Influence of composition and processing parameters on mechanical properties and erosion response of Ni–TiB2 coatings

Abstract

Sputtered Ni–TiB₂ coatings have been shown to protect Ti–6Al–4V and Inconel 718 substrates from solid particle erosion. However, before new erosion resistant coatings can be efficiently designed, it is essential that the role of mechanical properties in determining erosion resistance be fully understood. In this investigation, nanoindentation techniques were used to quantify the effects of substrate preparation, coating composition, and sputtering process parameters on the elastic moduli and indentation hardness of thin coatings deposited on Ti–6Al–4V and Inconel 718 substrates. The influence of these parameters on coating adhesion was determined using a conventional scratch test. Elastic moduli, indentation hardnesses, and coating adhesion were correlated with erosion behaviour. The erosion resistance of the coatings that exhibited microscopic ductility is dependent on the nodule diameter and coating properties such as hardness, elastic modulus, and fracture toughness.

MST/1697     

Scanning AES and XPS analysis of a thin Au emissivity barrier on Ni alloy

Scanning Auger electron spectroscopy and x-ray photoelectron spectroscopy were used to analyze discolored gold plating on nickel alloys. Gold plated nickel alloy sheets have been used as a thermal shield inside nacelle housings for various jet engines. The thin gold film is applied to serve as a low emissivity coating to reflect thermal radiation. Inconel 625 sheet was gold plated and exposed to 590°C in air for 924 hours to achieve an appropriate service use reference point. The visual appearance of the gold thin-film surface had noticeably dulled after this prolonged exposure. In some cases, several dark spots a few microns in size also appeared on the dulled gold surface. Our hypothesis was that nickel or some alloy constituent had diffused through the gold film and changed the color of the gold surface. X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to differentiate the composition of the gold plated Inconel samples prior to thermal exposure and after the prolonged exposure. Scanning Auger micrographs showed that the composition of the dulled gold surface had changed due to the diffusion of nickel from the substrate alloy through the gold thin film. Nickel was absent at the surface of the unexposed samples while significant nickel concentrations were detected on the discolored gold surface and with the highest nickel levels detected in the dark spots on the gold surfaces. Auger depth profiles made on the exposed gold film verified that a discrete gold layer remained on top of the Inconel with a broad Ni-Cr-Au zone beneath this gold layer.     

Preparation and characterization of thin oxides films formed at a brass surface oxidized by plasma treatment

The surface of a 90Cu10Zn alloy exposed to a low pressure inductively coupled oxygen plasma gives rise to an oxide layer, the composition of which is determined by FTIR spectroscopy and X-ray diffraction techniques. The thickness of the oxide layer depends on the time of exposure to the plasma and on the distance between the sample and the first high voltage (HV) coil for given primary treatment parameters and on the preparation technique of the samples.     

阴极电弧沉积多元合金膜层的织构及其形成

采用阴极电弧沉积方法，制备了与靶材成分基本相同的多元合金Inconel625膜层[1]。用XRD，SEM，TEM研究了不同入射角下所获膜层中的织构分布及其成因。     

Life Enhancement of Gas Turbine Combustor Liner Through Thermal Barrier Coating

The life enhancement program of an aero gas turbine combustor liner has been taken up through thermal barrier coating. Yttria-stabilized zirconia with a composition of Zr₂O₂ + 8 wt.% Y₂O₃ has been applied by atmospheric plasma spray on newly manufactured liner. A remarkable improvement in liner life has been observed under severe service condition. However, peel off of coating is noticed on the serviced components which are premature withdrawn for any other reasons. Reason for peel off has been studied metallurgically in detail. Coated samples were subjected to cross-sectional microanalysis. Based on the microanalysis suitable repair procedures are being adopted for serviced components. The process found very effective for a better life.     

XPS study of the surface composition modification of nc-TiC/C nanocomposite films under in situ argon ion bombardment

X-ray Photoelectron Spectroscopy (XPS) is commonly used to study the chemical composition of TiC/C nanocomposite films. Nevertheless, XPS remains a surface analysis technique and the obtained chemical information can be strongly affected by the surface oxidation and carbon contamination of the nanocomposite samples due to their exposure to air. Generally, an erosion stage is performed before XPS analysis using argon ion bombardment to remove the surface contamination. Since ion bombardment is likely to modify the surface chemical composition of the films, the question of whether XPS results are really representative of the bulk nanocomposite material can be addressed. Therefore, this study is devoted to the effect of ion bombardment on the surface chemical composition of nanocomposite films. TiC_x and TiC_xO_y films were grown by a hybrid plasma process combining Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition. Then, the samples were transferred to the XPS system where an in situ study of the modification of the surface chemical composition under argon ion bombardment was performed. XPS results are compared to Energy Dispersive X-ray analysis.     

