Zr Coatings Research Articles

Internal oxidation of laminated ternary Ru–Ta–Zr coatings

Researchers have observed the internal oxidation phenomenon in binary alloy coatings when developing refractory alloy coatings for protective purposes by conducting annealing at high temperatures and in oxygen-containing atmospheres. The coatings were assembled using cyclical gradient concentration deposition during cosputtering by employing a substrate holder rotating at a slow speed. The internally oxidized zone demonstrated a laminated structure, comprising alternating oxygen-rich and oxygen-deficient layers stacked in a general orientation. In the current study, Ru–Ta–Zr coatings were prepared with various stacking sequences during cosputtering. The Ru–Ta–Zr coatings were annealed at 600°C in an atmosphere continuously purged with 1% O2–99% Ar mixed gas for 30min. A transmission electron microscope was used to examine the periods of the laminated layers and crystallinity of the annealed coatings. Depth profiles produced using an Auger electron spectroscope and X-ray photoelectron spectroscope were used to certify the periodic variation of the related constituents and chemical states of the elements, respectively. The results indicate that the internally oxidized ternary coatings are stacked of Ru-, Ta2O5-, and ZrO2-dominant sublayers and that the stacking sequences of the sublayers affect the crystalline structure of the coatings. Zr is oxidized preferentially in the Ru–Ta–Zr coatings, increasing the surface hardness of the oxidized coatings.

The effect of C content on the mechanical properties of Ti–Zr coatings

In this study, Ti–Zr and Ti–Zr–C coatings were deposited at room temperature via pulsed-DC magnetron sputtering. A 70Ti–30Zr at% target and a 99.99% graphite plate were used to deposit samples. In order to modify C content, coatings were deposited at different target powers such as 50, 75 and 100W. Changes on the structure, microstructure and mechanical properties due to C addition were studied. Results indicate that the as-deposited coatings were partly crystalline and that an increment on C content stabilized α′ phase and inhibited the appearance of ω precipitates. Therefore, Ti–Zr–C alloys with C>1.9at% showed only α′ phase whereas the others alloys exhibited α′+ω structures. Hardness values from 12.94 to 34.31GPa were obtained, whereas the elastic modulus was found between 181.84 and 298GPa. Finally, a high elastic recovery ratio (0.69–0.87) was observed as a function of composition. The overall properties of these coatings were improved due to C content increment, martensitic α′ phase and nanocrystalline grain size (10–16nm).

Refractory Metal Coatings on High Creep Strength Steel for Oxyfuel Coal Combustion

Oxyfuel coal combustion, where coal is burned in oxygen instead of air, offers the potential for simplified CO2 sequestration, since the flue contains little N2 and is mainly CO2. However, the widespread use of flue gas recycling to dilute the pure oxygen feed stream exacerbates corrosion problems in the furnace and boiler tubes by increasing the concentrations of SO2, SO3, HCl, and H2O. In addition, the dew point temperature is raised, making condensation of H2O, H2SO4 and H2SO3more likely during downtime. P91 steel, which contains ~8.4% Cr, 0.9% Mo and 2.2% V, is are widely utilized for high temperature applications in the power industry due to its increased creep strength. However, Cr-containing steels are susceptible to failure in H2O-containing oxidizing environments due to formation and volatilization of compounds such as CrO2(OH)2. We report the formation of Ti and Zr diffusion coatings atop high creep strength steels to improve their corrosion resistance. Ti coatings 10-30 µm thick can be formed on P91 steel by pack cementation at 1000°C in flowing Ar. Similarly, Zr coatings 10-30 µm thick can be formed by pack cementation at 1080°C. The composition as a function of position for both Ti and Zr diffusion coatings is studied as a function of position by scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDX). This demonstrates formation of an inter-diffusion zone, with no sharp interface exists between coating and substrate, which may help limit delamination. Results will also presented for thermogravimetric analysis (TGA) of both Ti and Zr coatings on P91 steel in gas mixtures that contains 5% N2, 70% CO2, 2% CO, 0.3% SO2, 21.7% H2O, 1% O2, and trace levels of HCl.

