Tribological Properties Of Coatings Research Articles

Effect of process parameters on the properties of Stellite-6 coatings deposited by Cold Gas Dynamic Spray

This study analyzes the effects of process parameters on mechanical and tribological properties of Stellite-6 coatings obtained by Cold Gas Dynamic Spray (CGDS). The gas pressure and temperature as well as the speed of the deposition torch were considered as significant process parameters. The aim is to overcome some technical issues arising in the cold spray deposition of hard anti-wear metallic coatings, such as stellite, due to their high strength and melting point. A High-Pressure CGDS equipment was used and systematic studies were carried out for a deeper understanding of the effects of all investigated process parameters. A particular focus has been put on the substrate temperature, that can be regarded as an indirect process parameter. This latter, in fact, was monitored in-situ during deposition, by infrared thermography (IR). The microstructure was analyzed by scanning electron microscopic observations. Mechanical properties were analyzed by instrumented micro- and nano-indentation measurements. Hardness (H) and Young's modulus (E) were considered as affective parameters to estimate the inter-particle cohesion strength and the work hardening of the coating. Results revealed that the substrate temperature, that is affected by the process parameters, plays a fundamental role in the coating formation process. In particular, the lower the scanning speed the higher the quality of the coatings, in terms of compactness, hardness and elastic modulus. Finally, tribological properties of the coatings were analyzed by pin-on-disk tests. Wear coefficient is strongly related to the strain-to-failure ratio (H/E) that is higher when high values of scanning speed were chosen. In fact, it was observed that decreasing scanning speed elastic modulus increases more quickly if compared with trend of the hardness response. In conclusion, it was demonstrated that both mechanical and tribological properties of CGDS Stellite-6 coatings are mainly affected by the impact temperature of the particle-substrate system and effective deposition windows were identified.

Effects of spraying conditions on the microstructure and properties of NiCrBSi coatings prepared by internal rotating plasma spraying

NiCrBSi alloy coatings were fabricated via internal rotating plasma spraying (IRPS) inside the cylinder liner and in open space using the same processing parameters. The effects of spraying condition on the microstructural, mechanical and tribological properties of the IRPS coatings were investigated. Simultaneously, the effects of the flow rate of primary gas (FRPG) on the coatings at a short spray distance were thoroughly evaluated. The microstructure, Vickers hardness, bond strength and tribological properties of the coatings were experimentally determined and characterized in detail. The results demonstrated that all coatings fabricated by IRPS had a dense structure and high microhardness. The bond strength and tribological properties were effectively promoted inside the cylinder, in contrast to open space condition. It is also found that coefficient of friction and wear volume of the coatings declined with the increasing of FRPG. Especially, the coatings prepared with FRPG at 100 L⸱min−1 exhibited the lowest friction and best wear resistance despite their higher porosity. The main wear mechanisms were abrasive and fatigue wear for the coatings deposited in open space, while the dominant wear mechanisms for the coatings prepared inside the cylinder were adhesive wear and tribolayer delamination.

Structural and tribological characterization of amorphous and crystalline titanium-nickel coatings

The interest in titanium-nickel (TiNi) alloys has increased with the discovery of the versatile properties of these alloys. In this study, the structural, mechanical and tribological properties of amorphous and crystalline TiNi coatings were investigated. The TiNi coatings were deposited with magnetron sputtering system. The crystallization process was conducted in a vacuum heat treatment furnace. The structural properties of the coatings were investigated with XRD, SEM and EDS analyses. Micro-hardness and pin-on-disc wear tests were used to obtain the mechanical and tribological properties of the coatings. AISI D2 steel, AISI 52100 steel, Aluminum 2024 alloy and copper were used as substrate materials, hence the effects of different substrates were also investigated. The highest coating hardness was obtained as 8.5 GPa and the lowest coefficient of friction value was obtained as 0.18. The tribological tests showed that the amorphous and crystalline TiNi coatings have different coefficient of friction and wear rate and using different substrate affects these properties.

