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Volcanic ash is a major threat to aviation safety. The softening/melting temperatures of volcanic ash lie far below typical aero‐engine operating temperatures. Thus, molten ash can accelerate the failure of thermal barrier coatings (TBCs). Here, inspired by natural superhydrophobic surfaces (e.g., the lotus leaf), a molten‐volcanic‐ash‐phobic TBC, which provides a large possibility to eliminate molten ash issues of TBCs, is developed. A hierarchically structured surface is first prepared on a (Gd0.9Yb0.1)2Zr2O7 (GYbZ) pellet by ultrafast laser direct writing technology, aiming to confirm the feasibility of the biomimetic microstructure to repel molten volcanic ash wetting. Then biomimetic‐structured GYbZ TBCs are successfully fabricated using plasma spray physical vapor deposition, which reveals "silicate" phobicity at high temperatures. The exciting molten‐volcanic‐ash‐phobic attribute of the designed surfaces is attributed to the lotus‐leaf‐like dual‐scale microstructure, emulating in particular the existence of nanoparticles. These findings may be an important step toward the development of next‐generation aviation engines with greatly reduced vulnerability to environmental siliceous debris. [ABSTRACT FROM AUTHOR]

Plasma spray-physical vapor deposition (PS-PVD) is an emerging coating technique that can produce columnar thermal barrier coatings from vapor phase. Feedstock treatment at the start of its trajectory in the plasma torch nozzle is important for such vapor-phase deposition. This study describes the effects of the plasma composition (Ar/He) on the plasma characteristics, plasma-particle interaction, and particle dynamics at different points spatially distributed inside the plasma torch nozzle. The results of calculations show that increasing the fraction of argon in the plasma gas mixture enhances the momentum and heat flow between the plasma and injected feedstock. For the plasma gas combination of 45Ar/45He, the total enthalpy transferred to a representative powder particle inside the plasma torch nozzle is highest (~9828 kJ/kg). Moreover, due to the properties of the plasma, the contribution of the cylindrical throat, i.e., from the feed injection point (FIP) to the start of divergence (SOD), to the total transferred energy is ~69%. The carrier gas flow for different plasma gas mixtures was also investigated by optical emission spectroscopy (OES) measurements of zirconium emissions. Yttria-stabilized zirconia (YSZ) coating microstructures were produced when using selected plasma gas compositions and corresponding carrier gas flows; structural morphologies were found to be in good agreement with OES and theoretical predictions. Quasicolumnar microstructure was obtained with porosity of ~15% when applying the plasma composition of 45Ar/45He. [ABSTRACT FROM AUTHOR]

Plasma spray physical vapor deposition (PS-PVD) was used to deposit yttria stabilized zirconia (YSZ) coatings with microstructures varying from dense lamellae to quasi-columns out of vapor, as well as hybrid microstructure resulting from liquid droplet and vapor co-deposition. Among the coatings investigated, the quasi-columnar coating exhibited the lowest thermal conductivity of around 1.1 W/mK at 1200 °C due to high porosity and defects. The quasi-columnar coating also had an average life of around 2000 cycles during flame shock testing with a coating surface temperature of ~ 1200 °C. The failure of the coating occurred through cracking at the interface between the thermally grown oxide (TGO) layer and YSZ top coat. [ABSTRACT FROM AUTHOR]

Plasma spray physical vapor deposition (PS-PVD) was used to deposit yttria stabilized zirconia (YSZ) coatings with different columnar morphologies by varying the spray distance. Although similar quasi-columnar structures were formed at the spray distances of 600 mm and 1400 mm, the formation mechanisms of particles in the coatings were different. Besides, an electron beam physical vapor deposition (EB-PVD) like columnar coating out of pure vapor was deposited at a spray distance of 1000 mm and the columnar consisted of elongated nano-sized secondary columns. The hardness and Young׳s modulus of the coatings were investigated. Compared to the other two quasi-columnar structures, the EB-PVD like columnar coating exhibited higher hardness (~9.0 GPa ) and Young׳s modulus (~110.9 GPa), mainly due to its low porosity and defect. [ABSTRACT FROM AUTHOR]

As a novel processing technology, plasma spray-physical vapor deposition (PS-PVD) has exhibited potential capability to shape the sprayed coating microstructures. In this paper, yttria-stabilized zirconia (YSZ) coatings were produced at spray distances in the range of 450-1400 mm by PS-PVD. The morphologies of the coatings, going from a denser type of layer to the columnar structure, along the axial and radial directions of the plasma plume were studied. Along the axial direction, five YSZ coating microstructures including 'dense lamellar structure,' 'closely packed columnar structure,' 'quasi-columnar structure with more nanoparticles,' 'EB-PVD-like columnar structure,' and 'quasi-columnar structure with less nanoparticles' were achieved, respectively. Along the radial direction, similar microstructures of coatings were obtained. A simple structure spatial distribution model was developed for demonstrating the mapping of various YSZ coating microstructures. [ABSTRACT FROM AUTHOR]

