Mo Coatings Research Articles

Wear properties of Ni–Mo coatings produced by pulse electroforming

Ni–Mo coatings with good mechanical properties were obtained by pulse plating. This study is focused on the current efficiency, molybdenum content and microhardness of the Ni–Mo coatings, which were affected by the pulse electroforming parameters. In addition, the wear resistance of the coatings was examined. The experimental results indicate that the Mo content in the PC-plated coatings increases upon increasing the frequency in the range 10–1000Hz. The maximum Mo content (30.2wt.%) in the coating occurred at a current density of 10A/dm2, a duty cycle of 0.7, and a frequency of 1000Hz. The XRD results indicate that the NiMo coatings prepared by pulse current are nanocrystalline and amorphous. The wear test results indicate that the wear resistance of the Ni–Mo coatings produced by pulse electroforming was higher than that produced by direct current plating.

Effect of powder particle size on wear resistance of plasma sprayed molybdenum coating

Plasma-sprayed molybdenum coatings are used in automotive, aerospace, pulp and paper industries in order to guard the machine parts against wear and corrosion. In this work, an attempt has been made to study the effect of particle size on wear behaviour of molybdenum coated steel. Two types of Mo coatings were deposited on American Iron and Steel Institute (AISI) 1020 steel substrate, one is with particle size of 15–40 µm (type I) and another one is with 40–90 µm (type II) using plasma spraying. The microstructures and worn surface morphologies of the coatings were analysed by means of X-ray diffractometer and scanning electron microscopy. It was found that the as-sprayed type I and type II coatings consist of molybdenum (Mo) as the major phase and molybdenum oxide (MoO2) as the minor phases. For the evaluation of influence of coating powder particle size on wear characteristics, the sliding wear tests were performed on a pin-on-disc apparatus. The variation of volume loss with applied load, sliding speed and sliding distance was monitored. The type I sprayed coating exhibits better wear resistance. Tribological testing was also supported by metallographic examination for the identification of wear mechanisms. It was verified that the wear of coating is dominated by fracture of splats, crack propagation, delamination and plowing.

Thermal Aging Behavior of CoSb<sub>3</sub> with Protective Mo Coating

In order to prevent the sublimation of Sb, protective Mo coatings were deposited on the CoSb3 substrate by DC magnetron sputtering. Thermal aging behavior of CoSb3 with Mo coating was investigated by accelerated experiment at 650oC for 24h. The results indicated that Mo coatings exhibit columnar crystal and body-centered cubic structure. It was found that the weight loss decreases with the increasing thickness of Mo coating. In comparison with naked CoSb3 material, the degradation of thermoelectric properties of CoSb3 with Mo coatings decreases under accelerated thermal aging test.

Dry Sliding Wear Behaviour of Plasma SprayedAl2O3-30%Mo and Mo Coating

Two kinds of plasma sprayed coatings Al2O3-30%Mo and Mo materials are used in industries in order to shield to machine parts against wear and corrosion. In the present study, wear behaviour of plasma sprayed Al2O3-30%Mo coating was studied for different loads, sliding distance and sliding speed and compared with plasma sprayed Mo coatings deposited on AISI1020 steel substrate. A pin-on-disc result shows that Mo coatings had a significantly better tribological performance as compared with that of Al2O3-30%Mo coatings. The wear mechanisms were investigated through the scanning electron microscopy (SEM). The worn surface of the both the coatings shows that the formation of grooves, de-lamination and fractured splats on the surface of the pin.

Improvement of Microstructural and Mechanical Properties of Plasma Sprayed Mo Coatings Deposited on Al-Si Substrates by Pre-mixing of Mo with TiN Powder

Improvement of Microstructural and Mechanical Properties of Plasma Sprayed Mo Coatings Deposited on Al-Si Substrates by Pre-mixing of Mo with TiN Powder

Improvement of microstructural and mechanical properties of plasma sprayed Mo coatings deposited on Al-Si substrates by pre-mixing of Mo with TiN powder

The present work embodies development of a new class of mechanically improved Mo-TiN coating material using plasma spray technique. The coatings are developed on Al-Si alloy at different torch input power levels ranging from 15 kW to 30 kW. Pre-mixing of TiN with molybdenum enhances adhesion strength and hardness of the coatings. Maximum adhesion strength of 22 MPa (±0.75) and hardness of 748 HV (±30) are found for the coating when molybdenum is pre-mixed with 10% TiN. FESEM micrographs of the as-sprayed coatings showed formation of plate-like structures of splats which indicates TiN sites as reinforcement in Mo matrix. X-ray diffraction study reveals the formation of both MoO2 and TiN as minor phases in the coating microstructure. The significant enhancement of mechanical properties like adhesion strength and hardness is attributed towards the presence of these phases.

