In our previous work 1, the scratch behaviors of alternating multi-layered polymethyl methacrylate (PMMA)/polycarbonate (PC) laminates were studied. Generally, a hard coating layer must be introduced ...to the surface of PMMA + PC laminate to further enhance its hardness and scratch resistance. In this work, the same laminates used in our previous work were coated by a UV-cured polyacrylate hard layer, and the scratch behaviors and relating mechanisms of hard coating (HC) systems were investigated via both progressive normal load scratch test and pencil hardness test. Sliding counterfaces of two tests were stainless steel ball with a diameter of 1 mm and cylinder made of pencil core with a diameter of 2 mm, respectively. Length, width and thickness of test specimen were 150 mm, 33 mm and 1.6 mm, respectively. The effects of HC's thickness and substrate's hardness on scratch behaviors of HC systems were also included. In both scratch tests, experimental results demonstrated that scratch damages of HC systems were featured with dense periodic cracks. Finite element modeling (FEM) revealed that the formation of such crack types was attributed to the maximum principal stress perpendicular to crack propagation direction. Furthermore, it was found that the scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased, the mechanism behind which were found to be decreasing of the maximum principal stress and consequent delaying of crack formation as revealed through FEM.
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•Scratch behaviors of hard coating (HC) laminates were studied via two test methods.•Scratch resistances of HC systems were enhanced as thickness of HC or hardness of substrate increased.•Scratch damages of HC systems were featured with dense periodic cracks.•Crack formation was caused by the maximum principle stress perpendicular to crack propagation direction.•Good agreement was achieved between experimental results and FEM.
Bearings for aerospace applications Rejith, R; Kesavan, D.; Chakravarthy, P ...
Tribology international,
March 2023, 2023-03-00, Letnik:
181
Journal Article
Recenzirano
Rolling element bearings are the most critical parts of any rotary mechanism. One of the challenges in any bearing design is to minimize the friction and maximize life for a particular service ...environment. For critical aerospace systems such as jet/liquid rocket engines, bearings are the key to improving performance benchmarks. Though bearings are a common machine element, literature related to criticality of bearings used in aerospace industries is very limited. The selection of precision class of bearings, surface finish and overall quality of critical contact surfaces in bearings, lubricant selection, lubrication scheme, processing of bearings, integration into mechanisms have been discussed in this review. A glimpse of emerging technologies in active bearing systems and smart bearing solutions has been included.
The high entropy nitride coatings (Cr0.35Al0.25Nb0.12Si0.08V0.20)Nx with different nitrogen concentrations were fabricated via varying the N2/(Ar + N2) ratio in a RF magnetron reactive sputtering ...system. The effect of the N2/(Ar + N2) ratio on the crystal structure, chemical composition variation, deposition rate, residual stress, and hardness were investigated in details and revealed in this work. The crystal structure of the metallic coating was amorphous, while the nitride coating exhibited the B1–NaCl structure as the nitrogen concentration of coating exceeded 43 at%. The residual stress was compressive in all coatings, ranging from −0.95 GPa to −3.61 GPa. As the coating nitrogen concentration reached 50 at%, the maximum hardness of this high entropy nitride coating was around 35 GPa and the appealing H/E and H3/E2 value of 0.12 and 0.52, respectively, was also revealed. Finally, a new indicator “composition variation degree” was proposed and employed in this study. This indicator provided a rather effective usage as it could reduce the complexity of defining the composition difference between the deposited coating and the designed value in a multi-component system, especially when the coating nitrogen concentration was varied.
•Mechanical properties evolution with nitrogen incorporation.•Nitriding of high entropy alloy materials system.•“Composition variation degree” is proposed to describe composition variation in multi-component system.
Coated hardmetals are commonly used tool materials for metal cutting applications. For these applications, the substrate- and the coating surface qualities are improved by grinding, polishing, or ...blasting. The focus of the current work was to study the influence of different combinations of substrate-coating surface processing techniques on the induced damage in Al2O3/TiCN hard-coated WC-12 wt% hardmetal substrates and the depth to which the damage reaches into the substrate. The substrate and coating surfaces were prepared by grinding, polishing, dry blasting, wet blasting, or remaining in the deposited state. Investigations were performed using cyclic indentation with a novel ball-in-cone test method in a vacuum at 700 °C, under conditions that imitate the combined shear-compression loads that occur at the cutting edges of metal cutting tools. Additionally, finite element simulations were performed to characterize the stress state arising during ball-in-cone testing. The kinetics of defect formation and accumulation in the hardmetal substrate as a function of the loading situation during the ball-in-cone test will also be discussed. The defects that formed in the substrate during cyclic loading were studied using scanning electron microscopy in cross-sections prepared by focused ion beam milling. A larger increase in defect frequency was observed for rougher coating surfaces and substrate-coating interfaces than for smoother ones. Furthermore, 6 μm thick coatings exhibited a higher defect frequency after cyclic loading than 15 μm thick coatings. Most of the observed defects were in the nm-size range close to the substrate-coating interfaces and tended to have increased in size after cyclic loading. The ball-in-cone test set-up enables the study of the damage mechanisms in coated hardmetal substrates with different treatments prior to and after deposition under tunable milling-like stress and temperature conditions.