Highlights: [•] Dy/Hf-doped β-NiAl coatings are produced by electron beam physical vapor deposition. [•] Cyclic oxidation behavior of the Dy/Hf-doped coatings is compared. [•] The microstructure of scales and chemistry of scale/coating interfaces are studied. [•] Dy and Hf may directly improve the adhesion of the scale/coating interfaces. [Copyright &y& Elsevier]

Abstract: Flame shock treatment of electron beam physical vapor deposited (EB-PVD) thermal barrier coatings (TBCs) was carried out to investigate the degradation of TBCs exposed to a temperature gradient. The flame treatment resulted in temperature gradients both in the surface plane and through the thickness of the TBCs. TBC densification occurred where the flame was centered and resulted in a fine crack network at the surface of the TBC. The TBCs with addition of 0.5wt% alumina were made, in which alumina was used as stress sensors for stress measurements by photoluminescence piezo-spectroscopy (PLPS). This allowed stress measurements to be made through the TBC thickness using a depth sensing method. Such stress measurements help us to better understand the densification of the TBCs. [Copyright &y& Elsevier]

Abstract: A contact-free method based on the digital image correlation (DIC) technology has been established to measure the in-plane thermal deformation of yttria stabilized zirconia (YSZ) bulk and YSZ free-standing coatings prepared by electron beam physical vapor deposition (EB-PVD). The results show a superb test agreement between the DIC method and the mechanical dilatometer. Moreover, thermal strain of the sintered YSZ bulk as well as the coatings caused by phase transformation of monoclinic-tetragonal phase after 15h thermal exposure at 1450°C are determined by the DIC method. The volumetric changes induced by the phase transformation of YSZ coatings are measured during heating and cooling, which are helpful for understanding the stress state and lifetime prediction of thermal barrier coating (TBC) system. [Copyright &y& Elsevier]

A (Gd 0.8 Yb 0.2) 2 Zr 2 O 7 /YSZ double ceramic layer thermal barrier coating (TBC) system prepared by electron-beam physical vapor deposition (EB-PVD) is a promising choice for protecting hot-section parts of areo-plane gas-turbine engines at ultra-high temperature. The microstructure and further thermal cycling lifespan are strongly dependent on the EB-PVD process parameters (sample rotational speed, deposition temperature, chamber pressure, etc.). In the current study, three kinds of (Gd 0.8 Yb 0.2) 2 Zr 2 O 7 /YSZ double ceramic layer TBCs were manufactured with different sample rotation speeds by EB-PVD. The thermal cycling behaviour of the three TBCs with different microstructures was investigated at 1150°C in comparison with the single YSZ-TBC. The results showed that TBCs prepared with low sample rotation speed were made of small and irregular columnar grains and exhibited the best thermal cycling behaviour among all the tested TBCs. The effect of sample rotation speed during deposition on microstructure and further thermal cycling behaviour, including crack evolution and TGO growth were discussed. [ABSTRACT FROM AUTHOR]

Abstract: A novel NiCoCrAlY coating was fabricated by plasma activated electron beam-physical vapor deposition (PA EB-PVD). Within the duplex coating, the β-NiAl phase precipitated as small lamellae (less than 1μm thick) in a γ matrix, predominantly oriented perpendicular to the coating surface. The oxidation results at 1373K show that the scaling rate constant during the steady-state oxidation of the novel coating is reduced by approximately 70% as compared with the conventional coating of similar composition produced by electron beam-physical vapor deposition (EB-PVD). This reduction in oxidation rate is attributed to a slower θ→α Al2O3 phase transformation during the initial stages of oxidation. [Copyright &y& Elsevier]

Abstract: The microstructure of thermally grown oxide (TGO) in thermal barrier coatings (TBCs) oxidized under dry/humid atmosphere at 1100°C has been characterized by transmission electron microscopy. A thin and continuous oxide layer is formed in the as-deposited TBCs produced by electron beam physical vapor deposition. The TGO formed in dry atmosphere consists of an outer layer of fine α-alumina, zirconia grains and an inner layer of columnar α-alumina grains. However, a small amount of spinel is observed in the TGO under humid atmosphere. The presence of water vapour promotes the formation of spinel. [Copyright &y& Elsevier]

Abstract: A double-layer (DL) NiCoCrAlY coating was coated onto a Hf-containing Ni-based superalloy DZ125. The bottom layer produced by plasma activated electron beam-physical vapor deposition (PA EB-PVD) was featured by coarse-grained equiaxed microstructure, which is different from the columnar microstructure of the top layer produced by EB-PVD. Oxidation resistance of the DL coating and a conventional single-layer (SL) NiCoCrAlY coating produced by EB-PVD was investigated at 1373K. The DL coating exhibited an improved oxidation resistance as compared with the SL coating. The bottom layer in the DL coating effectively inhibited outward diffusion of refractory elements, such as Hf and W from the superalloy substrate. Oxidation and diffusion barrier mechanisms of the DL coating were also discussed. [Copyright &y& Elsevier]