J-T characterized stress fields of surface-cracked metallic liners bonded to a structural backing - I. Uniaxial tension

Surface crack-tip stress fields in a tensile loaded metallic liner bonded to a structural backing are developed using a two-parameter J-T characterization and elastic-plastic modified boundary layer (MBL) finite element solutions. The Ramberg-Osgood power law hardening material model with deformation plasticity theory is implemented for the metallic liner. In addition to an elastic plate backed surface crack liner model, elastic-plastic homogeneous surface crack models of various thicknesses were tested. The constraint effects that arise from the elastic backing on the thin metallic liner and the extent to which J-T two parameter solutions characterize the crack-tip fields are explored in detail. The increased elastic constraint imposed by the backing on the liner results in an enhanced range of validity of J-T characterization. The higher accuracy of MBL solutions in predicting the surface crack-tip fields in the bonded model is partially attributed to an increase in crack-tip triaxiality and a consequent increase in the effective liner thickness from a fracture standpoint. After isolating the effects of thickness, the constraint imposed by the continued elastic linearity of the backing significantly enhanced stress field characterization. In fact, J and T along with MBL solutions predicted stresses with remarkable accuracy for loads beyond full yielding. The effects of backing stiffness variation were also investigated and results indicate that the backing to liner modulus ratio does not significantly influence the crack tip constraint. Indeed, the most significant effect of the backing is its ability to impose an elastic constraint on the liner. Results from this study will facilitate the implementation of geometric limits in testing standards for surface cracked tension specimens bonded to a structural backing.     

Design and statistical analysis of plasma coatings on superalloy for gas turbine applications

The Influence of plasma sprayed NiCr–Cr₂O₃ and Al₂O₃–40% TiO₂ (A40T) coatings on Inconel 617 are investigated at 900 and 1000 °C under mixed salt environment for gas turbine applications. The results revealed that the plasma coated alloy exhibits lower mass change than bare alloy in the Na₂SO₄ and NaCl salt mixture with and without V₂O₅. The response to the experimental analysis is statistically evaluated using 2³ factorial design. Further the exposed samples were analyzed by means of optical image, SEM, EDS and XRD results. The EDS and XRD analysis revealed that the oxides are rich in Ni and Mo on the surface of the samples. The coated samples exhibited better corrosion resistance in A40T when compared to NiCr–Cr₂O₃ coatings than bare alloy.     

Weldability in dissimilar welds between Type 310 austenitic stainless steel and Alloy 657

Microstructural evolution and solidification cracking susceptibility of dissimilar metal welds between Type 310 austenitic stainless steel and Inconel 657, a nickel-based alloy, were studied using a combination of electron microscopy analysis and Varestraint testing techniques. In addition, the effect of filler metal chemistry on the fusion zone composition, microstructure, and resultant weldability was investigated. The good cracking resistance of welds prepared with Inconel A was due to a small amount of secondary phase (NbC) and narrow solidification temperature range. The relatively poor cracking resistance of welds prepared with Inconel 82 and Type 310 stainless steel (310 SS) was a result of a wide solidification temperature range and an increase in the amount of secondary phases. Consequently, it is concluded that for the joint between Inconel 657 and 310 SS, filler material of Inconel A offers the best weldability.     

Preparation and magnetic properties of SrFeO3−x (x = 0.25 ∼ 0.5) using RF magnetron sputtering optimized through sputtering plasma analysis

We investigated the preparation and the magnetic properties of SrFeO_3−x using conventional RF magnetron sputtering. Photoluminescence spectrum analyses of the sputtering plasma revealed that the film composition was changed even using the stoichiometry target. After fixing the composition of the targets from an intensity ratio of the Sr and Fe plasma, the polycrystalline SrFeO_3−x films with different oxygen deficiencies were able to prepare using the various sputtering gas ratio. The magnetic properties of the samples were also changed with changing the sputtering gas ratio. This magnetic property change was likely due to the suppression of the oxygen deficiency in the film.     

