Hard Nanocomposite Coatings Research Articles

Highly conductive and durable nanocomposite hard coatings of carbon fiber reinforced thermoplastic composites against lightning strikes

The growing use of thermoplastic composites (TPCs) like low-melting polyaryletherketone (LM-PAEK) matrices reinforced with unidirectional carbon fiber (CF) in aircraft structures presents a significant challenge in terms of lightning strikes and electromagnetic interference shielding during aircraft operations. This is due to the weak electrical conductivity of TPC structures, which results in widespread damage when struck by lightning. The repair and maintenance of these extended damaged sites can increase operational costs and loss of flights. Several lightning strike protection (LSP) systems have been developed and implemented to address these concerns. This study evaluated a highly conductive coating with a low filler rate for its effectiveness as an LSP solution for TPCs on exterior aircraft surfaces. The TPC panel without any coatings was first studied. Subsequently, the level of conductivity was increased by incorporating the nanoscale conductive fillers, silver-coated copper (Ag/Cu) nanoflakes, with a silver content of 20 wt.% (Ag20/Cu) and 30 wt.% (Ag30/Cu), correspondingly, into the coating at two loadings of 55 wt.% and 70 wt.% in an epoxy carrier for the surface coatings. The behavior of electrical and surface conductivity was thoroughly examined to understand the impact of Ag/Cu with a high aspect ratio and the effectiveness of the LSP solution. In addition, the spray-coated TPC panels underwent rigorous Zone 2A lightning strike testing using simulated lightning current, in agreement with the industry standard of Society of Automotive Engineers (SAE) Aerospace Recommended Practice (ARP) 5412B. Despite the higher resistance due to the lower conductive coating weight, the TPC panels with Ag30/Cu at loading of 70 wt.% achieved better results than those with Ag30/Cu at loading of 55 wt.%. This is evidenced by the minor structural delamination and CF breakage on the front surface, which proposes a new economic route for a sustainable post-processed LSP system in the aviation industry.

Stress distribution variations during nanoindentation failure of hard coatings on silicon substrates

Regarding quality inspection of technologically important nanocomposite hard coatings based on Ti, B, Si, C, and N and bioceramics such as hydroxyapatite that are used in small-scale high-precision devices and bio-implants, it is essential to study the failure mechanisms associated with nanoindentation, such as fracture, delamination, and chipping. The stress imposed by the indenter can affect the fracture morphology and the interfacial fracture energy, depending on indenter shape, substrate type, crystallographic properties, pre-existing flaws, internal micro-cracks, and pre-strain. Reported here are finite-element-based fracture studies that provide insights into the different cracking mechanisms related to the aforementioned failure process, showing that the fracture morphology is affected by the interaction of different cracking events. The interfacial fracture energy, toughness, and residual stress are calculated using existing models with minor adjustments, and it is found that increasing the indenter sharpness improves the shear stress distribution, making the coating more prone to separation. Depending on the prevailing type of stress, the stress distribution beneath the depression results in either crack formation or a dislocation pile-up leading to strain hardening. Different forms of resistances resulting from the indentation process are found to affect the tip–sample conduction, and because of its stronger induced plasticity than that of a Berkovich indenter tip, a sharper cube-corner tip produces more resistance.

Magnetron sputtered films prepared from sintered Ti-based target and evaluation of tribological properties under the ball on disc condition with varying thickness and load