Abstract: CoCrAlY alloy has been widely used as metallic protective coatings or the bond coats in thermal barrier coatings (TBCs) to protect the underlying superalloy from oxidation and hot-corrosion. In this paper, the TBC consisting of yttria stabilized zirconia (7YSZ) ceramic top coat and CoCrAlY bond coat was deposited onto directionally solidified nickel based superalloy DZ 125 by electron beam physical vapor deposition (EB-PVD). The microstructural evolution of the bond coat on this superalloy was investigated after thermal exposure for 100h at 1050°C. Due to a significant inward diffusion of Al, Co and Cr from the coating and outward diffusion of Ni, Hf, W and Ti from the substrate, the phase transformation from the Co-based Al-rich β-CoAl phase to the Al-deficient γ-CoNi solid solution phase occurred in the bond coat. Simultaneously, a large amount of Ni-based β-NiCoAl phase was present in the bond coat. In addition, the particles containing substrate strengthening elements Hf and/or W are abundant in the thermally grown oxides (TGO) and within the bond coat. The mechanism for the microstructural evolution is discussed. [Copyright &y& Elsevier]

Abstract: The cyclic oxidation behaviour of β-NiAlDy coatings produced by electron beam physical vapour deposition (EB-PVD) was investigated. For the Dy-free NiAl coating, numerous voids developed at the Al2O3 scale/NiAl interface and sulfur was found to segregate at the void surfaces, leading to early spallation of the scale. The addition of Dy prevented sulfur segregation and void formation at the scale/NiAl interface. As a result, the scale grown on the NiAlDy coating remained adherent and no spallation occurred even after 400h cyclic oxidation. The 0.05at.% Dy doped coating revealed lower oxidation rate than the more Dy doped coatings. [Copyright &y& Elsevier]

Abstract: NiCoCrAlY has been used as the bond coat material in thermal barrier coating (TBC) to protect the superalloy substrate from oxidation and hot-corrosion. Inter-diffusion of elements between the coating and substrate could degrade the oxidation resistance of the coating and the mechanical properties of the superalloy. In this work, a gradient oxide dispersed (OD) NiCoCrAlY coating was produced onto DZ125 superalloy using electron beam-physical vapor deposition (EB-PVD). For comparison, conventional NiCoCrAlY (OD free) coated specimens were also produced by EB-PVD. The oxidation and inter-diffusion behaviors of the coated specimens at 1373 K were investigated. As compared to OD free coating, the OD coating exhibits not only a lower oxidation rate but also an improved oxide scale adherence because outward diffusion of the elements such as Ta, W and Hf from the superalloy was effectively blocked by the OD zone. Meanwhile, the presence of minor Hf in the OD coating contributes to the improved oxide scale adherence by reactive element mechanism. [ABSTRACT FROM AUTHOR]

Abstract: NiCoCrAlY has been widely used as the bond coat material in thermal barrier coatings (TBCs). Inter-diffusion between the bond coat and superalloy could degrade the performance of the coating and the mechanical properties of the superalloy. In this paper, oxide dispersed (OD) NiCoCrAlY coatings were deposited onto superalloy DZ 125 using EB-PVD by introducing oxygen during the deposition process. Cyclic oxidation and inter-diffusion behaviors of the coated specimens at 1323K were investigated. The OD coating deposited with high level oxygen input effectively prevented outward diffusion of the elements such as Hf and W in superalloy. For the conventional NiCoCrAlY coating, Hf migrated to the coating surfaces and caused accelerated thickening and chipping spallation of TGO. The OD coating with high level oxygen input exhibits an improved cyclic oxidation resistance as compared to the conventional NiCoCrAlY coating and the OD coating with lower level of oxygen input. [Copyright &y& Elsevier]

Abstract: Oxide dispersed (OD) β-NiAl coatings and OD-free β-NiAl coatings were deposited onto a Hf-containing Ni-based superalloy by electron beam physical vapor deposition (EB-PVD). Excessive enrichment of Hf was found in the TGO on the OD-free coating due to outward diffusion of Hf from the superalloy, causing accelerated TGO thickening and spalling. The OD-coating effectively prevented Hf from outward diffusion. Only small amount of Hf diffused to the coating surface and improved the TGO adherence by virtue of the reactive element effect. The OD-coating exhibited an improved oxidation resistance as compared to the OD-free coating. [Copyright &y& Elsevier]

β-NiAl coatings on a superalloy substrate will inevitably result in severe rumpling at elevated temperatures; however, the associated rumpling mechanisms are not completely understood. The scale rumpling behavior of a β-NiAlHf coating deposited by electron beam physical vapor deposition (EB-PVD) on single crystal superalloy IC21 was investigated in this work. Some internal factors, including the mismatch in the coefficient of thermal expansion and the stress induced by the growth of oxide scale and the phase transformation, were taken into consideration. The thermal mismatch stress between the coating and substrate was the main internal factor responsible for rumpling behavior during thermal cyclic loads, while the phase degradation from β-NiAl to γ'-Ni3Al in the coating played a dominant role during static thermal loads. [ABSTRACT FROM AUTHOR]

