Mo Coatings Research Articles

Effect of texture, grain boundary constitution, and molybdenum partitioning on corrosion and hydrogen permeation behavior of pulse electrodeposited Ni-Mo coatings

Microstructural evolution, electrochemical corrosion and hydrogen permeation in pulse electrodeposited Ni-Mo coatings (2, 4, 8, and 11wt% Mo) were investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements revealed improved corrosion resistance at an optimum Mo content. The corrosion current density icorr and polarization resistance Rp values obtained were 13.8 μA/cm2 and 1745 Ωcm2 respectively for pure Ni coating while the icorr and Rp values obtained were 1.7 μA/cm2 and 5406 Ωcm2 respectively for Ni-4wt% Mo coating. Further, increase in the Mo content beyond 4 wt% increased the corrosion rate. Nevertheless, corrosion resistance of Ni-Mo coatings was found to be higher than the pure Ni coating. Ni-Mo coatings contained relatively Mo-enriched clusters in a solid solution matrix. The highest corrosion resistance of Ni-4wt% Mo coating was due to lower energy (001) and (111) textures, lower energy grain boundary constitution, and low coating strain. In Ni-4wt% Mo coating, Mo-enriched Ni-Mo nanoclusters inhibited hydrogen passage by providing a torturous path. In contrast, a high fraction of high-angle grain boundaries (compared to pure Ni coating) facilitated hydrogen permeation leading to a similar extent of hydrogen permeation through pure Ni and Ni-4wt% Mo coatings.

Characterization and electrodeposition mechanism of Ni–Mo coatings from self-regulating electrolyte

Electrochemical Ni–Mo coatings were obtained on a low-carbon steel substrate using a stable, environmentally safe, self-regulating electrolyte containing 0.2 M NiCl2, 0.3 M Na3C6H5O7, and SrMoO4 (saturated). The effects of electrolyte pH, temperature, deposition current density, and hydrodynamic conditions on chemical composition and morphology of the coatings were studied. It was established that the addition of ammonia to the electrolyte contributes to the deposition of a more uniform, globular, nonporous coatings morphology. The effect of ammonia on the formation mechanism of coatings was substantiated. The stages of deposition and the limiting stage of the formation of Ni–Mo coatings from citrate-ammonia electrolytes, which involves the chemical reduction of molybdenum oxide (IV) to molybdenum, were determined using cyclic voltammetry.

Investigation of Cyclic Oxidation and Hot Corrosion Behaviour of Plasma-Sprayed NiCrAlY/Cr3C2/h-BN/Mo Coatings on T22 Boiler Steel Alloy

Investigation of Cyclic Oxidation and Hot Corrosion Behaviour of Plasma-Sprayed NiCrAlY/Cr3C2/h-BN/Mo Coatings on T22 Boiler Steel Alloy

Enhancement of wear and corrosion resistance of pulsed electrodeposited Ni–Mo amorphous/nanocrystalline coatings by heat treatment

In this study, Ni–Mo coatings with various sodium molybdate concentrations were designed and successfully electrodeposited. The effects of treatment with different temperatures (200 °C,400 °C, 600 °C) on the microstructure and properties of the best-performing coating (4 g/L) were investigated. The surface morphologies, elemental content, and phase structure of the prepared coatings were obtained and analyzed by SEM, EDS, XRD, WFI and TEM. The Ni–Mo coating after heat treatment at 400 °C formed the compact and uniform amorphous/nanocrystalline coating. As shown by the electrochemical and wear test. Heat treatment at 400 °C improved the coating properties, and the corrosion current density was decreased by 66 % to 6.2532 × 10−7 A/cm2. The wear rate reduced from 8.3 × 10−4 mm3/N·m to 3.6 × 10−4 mm3/N·m, and the average friction coefficient minimized to 0.079. Additionally, compared with the as-deposited coating, the microhardness reaches the maximum (1048 HV). The formation of the oxide layer and the intermetallic compound MoNi on the surface of the coating plays a carrying and hindering role, thus the surface of the coating shows excellent wear and corrosion resistance. In addition, the corrosion inhibition mechanism during the heat treatment of Ni–Mo coatings was further explored.