The hard nanocomposite coatings comprised of titanium, silicon, boron, and carbon (Ti-Si-B-C) and titanium, silicon, boron, carbon, and nitrogen (Ti-Si-B-C-N) were deposited on SS 304 substrate using magnetron sputtering technique. The tribological properties of these Ti-Si-B-C and Ti-Si-B-C-N coatings were explored with the variation of load (200–600 g) and thickness (3–25 µm) against high strength steel ball using a ball on a disc tribometer. The nanoindentation technique was used to investigate the wear tracks and its consequent effect on the mechanical behaviour of uncoated and coated films. The analyses of the phases, microstructure, states of valence, shift of electron, and elemental compositions of the coatings were carried out by HRTEM, FESEM, AFM, XPS, EDX, and Raman spectroscopy techniques, respectively. The 2D cross-sectional profiles and 3D topographies of the wear tracks were explored using a 3D profilometer. All these studies established that the 10 µm thick titanium-based sputtered nanocomposite coatings on SS 304 are efficient wear-resistant materials that showed excellent protection of the substrates from wear up till application of 500 g load. A good correlation between the composition, structure, properties, and processing of materials has been discussed based on the obtained wear behaviour. HIGHLIGHTS The multicomponent Ti-Si-B-C and Ti-Si-B-C-N films were deposited on SS 304 using the magnetron sputtering technique. The 10 µm thickness of Ti-Si-B-C and Ti-Si-B-C-N sputtered films on SS 304 showed excellent anti-wear performance. The specific wear rate of Ti-Si-B-C coated SS 304 (1.10 × 10−5 mm3/Nm) exhibited almost negligible in comparison to bare SS 304 (13.78 × 10−5 mm3/Nm). The average hardness and modulus values of the worn region of Ti-Si-B-C film were investigated at 23 and 320 GPa, respectively even after using a 600 g load. The roughness values on the worn region of uncoated surfaces are higher than on coated surfaces.

Observation of Coating-Substrate Adhesion of Nanocomposite Hard Coating with Respect to the Deposition Parameters and Surface Finishing of Cemented Carbide Substrate

The paper deals with the issue of coating and surface finishing with edge preparation prior to the coating. Nanocomposite AlCrSiN hard coatings were deposited on WC-Co substrates with a negative substrate bias voltage in range of-80 to-120 V using cathodic arc evaporation system. The effect of variation in the bias voltage on the coating-substrate adhesion and nanohardness was investigated. The maximum nanohardness of coating was 37.7 ± 1.5 GPa with the good coating-substrate adhesion. Static Mercedes indentation test was performed on a Rockwell-type hardness tester. The indents were studied by scanning electron microscope to evaluate the coating-substrate adhesion. The H to E ratio that represents resistance to the plastic deformation was determined. The influence of surface roughness and time of used surface finishing methods on the coating-substrate adhesion was also investigated.

Influence of overstoichiometric boron and titanium addition on the properties of RF magnetron sputtered tungsten borides

In this work, (W,Ti)B2 films with different stoichiometric ratio Ti/W deposited on silicon and 304 stainless steel by radio frequency magnetron sputtering are presented. The coatings were deposited from plasma spark sintered targets obtained from the mixture of pure boron, tungsten and titanium powders. It is shown that during plasma spark sintering process using overstoichiometric boron and a low content of titanium change the WB2 to WB4 phase with almost no secondary phases. Subsequently, the impact of titanium content on the films properties is investigated systematically, including the chemical and phase composition, crystalline structure, surface and cross-section morphology. Simultaneously, nano-indentation test and ball-on-disk tribometery are performed to analyse the hardness and tribological properties of the films. It is shown that deposited films with titanium content of 3.6 and 5.5 at.% are formed in the zone T of the Thornton's Structural Zone Model. In opposite to α-WB2 magnetron sputtered coatings they are more flexible and hard nanocomposite coatings. The results show that the addition of titanium is apparently changing the film structure from nanocrystalline columnar to amorphous, very dense and compact structure with the addition of TiB2 phase. That films are simultaneously hard (H > 37.5 GPa), have high hardness to effective Young's modulus ratio values (H/E⁎ > 0.1) and elastic recovery (We > 60%) appropriate for tough and resistant to cracking materials. The presented (W,Ti)B2 films exhibit also tribological and corrosion properties better than unalloyed coatings.