Reactive elements like Hf- and Zr-doped β-NiAl are considered to be promising candidate materials for protective coatings used at ultra-high temperatures. However, the role of reactive element co-doping on cyclic oxidation behavior and the surface rumpling of β-NiAl coatings remains unclear. Thus, in this paper, Hf and Zr single-doped and co-doped β-NiAl coatings were deposited on a single crystal superalloy by electron beam physical vapor deposition and the cyclic oxidation at 1150 °C was investigated. The coatings yielded a similar oxidation rate during cyclic oxidation. Obvious surface rumpling appeared in the single-doped coatings, whereas it was effectively alleviated in the co-doped coating. Related mechanisms were discussed, including thermal expansion mismatch, martensitic transformation and phase transformation from β-NiAl to γ′-Ni3Al. The non-uniform phase transformation from β to γ′ was finally believed to be responsible for the discrepancy in the rumpling extents between the single-doped and co-doped coatings. [ABSTRACT FROM AUTHOR]

Ytterbium silicate coatings were deposited on SiCf/SiC ceramics matrix composite (CMC) substrates by plasma spray-physical vapor deposition (PS-PVD), and the microstructures and phase constituents of the coatings were studied. The results show that the Yb2SiO5 coating prepared with high power and low pressure (65 kW/2 mbar) had quasi-columnar structure, mainly deposited from the vapor phase, whereas the coating prepared with low power and high pressure (40 kW/10 mbar) had a typical layered structure, mainly deposited from the liquid phase. The deposition efficiency of parameter A (~2 μm/min) was also significantly lower than that of parameter B (~20 μm/min). After annealing at 1300 °C for 20 h, the coating prepared by 65 kW/2 mbar was mainly composed of ytterbium disilicate phase (77.2 wt %). The coating also contained some silicon-rich phase. The coating prepared by 40 kW/10 mbar basically consisted of ytterbium monosilicate (63.6 wt %). In addition, a small amount of silicon-rich phase and ytterbium-rich phase were also present in the coating. Accompanied with calculation results by the FactSage software, the cause of deviations in phase compositions was analyzed. [ABSTRACT FROM AUTHOR]

Thermal barrier coatings (TBCs) produced by electron beam physical vapor deposition (EB-PVD) or plasma spray (PS) usually suffer from molten calcium-magnesium-alumino-silicate (CMAS) attack. In this study, columnar structured YSZ coatings were fabricated by plasma spray physical vapor deposition (PS-PVD). The coatings were CMAS-infiltrated at 1250 °C for short terms (1, 5, 30 min). The wetting and spreading dynamics of CMAS melt on the coating surface was in-situ investigated using a heating microscope. The results indicate that the spreading evolution of CMAS melt can be described in terms of two stages with varied time intervals and spreading velocities. Besides, the PS-PVD columnar coating (∼100 μm thick) was fully penetrated by CMAS melt within 1 min. After the CMAS attack for 30 min, the original feathered-YSZ grains (tetragonal phase) in both PS-PVD and EB-PVD coatings were replaced by globular shaped monoclinic ZrO 2 grains in the interaction regions. [ABSTRACT FROM AUTHOR]

The crystal orientations in YSZ coatings produced by electron-beam physical vapor deposition (EB-PVD) were analyzed. Two different coatings have been prepared by distinct substrate rotation mode, including S1 prepared by the conventional method and S2 prepared by controlling the rotation and oscillation of the substrate. The substrate rotation modes were implemented by a rotating holder. Based on investigations of crystallographic microstructure and texture characterization methods indexed with reference to be tetragonal lattice symmetry, it concluded that S1 has an [001] in-plane orientation, whilst S2 has an [001] out-of-plane orientation. [ABSTRACT FROM AUTHOR]

Quasi-columnar yttria stabilized zirconia (YSZ) ceramic coatings were prepared by plasma spray physical vapor deposition (PS-PVD). In order to study the formation of quasi-columnar microstructure, coating morphologies and phases were investigated for each set of deposition times and standoff distances. Co-deposited by solid particles, liquid droplets, and vapor phases, the quasi-columnar coating was featured with “wedge” structure where vapors nucleated on micron-sized particles and grew to columns. Compared to the quasi-columnar coating deposited at 1000 mm, an extended spray distance of 1900 mm had lower growth rates, and resulted in the coating with larger columns and more solidified YSZ particles. A three-dimensional deposition model for quasi-columnar coatings was established. Moreover, the quasi-columnar YSZ TBCs exhibited low thermal conductivity of around 1.1 W/m K at 1100 °C and had a lifetime of more than 1000 cycles during thermal cycling test. [ABSTRACT FROM AUTHOR]

As a new processing technology, plasma spray physical vapor deposition (PS-PVD) offers the possibilities to deposit coatings with microstructures varied in a wide range, including fully dense structure, columnar structure and hybrid structure. In this paper, the deposition mechanisms related to the above three microstructures were investigated by looking into the morphologies and phase compositions of the initial deposits during several seconds spraying. The dense coating was stacked up mainly by liquid droplets, un-melted/semi-melted particles and vapor phases. The columnar coating was mostly deposited from vapor phases which were transported to the substrate surface in the state of vapor atoms and clusters, growing in a new growth mechanism different from that in EB-PVD process. The hybrid coating was formed by co-deposition of vapor phases and liquid droplets. [ABSTRACT FROM AUTHOR]