The influence of APTES interlayer on the assembly and tribological properties of graphene coatings on titanium substrate

In order to improve the tribological properties of titanium substrate, self-assembly technique was used to prepare a graphene-silane coating: RGO-APTES coating on titanium substrate. The γ-aminopropyltriethoxysilane (APTES) was used to prepare a self-assembled APTES coating as a function of adhesive interlayer, aiming to improve the assembly efficient for graphene coating. The influence of that interlayer on the assembly and tribological properties of graphene coatings on titanium substrate was investigated. Morphology, thickness, chemical characteristic and tribological tests were utilized to investigate the assembly process and tribological properties of coatings. The results show that: (1) the pH values of APTES aqueous solution plays an important role in the molecule orientation of the APTES interlayer, and thus the properties of graphene coating is influenced. When pH is approximately 8.5, the molecule orientation of the interlayer is consistent, so that it has improved adsorption effect on graphene sheets and the graphene coating is uniformly distributed and well-covered; (2) the thickness influences the tribological properties of graphene-APTES coating -- single layered APTES interlayer provides a stronger interlayer strength. The obtained RGO-APTES2 samples have novel friction reducing and wear resisting properties, and can be applied on the surface of titanium substrate as lubricating coating.

Synthesis of Ni-Al-Ta composite coatings on Al alloy plates and the transfer of Al powder via mechanical milling technique

In the present work, Ni-Al-Ta composite coatings were successfully fabricated on Al alloy substrate by mechanical milling technique. The microstructure, phase composition, tribological properties of coatings and the transfer of Al powder have been studied. It was found that the microhardness of the coatings were higher than the Al substrate, especially 10% and 15% Ta were added into the coating, and the composite coatings demonstrated excellent protective effect to the Al substrate. From the evolution of Al, Al3Ni, Al3Ni2, AlNi and Ni to conclude the content of Al element (at.%) is: composite coating > coarse particle (+80 mesh) > fine particle (−80 mesh).

Properties of Electro-Spark Deposited Coatings Modified Via Laser Beam

The main purpose of this work was to determine the influence of laser treatment on microstructure, X-ray diffraction, microhardness, surface geometric structure, corrosion resistance, adhesion tests and tribological properties of coatings deposited on C45 carbon steel by the electro-spark deposition (ESD) process. The studies were conducted using WC–Cu electrodes produced by the powder metallurgy method. The tests show that the laser-treated electro-spark deposited WC–Cu coatings are characterized by higher corrosion resistance, adhesion, surface geometric structure and seizure resistance which result from lower microhardness. The laser treatment process causes the homogenization of the chemical composition, structure refinement and healing of microcracks and pores of the electro-spark deposited coatings. Laser treated ESD coatings can be applied in sliding friction pairs and as protective coatings.

Mechanical, tribological and oxidation resistance properties of Ni-based self-lubricating composite coatings at elevated temperature by APS

Abstract NiCrAlY-Mo-20Ag composite coating was fabricated by atmospheric plasma spraying. The influence of heat treatment on the mechanical properties, high temperature oxidation resistance properties and tribological properties of the coating were investigated. After 500°C heat treatment, the microstructure of the coating becomes more homogeneous and the amount of precipitated Y2O3 phase clearly increases. The micohardness and adhesive strength of the composite coating are effectively improved after heat treatment. The coating heat-treated at 500°C shows the highest micohardness and adhesive strength of 433.3 HV and 42.9 MPa as well as excellent lubricating properties over a wide range of temperature. Furthermore, the coating presents excellent oxidation resistance properties at 700°C and 800°C.

Microstructure, mechanical and tribological properties of TiBC coatings by DC magnetron sputtering onto AISI M2 steel using independent TiB2 and graphite targets