Depth profile analysis of solar cells by Secondary Neutral Mass Spectrometry using conducting mesh

Depth profile analysis of solar cells was performed by Secondary Neutral Mass Spectrometry (SNMS), which is a suitable technique for quantitative analysis of the composition of layered structures. However, in the case of insulating samples or samples prepared on non-conductive substrates (e.g. microslide, oxidized silicon wafer) the charge accumulation on the sample surface due to ion beam bombardment can cause a serious problem by destroying the resolution of depth profile. The high frequency (HF) mode of electron-gas SNMS seems to be a good solution for this problem. Another method to prevent the charge accumulation on a sample surface can be a conducting mesh (e.g. copper, stainless steel) placed on the surface. Using one of the two methods mentioned above can help us to get rid of the charging effect, i.e. to neutralize the surface charge during measurements. But in the case of solar cell analysis these two methods should be applied simultaneously during depth profiling. The experimental results performed on p-i-n:Si (p-type/intrinsic/n-type) diodes have proved that SNMS measurement in HF operation mode combined with a mesh is very efficient in the determination of doping levels of phosphorus and boron with good depth resolution, even in the case of 500-600 nm thick samples.     

Thermal conductivity of Inconel 718 and 304 stainless steel

The results of thermal conductivity measurements on Inconel 718 and 304 stainless steel by the comparative and flash diffusivity techniques are reported for the temperature range 0–700°C. For 304 stainless steel, excellent agreement with published data is found for the specific heat, thermal diffusivity, and thermal conductivity. In the case of Inconel 718, the measurements show that the conductivity depends critically on the sample thermal history and the metallurgical condition of the alloy. Measurements on a solution-treated sample indicated a conductivity function close to that reported previously, while precipitated samples showed a higher conductivity, similar to the conductivityvs-temperature function used for reduction of comparative thermal conductivity data with Inconel 718 references. These results indicate that Inconel 718 is not a suitable reference for high-accuracy comparative thermal conductivity measurements unless its thermal history and associated conductivity function are known.     

Metallic and ceramic powders for vacuum plasma spraying

All product families, including hard materials, hard metals, hard alloys, cermets, intermetallics and refractories, are usable for vacuum plasma spraying. Fine powders (less than 45 μm) that are narrowly classified within well-defined limits for oversize and undersize are used. The determination of the size distribution is of particular importance.The morphology of powders for vacuum plasma spraying has to be stressed in particular, e.g. the particle shape, the surface area, the density and the composition (agglomerate, primary grain, crystal formation).In addition, the chemical composition, i.e. the main, secondary and trace elements and the gas contents (O₂, N₂, H₂, noble gases), is specified and the lowest specification values have to be met for vacuum plasma spray powders such as M-Cr-Al-Y.Single-phase and refractory compounds with uniformity of structure as well as solid solutions can be vacuum plasma sprayed without any changes and with strict maintenance of phase uniformity and stoichiometry.     

Machining Parameter Optimization in High-Speed Milling for Inconel 718 Curved Surface

Machining technology for nickel-based alloy Inconel 718 is a hotspot and difficult problem in industrial fields and the high-speed milling (HSM) shows obvious superiority in difficult-to-process material machining. As the machining parameters are crucial in processing of Inconel 718 and the study of chip is important in metal cutting, there is an urgent need for deep research into the machining parameter optimization based on chip variation in HSM for Inconel 718 curved surface, so as to further increase the productivity of Inconel 718 in aerospace field. Regarding Inconel 718 curved surface, an experimental study about the machining parameter optimization based on chip variation in HSM is conducted. The relationship between chip shape and machining parameters is studied, and the roughness is measured and discussed for the machined curved surface. Results indicate that the chip area relates to geometric feature of curved surface, the optimal range for spindle speed is from 9000 to 11000 rpm based on chip variation, the feed per tooth should be large in case that condition permitted, and the cutting depth can be selected according to other constraint conditions. This study is significant for improving the machining quality and efficiency of Inconel 718 curved surface.     