A novel tri-layer (Gd 0.9 Yb 0.1) 2 Zr 2 O 7 /Yb 2 SiO 5 /Si (GYbZ/YbMS/Si) thermal and environmental barrier coatings (TEBCs) was first proposed for protecting SiC-based ceramic matrix composites (CMCs). Wherein, the GYbZ layer by plasma spray physical vapor deposition (PS-PVD) was quasi-columnar structured while the YbMS and the Si layers by atmospheric plasma spray (APS) were lamellar structured. The oxidation behavior and the failure mechanisms of the GYbZ/YbMS/Si TEBCs at 1300 °C/1400 °C are revealed. At 1300 °C, the mud-cracks penetrated through the GYbZ/YbMS layer and transversely deflected in the Si layer are responsible for the oxidation at YbMS/Si interface. When the temperature increased to 1400 °C, the propagation of mud-cracks, cavities, and TGO channel cracks occurred due to the sintering of GYbZ and the fast growth of cristobalite. Eventually, these defects caused delaminating failure at interface. Moreover, another de-bonding failure of the coating was observed resulting from the significant thickening of oxide scale at the edge region. [ABSTRACT FROM AUTHOR]

The threat of calcium‑magnesium-alumina-silicate (CMAS) melt corrosion in thermal barrier coatings (TBCs) is significant at elevated working temperatures. In this study, a gradient Y 2 O 3 stabilized ZrO 2 coating (gradient YSZ coating) was designed and prepared by electron beam physical vapor deposition (EB-PVD) and its CMAS corrosion resistance was examined. The CMAS corrosion resistance test on the YSZ pellets highlighted the significance of dissolved Y 2 O 3 and identified the critical Y 2 O 3 content. Compared with the classical 8 wt% Y 2 O 3 stabilized ZrO 2 (8YSZ) coating, new crystal phases generated in the gradient YSZ coatings effectively blocked the CMAS melt infiltration for a short time; further, even after a long time, the CMAS melt was primarily distributed in the upper part of the gradient YSZ coating. In addition, the impact of coating microstructure on the CMAS resistance was investigated. The results showed the dense-gradient YSZ coating outperformed the 8YSZ coating on the resistance to CMAS infiltration. Finally, it is demonstrated that the gradient YSZ coating has potential applications against CMAS attacks, providing valuable design guidelines for TBCs with balanced corrosion resistance and promising mechanical properties. • A gradient Y 2 O 3 stabilized ZrO 2 (YSZ) coating was deposited by EB-PVD and exposed to CMAS corrosion. • New phases, which blocked CMAS melt permeation for a short time, generated in the gradient YSZ coating. • Over a prolonged period, the gradient YSZ coating remained intact and exhibited better CMAS corrosion resistance. • The gradient composition modification also enhanced the CMAS resistance of dense coatings. [ABSTRACT FROM AUTHOR]

Abstract Optimization of the resistance of thermal barrier coatings (TBCs) to environmental particles is an area of considerable current research. Here, we present a novel methods, incorporating plasma spray physical vapor deposition (PS-PVD), in order to fabricate a novel yttria-stabilized zirconia (YSZ) TBC which is highly phobic (i.e. non-wettable) with respect to CaO-MgO-Al 2 O 3 -SiO 2 (CMAS) particles. At 1250 °C, CMAS particles form liquid droplets which are readily repelled by the TBC surface, diminishing adherence to and penetration into the TBC. This effectiveness of the TBC in resisting wetting by molten CMAS deposits is interpreted to result from its lotus-leaf-like dual-scale microstructure. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Three types of (Gd 0.8 Yb 0.2) 2 Zr 2 O 7 (GYbZ)/YSZ double ceramic layer thermal barrier coatings (TBCs) were prepared with different microstructures by electron beam physical vapor deposition. The CMAS corrosion performance of the three TBCs was studied at 1250 ℃ compared with YSZ-TBC. The results showed that the CMAS corrosion resistance strongly depends on their microstructures. TBCs consisting of smaller inter-column gaps and larger specific surface area exhibited superior CMAS corrosion performance. The reaction products of GYbZ-TBCs are mainly composed of Gd-apatite and fluorite c-ZrO 2 based fluorite. The effect of microstructure on CMAS infiltration depth was discussed. • Effect of the GYbZ ceramic layer microstructure on CMAS corrosion behavior was investigated. • The reaction products of GYbZ-TBCs were mainly composed of Gd-apatite and fluorite c-ZrO 2 based fluorite. • GYbZ microstructure with smaller inter-column gaps and larger specific surface area exhibited superior CMAS corrosion performance. [ABSTRACT FROM AUTHOR]