Characterization of pulse reverse Ni–Mo coatings on Cu substrate

The effect of pulse reverse current (PRC) method on Ni–Mo coatings electroplated from chloride solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. By increasing the anodic duty cycle and anodic current density, the Mo content of coatings reached 68wt.% and 78wt.%, respectively at cathodic current densities of 500 and 300mAcm−2. The Mo content of coatings increases by the preferential dissolution of Ni on the anodic pulse and also by the replenishment of Mo complexes in the diffusion layer near the substrate surface during the anodic pulse. In comparison with the direct current (DC) and the pulse current (PC) methods, the PRC method deposited coatings having grain-refined morphology and more porosity especially at the anodic current density of 200mAcm−2. This is related to preferential dissolution of the high stress zones and the increase of Mo oxide. The PRC method made coatings with the crystallite size of 125Å which is less than 287Å crystallite size of coatings deposited by the PC method. Moreover, the PRC method made coatings with a higher crystalline state than coatings deposited by the DC method. The chemical composition, the surface morphology and the crystal structure of all deposited Ni–Mo coatings were evaluated by atomic adsorption spectroscopy (AAS), scanning electron microscopy (SEM) and X-ray diffraction (XRD) methods, respectively.

Roughening and reflection performance of molybdenum coatings exposed to a high-flux deuterium plasma

Optical diagnostic systems of ITER are foreseen to include metallic, plasma-facing, electromagnetic radiation reflecting components called first mirrors (FMs). Molybdenum coatings are important candidates for these components. Depending on the local plasma parameters of the reactor, the mirrors may be under net erosion or deposition conditions. In this work, we exposed molybdenum coatings to a high-flux deuterium plasma in order to test their roughening limits under erosion conditions. The high energy of deuterium ions (500 eV on average) results in more vigorous roughening of the surface compared with lower energy ions (200 eV). Longer exposure (3 × 1020 ions cm−2) of the 200 eV ions results in only a slightly increased roughness compared with shorter exposure (6.8 × 1019 ions cm−2). Both phenomena match to the theory regarding roughening dynamics of physical sputtering. A comparison of results in this work with previous studies gives support to the hypothesis that roughening is flux and temperature dependent. Partial delamination of the coatings is observed upon exposure at room temperature, but not at an elevated temperature (200 °C). In summary, Mo coatings will remain functional in the ITER environment under the expected conditions. However, changes in the expected conditions such as 500 eV mean energy of impinging charge exchange neutrals or <100 °C surface temperature of the mirrors can lead to gradual or sudden failure of the coatings.

Tribological properties of adaptive NiCrAlY–Ag–Mo coatings prepared by atmospheric plasma spraying

Adaptive NiCrAlY–Ag–Mo composite coating was deposited by atmospheric plasma spraying and its tribological properties from 20°C to 800°C under unlubricated conditions were evaluated using CSM high temperature tribometer. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy were used to characterize the coating and the corresponding wear tracks to determine the lubrication mechanisms. The results showed that NiCrAlY–Ag–Mo composite coating exhibited low friction coefficients around 0.3 in the entire temperature range and its wear rates were at the order of 10−5mm3/Nm at all test temperatures. Characterization of NiCrAlY–Ag–Mo coating revealed that silver provided lubrication at temperatures below 400°C. Silver molybdate and molybdenum oxide, which were formed as the temperature raised, act as lubricants at higher temperature (above 400°C). Meanwhile, the formation mechanism of silver molybdate and molybdenum oxide was also briefly discussed.

Studies on Pt–Mo phases using analytical techniques with high resolution

Pt–Mo coated system annealed at 1050°C for 24h was investigated using several analytical techniques with high resolution (SEM/EDX, μ-PIXE, RBS and XRD). These techniques provide structural and compositional data throughout the material depth and probing area. The results depend on the applied beam, its energy and size. They contribute to a better understanding of thermal annealing effects on the solid-state phase transformation and morphological changes in Pt–Mo coatings. The results indicate the presence of Pt- and Mo-solid solutions and two Pt–Mo phases (PtMo and Pt2Mo3), changes in the coating morphology, such as increased surface roughness and formation of “lace morphology”, as well as an increase in coating thickness.