Despite TiB2 being a ceramic material widely known for its high hardness, chemical resistance and high thermal stability; its use in coatings for industrial conditions has been limited due to low adhesion, which is associated with high residual stresses. Recently, several investigations have shown that the incorporation of carbon within TiB2 coatings reduces residual stresses and increases adhesion, making Ti-B-C coatings excellent candidates for applications at high temperatures. In this research, DC UBMS Ti-B-C coatings were deposited onto AISI M2 steel substrates. The power density of TiB2 was fixed at 2.4W/cm2 and four different graphite power densities were made in order to obtain four different power ratios (WC/WTiB2) and carbon content in the Ti-B-C coatings. XRD and AFM results suggest the formation of nanocomposite coatings, with TiB2 nanocrystals embedded in an amorphous carbon matrix. SEM images revealed a glass-like structure for coatings with a low power ratio, which became a dense and featureless-like structure with a higher power ratio. A progressive decrease in hardness and Young's modulus was observed with the increase in carbon content. Hardness up to 27GPa was reached with lower carbon content and decreasing under 5GPa with the higher carbon content. The Young's modulus exhibited the same feature. Tribological properties of the coatings were investigated using a pin-on-disk tribometer. All coatings showed μ higher than the AISI M2 substrate, and only the coatings with a power ratio of 1.30 showed μ over 0.30. Regarding the wear rate, it remained almost constant for all the Ti-B-C coatings.

The varying temperature tribological properties of TiAlN-Ag coatings deposited by magnetron sputtering

TiAlN-Ag coatings were prepared on the AISI304 stainless steel by magnetron sputtering. The surface and cross-section morphology, microstructure, hardness and tribological properties of the coatings were investigated by scanning electron microscope(SEM), X-ray diffraction(XRD), micro-hardness tester and tribometer. The thickness of the TiAlN-Ag coating was about 10.2 μm, which consisted of face centered cubic TiAlN phases. Its hardness was 1044.8 Hv0.05. The tribological properties of the coatings were investigated by ball-on-disc tribometer against Al2O3 balls at RT-600 °C and 600 °C-300 °C. When at RT-600 °C, the coatings were worn badly, which resulted from that the adsorbed water film was destroyed due to the lower relative humidity. The wear mechanisms were mainly adhesive wear and fatigue fracture. When at 600 °C-300 °C, Ag diffused to the surface of the coating and acted as lubricant.

Surface topography and tribological properties of coatings prepared from microparticle size polyurethane dispersions studied by atomic force microscopy

The surface topography and mechanical properties of coatings prepared using large particle size polyurethane dispersions (PUD) are investigated using atomic force microscopy (AFM) imaging, AFM-based force measurements, and friction force microscopy. PUD coatings, which are prepared from dispersions containing particles of micron size, have surface roughness of 250–300 nm and waviness of 2.5–3 μm resulting from the particle size. The surface moduli of the PUD coatings are varied by tuning the ratio of hard-to-soft segmentation in the polyurethanes and are found to be between 40 and 100 MPa. The friction coefficient obtained in the study is found to be correlated with both the surface modulus of the coatings and the adhesion between the probe and the samples and is well in line with the perceived feel of an experienced human panel. The data are very well behaved and clearly show the utility of this technique in characterizing these types of surfaces.

Gradient Structure of the Layer Applied to Hardox 450 Steel by Fe–C–Cr–Nb–W Powder Wire after Electron-Beam Treatment

Surfacing with composite coatings strengthened by carbide, boride, and other particles is currently of great interest in materials physics. The performance of the applied layer is primarily determined by the phase composition of the coating. To permit the selection of coatings capable of withstanding extremal operating conditions, including high loads and abrasive wear, their properties and structure must be investigated in detail. In the present work, state-of-the-art techniques in materials physics are used to study the structure, phase composition, and tribological properties of coatings applied to Hardox 450 low-carbon martensitic steel by Fe–C–Cr–Nb–W powder wire and then subjected to electron-beam treatment. The electron-beam parameters are as follows: in the first stage, energy density per pulse ES = 30 J/cm2; pulse length τ = 200 μs; and number of pulses N = 20; in the second stage, ES = 30 J/cm2; τ = 50 μs; and N = 1. These conditions are selected on the basis of calculations of the temperature field formed in the surface layer of the material by a single pulse. It is found that electron-beam treatment of an applied layer of thickness about 5 mm leads to modification of a thin surface layer (about 20 μm), consisting largely of α iron and the carbide NbC; small quantities of the carbides Fe3C and Me6C (Fe3W3C) are also present. This modified surface layer differs from the unmodified coating mainly in terms of the morphology and dimensions of the secondary-phase inclusions. In the modified surface layer, the inclusions are smaller and take the form of thin layers along the grain boundaries. In the unmodified coating, the inclusions are mainly rounded particles, chaotically distributed within the grain. After electron-beam treatment, the wear resistance of the applied layer increases by a factor greater than 70 with respect to Hardox 450 steel, while the frictional coefficient is significantly less (about a third as much).