Co-sputtered amorphous Nb–Ta, Nb–Zr and Ta–Zr coatings for corrosion protection of cyclotron targets for [18F] production

Protective corrosion resistant coatings serve for decreasing the amount of ionic contaminants from Havar® entrance foils of the targets for [18F] production. The corrosion damage of coated entrance foils is caused mainly by the diffusion of highly reactive products of water radiolysis through the protective film toward Havar® substrate. Since amorphous metal alloys (metallic glasses) are well-known to perform a high corrosion resistance, the glass forming ability, microstructure and diffusion barrier efficiency of binary alloys containing chemically inert Nb, Ta, Zr were investigated. Nb–Ta, Nb–Zr and Ta–Zr films of different alloy composition and ∼1.5μm thickness were co-deposited by magnetron sputtering. Diffusion barrier efficiency tests used reactive aluminum underlayer and protons of acid solution and gallium atoms at elevated temperature as diffusing particles. Though co-sputtered Nb–Ta and Nb–Zr alloy films of different contents were crystalline, Ta–Zr alloy was found to form dense amorphous microstructures in a range of composition with 30–73% atomic Ta. The diffusion barrier efficiency of Nb–Zr and Nb–Ta alloy coatings decreased with increase of Nb content. The diffusion barrier efficiency of sputtered Ta–Zr alloy coatings increased with the transition from nanocrystalline columnar microstructure to amorphous for coatings with 30–73at.% Ta.

Characterisation of electrodeposited Ni–Zr coatings prepared at different current densities

In this work, Zr particles reinforced Ni–Zr composite coatings were prepared by eletrodeposition from a Watts bath at different current densities. The effects of current density on the surface morphology, composition, texture, grain size, microstrain, hardness, residual stresses and corrosion resistance of the composite coatings were investigated in detail. The results showed that the Zr particle contents in the coatings increased with reducing current densities and have an effect on the microstructures and the properties of the composite coatings. As the current densities decreased, the (200) preferred orientation of the coating changed to the random orientation or the slight (111) preferred orientation and the grain size decreased. The residual stress and hardness of the composite coatings increased with reducing current densities. The corrosion resistance of coatings increased with reducing current densities and attained the best corrosion resistance at 2 A dm−2.

Bulge Testing and Interface Fracture Characterization of Plasma-Sprayed and HIP Bonded Zr Coatings on U-Mo

Bulge testing using a pressurized fluid to fracture the interface between bonded material layers along with three-dimensional digital image correlation to measure the sample distortion caused by pressurized fluid was applied to plasma-sprayed coatings. The initiation fracture toughness associated with the bonded materials was measured during the testing. The bulge testing of the uranium-molybdenum alloy plasma sprayed with zirconium and clad in aluminum is presented. The initiation fracture toughness was observed to increase with the increasing cathodic arc-cleaning current and the use of alternating polarity transferred arc current. This dependence was linked to the interface composition of oxide and mixed metal phases along with the interface temperature during spray deposition.

Influence of Zr alloying on the mechanical properties, thermal stability and oxidation resistance of Cr–Al–N coatings

Cr–Al–N coatings with Zr alloying (Zr contents from 0 to 29.5at.%) were deposited by d.c. reactive magnetron sputtering. The chemical composition and the morphology of as-deposited coatings were characterized, and the phase structure, mechanical properties and wear resistance of the coatings before and after thermal annealing were analyzed and evaluated. With the increase of Zr content, both Cr and N contents decrease whereas Al shows a growing trend. Low Zr (<26.9at.%) coatings are stoichiometric and present a fcc NaCl-type B1 structure with columnar morphology, while high Zr (≥26.9at.%) coatings are in N deficiency and have low crystallinity degree. The alloying of low contents of Zr improves the coating hardness and H/E ratio; however, for low ordered coatings these properties decrease significantly. After thermal annealing, fcc structure is kept in low Zr films whereas the crystalline degree is improved in the high Zr ones and their mechanical properties were slightly improved. Two coatings were selected for further testing, representatives of low (CrAlZr5N) and high (CrAlZr27N) Zr contents. The onset oxidation temperature is ∼900°C and 600°C for CrAlZr5N and CrAlZr27N coatings, respectively. Mainly Cr2O3 is formed on low Zr coatings whereas mixed oxides of ZrO2 and Cr2O3 are detected on CrAlZr27N sample after thermal exposure. In all tribological tests, low Zr coating presents lower wear rate than the CrAlZr27N coating. In general, the addition of very high Zr contents (>20at.%) with N deficiency markedly weakens the mechanical properties and the oxidation resistance of Cr–Al–Zr–N coatings.