Effects of Al, Co and Mo additions on microstructure, corrosion-wear and electrochemical properties of laser-cladded Fe30-15TiC coating

ABSTRACT Fe30-15TiC, Fe30-15TiC-10Al, -10Co and -10Mo coatings were prepared on 45 steel by laser cladding, and their microstructure, hardness and phases were analysed using an optical microscope, microhardness tester and X-ray diffraction, respectively. The effects of Al, Co and Mo additions on the corrosive-wear and electrochemical properties of Fe30-15TiC coating were investigated using a wear tester and electrochemical workstation, and the corrosive-wear mechanism was also discussed in detail. The results show that the microstructure of the coating surfaces mainly presents cellular and chrysanthemum and a few dendritic structures, and the gains of Fe-15TiC coating were refined by the additions of Al, Co and Mo. The hardness of Fe30-15TiC, Fe30-15TiC-10Al, -10Co and -10Mo coatings are 704.51 ± 35, 779.21 ± 38, 718.48 ± 36 and 817.53 ± 41 HV0.5, respectively, and the corresponding wear rates are 267.87, 258.68, 359.54 and 188.93 µm³•s−¹•N−¹, respectively, showing that the wear resistance of Fe30-15TiC coating is improved by the addition of Al and Mo. Moreover, the corrosion rates of Fe30-15TiC, Fe30-15TiC-10Al, -10Co and -10Mo coatings are 1.37 × 10−2, 0.98 × 10−2, 2.72 × 10−2 and 0.99 × 10−2 cm2•year−1, respectively, showing that the corrosion resistance of Fe30-15TiC coating is improved by the additions of Al and Mo.

Elevated temperature wear and friction performance of WC-CoCr/Mo and WC-Co/NiCr/Mo coated Ti-6Al-4V alloy

The effect of adding Mo to WC-based coatings on the microstructure and dry sliding wear performance at elevated temperatures is investigated. The WC-based coatings are deposited using a high-velocity oxy-fuel process on the titanium-31 substrate. The coating was characterized by microstructure, microhardness, porosity, surface roughness, density, and bond strength. The wear and friction behavior of coatings was evaluated using a ball-on disc tribometer at temperatures of 200, 400, 600, and 800 °C and loads of 20 and 30 N. SEM-EDS and an optical profilometer were utilized to evaluate the wear rate and mechanism. The microhardness and bond strength of WC-CoCr/10%Mo coating is more than that of WC-Co/20%NiCr/10%Mo coatings. The WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coatings exhibited decreasing wear rates up to 600 °C, transitioning to an increase at 800 °C. The oxide phases of CoWO4, WO3, MoO3, CoMoO4, and NiMoO4, formed at 600 °C, aid in reducing the rate of wear and friction coefficient. However, the wear rate slightly increased at 800 °C due to vigorous oxidation and softness of coatings. The friction coefficient of WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coating decreases with increasing temperatures due to the lubricating properties of oxide phases on the worn surface. The WC-CoCr/10%Mo coating demonstrates a lower friction and wear rate than the WC-CoCr and WC-Co/20%NiCr/10%Mo coating. At 200 °C, the predominant wear mechanisms were abrasive and fatigue wear, while at 800 °C, oxidative wear, abrasive wear, and adhesive wear were observed.

Tribological Properties and Wear Mechanisms of Laser Cladded Cu–Mo Coatings at 25–500 °C

Abstract Surface modification is the major means to improving the wear resistance of copper alloys. In this study, Cu–Mo coatings were prepared on Cu–Cr–Zr alloy by laser cladding, and the high-temperature tribological properties against 7075 aluminum alloy were explored. The results show that the coatings are a two-phase structure of Mo encapsulated in Cu-mesh. The hardness and resistivity of the coatings are 61–73 Hb and (3.2–6.3) × 10−8 Ωm, respectively. The wear resistance of the coatings is determined by the hardness, which is related to the Mo content at lower temperatures, and it is controlled by the tribo-oxides layer composed of copper and molybdenum oxides at higher temperatures. As the temperature increases, the main wear mechanism of the coatings changes from abrasive wear to adhesive wear.