Characterisation of Zn–Mo alloy layers electrodeposited from aqueous citrate solution

• The conditions for electrodeposition of zinc–molybdenum alloy have been studied. • The content of Mo in coatings can be controlled by the electrolyte composition. • The surface morphology of Zn–Mo coatings differs according to the contents of Mo. • Two Zn–Mo phases are formed in deposits. The conditions for molybdenum with zinc electrodeposition from citrate electrolytes were studied. Partial polarisation curves were determined. The surface composition of deposits was ascertained by chemical analysis (EDS and WDXRF) and profile chemical analysis (GDOES). The morphology of coatings was studied by SEM. The electrolysis parameters allowing electrodeposition of homogeneous Zn–Mo coatings containing various amounts of molybdenum (in the range from about 0.5 wt.% to 8 wt.%) were selected. The deposits’ morphology depends significantly on the content of molybdenum and on the substrate used. Two Zn–Mo phases are formed in deposits: a hexagonal phase with low content of molybdenum, and an amorphous or nanocrystalline phase enriched by molybdenum.

Structural and morphological characterization of Mo coatings for high gradient accelerating structures

A series of Mo coatings grown on Al2O3 and Cu were prepared via sputtering method. XAS experiments were performed at the Mo K edge to characterize the coating structure and the chemical status of Mo atoms. From the XANES analysis we recognized that all Mo coatings on Al2O3 have a slightly disordered structure with a negligible Mo oxide contribution. Moreover, the chemical state is that of the Mo metal with a negligible oxygen contribution. Compared with Cu based materials, molybdenum is an attractive material for accelerator components and a reliable option for RF linear accelerating structures to achieve high accelerating gradients and low breakdown rates, two fundamental parameters for the next generation of linear accelerators.

Analyse microstructurale et tribologique de deux types de dépôts en acier inoxydable 18/8 et en molybdène obtenus par projection thermique

The aim of this work is to produce metallic coatings onto a steel substrate type E335 in order to hardening and improving the tribological properties of contact surfaces. In this study, two different coatings of stainless steel 18/8 and molybdenum realized with and without bond coat in Ni-Al were sprayed using a thermal flame spray technique. The microstructures of the two deposits are obtained using an optical microscope (OM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Measures microhardness under a load of 200 g, are performed on the polished surfaces of these two types of deposits. The wear and the determination of the coefficients of friction of the two deposits tests were performed in dry conditions. A pin on disc configuration on a tribometer type TE 91 was used with different normal loads and a sliding speed of 0.5 m/s. The results showed that the microstructures obtained by OM and SEM of stainless steel present a dense and compact microstructure. It contains a low porosity and unmelted particles in comparison with the coatings of Mo. In addition, it was found that the spray-coated stainless steel 18/8 exhibited higher microhardness, higher wear resistance and significantly low friction coefficient in comparison with those of Mo coatings.

Annealing effect on mechanical properties of Ta–Mo sputtered coatings

The annealing parameters play a vital role in determining and understanding the microstructures and mechanical properties of Ta–Mo nanostructured coatings in the annealing processes. This investigation aims at finding the best annealing parameters and predicting the behaviour of the annealing parameters during the preparation of Ta–Mo coatings by cosputtering deposition. This study reveals that phase transformation and grain growth of the coatings were strongly dependent on the annealing processes. Low temperature annealing process within 600°C can increase the hardness H and elastic modulus E due to the increased grain size and decreased crystal defect. However, severe oxidation occurred in the coatings by the high temperature annealing process that exceeded 700°C. Finally, a three stage model related to the low and high temperature annealing mechanisms of Ta–Mo coating was proposed.

Experimental Analysis on the Environment of Internal Plasma Spraying Techniques

The effects of internal spraying environment on the microstructures and mechanical properties of plasma spraying NiCrBSi+15%Mo coatings were investigated. For experimental analysis of spraying environment, a specialized internal plasma device and its test unit were developed. Firstly, microstructures of spraying coatings and powders were analyzed by scanning electron microscopy (SEM). Furthermore, the boding strength, porosity and micro-hardness of the coatings were investigated and determined separately. According to these properties of plasma spraying coating, the influence of spraying environment on the coating properties and specimen temperature could be investigated. The results show that that the coating performances decreased because of the dust, smog and high temperature of the internal spraying environment. The high-performance internal coatings can be obtained by properly designing spraying process and using the special spraying device.