Plasma spray physical vapor deposition (PS-PVD) is a new promising technology for processing thermal barrier coatings (TBCs). In this study, the microstructural evolution of PS-PVD yttria-stabilized zirconia (YSZ) TBCs at 1150 °C was investigated by scanning electron microscopy, electron backscattered diffraction, and impedance spectroscopy. Bridging is observed between the secondary columns of the coatings during the first 8 h of heat treatment, while sintering necks are observed between the quasi-columns over the heat-treatment interval of 12–20 h. As the heat-treatment time increases to 100 h, the nanogaps between the secondary columns disappear and a large number of shrinkage pores are observed in the columns, leading to a typical cellular structure. Besides, the average grain size of the YSZ coatings increases from 0.20 (as-deposited) to 0.55 µm (after 50 h of heat treatment). The resistance of the YSZ grains increases while that of the YSZ grain boundaries decreases because of grain coarsening. During the first 4 h of heat treatment, the resistance of the thermally grown oxide (TGO) scale increases because of its thickening. However, its resistance decreases during the next 4 h of heat treatment mainly because of the change in its composition (from pure alumina to mixed oxides). [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia (YSZ) thermal barrier coatings with quasi-columnar structure were produced by plasma spray physical vapor deposition (PS-PVD). To form this typical structured coating, the process-structure relationships response for substrate temperature, carrier gas flow and spray distance were investigated. Furthermore, this study revealed its characterization in coating microstructures. It was found that the substrate temperature played a governor role in determining the formation of quasi-columnar structure partially because it affected the nucleation rate of vapors during deposition. Appropriate carrier gas flow and spray distance were helpful to remove the un-melted particles and droplets from the plasma plume and promote the formation of quasi-columnar microstructure with high-ratio vapors. The quasi-columnar coating is featured with feather-like polycrystal structure with average misorientation angle of ~ 35.4° and average diameter of ~ 1.17 μm. [ABSTRACT FROM AUTHOR]

[Display omitted] • GYbZ TBCs with triple-scale micro/nano structure were successfully prepared by ultrafast laser direct writing along with PS-PVD technology. • The triple-scale structure consists of conical micro-pillars, cauliflower-like domed micro-protuberances and nano particles. • The re-constructed PS-PVD TBCs possesses superior thermal stability and long-term high-temperature silicophobicity. • The rapidly developed reaction layer on the coating surface could effectively resist the penetration of the molten silicate. Silicate material from environmental dust melts and adheres to the surfaces of thermal barrier coatings (TBCs) on hot-components of turbine engines accelerating their eventual failure. To mitigate against the wettability and spreadability of such molten deposits on TBCs, dual-scale structured (Gd 0.9 Yb 0.1) 2 Zr 2 O 7 TBCs with "lotus leaf" like surface morphology were fabricated using novel PS-PVD technology, which revealed an enhanced resistance to the wetting of molten silicate but experienced some degradation at high temperatures. By the ultrafast laser direct writing technology, the surface of the PS-PVD TBC was re-constructed, obtaining a triple-scale structure, consisting of conical micro-pillars, cauliflower-like domed micro-protuberances and nanoparticles. The contact angle of molten deposits at 1200 °C on this TBC was measured to be ∼ 127.2°, and after exposure to 1300 °C for 10 h, the TBC is still silicophobic (i.e., contact angle of ∼ 124.7°). This superior silicate phobicity is largely attributed to the increased surface roughness of the triple-scale structure. Further, the reaction layer appears to resist effectively further melt penetration. We thus propose that PS-PVD technology together with ultrafast laser direct writing may have great potential for the fabrication of molten silicophobic TBCs for turbine engines. [ABSTRACT FROM AUTHOR]

A β-NiAlHf coating was deposited by electron beam physical vapor deposition (EB-PVD) onto single crystal (SC) superalloy substrate. The microstructure evolution of the NiAlHf coating after annealing at 1100 °C was investigated and the mechanical properties of the coated substrate were also concerned. The crack initiation and propagation behavior of the coated substrate during three-point bending was studied. An interdiffusion zone (IDZ) was formed between the coating and substrate and the hardness of the precipitates in the IDZ layer was relatively higher than that of the coating and the substrate. The annealed specimen during bending revealed different crack initiation and propagation behavior from the uncoated specimen. Cracks were initiated at the carbides in the uncoated alloy. For the coated specimen after 10 h annealing, cracks were initiated mostly in the IDZ layer, due to the presence of μ-TCP phases. For the coated specimen after 50 h annealing, cracks were generated at the top of triangle-shaped γ′-Ni 3 Al phases where stress concentration occurred, which finally propagated into the substrate, leading to the reduction of the alloy in strength. [ABSTRACT FROM AUTHOR]

A NiAl coating was deposited onto a Ni-based single crystal superalloy with (001) crystal orientation by electron beam physical vapor deposition (EB-PVD). The as-deposited NiAl coating showed a columnar microstructure with (110) preferred orientation. The microstructure evolution behavior near interface between the NiAl coating and superalloy substrate at 1100 °C was investigated. Kirkendall voids were formed in the NiAl coating, indicating the different elements diffusion coefficients in the coating and substrate. Interdiffusion zone (IDZ) with rod-like and granular topological close-packed (TCP) phases and substrate diffusion zone (SDZ) with needle-like TCP phases were formed during diffusion annealing at elevated temperature. The equi-axed β-NiAl grains were developed in the IDZ after diffusion annealing at 1100 °C for 10 h, which showed different orientations from the coating and substrate. However, after 50 h diffusion annealing, the equi-axed β-NiAl phases in the IDZ were transformed into γ′-Ni 3 Al phases which had the same orientation as the substrate. Furthermore, oriented rafting of the substrate occurred during diffusion annealing and the rafts were parallel to the coating/substrate interface. [ABSTRACT FROM AUTHOR]