Toughening of nanocomposite hard coatings

AbstractFor engineering applications, hardness must be complimented with high toughness for applications where high contact loads are there. A good combination of hardness, toughness and low coefficient of friction can be achieved, by suitable tailoring of microstructures of coating in hard nanocomposite coatings. Tribologocal applications require hard coatings with tailored functionalities for different applications; hard nanocomposite coatings are potential materials for such applications. Ti and amorphous carbon based systems have shown more promising material. The present review discusses the nanocomposite hard coatings, mechanism of enhancement of toughness, multilayer hard nanocomposite coatings. Here, mainly Ti and Si based nanocomposite has been discussed as carbon based reviews are available in plenty in literature and well documented. Ti-B-N, Ti-Si-B-C, Ti-Si-B-C-N, Si-C-N, Ti-Al-N, Ti-Al-Si-N, Al-Si-N, Ti-Cr-Al-N, Zr-Si-N and some other similar system nanocomposite hard coatings are important where the gradual and intelligent additions of different elements in hard single component phase provides the combination of hardness, toughness and low coefficient of friction. Some of these systems are discussed. In the end, the future directions of research, Technology„ which are required to achieve tough nanocomposite hard coatings for actual applications are also highlighted.

Effect of Silicon Content on the Microstructure and Mechanical Properties of Ti-Si-B-C Nanocomposite Hard Coatings

The content of the individual elements in the nanocomposite hard multicomponent coatings is known to affect the phase formation during deposition and the properties of the coatings. Silicon is one such element, which has been shown to improve or alter the properties of the nanocomposite hard coating systems. In the present work, we investigated the effect of Si addition on the microstructure, phase, and mechanical behavior of Ti-Si-B-C nanocomposite hard films deposited by direct current (DC) magnetron sputtering. X-ray photoelectron spectroscopy (XPS) analyses reveal that, with the increase of Si content, SiB4 and TiSi2 softer phases (compared to the hard phases of TiB2 and B4C) are formed. The Ti-Si-B-C films deposited with 13.4 at. pct Si content show maximum hardness ~ 32.55 GPa and modulus ~ 381.6 GPa. With the increase of Si content in the films, the hardness and modulus are decreased. The H/E ratio, which is a measure of materials’ ability to take the strain prior to deformation, is also decreased with the increase of Si content, suggesting the lowering of toughness of the films with higher Si content.

Effect of substrate bias on microstructure and mechanical properties of WC-DLC coatings deposited by HiPIMS

The hardness and friction coefficient of the molding tools are the two key factors in influencing their performance during the cutting process. In this regard deposited by physical vapor deposition (PVD), WC-DLC nanocomposite hard coatings featuring high hardness and low friction coefficient are highly preferred to be used as protective coatings. As a newly developed PVD technology, high power impulse magnetron sputtering (HiPIMS) is quite advantageous in terms of the deposition of hard coatings. Substrate bias voltage exerts significant influences on the discharge characteristic of HiPIMS, plasma energy, chemical composition and the microstructure of the deposited coatings, which subsequently affect the coating's mechanical properties and performance in production. This article aims at investigating the effects of substrate bias on the plasma discharge characteristic of HiPIMS and on the mechanical properties, surface morphology, deposition rate, cross-sectional morphology, element concentration, crystal phase composition and tribological properties of the deposited coatings. The results show that the peak discharge current rises up from 57 A to 76 A with the increase of substrate bias from −40 V to −200 V. By controlling the bias voltage, WC-DLC coatings with different microstructures, mechanical properties and tribological properties have been produced. Meanwhile, the C concentrations of deposited coatings decline and the composed phase of the coating is transformed from hexagonal α-C at low bias voltage to equiaxial β-WC1−x and then hexagonal β-W2C accompanied by the rising bias voltage. The deposited WC-DLC coatings exhibit a decrease in surface roughness from Ra 16.1 nm to Ra 9.2 nm. Crystal phase evolutions also play a part in addition to the biased voltage upon the grain size and the hardness of the coating. It is found that the minimum grain size of 6 nm and the maximum hardness of 40.1 GPa appear at −160 V bias voltage when the coating is composed mainly of equiaxial β-WC1−x phase and mixture of β-WC1−x and β-W2C. The friction coefficient of the WC-DLC coating measured by ball-on-disk test increased correspondingly with the increase of the bias voltage except that the wear rate reaches the lowest at −120 V bias voltage, indicating that the wear rate is related not only to friction coefficient but also to coating hardness.