The induced co-deposition of Ni–Mo–W ternary alloy; Coatings for hardness and corrosion resistance applications

Ni–Mo–W ternary alloy coatings were electrodeposited on mild steel substrate using citrate electrolyte for hardness and corrosion resistance applications. The influences electrolyte pH, electrolyte temperature and sodium molybdate concentrations on deposit qualities were studied. The sodium molybdate concentrations were varied from 0.025 to 0.1 M for obtaining alloy coatings with various molybdenum (Mo) compositions. The deposition condition such as electrolyte concentration, pH and temperature were optimized for obtaining good aesthetic (bright) appearance, surface stability and microhardness properties. The maximum Mo composition (47.71 wt %) in alloy deposit was achieved is 47.71 wt % using 0.1 M sodium molybdate concentration. The microhardness properties were increased from 850 HV to 946 HV by introducing molybdenum (47.71 wt %) as third alloying element in to Ni–W alloy matrix. The obtained mechanical and corrosion resistance properties of these ternary alloy coatings were compared with binary alloy and metallic coatings viz., Ni–W and Ni–Mo and metallic Ni coatings. The superior corrosion rate was observed for Ni–Mo–W alloy deposits (5.8 mpy) compared to Ni–W (9.04 mpy) and Ni–Mo (8.89 mpy) alloy.

Wear and Corrosion Properties of Pure Mo Coating Layer Manufactured by Atmospheric Plasma Spray Process

A pure molybdenum (Mo) coating layer was manufactured by using the atmospheric plasma spray (APS) process and its wear and corrosion characteristics were investigated in this study. A Mo coating layer was prepared to a thickness of approximately 480 μm, and it had sound physical properties with a porosity of 2.9% and hardness of 434 Hv. Room temperature dry wear characteristics were measured through a ball-on-disk test under load conditions of 5 N, 10 N and 15 N. Based on the coefficient of friction graph at 5 N and 10 N, the oxides formed during wear functioned as a wear lubricant, thereby confirming an increase in wear resistance. However, at 15 N, wear behavior changed, and wear occurred due to splat pulling out. A potentiodynamic polarization test was conducted under an artificial seawater atmosphere, and Ecorr and Icorr measured 0.717 V and 7.2E-5 A/cm2, respectively. Corrosion mainly occurred at the splat boundary and pores that were present in the initial state. Based on the findings above, the potential application of APS Mo coating material was also discussed.

Preparation of Electrochemical Ni–Mo Coatings from Self-Regulating Electrolytes

Preparation of Electrochemical Ni–Mo Coatings from Self-Regulating Electrolytes

High-Temperature Heat Treatment of Plasma Sprayed Ti–Si–C–Mo Coatings

In this work, the effect of 800 °C and 1100 °C post-heat treatment on the plasma spraying of Ti–Si–C–xMo (x = 1.0, 1.5) composite coatings was investigated. The composite coatings were composed of TiC, Ti3SiC2, Ti5Si3 and Mo5Si3 reacted phases. After heat treatment, the Ti3SiC2 and Mo5Si3 phases increased. The coating microhardness decreased by 16% and 18% for Ti–Si–C–1.0Mo and Ti–Si–C–1.5Mo coatings, respectively, after heat treatment at 1100 °C. Fracture toughness increased by 16% for the Ti–Si–C–1.5Mo coating after heat treatment at 1100 °C, which was mainly due to the heat treatment promoting Ti3SiC2 formation, healing micro-cracks, reducing the internal stress and making the microstructure dense. The coating friction coefficient before and after heat -treatment was between 0.4 and 0.6. After heat treatment, the wear amount of the coating was first reduced and then increased, and the minimum wear loss occurred after heat treatment at 800 °C. The wear mechanism was mixed abrasive wear, adhesive wear and tribo-oxidation wear.