This paper presents a new plasma activation process for electron beam evaporation. The plasma is generated by an interaction between the evaporated vapor (serving as anode) and the thermal electrons emitted from molten Nb (serving as cathode). Besides, an arc discharge burning in the anode vapor further enhances the plasma density. This process is demonstrated by means of the plasma activated deposition of TiN coating. Deposition rate of ~ 170 nm/min has been measured. Contamination caused by the slight evaporation of Nb to the coating is ~ 0.1 at.%. [ABSTRACT FROM AUTHOR]

The reactive element of Hf or Zr doped and Hf/Zr co-doped β-NiAl coatings was prepared by electron beam physical vapor deposition (EB-PVD). Cyclic oxidation behavior of the coatings at 1200 °C was compared. The Hf/Zr co-doped NiAl coating revealed finer grain size than the Hf or Zr single-doped coatings. Hf/Zr co-doping led to lower oxide scale growth rate than Hf or Zr single-doping. No oxide scale spallation was observed on the surfaces of the NiAlHf and NiAlHfZr coatings after 100 h cyclic oxidation, indicating improved high-temperature cyclic oxidation resistance, as compared to the NiAlZr coating. Related mechanisms were preliminarily discussed. [ABSTRACT FROM AUTHOR]

NiAlDy coatings doped with 0.05 at.% and 1.00 at.% B were produced by electron beam physical vapour deposition (EB-PVD). The mechanical properties and cyclic oxidation behaviour of the coatings were investigated. Compared to the undoped NiAlDy coating, the B doped coatings exhibited improved ductility, higher micro-hardness and elastic modulus. The NiAlDy alloys revealed similar thermal expansion behaviour in a temperature range of 200–1100 °C. However, the addition of B did not show significant improvement in the cyclic oxidation resistance of NiAlDy coatings, on the contrary, the addition of 1.00 at.% B accelerated the scale growth rate and aggravated the scale rumpling, which led to severe spallation. Related mechanisms were preliminarily discussed. [ABSTRACT FROM AUTHOR]

NiAlHf coatings were deposited onto Ni-based single crystal (SC) superalloy with different crystal orientations by electron beam physical vapor deposition (EB-PVD). The effects of the crystal orientations of the superalloy substrate on inter-diffusion behavior between the substrate and the NiAlHf coating were investigated. Substrate diffusion zone (SDZ) containing needle-like μ phases and interdiffusion zone (IDZ) mainly consisting of the ellipsoidal and rod-like μ phases were formed in the SC alloy after heat-treatment 10 h at 1100 °C. The thickness of secondary reaction zone (SRZ) formed in the SC alloy with (0 1 1) crystal orientation is about 14 μm after 50 h heat-treatment at 1100 °C, which is relatively thicker than that in the SC alloy with (0 0 1) crystal orientation, whereas the IDZ revealed similar thickness. [ABSTRACT FROM AUTHOR]

Gradient thermal barrier coatings of (Gd 0.9 Yb 0.1 ) 2 Zr 2 O 7 –yttria stabilized zirconia (8YSZ) were deposited on Hf-doped NiAl bond coat by EB-PVD. The effect of the structure at the interface between (Gd 0.9 Yb 0.1 ) 2 Zr 2 O 7 (GYbZ) and 8YSZ layers on the thermal cycling behavior has also been investigated by comparing the double-ceramic-layer (DCL) coatings with gradient thermal barrier coatings (GTBCs). The results of thermal cycling tests show that the GTBCs have a more extended lifetime than the DCL coatings. The failure of GYbZ-8YSZ DCL coating with clear interface between different ceramic layers occurred in the way of delamination cracking, which is mainly a result of crack initiation and propagation generated by stress concentration within the ceramic layers. On the other hand, the failure mechanism of GTBC is due to the thermal mismatch between the Hf-doped NiAl bond coat and TGO layer. [ABSTRACT FROM AUTHOR]

Compressor blades used in gas turbine engines for marine applications must work in harsh environment such as erosion and corrosion. Multilayer nitride coatings produced by physical vapour deposition (PVD) have exhibited promising potential in improving the corrosion resistance. In this paper, three types of Ti/TiN multilayer coatings with different thickness ratios (M1: 10 nm/40 nm, M2: 20 nm/80 nm, M3: 30 nm/80 nm) were deposited onto 1Cr11Ni2W2MoV stainless steel substrates by plasma activated electron beam physical vapour deposition (EB-PVD). The microstructure, hardness and corrosion behaviour of the Ti/TiN multilayer coatings and TiN single layer coating were comparatively studied. The columnar grain growth of the TiN single layer coating was suppressed by the introduction of the Ti metallic sublayers. With the increase of the Ti sublayer thickness, the characteristics of the layered microstructure became more apparent. The substrates coated with Ti/TiN multilayer coatings exhibited better corrosion resistance (maximum 87% protection efficiency for M3) and higher hardness value (maximum 34.1 GPa for M1) than those coated with TiN single layer. [ABSTRACT FROM AUTHOR]