Synthesis and characterization of zirconium oxynitride ZrOxNy coatings deposited via unbalanced DC magnetron sputtering

A study of structure, morphology, and corrosion resistance was performed on zirconium oxynitride thin films deposited on 304 and 316 stainless steels by the DC sputtering magnetron unbalance technique. Structural analysis was carried out using X-ray diffraction (XRD), while morphological analysis was performed by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). These studies were performed as a function of deposition time via DC sputtering at room temperature (287 K) with an Ar/air flow ratio of 3.0 and a total deposition time of 30 min. The oxynitride films were grown with cubic crystalline structures Zr2ON2 and preferentially oriented along the (222) plane. Chemical analysis determined that in the last 5.0 nm, the Zr coatings present the following spectral lines: Zr3d3/2 (184.6 eV) and 3d5/2 (181.7 eV), O1s (531.3 eV), and N1s (398.5 eV).The zirconium oxynitride films enhance the stainless steel's resistance to corrosion. The protective efficacy has been evaluated using electrochemical techniques based on linear polarizations (LP). The results indicate that the layer provides good resistance to corrosion in chloride-containing media. SEM analysis presented the homogeneity of the films. AFM studies indicated that the average roughness of the film is 20.2 nm in the two steels and a particle size ranging between 150 and 208 nm in ZrOxNy-AISI 316 and 115–180 in ZrOxNy-AISI 316. TEM analysis indicated columnar growth.

A-C(:H) and a-C(:H)_Zr coatings deposited on biomedical Ti-based substrates: Tribological properties

Amorphous carbon (a-C) based coatings are possible candidates as a surface treatment for various biocompatible materials used in medicine. In this study, the carbon coatings co-sputtered with Zr, deposited by dc unbalanced magnetron sputtering in Ar (non-hydrogenated, i.e. a-C/Zr) and Ar+CH4 (hydrogenated, i.e. a-C:H/Zr) discharges, were investigated and compared with pure carbon films. Polished pure commercial Ti grade 2 and Ti grade 5 ELI (Ti6Al4V) discs were used as substrates. To improve the coating/substrate adhesion, a gradient Ti-based interlayer was deposited (~450nm). The coating structure was characterized by X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy; the chemical composition was measured by electron probe microanalysis. The adhesion was evaluated by scratch-test and the hardness was measured by nanoindentation. Tribological testing of the coatings was carried out using unidirectional pin-on-disc experiments; pure titanium balls were used as counterparts. The wear rate of the coatings was negligible except for the films with the highest Zr content deposited on Ti grade 2 substrates.

Bond Characterization of Plasma Sprayed Zirconium on Uranium Alloy by Microcantilever Testing

The future production of low enriched uranium nuclear fuel for test reactors requires a well-adhered diffusion barrier coating of zirconium (Zr) on the uranium/molybdenum (U-Mo) alloy fuel. In this study, the interfacial bond between plasma sprayed Zr coatings and U-Mo fuel was characterized by microcantilever beam testing. Test results revealed the effect of specific flaws such as cracks and pores on the bonding of interfaces with a sampling area of approximately 20 μm2. TEM examination showed the Zr/U-Mo interface to contain rows of very fine grains (5-30 nm) with the Zr in contact with UO2. Bond characteristics of plasma sprayed samples were measured that are similar to those of roll bonded samples showing the potential for plasma sprayed Zr coatings to have high bond strength.

Annealing effects on nanostructure and mechanical properties of nanolaminated Ta–Zr coatings

This paper proposes Ta–Zr multilayer coatings fabricated by using magnetron co-sputtering, achieving high nanohardness and low roughness after annealing, as appropriate protective coatings for die materials. The as-deposited nanolaminated Ta–Zr coatings exhibited nanocrystalline or amorphous phases, depending on the chemical compositions. The Zr oxidized preferentially when annealed in oxygen-containing atmospheres. The nanohardness increased in relation to the oxygen content in the coating, which was attributed to the formation of a crystalline tetragonal ZrO2 phase. To serve as a protective coating when applied in high-temperature conditions with an appropriate nanohardness, such as coatings on glass molding dies, the coating must endure an annealing treatment in an oxygen-containing atmosphere at 600°C. In this study, the periods of nanolaminated coatings were controlled by the rotation speed of the substrate-holder. The annealing treatments were conducted at 600°C in atmospheres of 20-ppm and 50-ppm O2–N2. The variations in crystalline structure, nanohardness, and in-depth chemical composition profiles after various annealing durations were investigated. The feasibility of a protective Ta–Zr coating was improved by annealing the coating in a 1% O2–Ar environment for 30min at 600°C to achieve a nanohardness of 10GPa, which is higher than the hardnesses of molded glasses, and by being subsequently exposed to a 10-ppm O2–N2 atmosphere, which is a realistic glass molding atmosphere.