Progress in Tribological Properties of Nano-Composite Hard Coatings under Water Lubrication

The tribological properties, under water-lubricated conditions, of three major nano-composite coatings, i.e., diamond-like carbon (DLC or a-C), amorphous carbon nitride (a-CNx) and transition metallic nitride-based (TiN-based, CrN-based), coatings are reviewed. The influences of microstructure (composition and architecture) and test conditions (counterparts and friction parameters) on their friction and wear behavior under water lubrication are systematically elucidated. In general, DLC and a-CNx coatings exhibit superior tribological performance under water lubrication due to the formation of the hydrophilic group and the lubricating layer with low shear strength, respectively. In contrast, TiN-based and CrN-based coatings present relatively poor tribological performance in pure water, but are expected to present promising applications in sea water because of their good corrosion resistance. No matter what kind of coatings, an appropriate selection of counterpart materials would make their water-lubricated tribological properties more prominent. Currently, Si-based materials are deemed as beneficial counterparts under water lubrication due to the formation of silica gel originating from the hydration of Si. In the meantime, the tribological properties of nano-composite coatings in water could be enhanced at appropriate normal load and sliding velocity due to mixed or hydrodynamic lubrication. At the end of this article, the main research that is now being developed concerning the development of nano-composite coatings under water lubrication is described synthetically.

Effect of nitrogen on mechanical, oxidation and structural behaviour of Ti–Si–B–C–N nanocomposite hard coatings deposited by DC sputtering

Ti–Si–B–C–N film was deposited by DC magnetron sputtering at different argon and nitrogen ratios such as N2/Ar = 1 : 5, 2 : 4, 3 : 3, 4 : 1 and 5 : 0. The formation of TiN and TiB phases was observed because of incorporation of nitrogen. The hardness, modulus, microstructure, structure and bond formation with different nitrogen contents during the deposition were studied by nanoindentation, scanning electron microscope, X‐ray diffraction and X‐ray photoelectron spectroscopy, respectively. The oxidation kinetics of Ti–Si–B–C–N was investigated. The nitrogen incorporation during deposition influences different properties of the coating. Hardness and modulus decreased, and microstructure showed very fine grain presence, and film changes to fully amorphous because of incorporation of nitrogen in the film. Copyright © 2016 John Wiley & Sons, Ltd.

Deposition and characterisation of Mo2N/CrN multilayer coatings prepared by cathodic arc evaporation

This paper presents the evaluation of the surface quality and properties of Mo2N/CrN multilayer coating, compared to Mo2N and CrN coatings, deposited onto HS6-5-2 steel substrates using pure Mo and Cr targets in a nitrogen atmosphere by cathodic arc evaporation. The coatings were investigated by X-ray diffraction to evaluate the phase composition, scanning electron microscopy and optical microscopy to calculate the surface density of macroparticles of the coating and their dimensions. Hardness, friction, wear and adhesion of the coatings using the scratch test and Daimler–Benz test were also estimated.The Mo2N/CrN coating shows hardness above 25GPa and good adhesion with the critical load Lc2 about 60. The coefficient of friction of coatings studied is relatively low, 0.51 (CrN) and 0.44 (Mo2N). The Mo2N/CrN multilayer coating shows the lowest coefficient of friction of 0.40. A similar correlation holds for wear the highest wear rate in the test conditions is for a CrN coating ̶ about 5.7×10−7 mm3N−1m−1 for Mo2N about three times lower, and the multilayer coating Mo2N/CrN 9×10−8 mm3N−1m−1. Despite the relatively low critical load, investigated coatings show excellent wear resistant properties.This work is part of the research on nanocomposite hard coatings for tribological applications where molybdenum nitrides are dedicated as a component reducing friction and wear.

Flexible hard nanocomposite coatings

The article reports on flexible hard nanocomposite coatings prepared by magnetron sputtering.