Electrodeposition of CIS films on the Mo back electrodes with different crystallinities

Electrodeposition of copper indium diselenide (CuInSe2), which is an absorption layer for thin film solar cells, has been studied on a molybdenum (Mo)-coated glass with different crystallinities. Metastable FCC Mo and BCC Mo coatings were prepared by R.F. sputtering with varying R.F. power (100–170W) and Ar pressure (3–11mTorr). Experimental results indicated that the Mo coating deposited at lower power and higher pressure had smaller crystallite size. Cross-sectional transmission electron microscopy showed that the Mo coating deficient in crystallinities contained micro voids residing in the boundaries of the columnar grains and had higher oxygen content, as measured by energy dispersive spectroscopy. The crystallinity of Mo coatings strongly influenced the open circuit potential in the electrolyte for CIS electrodeposition. Consequently, the Cu/In ratio of CIS deposits plated at a constant potential (−0.7 vs. SCE) varied with the distinct Mo coatings. Moreover, the CIS deposit on the various Mo-coated glasses displayed a different morphology. The effect of the crystallinity of Mo coatings on hydrogen evolution reaction at pH 1.55 was also explored. Hydrogen evolution during the CIS electrodeposition may be one of the key factors to influence the CIS morphology. How the crystallinity of the Mo coating affects the composition and morphology of the CIS deposits can be useful for device fabrication and deserves for further study.

Rhenium and molybdenum coatings for dendritic tungsten armors of plasma facing components: Concept, problems, and solutions

Abstract Fusion technology development requires materials resistant to heat, erosion and activation. Tungsten (W) could fulfill these requirements for plasma facing components of fusion power plants. A method developed by SNL to enhance the thermal and dimensional stability of W requires depositing a thin coating on the surface of dendritic W armors for IFE plasma facing components. This paper examines the waste disposal rating (WDR) associated with the activation of thin coatings of Re and Mo on the ARIES-ACT W-based divertor. Our results indicate that Re coatings must be limited to fewer than 30 μm in order to classify the Re/W-based divertor as low-level waste (LLW). Mo coatings that are larger than a few microns thick exceed the LLW disposal limit. It is recommended that, in addition to limiting the Mo thickness to 25 μm, natural Mo should be tailored to remove the Mo-94, Mo-98, and Mo-100 isotopes in order to reduce the WDR of the Mo/W-based divertor below the LLW disposal limit. If the isotopic tailoring process is inefficient or costly, SNL could focus their effort on the further development of the Re dendrite coating while Mo experiments would be regarded as a comparative study only.

Mechanical and corrosion properties of Ta–Mo coatings by heating processes

In this research, substrate heating process has been used for the production of Ta–Mo high temperature protective coatings. The microstructures of the alloy coatings have been studied through X-ray diffraction and scanning electron microscopy. Mechanical and corrosion properties of different alloys have been investigated in both low and high temperature heating processes. Substrate heating processes (from 250 to 550°C) were expected to produce partially recrystallised and fully recrystallised microstructures. Higher heating temperature results in recrystallised microstructures, but adversely affects the density of atoms Vt and bond energy G. The behaviour of low and high temperature heating processes on corrosion and mechanical properties of Ta–Mo nanostructured coatings was studied.

Electrodeposition and characterisation of nanocrystalline Ni–Mo coatings

In the present study suitable plating conditions for electrodeposition of thick, crack-free coatings at moderate temperatures and current densities with reasonable current efficiency have been developed. Ni–Mo coatings (5–22wt.% Mo) were electrodeposited on steel substrates from sulphate–citrate baths under controlled hydrodynamic conditions. The microstructure, residual stresses, adhesion, microhardness and wear resistance of the coatings, deposited at different current densities were examined. The tribological properties of compact and adherent Ni–Mo deposits obtained in optimum conditions were compared with the behaviour of the electrodeposited chromium coatings.

Alloying of structural steel with molybdenum and titanium under the action of compression plasma

Deposition of Ti and Mo coatings on low-carbon steel followed by its treatment with compression flows of nitrogen plasma leads to a deep alloying of the steel (up to 10 μm) with the substances of the coating and the plasma-forming substance (nitrogen), to changes in the elemental and structure-phase compositions (the formation of solid solutions based on Fe and (Ti, Mo)N), and consequently to changes in the properties of the treated surface.