Scratch Adhesion Strength Research Articles

Taguchi optimization of hardness and scratch adhesion strength of multilayer Ti/TiN coatings on Ti- 51 at%Ni alloy deposited via magnetron sputtering technique

The near equiatomic Ti-51at %Ni alloy has excellent corrosion resistance, strength, shape memory and pseudo-elastic behaviour. However, it is lacking biocompatibility due to the release of hazardous Ni-ions when used as an implant. Thus, this research proposes optimizing the fabrication of multilayer Ti/TiN coating on Ti-51at %Ni alloy using magnetron sputtering. The hardness and adhesion strength are crucial properties to sustain external bearing loads and to ensure the durability of the coating. The process parameters of magnetron sputtering were optimized using Taguchi method. The analysis showed that optimum adhesion strength was obtained at 370 W, 100 °C, 50 V and 5 sccm with respect to DC power, substrate temperature, bias voltage and nitrogen flow, respectively. Whereas, the optimum hardness was obtained at 370 W, 150 °C, 75 V and 5 sccm. The confirmation test evidenced the hardness and adhesion strength improvement by 6.83 % and 10.74 %, respectively. The results of the optimized substrate surface showed a dense and compact growth of the deposited layer with the absence of cracks and pores. Finally, this research demonstrated a promising durable multilayer Ti/TiN coating on Ti-51at %Ni for biomedical applications.

Hard and Highly Adhesive AlMgB14 Coatings RF Sputtered on Tungsten Carbide and High-Speed Steel

We report a new industrial application of aluminum magnesium boride AlMgB14 (BAM) coatings to enhance the hardness of tungsten carbide ceramic (WC-Co) and high-speed steel tools. BAM films were deposited by RF magnetron sputtering of a single dense stoichiometric ceramic target onto commercial WC-Co turning inserts and R6M5 steel drill bits. High target sputtering power and sufficiently short target-to-substrate distance were found to be critical processing conditions. Very smooth (6.6 nm RMS surface roughness onto Si wafers) and hard AlMgB14 coatings enhance the hardness of WC-Co inserts and high-speed R6M5 steel by a factor of two and three, respectively. Complete coating spallation failure occurred at a scratch adhesion strength of 18 N. High work of adhesion and low friction coefficient, estimated for BAM onto drill bits, was as high as 64 J/m2 and as low as 0.07, respectively, more than twice the surpass characteristics of N-doped diamond-like carbon (DLC) films deposited onto nitride high-speed W6Mo5Cr4V2 steel.

Construction of superhydrophobic GO/Ca coating on AZ31 magnesium alloy for enhanced anti-corrosion performance

The application of magnesium alloys has garnered increasing interests in transportation, electronics and biomedical engineering fields, and the fabrication of superhydrophobic coatings on the surface of magnesium alloys is considered as an effective means to improve the corrosion resistance. However, major technical barriers restricting its application lie in the long-term durability and mechanical properties of superhydrophobic coatings. Herein, a calcium myristate coating with graphene oxide (GO) is fabricated on AZ31 magnesium alloy by electrodeposition. The coating is constructed in a particularly simple and gentle way by the synergy of inorganic nanomaterials and organic acid salts. It was found that the deposition time significantly affected the morphology, thickness and wettability of the GO/Ca coating and further influenced the corrosion resistance and durability. The best corrosion resistance is obtained when the deposition time is 30 min. With 30 min deposition, the corrosion current density of the substrate was reduced by 3 orders to (2.38 ± 1.02)× 10−9 A cm−2, and the impedance modulus at the lowest frequency could reach 108 Ω cm2. And after 21 days of immersion, the impedance modulus at low frequency of GO/Ca-30 is still as high as 105. It could be attributed to the tortuous path and denser structure with introduction of GO. Besides this, the scratch test and adhesion strength describe that the GO/Ca coating presents a good adhesion to the substrate. Considering its satisfying corrosion resistance, long-term durability and high adhesion strength, it is expected that the as-prepared superhydrophobic coating on AZ31 alloy is promising for anti-corrosion application.