Titanium carbide/carbon nanocomposite hard coatings: A comparative study between various chemical analysis tools

Titanium carbide/carbon nanocomposite hard coatings, which consist of TiC nanoparticles buried in amorphous carbon matrix, are prepared by a hybrid plasma process combining magnetron sputtering of a titanium target and plasma enhanced chemical vapor deposition using methane as a source for the growth of amorphous carbon. A particular attention was paid to the comparison of the surface and the bulk chemical compositions of the films determined by different analysis techniques: X-ray photoelectron spectroscopy (XPS), Rutherford backscattering spectrometry (RBS), wavelength dispersive X-ray spectroscopy (WDS) and energy dispersive X-ray spectroscopy (EDS). XPS and EDS show an underestimation in carbon concentration compared to RBS and WDS which provide similar values. This underestimation is more important in case of XPS and it is mainly attributed to the presence of oxygen contamination on the surface of the films strongly bonded to titanium. In case of EDS, the underestimation is related to the poor sensitivity of the used probe in regard to light elements such as carbon. Moreover, the structure of the coatings has been extensively probed by transmission electron microscopy, which has shown that the size of the TiC nanoparticles shrinks when increasing the carbon content within the films. We further demonstrate that this structural evolution has a direct impact on the hardness of the coatings which gets reduced when the grain size decreases.

Multilayer and Nanocomposite Hard Coatings for Biomedical Applications

Multilayer and Nanocomposite Hard Coatings for Biomedical Applications

Abrasion resistance of biaxially oriented polypropylene films coated with nanocomposite hard coatings

KMnO4-treated, functionalized, biaxially oriented polypropylene (BOPP) films coated with nano-silica hybrid material were synthesized. The abrasion resistance of the films was examined using a reciprocating fabric abrasion tester. Functional groups were confirmed by Fourier-transform infrared spectroscopy. Contact angle measurements were performed on the BOPP film surface to quantify the effectiveness of the functionalization. Results indicate that the abrasion resistance and roughness of the composite film were significantly affected by the modification of the BOPP film. Water surface contact angle of the modified BOPP films decreased from 90.1° to 71.4°,when KMnO4 concentration increased from 0M to 0.25M. Wettability of the BOPP films clearly improved after KMnO4 treatment. Abrasion resistance of the functionalized films coated with hybrid materials improved by 27.4% compared with that of the original film.

Effect of the metal concentration on the structural, mechanical and tribological properties of self-organized a-C:Cu hard nanocomposite coatings

The influence of the metal content (Cu: 0–28at.%) on the structural, mechanical and tribological properties of amorphous carbon films grown by pulsed filtered cathodic vacuum arc deposition is investigated. Silicon and AISI 301 stainless steel have been used as substrate materials. The microstructure, composition and bonding structure have been determined by scanning electron microscopy, combined Rutherford backscattered spectroscopy-nuclear reaction analysis, and Raman spectroscopy, respectively. The mechanical and tribological properties have been assessed using nanoindentation and reciprocating sliding (fretting tests) and these have been correlated with the elemental composition of the films. A self-organized multilayered structure consisting of alternating carbon and copper metal nanolayers (thickness in the 25–50nm range), whose formation is enhanced by the Cu content, is detected. The nanohardness and Young’s modulus decrease monotonically with increasing Cu content. A maximum value of the Young’s modulus of about 255GPa is obtained for the metal-free film, whereas it drops to about 174GPa for the film with a Cu content of 28at.%. In parallel, a 50% drop in the nanohardness from about 28GPa towards 14GPa is observed for these coatings. An increase in the Cu content also produces an increment of the coefficient of friction in reciprocating sliding tests performed against a corundum ball counterbody. As compared to the metal free film, a nearly four times higher coefficient of friction value is detected in the case of a Cu content of 28at.%. Nevertheless, the carbon–copper composite coatings produced a clear surface protection of the substrate despite an overall increase in wear loss with increasing Cu content in the range 3–28at.%.

Thermal stability and effect of substrate temperature of TiSiBC hard nanocomposite coatings on microstructure, mechanical, thermal behaviour deposited by magnetron sputtering

The TiSiBC nanocomposite thin films deposited on steel (SS 304) at different substrate temperatures have been investigated. TEM analysis showed that film morphology consist of very fine grain size in the range of 10nm. With the increase of substrate temperature the crystallinity of the film was also increased. At 500°C substrate temperature other crystalline phase containing Ti and Si also appear along with the TiB2. The optimum temperatures were around 400–450°C, where the film had higher hardness and modulus, further increase of temperature led to decrease in the hardness and modulus, which is due to formation of softer phases. The film deposited at 400°C was smooth with the average engineering roughness of about 11nm. The nanocomposite film was thermally stable in air up to 900°C with little decrease in hardness.