Oxidation study of Ta–Zr coatings

Refractory metal alloy coatings, such as Mo–Ru and Ta–Ru coatings, have been developed to protect glass molding dies. Forming intermetallic compounds in the coatings inhibits grain growth in high temperature environments when mass producing optical components. After annealing in oxygen containing atmospheres, a surface roughening of the Mo–Ru coatings and a soft oxide layer on the Ta–Ru coatings have been observed in our previous works. Oxidation resistance becomes critical in high-temperature applications. In this study, Ta–Zr coatings were deposited with a Ti interlayer on silicon wafers using direct current magnetron sputtering at 400°C. The as-deposited Ta–Zr coatings possessed nanocrystallite or amorphous states, depending on the chemical compositions. The annealing treatments were conducted at 600°C under atmospheres of 50ppm O2–N2 or 1% O2–Ar, respectively. After the annealing treatment, this study investigated variations in crystalline structure, hardness, surface roughness, and chemical composition profiles. Preferential oxidation of Zr in the Ta–Zr coatings was verified using X-ray photoelectron spectroscopy, and the microstructure was observed using transmission electron microscopy.

Microstructural differences between two Zr(C,N) coatings revealed by analytical transmission electron microscopy

The microstructures of two samples of a Zr(C,N) coating on steel, which unexpectedly differed in their tribological properties, were investigated by analytical transmission electron microscopy. The samples were produced by a cathodic arc evaporation process in two commercial coating devices under similar coating conditions with the exception of the number of Zr targets.The source of the differing tribological properties of the samples was detected by analytical transmission electron microscopy (TEM) methods energy-dispersive X-ray spectroscopy (EDX), energy filtering TEM (EFTEM), electron diffraction, high resolution electron microscopy, and high angel annular dark field. The TEM preparation and the results of the TEM investigations are shown in detail. The origin of the unexpected behavior was determined to be a nano-scale multilayer structure that existed only in the tribologically superior specimen. EDX and EFTEM investigations indicated enrichment in oxygen at the interface between coating and steel substrate in the tribologically inferior sample. Findings of the microstructural configuration were obtained by taking a closer look at the structure and comparing the results of the several analytical TEM techniques. This allows the allocation of the concentration fluctuations in N, C, and Zr to the two thickness fractions of the nano multilayers and a local correlation of the identified minority phase Zr3(C,N)4 to the higher N content in the narrower type of the multilayer fraction of the sample with the excellent tribological properties. The minority phase Zr3(C,N)4 is randomly distributed in the sample with the defective tribological properties.Coating conditions are not topic of this work, but after discussion of the TEM results, the fact that one of the coating devices worked with one Zr target and the other one with two, could be identified as cause for the formation of the nano multilayer structure in the sample with the superior tribological properties.

Temperature and Time-Dependent Ion Diffusion Across Stainless Steel-Zirconium Film Interface Studied by Scanning Surface Potential.

ABSTRACTZirconium is of interest in the development of high-density diffusion barriers in nuclear reactor applications because of its low thermal neutron absorption cross section and good thermal and mechanical properties. It is used in these applications to protect the low enriched fuel from interacting directly with the cladding material to prevent swelling and cracking of the fuel. In this work, we investigated the use of plasma spraying as a method to produce high quality, dense Zr barrier coatings over large surface areas. A thin sheet of 21Cr-6Ni-9Mn stainless steel (SS) was used as the substrate material. Both sides of the SS sheet were coated, one side at a time. A transfer arc (TA) current between a torch and the substrate was used to vary the substrate temperature to explore the effect of temperature and time on the film grain size, interface quality, and film porosity. The films were characterized using light optical microscopy (LOM), scanning probe microscopy (SPM) and Kelvin probe force microscopy (KPFM) and EDS-SEM Although the film quality did improved with temperature, at the elevated substrate temperatures used in this study, metal atoms from the substrate diffused into and, at the highest temperature and longest time, through the Zr coatings.

Characterization of Thermal Diffusion Related Properties in Plasma Sprayed Zirconium Coatings

Zirconium (Zr) metal is of interest for chemical corrosion protection and nuclear reactor core applications. Inert chamber plasma spraying has been used to produce thin Zr coatings on stainless steel (SS) substrates. The coatings were deposited while using transferred arc (TA) cleaning/heating at five different current levels. In order to better understand thermal diffusion governed processes, the coating porosity, grain size and interdiffusion with the substrate were measured as a function of TA current. Low porosity (3.5 to <0.5%), recrystallization with fine equiaxed grain size (3-8 μm diameter) and varying elemental diffusion distance (0-50 μm) from the coating-substrate interface were observed. In addition, the coatings were low in oxygen content compared to the wrought SS substrates. The Zr coatings sprayed under these conditions look promising for highly demanding applications.