Mo, as a typical refractory element in Ni-base superalloys, will diffuse outward to the protective coating on the alloy surface during high-temperature oxidation, which will do harm to mechanical properties of the alloy and oxidation resistance of the coating. In this paper, (γ' + β) two-phase Ni-34Al-0.3Dy coatings with or without Pt were prepared on a single crystal superalloy with high Mo content by electron beam physical vapor deposition (EB-PVD) and Pt electroplating. The short-term oxidation behavior of the coatings was investigated at 1100 °C aiming to explore the role of Dy and Pt on the harmful effect of Mo diffusion and its oxides. The results show that for Pt-free coating, Mo had already diffused to the coating surface after only 1 h. The pre-existing Dy 2 O 3 would react with MoO 3 to form Dy 2 MoO 6 thus suppressed the volatilization of MoO 3 at the early stage of oxidation. However, as the oxidation proceeded, Dy 2 MoO 6 would decompose due to its poor thermal stability. While for Pt-doped coating, no Mo-rich oxides were detected throughout the entire oxidation process due to the suppression of outward Mo diffusion by the Pt layer at coating/substrate interface. The possible mechanisms were discussed in detail. [Display omitted] • Pt-free/doped (γ' + β) NiAlDy coatings are prepared on IC21 with high Mo content. • The role of Dy and Pt on suppressing the formation of harmful MoO 3 is focused on. • Dy delays volatilization of MoO 3 by forming Dy 2 MoO 6 which is not completely stable. • Pt inhibits diffusion of Mo by enhancing Al content in Pt-rich layer at interface. • Weak inter-attraction between Pt and Mo contributes to the Mo diffusion inhibition. [ABSTRACT FROM AUTHOR]

Conventional two-layered structure thermal barrier coatings (TBCs), graded thermal barrier coatings (GTBCs) and graded thermal barrier coatings with micropores were prepared onto superalloy DZ22 tube by electron beam physical vapor deposition (EB-PVD). Thermal gradient of the TBCs was evaluated by embedding two thermal couples in the surfaces of the tube and the top coat at different surrounding temperatures with and without cooling gas flowing through the tube. The results showed that higher thermal gradient could be achieved for the GTBCs with micropores compared to the two-layered structure TBCs and GTBCs. However, after the samples were heated at 1050°C, the thermal gradient for the GTBCs with or without micropores decreased with the increase of heating time. On the other hand, the thermal gradient for the TBCs increased with the increase of heating time. Cross-section observations by scanning electron microscopy showed that the change in microstructure was the main reason for the change of the thermal gradient. [Copyright &y& Elsevier]

In combination with the electroplating and electron beam physical vapor deposition (EB-PVD), four types of (Ni,Pt)Al coatings, namely Ni45Al, (Ni,Pt)45Al, Ni50Al, and (Ni,Pt)50Al were prepared. In order to study the interdiffusion and topologically close-packed (TCP) phases precipitation behavior, annealing experiments were carried out at 1100 °C for 20 h in vacuum. The addition of Pt layer has little effect on the thickness of interdiffusion zone (IDZ) because the inhibition effect of Pt on the Al diffusion weakens with the continuous diffusion of Pt. Meanwhile, the increase of Pt content in substrate promotes the Al diffusion. Besides, the effect of Pt on the TCP phases precipitation depends strongly on the Ni content in coating-For Ni45Al coating, adding Pt makes the volume fraction of TCP phases reduces from ~16.35 % to ~3.15 %, whereas this value is comparable in both Ni50Al and (Ni,Pt)50Al coatings (18.3 % and 17.9 %). This phenomenon is attributed to the competition mechanism between the acceleration effect of Pt on Al diffusion and the inhibition effect of Pt on TCP phases growth. The results provide a better understanding about the microstructure, especially the IDZ and TCP characteristics of (Ni,Pt)Al coating, which is significant for controlling the interdiffusion and TCP precipitation behavior in (Ni,Pt)Al coating. • (Ni,Pt)Al coating is manufactured by electroplating and EB-PVD. • The evolution of element diffusion path is: dense Pt layer→dilute Pt layer→(Ni,Pt)Al coating. • The addition of Pt has little effect on the thickness of IDZ. • The relatively low Ni content facilitates the suppression effect of Pt on TCP precipitation. [ABSTRACT FROM AUTHOR]

The characteristics of powder feedstock are very critical in the plasma spray physical vapor deposition (PS-PVD) process to produce columnar structured ceramic coatings. In this study, gadolinium zirconate (GZO) powder feedstocks for PS-PVD process were prepared by solid-state reactions and spray drying. Initially, the GZO coating sprayed from the as-prepared powder revealed a low deposition rate of ~4 μm·min−1 because the powder couldn't reach to the hottest zone of the plasma plume due to the weak binding between the primary particles. Therefore, heat treatment of the powder was performed at temperatures between 1000 °C and 1300 °C to enhance the binding strength and the powder after 1 h heat treatment at 1200 °C exhibited a moderate improved binding strength. The coating sprayed from the sintered powder showed a typical columnar structure and nearly stoichiometric composition as well as a deposition rate of 24 μm·min−1. • The GZO feedstocks for PS-PVD were prepared. • Effects of heat treatment on GZO feedstocks and coating deposition were studied. • Sintering of feedstocks at 1200 °C helps to improve deposition rate of the coating. [ABSTRACT FROM AUTHOR]