Hard nanocomposite coatings: Thermal stability, oxidation resistance and toughness

The article reports on the enhanced hardness of nanocomposite coatings, their thermal stability, protection of the substrate against oxidation at temperatures above 1000°C, X-ray amorphous coatings thermally stable above 1000°C and new advanced hard nanocomposite coatings with enhanced toughness which exhibit (i) low values of the effective Young's modulus E⁎ satisfying the condition H/E⁎>0.1, (ii) high elastic recovery We≥60%, (iii) strongly improved tribological properties, and (iv) enhanced resistance to cracking; here E⁎=E(1−ν2), E is the Young's modulus and ν is the Poison's ratio. At the end trends of next development of hard nanocomposite coatings are briefly outlined.

Investigations on the mechanical properties of hybrid nanocomposite hard coatings on polycarbonate

Hybrid nanocomposite coatings derived from titanium tetraisopropoxide and epoxy or acrylic modified silanes were deposited on polycarbonate (PC) by dip coating employing various withdrawal speeds followed by ultraviolet and thermal curing. The effect of different organic functional groups in the precursors and ageing effect of these sols were systematically studied with respect to thickness, abrasion resistance, pencil scratch test, nanoindentation hardness and transmittance. The gels derived from the freshly prepared and aged sols were structurally characterized by FT-IR and TEM analysis. The viscosities of the sols were monitored with time. The change in viscosity is rapid for sol from epoxy modified silane. The thickness of the coatings increases with increase in viscosity in case of both the silane precursors. The scratch as well as abrasion resistance increases as a function of coating thickness. The pencil scratch hardness improves from 2B for the bare PC to a maximum of 3H for the coating obtained from an aged sol derived from epoxy modified silane. Also, the abrasion resistance of the coatings from same sol was maximum as evidenced by a <6% change in haze after 500 cycles, vis-a-vis 40% for the bare PC. The coatings from a freshly prepared sol of acrylic modified silane and titania showed the maximum nanoindentation hardness of 0.52GPa, when compared to 0.23GPa for the bare PC.

WITHDRAWN: Hard and superhard nanolaminate and nanocomposite coatings for machine elements based on Ti6Al4V alloy

Purpose: Verification of a series of hybrid treatments of Ti6Al4V alloy consisting of primary diffusion hardening of the substrate with subsequent deposition of wear resistant coatings. Design/methodology/approach: Different nanolaminate and nanocomposite coatings were deposited with use of four different methods including a newly developed high density gas pulsed plasma MS technique. After deposition the coatings were investigated using OM, SEM, HRTEM, XRD, XPS, nanoindentation, DaimlerBenz, ball-on-plate and scratch tests. Findings: Besides an important increase of Ti6Al4V alloy hardness much greater further increase of hardness was obtained due to coatings deposition up to 53 GPa in case of a nanolaminate coating and to 47 GPa in case of a nanocomposite nc-TiN/a-SiN coating. At the same time the volume wear coefficient decreases several orders of magnitude for all the coatings. Simultaneously the friction coefficient decreased to a great extent except for the nc-TiN/a-SiN coating. Research limitations/implications: High density gas pulsed plasma magnetron sputtering is an effective method for superhard coatings deposition, however the roughness of the deposited nc-TiN/a-SiN coating was greater than after conventional magnetron sputtering. This finding needs further experimental and theoretical investigation. Practical implications: Greater surface roughness and high resistance to wear of the coatings synthesized using the newly developed gas pulsed plasma magnetron sputtering deposition limits their application to wear protection of cutting tools rather than for friction reduction in tribological couples. Originality/value: Applicability of the broad spectrum of nanolaminate and nanocomposite coatings as well as different CVD and PVD techniques for an improvement of tribological properties of Ti6Al4V alloy was analyzed in the paper including a newly developed original high density gas pulsed plasma magnetron sputtering technique.