Fracture toughness and sliding properties of magnetron sputtered CrBC and CrBCN coatings

CrBC and CrBCN coatings with low and high B contents were deposited on 316L steel and Si wafers using an unbalanced magnetron sputtering system. Mechanical properties including hardness (H), elastic modulus (E) and fracture toughness (KIc) as well as residual stresses (σ) were quantified. A clear correlation between structural, mechanical and tribological properties of coatings was found. In particular, structural analyses indicated that N incorporation in CrBC coatings with high B content caused a significant structural evolution of the nanocomposite structure (crystalline grains embedded into an amorphous matrix) from nc-CrB2/(a-CrBx, a-BCx) to nc-CrN/(a-BCx, a-BN). As a result, the hardness of CrBC coating with high B content decreased from 23.4 to 16.3 GPa but the fracture toughness was enhanced. Consequently, less cracks initiated on CrBCN coatings during tribological tests, which combined with the shielding effect of a-BN on wear debris, led to a low friction coefficient and wear rate.

Tribological properties of wear-resistant coatings obtained by cold gas dynamic spray

The aim of this study was obtaining good deposits of stellite-6 by Cold Gas Dynamic Spray (CGDS), in terms of low porosity and good adhesion and cohesion. In fact, the high strength and melting point of the investigated alloy lead to a high value of the particle critical velocity in CGDS and, therefore, good quality results are difficult to achieve. The tribological properties of the coatings were analyzed by micro-hardness measurements and pin-on-disk wear tests. Results revealed that spraying parameters can be optimized to obtain almost pore-free coatings.

A comparative study of microstructure, oxidation resistance, mechanical, and tribological properties of coatings in Mo–B–(N), Cr–B–(N) and Ti–B–(N) systems

M–B–(N) (M = Mo, Cr, Ti) coatings were obtained by the magnetron sputtering of MoB, CrB2, TiB, and TiB2 targets in argon and in gaseous mixtures of argon with nitrogen. The structure and composition of the coatings have been investigated using scanning electron microscopy, glow-discharge optical emission spectroscopy, and X-ray diffraction. The mechanical and tribological properties of the coatings have been determined by nanoindentation, scratch-testing, and ball-on-disk tribological tests. The experiments on estimating the oxidation resistance of coatings were carried out in a temperature range of 600–1000°С. A distinctive feature of TiB2 coatings was their high hardness (61 GPa). The Cr–B–(N) coatings had high maximum oxidation resistance (900°С (CrB2) and 1000°С (Cr–B–N)) and possessed high resistance to the diffusion of elements from the metallic substrate up to a temperature of 1000°С. The Mo–B–N coatings were significantly inferior to the Ti–B–(N) and Cr–B–(N) coatings in their mechanical properties and oxidation resistance, as well as had а tendency to oxidize in air atmosphere after long exposure at room temperature. All of the coatings with nitrogen possessed a low coefficient of friction (in a range of 0.3–0.5) and low relative wear ((0.8–1.2) × 10–6 mm3 N–1 m–1.

Microstructures and Tribological Properties of Fe-Based Amorphous Metallic Coatings Deposited via Supersonic Plasma Spraying

The effects of the Ar flow rate and spraying power of a supersonic plasma spraying process on the microstructures and amorphous phase contents of Fe48Cr15Mo14C15B6Y2 amorphous coatings were systematically investigated. The tribological properties of the coatings were evaluated in pin-on-disk mode using a sliding tribometer. The results show that the amorphous phase content and microhardness initially increase with the Ar flow rate and then gradually decrease. However, the amorphous phase content and microhardness increase with the power. In particular, the amorphous phase content of the coating reaches 96.78% with a spraying power of 62 kW and a 110 L min−1 Ar flow rate. Tribological testing demonstrates that the coatings exhibit similar steady-state coefficients of friction (0.75–0.82) with a total test time of 20 min and an applied load of 20 N. However, the wear rates vary with the spraying parameters. In particular, the relative wear rate of the coating can be enhanced up to sixfold under optimal spraying conditions, resulting in excellent wear resistance. Detailed analysis of the coating wear surfaces indicates that the dominant wear mechanisms are abrasive and oxidative wear. Moreover, delamination may occur during the wear process.