Corrosion studies on pulse reverse Ni–Mo coatings electrodeposited on Cu substrate

This study conducts a thorough analysis of Ni–Mo coatings electrodeposited on copper substrates, assessing the corrosion resistance of the coated system in a 3.5 M NaCl solution. It focuses on how deposition methods and anodic current densities affect both the coating's integrity and its ability to protect the substrate from corrosion. Three distinct techniques were employed to form Ni–Mo coatings: Direct Current (DC), Pulse Current (PC), and Pulse Reverse Current (PRC). Notably, coatings fabricated using the PRC method demonstrated significant morphological and corrosion behavioral variations compared to their DC and PC counterparts. Emphasis was placed on the role of porosity type and grain boundaries of the coatings, in addition to their composition, highlighting their considerable influence on corrosion dynamics. The standout performer was the one electrodeposited at the supreme anodic current density of 200 mA.cm⁻², exhibiting a composition of 25.2 wt% Mo, 57.4 wt% Ni, and 17.4 wt% O, and incorporating Ni–Mo alloy with oxide and hydroxide phases along with a small average grain size of less than 192 nm. The findings underscore the PRC method's efficacy in producing optimized Ni–Mo coatings, highlighting its broad potential for enhanced corrosion resistance applications.

Corrosion Behavior of Ni–Mo Coatings Prepared by Different Electrodeposition Methods in Na2S Solution

Corrosion Behavior of Ni–Mo Coatings Prepared by Different Electrodeposition Methods in Na2S Solution

THE EFFECT OF BATH TEMPERATURE ON THE STRUCTURE AND TRIBOLOGICAL BEHAVIOR OF ELECTROLESS NI-B–MO COATINGS OBTAINED FROM STABILIZER-FREE BATH

Conventional electroless Ni–B–Mo (ENB–Mo) deposits are formed using hazardous lead or thallium-containing solutions, which must be removed. In this study, ENB–Mo deposits were developed in a bath free of stabilizers and harmful heavy metals. This study estimates the effect of variation of coating bath temperature on tribological performance of ENB–Mo coating developed over AISI 1040 steel. The chosen bath temperatures were [Formula: see text]C, [Formula: see text]C, and [Formula: see text]C to achieve ENB–Mo coating with varying B and Mo content. The 12–15 [Formula: see text]m thick coating was uniform. In comparison to steel substrate, all of the coatings show enhanced corrosion resistance. In the as-deposited state, coatings were mixed amorphous and nanocrystalline with peak of Fe overlapping with Ni. Moreover, TGA results revealed that inclusion of molybdenum enhanced coatings thermal stability. The worn specimens at [Formula: see text]C reveal development of shielding tribo-oxide coatings and existence of microstructural changes. At high working temperatures ([Formula: see text]C), wear debris also has a major impact on tribological mechanisms of coatings. Correlation between microstructure, tribological behavior, and corrosion resistance have also been conducted for ENB–Mo coatings.

Microstructures and Wear Resistance of Mo Coating Fabricated by In Situ Laser-Assisted Plasma Spraying

Microstructures and Wear Resistance of Mo Coating Fabricated by In Situ Laser-Assisted Plasma Spraying

Effect of low nitrogen concentration on reactive RF sputtering of boron

Monolayer boron and B/Mo/B/Mo coatings were prepared by reactive magnetron sputtering in the N2/Ar atmosphere with different RF powers, and the effect of the N2:Ar flow ratio was studied. It was found that as the N2:Ar flow ratio increased, the deposition rate of boron coatings exhibited three different stages of variation due to different mechanisms. The variation of deposition rate with increasing N2:Ar flow ratio was consistent for different RF powers. Berg's model explained experimental findings. XPS revealed that the coatings contained more than 86 % boron nitride (BN) when the N2 flow ratio was above 0.053 at 300W RF power. An optimal ratio exists that maximizes the boron deposition rate and produces a nearly pure boron nitride coating without target poisoning.