Tailoring the scratch adhesion strength and wear performance of TiNiN nanocomposite coatings by optimising substrate bias voltage during cathodic arc evaporation

The tribological properties of TiN-based coatings can be substantially influenced by the choice of substrate bias employed during physical vapor deposition. However, the effects of applied substrate bias voltages during cathodic arc evaporation on to the scratch adhesion strength and wear resistance of TiNiN coatings have not been previously studied. In this present work, a series of TiNiN coatings were fabricated onto tool steel (M2) substrates using the cathodic arc evaporation method by applying a range of bias voltages to the substrate. The aim of this study is to investigate the scratch response and wear performance of these coatings along with an investigation of the deformation mechanisms in operation during scratch and wear tests. The best scratch adhesion strength (i.e., greater LC1, LC2 and CPRs values) was noted for the coating prepared at a bias voltage of −100 V, which was ascribed to the synergistic responses arising from superior mechanical properties, the influence of a high compressive residual stress and a fine, equiaxed nanocomposite structure, that acted to promote effective resistance against cohesive and adhesive failure. Further, the failure mechanisms under progressive loading conditions were also investigated through observation of the complex crack patterns generated, compressive residual stress values and the coatings' hierarchical design. An approximately 85 % enhancement in wear resistance for these TiNiN coatings was achieved as the bias voltage was increased from 0 V to −100 V. This −100 V coating exhibited the highest values of H/Er (>0.1) and We (>60 %), as well as the highest Ni concentration (~ 4 at.%).

Influence of preliminary metal-ion etching on the topography and mechanical behavior of TiAlN coatings on cemented carbides

Metal-ion etching is widely used in substrate surface modification before coating by physical vapor deposition . In this work, TiAlN coatings were synthesized onto cemented carbides with Ti-, Cr-, and Zr-ion pre-etching by cathodic arc evaporation and investigated concerning surface topography and mechanical failure. The pre-etching of energetic metal ions introduces droplet defects and increases surface roughness through uneven bombardment. The high interface roughness and deposition of nanoscale metal interlayers contributed to the upgraded adhesion between the coating and the substrate. As a result, the adhesion strength of TiAlN coatings advances to more than 95 N by applying Cr- and Zr-ion pre-etching. The rough substrate surface also gives rise to a rough coating surface associated with the pre-etching time. Under normal loading, the microscopic pit-like surface morphology , stemming from ion etching, interrupts the transverse propagation of the circumferential cracks but does not affect the longitudinal crack propagation inside the coating. In addition, the higher roughness of coatings with ion pre-etching causes a shorter run-in stage during ball-on-disc tests due to the higher contact stress between the friction pair. • TiAlN coatings were deposited on cemented carbide with various ion pre-etching. • The ion etching changes the substrate surface, significantly increasing roughness. • Scratch adhesion strength above 95 N can be obtained by suitable ion pre-etching. • Rough surfaces lead to intermitted circumferential cracks under normal loading. • The ion pre-etching can also shorten the run-in period during friction tests.

Influence of substrate bias on the scratch, wear and indentation response of TiSiN nanocomposite coatings

TiSiN coatings were synthesised onto AISI M42 tool steel substrates via closed field unbalanced magnetron sputtering ion plating , using bias voltages of −40 and −50 V. The aim of this study is to investigate the underlying deformation mechanisms of TiSiN coatings, prepared at two different substrate bias voltages, following scratching, wear and indentation tests . A graded columnar microstructure evolved in these coatings. A hardness value of ~30.2 GPa was determined in the coating prepared at the lower bias voltage (i.e., −40 V), which was correlated to the fine nanocomposite structure and the presence of a high compressive residual stress. Of note, for the coating deposited at −40 V enhanced scratch adhesion strength , i.e., higher critical loads (L c1 and L c2 ) against cohesive and adhesive failure were determined with the higher H/E r and H 3 /E r 2 values. The improved scratch resistance was ascribed to the hierarchical structure that hindered crack propagation in the TiSiN coatings during progressive loading. An approximately 21% decrease in wear rate was obtained at the lower bias voltage, which was attributed to the slightly lower Si concentration (~8.3 at.%) and, in turn, higher hardness. Deformation behaviour under indentation loading was dominated by shear sliding along the columnar grain boundaries. • ~20% increase in L c1 was found in the TiSiN coating with the lower Si content. • The scratch resistance was enhanced by the coating's hierarchical structure. • ~21% reduction in wear rate was achieved in the coating with the lower Si content. • Indentation deformation was governed by columnar shear sliding.

FeMnNiCoCr-based high entropy alloy coatings: Effect of nitrogen additions on microstructural development, mechanical properties and tribological performance

(FeMnNiCoCr)Nx high entropy alloy (HEA) coatings were deposited onto M2 steel substrates via direct current (DC) magnetron sputtering at several nitrogen flow rates (4, 8, 15, 25 sccm). The microstructures exhibit a fine columnar pattern. Higher flow rates promoted higher nitrogen contents that led to a transformation from a fcc to bcc structure. Self-organising behaviours of metallic atoms, enhanced by nitrogen gas flow, led to the formation of the bcc structure, wherein metal atoms randomly occupy equilibrium lattice sites and nitrogen atoms segregate at grain boundaries. Coatings with low nitrogen content (~6 at. %) exhibit a fcc structure, offering the best scratch toughness and adhesion strength, but inferior hardness (~11 GPa) and wear resistance; coatings with medium nitrogen contents (~15–22 at. %) exhibit a bcc structure, which display improved hardness (~13–15 GPa) and wear resistance, but inferior scratch responses, that was attributed to the presence of the harder, but more brittle bcc phase. At high nitrogen content (~26 at. %) an impressive combination of superior hardness (~17 GPa), wear resistance and good scratch response were identified with a well-defined bcc phase. It is these bcc grains, together with nitrogen-reinforced grain boundaries that overcame the incompatibility between the strength and ductility.