Tribological property of plasma-sprayed Al2O3-13wt%TiO2 coatings onto resin-based composites

The nanostructured Al2O3–13wt% TiO2 coatings were fabricated by atmospheric plasma spraying (APS) on the surface of resin-based composites. The mechanical and tribological properties of coatings were investigated systematically. The results reveal that the hardness and bonding strength of the coatings reach the optimization when the spraying current is 650A. The friction coefficient of the coatings remains at 0.2 during the steady wear stage. The wear resistance of the coatings is the highest at spraying current range from 600A to 650A.

Structure-Phase Condition and Tribological Properties of Coatings Based on Self-Fluxing Nickel Alloy PG-12N-01 After Laser Surfacing

Some parameters of laser surfacing of self-fluxing nickel alloy PG-12N-01 are considered. Different structures containing a low-melting γ-Ni – Ni3B eutectic and a γ-Ni – Cr3C2 eutectic that crystallizes at a higher temperature and forms the strength skeleton of the coating may form depending on the rate of the surfacing. The effect of the rate of the surfacing on the wear resistance of the coating and on the coefficients of dry friction are determined.

Single and Multielement Coatings in a Fluidized Bed Reactor

Heat treatments of alloys in fluidized bed reactors have been carried out for more than twenty-five years. Recently this technology has been used for surface engineering applications in the deposition of hard and/or corrosion resistant layers e.g. aluminizing, chromizing, nitriding, carburizing, boronizing. The fluidized bed method is simple, efficient, environmentally friendly and capable of immediate adjusting the furnace atmosphere for specific requirements e.g. production of multielement coatings. The boride coatings on steel have an excellent combination of properties e.g. high fatigue strength and wear resistance. On the other hand silicide coatings are well known for their excellent corrosion resistance. Boron-siliconizing in fluidized beds is a promising method to improve both the wear and corrosion properties of steels. In the present paper fluidized bed technology (FBT) was used to deposit boride and boron-silicide coatings on steels. The coatings were examined by means of electron and optical microscopy and X-Rays diffraction, in terms of the coatings composition, morphology, thickness and phase formation. The coatings tribological properties were evaluated under dry wear.

Laser Cladding of <i>In Situ</i> Al-AlN Composite on Light Alloys Substrate

In situ metal matrix composites are novel composites in which the reinforcement is formed within the parent alloy by controlling chemical reactions during the composite fabrication. In recent years, there have been attempts to produce AlN composites utilizing the reactions between molten Al and a reactive gas. However, the conventional processing methods are sub-optimal and result in porosity, interface matrix-reinforcement deterioration, and high processing costs. The aim of this research is to develop a methodology to manufacture good-quality in situ Al-AlN composites in a cost effective way. In situ Al-AlN composite was synthesized with a laser cladding equipment. This composite powder can be directly deposited as coating on aluminum alloys conventionally used in the transport sector. The increase in the coatings tribological properties was demonstrated.

Growth Structure and Properties of Gradient Nanocrystalline Coatings of the Ti–Al–Si–Cu–N System

Methods of electron microprobe analysis, X-ray structure analysis and electron microscopy were used to study the element composition and features of the structure-phase, elastic stress state of nanocrystalline coatings of the Ti–Al–Si–Cu–N system with gradient of copper concentration across their thickness. The authors established the effects of element composition modification, non-monotonous behavior of the lattice constant of alloyed nitride and rise in the bending-torsion value of the crystalline lattice in individual nanocrystals to values of around 400 degrees/μm with increase in copper concentration, whereas the sizes of alloyed nitride crystals remained practically unchanged. Mechanical (hardness), adhesion and tribological properties of coatings were examined. Comparative analysis demonstrates higher values of adhesion characteristics in the case of gradient coatings of the Ti–Al–Si–Cu–N system than in the case of single-layer (with constant element concentration) analogues.