Evaluation of the Fatigue Resistance of Chromium Slurry Coating Steel Substrate Compounds by Means of an Improved Impact Testing Procedure

Chromium coatings have been used for the protection of gas turbine blades in power plants during the last years due to their very good resistance against steam corrosion. Microhardness, scratch, adhesion and pin-on-disk sliding tests are commonly used for rapid evaluation of the mechanical properties of these coatings [1,2]. However, very limited information exists on their fatigue resistance. In this paper we present the experimental results of the impact testing examination of the above coatings. This experimental method is capable to assess the fatigue and the impact wear resistance of coatings working under cyclic impact loading conditions. From the experimental results it was concluded that the slurry Cr, Zr coatings deposited on P91 steel showed adequate fatigue strength for the above-mentioned kind of use.

Development and Analysis of Robust Anti-Wear Design of a-C:Zr Films by Taguchi Methods

Amorphous carbon (a:C-H) coatings with high hardness and low friction coefficient are widely applied in die and mold industries. Zirconium-containing a:C-H (a-C:Zr) coatings with double interlayered Zr/ZrC were deposited by unbalanced magnetron sputtering system. A L18 orthogonal array experiment was designed to investigate the effect of process parameter on the friction coefficient of deposited films. Control factors, such as methane flow rate, bias voltage, sputtering frequency, zirconium target current and work distance were schematized for experiments. The experimental results show that zirconium target current exhibits about 45% percent contribution in analysis of variance, and the friction coefficient of a-C:Zr coatings range from 0.13 to 0.31. From effect plots, the optimum parameters are bias voltage at -70V, zirconium target current at 0.6 A, pulse frequency at 90 kHz, methane flow rate at 6 sccm and work distance at 15 cm. The friction coefficient performs as 0.106 in verification experiments. Meanwhile, one-by-one factorial experiments were also carried out and discussed in this study.

Effect of zirconium addition on cyclic oxidation behavior of platinum-modified aluminide coating on nickel-based superalloy

The effect of Zr addition to Pt-modified aluminide coatings was investigated. Zr coatings on Pt-modified aluminide coatings were deposited by EB-PVD and heat treatments were conducted. SEM analysis indicated that Zr was situated at the surface and grain boundary near the surface as an agglomerated form of the NiAl–Zr alloy, which affected the growth rate of the thermally grown oxide during cyclic oxidation. Also, the interface and surface roughnesses of Zr-added Pt-modified aluminide coatings were smaller than that of the Pt-modified aluminide coating. Also, phase stabilities of Zr-added Pt-modified aluminide coating were enhanced as compared with the Pt-modified aluminide coating. Because Zr-added Pt-modified aluminide coatings had resistance to spallation of TGO caused by Zr-rich oxide pegs, they showed better resistance to cyclic oxidation than Pt-modified aluminide coating without Zr addition.

Examinations on the Oxidation Resistance of Innovative Carbon Based Materials

An overview on parameters influencing the oxidation behaviour of carbon based materials in oxidizing gases is presented in order to support the development of advanced carbon containing materials with high oxidation resistance. Facilities for testing the oxidation behaviour, as operated in FZJ, are explained. Results of exemplary oxidation tests in air at 700°C on diverse new developed materials are presented: Ti and Zr dopings and coatings were found less efficient, whereas Si coatings/dopings significantly reduce oxidation rates. Low oxidation rates of 3D-CFCs without doping/coating, which were manufactured under temperature treatment of &gt; 2200°C and used high purity starting materials, point out the relevance of the latter parameters. Future work on oxidation resistance of carbon based materials is shortly discussed.

Oxidation of CO on Zr-, Fe-, Cr-, Ni-, and Cu-containing Catalysts Prepared by Pyrolysis of Metal β-Diketonates on a Synthetic Ceramic Foam

Catalytic systems containing Zr, Fe, Cr, Ni, and Cu composite coatings were suggested for oxidation of CO to CO2. The coatings were prepared by gas-phase thermolysis of metal acetylacetonates and hexafluoroacetylacetonates on a synthetic ceramic foam. The kinetic and activation parameters of the CO oxidation on these catalysts were determined, and the relative activities of the catalysts were evaluated.