•Influence of substrate-coating-surface processing states on the formation of defects in WC-Co substrates.•FE simulation and laboratory test produced load and damage situations as in real cutting applications.•Novel ball-in-cone test to induce multi-axial cyclic loads at high temperatures to imitate cutting-edge loads.•Higher defect density for rougher substrate-coating interfaces and coating surfaces than for smoother ones.
A combination treatment of nitriding and induction hardening can achieve high hardness depths in short treatment times and can therefore be seen as an alternative to deep nitriding. However, the ...compound layer, which makes a significant contribution to the wear resistance of nitrided components, decomposes during the induction heat treatment of the nitrided part. Therefore, the tribological behavior of parts processed this way is affected. In the present work, the wear behavior of surface layers resulting from combined heat treatment of EN42CrMo4 and PVD a-C:H(:Si) coating is investigated and evaluated. For the wear testing, a two-disk test rig was used. The wear was determined gravimetrically and by optical evaluation of the wear tracks. It was found, that the wear resistance of the investigated heat-treatable steel can be improved by duplex surface treatments such as nitriding and induction hardening as well as nitriding and PVD a-C:H(:Si) coating compared to the heat treated-only condition. By triplex treatment, no further improvement of the wear resistance could be observed.
•Application of nitriding + induction hardening, nitriding + a-C:H-(Si) coating, nitriding, induction hardening + coating•All duplex and triplex surface treatments increased the wear resistance of the investigated heat treatable steel EN42CrMo4•Best wear behavior after a combination of nitriding and induction heat treatment
Hard coatings such as TiAlCN can improve the surface hardness， wear resistance and corrosion resistance of metal workpieces，thereby effectively improving the precision and service life of cutting ...tools， abrasive tools and auto parts in service under high-speed rotation conditions.In this paper， the structure and application of TiCN， TiAlN and TiAlCN coatings formed by adding Al and C elements to TiN were reviewed， the effects of adding Al and C elements on the structure and properties of the coatings and their mechanism of action were summarized.The preparation methods of TiCN， TiAlN and TiAlCN coatings in recent years were summarized， including DC magnetron sputtering(DCMS)， high power impulse magnetron sputtering (HiPIMS)， medium temperature chemical vapor deposition (MTCVD) and laser chemical vapor deposition (LCVD).In addition， the future development direction of multicomponent TiN coatings was prospected.
Progress in the design and exploration of hard coatings with high temperature adaptive behavior in tribological contacts is reviewed. When coupled with most recent surface engineering strategies for ...high temperature contact thermal management, this progress opens a huge opportunity for adaptive coating applications on machine parts, where oils and coolants are commonly used. The adaptive mechanisms discussed here include metal diffusion and formation of lubricant phases at worn surfaces, thermally- and mechanically-induced phase transitions in hexagonal solids, contact surface tribo-chemical evolutions to form phases with low melting point, formation of easy to shear solid oxides, and others. All of these adaptive mechanisms are combined in nanocomposite coatings with synergistic self-adaptation of surface structure and chemistry to lubricate from ambient temperatures to 1000°C and provide surface chemical and structural reversibility during temperature cycling to maintain low friction coefficients. The review also highlights emerging surface adaptive concepts, where advances with ab initio modeling of intrinsically layered solids point to new compositions for thermally stable, easy to shear ceramic coatings, load- and temperature-adaptive surfaces with arrays of compliant carbon and boron nitride nanotubes as well as low friction two-dimensional structures. Approaches for self-regulation of coating thermal conductivity, heat flow, and thermal spike mitigations are discussed in the context of surface structure evolution and phase transitions. Future progress is linked to the development of in situ exploration techniques, capable of identifying adaptive surface chemistry and structural evolutions in broad temperature regimes. When combined with predictive modeling, such approaches drastically accelerate adaptive coating developments. The review identifies opportunities, strategies, and challenges for designs and applications of hard coatings with high temperature adaptive lubrication and contact thermal management.