Scratch response and tribological behaviour of CrAlNiN coatings deposited by closed field unbalanced magnetron sputtering system

CrAlNiN coatings were deposited on M2 tool steels using closed-field unbalanced magnetron sputtering. The coating microstructure transformed from coarse columnar grains to fine equiaxed grains with increasing Ni content, which was accompanied by a general decrease in both hardness (H) and elastic modulus (Er) values. The scratch tests showed both scratch toughness and adhesion strength were improved for coatings with higher ratios of H/Er and H3/Er2, whereby higher critical loads (LC1 and LC2) are required to initiate cohesive and adhesive failure. For the coatings with coarser columnar grains, the improved scratch toughness may be ascribed to tortuous crack deflection patterns. Improved wear resistance was found in the columnar grained coatings, which also exhibited the higher H/Er and H3/Er2 values. The inferior wear resistance in the equiaxed grained coatings was suggested to arise from these coatings being more susceptible to grain pull-out processes during abrasive sliding. The wear debris composed of tribo-oxides serving as additional capacity for load bearing via re-distribution of the applied stress. This was believed to boost the wear resistance of the coatings.

Mechanical behavior of PVD coatings deposited on ADI

ABSTRACT In this work, the mechanical behavior of the coated ADI system is studied. For this purpose, single layer Ti and bilayer Ti/TiN and TiAl/TiAlN coatings, with different thicknesses, were deposited by the PVD technique of cathodic arc deposition on high strength ADI substrates using industrial and experimental devices. The characterization of the coatings includes the measurement of the layer thicknesses by the spherical abrasion method, the determination of existing phases and residual stresses by x-ray diffraction and the evaluation of the surface topography using a stylus profilometer. The analysis of the mechanical properties of the coatings comprises the measurement of the surface hardness by micro indentation tests and the evaluation of the scratch resistance. The scratch tests were performed on a scratch tester equipped with a Rockwell indenter. A progressive load from 1 to 100 N, a load rate of 99 N/min, a speed of 5 mm/min and a scratch length of 5 mm were employed. The influence of the coatings characteristics on the scratch resistance of the coated samples and the friction coefficients obtained are evaluated. The results show that Ti coated samples had tensile residual stresses, the lowest surface hardness and the lowest critical loads for scratch adhesion strength. The samples coated with Ti/TiN and TiAl/TiAlN had highly compressive residual stresses and the highest critical loads, while the hardness was higher for TiAl/TiAlN. On the other hand, the evolution of the friction coefficient was similar for all the coated samples.

Scratch adhesion strength of plasma sprayed carbon nanotube reinforced ceramic coatings

This report investigates the effect of both mechanical and thermal properties of Carbon nanotube (CNT) on scratch adhesion strength of ceramic coatings. Micro sized alumina and titania with 1 wt% CNT powders were prepared by three routes: dry/wet milling (with alcohol) and heterocoagulation. First, degree of CNT dispersion in the coatings was analysed. Heterocoagulated coatings displayed homogeneous dispersion of CNT. Next, the effect of homogeneous dispersion on phase transformation was studied. Higher thermal conductivity of CNT and its degree of dispersion seemed to affect the melting of powders and thus the phase transformations in the coatings. A higher fraction of stable phase was detected in the coatings. In addition, CNT/ceramic interface was analysed for the reaction layer. A stable phase layer was found covering the entire CNT surface, protecting it from thermal degradation. Finally, the scratch adhesion strength was quantified for both CNT reinforced and unreinforced coatings. The scratch resistance of heterocoagulated coatings improved by ∼36–176%. Improvement in strength was attributed to: a) a higher stable phase fraction in the coatings, b) Strong wettability at CNT/ceramic interface, c) improvement in elastic moduli of the coatings has also led to the improvement in the work of adhesion of the coatings, and d) a toughening mechanism, CNT bridging.

