS). Interdiffusion behavior of the coating at 1200, 1250 and 1300 °C in dry air was investigated. The results indicate that the thickness of the interdiffusion zone (IDZ) in the composite coating is smaller than that in the Al 2 O 3 -free coating. The Al 2 O 3 diffusion barrier effectively restrains coating-substrate interdiffusion. The activation energy for IDZ growth is increased to 367 kJ/mol correspondingly, and the interdiffusion coefficient of Si is decreased by one order of magnitude. Unlabelled Image • Al 2 O 3 diffusion barrier was prepared between Mo-Si-B coating and Nb-Si based alloy. • Interdiffusion zone consists of the middle layer and inner layer. • Al 2 O 3 diffusion barrier restrains interdiffusion between coating and substrate. [ABSTRACT FROM AUTHOR]

Magnetron sputter deposited Mo-based thin films are widely used as diffusion barriers and metallization layers for signal and data bus lines of flat panel displays or back electrodes of thin film solar cells. These films are deposited at large-scale from rectangular planar sputter targets, with the necessity of constant film thickness and properties over target usage. Within this work, a new 600 × 125 mm2 planar Mo-target was sputtered at a constant power of 3.5 kW until the erosion track reached 80% of the maximum useable target thickness. Every other 50 kWh, films were deposited onto a 9 × 5 matrix of (100) Si in different deposition modes (i.e. static and oscillation of the substrate carrier). By investigating the individual sample sets, the sputter behavior at different stages of target usage could be assessed. The sputter behavior changes with the progressing evolution of an erosion groove and affects thickness, stress and electrical resistivity of the films. In the beginning and end of target usage, films with low electrical resistivity and high tensile stresses are grown, whereas a medium target erosion leads to films with increased resistivity and lower tensile stresses. This time variance is attributed to two competing effects changing with proceeding target erosion, which affect the growth conditions of the films: (i) the increase of the reflection angle of Ar neutrals due to the evolution of an erosion groove, lowering the energy input into the growing film, and (ii) a rising number of Ar+ ions due to an increase of target current, directly affecting the overall number of reflected Ar neutrals, increasing the energy input into the growing film. • A rectangular planar molybdenum target was eroded until the end of its lifetime. • Films were deposited at different stages of target erosion. • Target erosion affects film microstructure and properties. • Film microstructure is influenced by substrate position and carrier movement. • Observed differences are explained by target cross-corner effect. [ABSTRACT FROM AUTHOR]

Benefiting from the unique structure, the copper‑tungsten (Cu-W) multilayered film is attractive due to its high strength and fracture toughness, diffusion barrier effects and radiation tolerance. However, the influence of period on the interfacial stability and strengthening mechanism during annealing has seldom been touched. Hence, the Cu-W multilayers with the periods from 1.6 to 27 nm were synthesized by altering substrate rotation speed using co-sputtering. In contrast to the findings in literature by sequential sputtering, kinetically constrained deposited atoms contribute to the more amorphous phase near interface in the films with smaller periods and result in the reduced hardness. During annealing, Cu and W atoms are thermal-activated and up-hill diffuse towards Cu- and W-rich layers, respectively, which can not only eliminate the amorphous phases but also enlarge the concentration ratio and result in the spinodal decomposition. In turn, the films with larger periods present higher thermal resistibility against phase separation due to the stronger diffusion barrier effect of thicker W-rich layers. The mechanical properties of the annealed films generally increase with the temperature up to 400 °C due to the reduced amorphous phases and the enhanced interfacial strengthening. At 500 °C, the separation of soft Cu phase and the loss of coherency mainly lead to the reduced mechanical properties. It is striking that the Cu-W film with the moderate thickness exhibits the highest hardness at higher temperature of 500 °C, indicating the significant importance of period to control their high temperature mechanical properties. • Cu-W multilayers (λ = 1.6–27 nm) were co-sputtered via rotating substrate. • Kinetically constrained deposition in faster rotated film leads to amorphous. • Phase separation during annealing occurs by vertically spinodal decomposition. • The coherent interface forms at 400–500 °C annealing, leading to higher hardness. • High temperature mechanical properties can be adjusted by co-sputtered period. [ABSTRACT FROM AUTHOR]

Increasing requirements on hard coatings in high-performance machining processes like high speed and dry cutting demands further developments even of the already well established TiAlN coatings. The aim of this work is to present a comparative study on oxidation behavior of Ti 0 · 5 Al 0 · 5 N coatings alloyed with X (X = V, Hf, Si) elements. Ab initio molecular dynamics results showed that a pronounced layered oxide appears due to the incorporation of these alloying elements thus affecting the thermal stability and antioxygenic properties. The additions of Hf and Si facilitate the formation of layered oxides with Ti-rich and Al-rich oxides, respectively, which improves the antioxidant performance at high temperatures. Contrarily, the Al-rich layer is absent during oxidation of V-containing coating. The Ti-oxides on the surface of TiAlVN and TiAlHfN coatings have different structures due to the discrepancy of O–Ti–O angle. The present findings clearly show that the V-addition results in more rutile-like TiO 2 whereas the Hf-addition leads to more anatase-like 2 with O–Ti–O angle of 156.3°. With further oxidation, the structures of coatings vary significantly with the alloying elements, which indicates that the alloying of Hf and Si retards the inward diffusion of O atoms, especially, the alloying of Si leads to an earlier formation of a dense sublayer rich in Al 2 O 3 , and thus promotes the oxidation resistance. The different diffusion barrier energies of Ti and Al in TiN bulk contribute to the formation of layered oxides on the surface of coating and the different oxidation behaviors. This study provides an atomistic insight to the initial as well as further stages of the oxidation process of quaternary TiAlXN, which together with the electronic structure analysis and diffusion of metal atoms gives a new basis for understanding of its oxidation behaviors. • Provide an atomistic insight to the initial stages of the oxidation process. • The impact of alloying elements and the oxidation temperature on oxidation behavior. • The addition of elements causes the surface to form a structurally different oxide layer. • Provide new explanations for the oxidation of TiAlN alloyed with V, Hf and Si. [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]

Abstract: The diffusion barrier properties of Zr–Ge–N thin films are reported, focusing on issues relevant to their application as diffusion barriers for Cu interconnections in Si devices. The Zr–Ge–N films were prepared by reactive r.f. magnetron sputtering with different bias voltage. The analyses of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) indicate that the final structure and composition of Zr–Ge–N film are very sensitive to the sputtering bias voltage. The N content in Zr–Ge–N film changes very little, and only decreases from 51.6 to 48.4at.% when sputtering bias voltage increases from 0V to −150V. However, the correlation between bias voltage change and the atomic ratio of Zr and Ge is very remarkable. These results clearly show that the Ge atoms are preferentially resputtered with increasing substrate bias voltage. The high sputtering bias appears to be in favor of the growth of ZrN grains. The copper diffusion barrier properties of Zr–Ge–N on Si have been examined and compared to ZrN. XRD and four-point probe method (FPP) both showed the onset of formation of copper silicide crystallites for ZrN barriers annealed at 650°C. In contrast, TEM on a Zr–Ge–N barriers annealed even at high annealing temperatures of 800°C revealed sharp interfaces and the energy dispersive X-ray spectroscopy (EDS) line scan showed no Cu diffusion through the barrier into Si substrate. The results suggest that Zr–Ge–N is superior to ZrN as a copper diffusion barrier on Si. [Copyright &y& Elsevier]