Corrosion Behaviour of Borohydride Reduced Ni–B, Ni–B–W, Ni–B–Mo, Ni–B–W–Mo Coatings with Varying Composition: A Comparison

Corrosion Behaviour of Borohydride Reduced Ni–B, Ni–B–W, Ni–B–Mo, Ni–B–W–Mo Coatings with Varying Composition: A Comparison

Preparing Ni–Mo coatings for high-temperature Na2S3 molten salt on aluminium

Pure aluminum was susceptible to corrosion as a casing material for sodium-sulfur batteries. In this context, the effects of different electrodeposition parameters on the sulfur anticorrosion of Ni–Mo alloy coatings on pure aluminum substrate were investigated through an orthogonal test. The corrosion process of aluminum with Ni–Mo composite coatings in Na2S3 molten salt at 350 °C was investigated by static immersion test. The results demonstrated that the optimum parameters for achieving high corrosion resistance coating were Na2MoO4·2H2O concentration of 10 g/dm3, current density of 5 A/dm2, pH value of 9 and temperature of 45 °C. The sodium molybdate content played a crucial role in determining the corrosion resistance of the coating. The grain size of the coating decreased and the Mo content increased accordingly as the sodium molybdate content increased. While the presence of Mo element exhibited inhibitory effects on corrosion, an increase in high-energy grain boundaries resulting from grain refinement had an adverse impact. Consequently, in the single-factor experiment with varying Na2MoO4·2H2O contents, when maintaining the sodium molybdate content of 10 g/dm3, the minimum corrosion rate was 0.02632 mm/y after corrosion in Na2S3 molten salt at 350 °C for 72 h. Additionally, it was found that NiS2 as a corrosion product could effectively inhibit further development of corrosion.

Preparation process and mechanical properties of laser cladding gradient molybdenum coating on copper alloy

Different types of Mo coatings were prepared on the surface of a copper alloy via laser cladding technology in this study to address the problem of low hardness of copper alloy current-carrying friction subsets. Meanwhile, the problems of high reflectivity of copper alloy materials to infrared laser light and mutual insolubility of Cu and Mo were solved by introducing an intermediate layer structure, and the coating process was optimized to obtain a coating with excellent formation. The microstructure, hardness, and interfacial shear bond strength of coatings were tested. Results showed that the Mo coating prepared using a plasma-spheroidized powder had a lower dilution rate and finer and tighter grain growth compared with the Mo coating prepared by crushing agglomerated powder. The coating phase mainly consisted of Mo, Ni3Mo, MoO2, and Cu0.81Ni0.19. The unfused particles present in the plasma-spheroidized powder coating acted as a second hard reinforcing phase, which could significantly increase the hardness of the coating. Three kinds of coatings exhibited strong bond strength, and coatings prepared from different powders fractured in diverse ways. In sum, the plasma-spheroidized Mo coating prepared using the three-way powder feeding method not only had good formation but also possessed the most excellent mechanical properties.

Investigation of the Hardness Development of Molybdenum Coatings under Thermal and Tribological Loading

The increasing global demand for innovative and environmentally friendly lubricants can be met through the use of solid lubricants. By switching from conventional lubricants such as various oils or grease to solid lubricants, new scopes of application can also be opened up. The main requirements for solid lubricants are a reduction in the coefficient of friction (CoF) and an increase in wear resistance. Due to the favourable material properties, molybdenum (Mo) coatings fulfil the tribological requirements and are therefore promising solid lubricants which can be applied via physical vapour deposition (PVD). In this work, the impact of substrate temperature on the hot hardness of deposited Mo coatings was determined. The specimen with the highest hot hardness was then tribologically examined both at the micro and nano level. Through an analysis of the wear tracks by means of nanoindentation and scanning electron microscopy (SEM), it was possible to detect the influence of the tribological load separately from that of the thermal loads. The results showed that the tribological load influenced the Mo coating by significantly increasing its hardness. This was achieved due to the work hardening of the Mo layer leading to an increase in the wear resistance of the coating.