•Hard coating adaptive lubrication for up to 1000°C and temperature cycling•Self-regulation of thermal conductivity, heat flow, and thermal spike mitigation•Intrinsically layered thermal stable and easy to shear coatings•Adaptive surface perspectives with nanotube arrays and 2D materials•In situ techniques for tracking high temperature phase and structural evolutions
Cold forming has required considerably superior hard coating on a die to manufacture net-shaped products. Especially, under poor lubrication conditions or a dry condition, the hard coating is ...indispensable for the success of manufacturing. Accordingly, the die has required the superior hard coating to prevent adhesion, reduce friction, and control wear. Recently, it has been also necessary to improve die life and product qualities under severe tribological conditions. However, the comprehension of damage such as cracking, flaking, and galling is insufficient for metal forming. This study focuses on initiation and growth of cracking in the hard coating. Assuming the hard coating is subjected to tensile stress, nominal stress, or frictional shear stress, the performances of typical four hard coatings are investigated by two tests. One is a uniaxial tensile test, and another is a rotating cross-cylinders wear and friction test. These tests are applied to estimate the mechanical performance of hard coatings: CrN, TiN, VC, and CrAlN. After the two test and analyses with detail observation, the CrAlN coating collectively exhibits the highest anti-cracking property of the tested four hard coatings.
•Synthesis of novel Mo2BC hard coatings by bipolar pulsed direct current magnetron sputtering in an industrial chamber•Mo2BC coatings reveal excellent hardness and Young’s modulus values•Mechanical ...properties depend on on the nanostructure•Nanostructure evolution from partially short-range ordered to fully crystalline with increasing substrate temperature.
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A reduction in synthesis temperature is favorable for hard coatings, which are designed for industrial applications, as manufacturing costs can be saved and technologically relevant substrate materials are often temperature-sensitive. In this study, we analyzed Mo2BC hard coatings deposited by direct current magnetron sputtering at different substrate temperatures, ranging from 380 °C to 630 °C. Transmission electron microscopy investigations revealed that a dense structure of columnar grains, which formed at a substrate temperature of 630 °C, continuously diminishes with decreasing substrate temperature. It almost vanishes in the coating deposited at 380 °C, which shows nanocrystals of ~1 nm in diameter embedded in an amorphous matrix. Moreover, Argon from the deposition process is incorporated in the film and its amount increases with decreasing substrate temperature. Nanoindentation experiments provided evidence that hardness and Young's modulus are modified by the nanostructure of the analyzed Mo2BC coatings. A substrate temperature rise from 380 °C to 630 °C resulted in an increase in hardness (21 GPa to 28 GPa) and Young's modulus (259 GPa to 462 GPa). We conclude that the substrate temperature determines the nanostructure and the associated changes in bond strength and stiffness and thus, influences hardness and Young's modulus of the coatings.
Wear-resistant coatings are critical to many industries for extending the life span of components and reducing costs. NiCrBSi coatings are one of the most utilized Ni-base wear-resistant coatings for ...both ambient and high temperature applications, capable of being applied by both welding and thermal spray processes. If thermal spraying is used to apply NiCrBSi coatings, a modification treatment is often needed to minimize imperfections of the coating layer and improve its properties. Here, use of friction-stir processing (FSP) and furnace re-melting (FR) processing are investigated in terms of their effect on the microstructure and wear properties of a NiCrBSi coating applied on plain carbon steel. Optical and electron microscopy, X-ray diffraction analysis, sliding wear test, and micro-hardness measurements have been used to characterize samples. Based on the results, FSP improved performance versus FR in terms of homogeneity, micro-hardness enhancement, and elimination of defects, leading to more homogeneous coating structures. Also, porosity in the coating layer drastically decreased from 14 % in the as-sprayed condition to 0 % after the FSP process. Additionally, by performing the friction-stir processing, the hardness of the coating increased by 60 % due to a reduction of defects in the layer while breaking down and homogeneously dispersing hard particles in the microstructure.
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•Wear-resistant NiCrBSi alloy coating was flame sprayed and post-treated.•Two different post-modification treatments of furnace re-melting (FR) and friction stir processing (FSP) were compared.•The best results were achieved from FSP modification using a pin-containing tool.•FSP displayed a superior impact on the hardening of coating overlay up to ∼60 % by modification.•Accordingly, a homogeneous distribution of fine and wear-resistant secondary phases was achieved.•Good mixing at the substrate/coating interface resulted in the formation of mechanical interlocking with superior bonding strength after FSP.
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