Optimization of sol-gel technique for coating of metallic substrates by hydroxyapatite using the Taguchi method

In this study, the Taguchi method of design of experiment (DOE) was used to optimize the hydroxyapatite (HA) coatings on various metallic substrates deposited by sol-gel dip-coating technique. The experimental design consisted of five factors including substrate material (A), surface preparation of substrate (B), dipping/withdrawal speed (C), number of layers (D), and calcination temperature (E) with three levels of each factor. An orthogonal array of L₁₈ type with mixed levels of the control factors was utilized. The image processing of the micrographs of the coatings was conducted to determine the percentage of coated area (PCA). Chemical and phase composition of HA coatings were studied by XRD, FT-IR, SEM, and EDS techniques. The analysis of variance (ANOVA) indicated that the PCA of HA coatings was significantly affected by the calcination temperature. The optimum conditions from signal-to-noise (S/N) ratio analysis were A: pure Ti, B: polishing and etching for 24 h, C: 50 cm min^?1, D: 1, and E: 300 °C. In the confirmation experiment using the optimum conditions, the HA coating with high PCA of 98.5 % was obtained.     

Plasticity characterization of the modified layer produced by plasma nitrocarburizing of nanocrystallized 18Ni maraging steel

The plasma nitrocarburizing of nanocrystallized 18Ni maraging steel was performed at 460 °C for 4 h. The surface phase composition, cross-sectional microstructure and hardness profile of the nitrocarburized layer were investigated by the X-ray diffractometer (XRD), optical microscope (OM) and microhardness tester. Plasticity of the surface layer of original and nitrocarburized samples was analyzed by Taylor factor obtained by electron backscattering diffraction (EBSD) data and nanoindentation tests. The nitrocarburized surface is composed of α-Fe, Fe₄N and a small fraction of low nitrogen compound FeN_0.049. The surface and core hardness of nitrocarburized samples are 200% and 130% of that of the original one, respectively. The Taylor factors for different slip systems of α-Fe grains are all decreased after nitrocarburizing and Taylor factors for Fe₄N grains are lower than those of basal slip system of α-Fe grains. Plasticity factor η_p, i.e. the ratio of plastic deformation work to total deformation work dissipated during loading-unloading process, of the surface layer is reduced about 20% after nitrocarburizing. This suggests that plasticity and wear resistance of the surface layer could be decreased and improved after nitrocarburizing, respectively. The surface layer of the nitrocarburized sample also possesses certain plasticity because its plasticity factor η_p is more than 60%.     

Reactive magnetron sputtering of Inconel 690 by Ar-N2 plasma

M and M-N coatings, where M is nearly the metal composition of Inconel 690 (57 at.% Ni, 32 at.% Cr, 9.5 at.% Fe…) were sputter-deposited on glass and steel substrates in pure argon and in Ar-N₂ mixtures using a round planar magnetron. The influence of nitrogen gas flow rate inlet in argon on chemical composition and microstructure was studied. The as-deposited (T < 100 °C) M-N films containing up to 30 at.% nitrogen are a nanocrystalline supersaturated face cubic centered (fcc) solid solution (γ_N). The pure metallic films have a pronounced<111>fcc crystallographic texture, while the M-N films exhibit a strong<100>fcc crystallographic texture. The effect of temperature on the microstructure of M-N films was studied by increasing the substrate temperature during preparation and by tempering of an as-deposited M-N films. For M-N films prepared at 400 °C, the X-ray diffraction analysis reveals a magnetic γ phase with a very low nitrogen content, while electron probe microanalysis gives an overall high nitrogen content in the layer (up to 25 at.%). It is concluded that the layers consist of two phases when prepared or tempered at high temperature (T > 400 °C): an fcc CrN nitride and a γ (Ni,Fe,Cr) depleted in nitrogen.     

Effect of Magnetic Flux Distribution and Magnetic Powder Addition on the Magnetic Levitation Force of Sm123 Superconductors

Sm123 and Sm211 were prepared by melt-powder-melt-growth and solid-state-reaction techniques, respectively, to have the nominal composition of (Sm123)_0.75(Sm211)_0.25. After the preparation of this composition, the Fe-B magnetic powder (MP) was added to the composition for 0.000, 0.010, 0.015, 0.025, 0.050 wt.% to investigate the effect of MP addition on the levitation force density (LFD). Additionally, different permanent magnets (PM) were used as magnetic-field source to investigate the effect of magnetic-field gradient on the LFD of MP added superconductors. Our findings indicate that the MP addition acts as a flux pinning centre in the sample and enhances the LFD up to 0.025 wt.% adding amount, and the optimum flux gradient which produces a screening current in the sample occurs when the B/d (magnetic-field intensity/ diameter of PM) ratio is equal to 0.060. These results imply that the experimental data can be useful for fabricating process of superconducting samples with larger MLF values, and designing of superconducting magnets, flywheel energy storage and maglev systems.