Nanoindentation and nanoscratch behaviors of DLC films growth on different thickness of Cr nanolayers

Metal interlayer is a promising method for improving the adhesion of DLC film to the substrate. In this study, Cr thin film, with different thickness of 10, 20, 40 and 80nm was applied as an interlayer, to investigate the influences on the tribological behavior of DLC films. Cr nanolayers were deposited by DC magnetron sputtering and DLC films were deposited by plasma enhancement chemical vapor deposition (PECVD) using methane and argon as precursors. Surface roughness and particle size distribution of Cr nanolayers were investigated by atomic force microscopy (AFM), which showed increasing the roughness from 0.17nm to 0.69nm by increasing Cr nanolayer thickness. Thickness and microstructure of DLC films obtained by cross-sectional field emission scanning electron microscopy images and Raman spectroscopy, respectively. Nanotribological behaviors of DLC films such as scratch resistance, adhesion strength, friction coefficient, hardness and wear resistance were investigated by nanoscratch and nanoindentation tests. Good adhesion for all samples was observed in which samples with Cr thickness of 10 and 20nm had the best hardness of 17GPa and 24GPa, respectively. The results indicated lower surface roughness and better particle distribution in Cr interlayer cause better tribological behavior.

Silver/silver oxide nanorod arrays from physical vapor deposition and subsequent anodization processes

Abstract Silver/silver oxide nanorod arrays (n-Ag/Ag2O) were successfully grown on Ti–6Al–7Nb (Ti67) through physical vapor deposition magnetron sputtering (PVDMS) and electrochemical techniques. The results showed that the formation of a well-defined n-Ag/Ag2O and the microstructural evolution were strongly dependent on the anodization time. While both the 10 and 20 min anodized specimens demonstrated polycrystalline structures, their morphological features were quite different. From the microscopic analysis, the 20 min anodized sample indicated a well-ordered nanorod structure with an average size of 4 μm in length and 200 nm in width. Compared to the pure Ti67 and as-deposited Ag film, the anodized sample showed the highest hydrophilicity. The scratch length, failure point, and adhesion strength were 1200 μm, 680 μm and 115 ± 1 MPa, respectively, for the sample with the strongest adhesion. This technique is applicable to extend to other transition metal oxides and to a variety of medical grade titanium alloys.

Abrasion resistant low friction and ultra-hard magnetron sputtered AlMgB14 coatings

Hard aluminum magnesium boride films were fabricated by RF magnetron sputtering from a single stoichiometric AlMgB14 ceramic target. X-ray amorphous AlMgB14 films are very smooth. Their roughness does not exceed the roughness of Si wafer and Corning glass used as the substrates. Dispersion of refractive index and extinction coefficient were determined within 300 to 2500 nm range for the film deposited onto Corning glass. Stoichiometric in-depth compositionally homogeneous 2 μm thick films on the Si(100) wafer possess the peak values of nanohardness 88 GPa and Young’s modulus 517 GPa at the penetration depth of 26 nm and, respectively, 35 GPa and 275 GPa at 200 nm depth. Friction coefficient was found to be 0.06. The coating scratch adhesion strength of 14 N was obtained as the first chipping of the coating whereas its spallation failure happened at 21 N. These critical loads and the work of adhesion, estimated as high as 18.4 J m−2, surpass characteristics of diamond like carbon films deposited onto tungsten carbide–cobalt (WC–Co) substrates.

Synthesis and properties of a green and self-cleaning hard protective coating

Abstract Polysiloxane coatings prepared by pre-hydrolysis/condensation of methyltrimethoxysilane (MTMS), etraethoxysilane (TEOS), methyltriethoxysilane (MTES) and polydimethylsiloxane (PDMS) in the presence of acid solution were presented in this paper in order to explore their potential use as protective and self-cleaning agents for car surface. The hardness and adhesion on the substrate properties of coatings were thoroughly examined by pencil hardness tester and adhesion tester. Contact angle meter was used to measure the hydrophobic angle properties of coatings. All the properties of coatings were related closely to the composition of coating and the hydrolysis degree of organoalkoxysilane. We found that the Scratch hardness can be improved by the controlling of TEOS quality ratio and acidity conditions, while more dosage of MTMS, MTES and PDMS favor raising the hydrophobic angle. Excellent adhesion property of paint coat was obtained with the presence of γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH-560). Whatever, the best self-cleaning coatings with excellent hardness and adhesion on the substrate was sample A4 synthesized by a sol–gel process of low-cost organoalkoxysilane, prepared at the quality ratio of (MTMS):(TEOS):(MTES):(PDMS):(KH-560) of 8:7:4:4:4 and water-to-precursor quality ratio of 1:7. Finally, ambient-curable self-cleaning coating suitable for large area application was obtained. The scratch hardness and adhesion strength of the coatings was 3H and 0 after hardening with a high speed, respectively. The contact angle after UV aging of the coating was 92°. The transmittance of the coating exceeded 98.5%. Meanwhile, the coating has good resistance to solvent and weather resistance.

GEP-based method to formulate adhesion strength and hardness of Nb PVD coated on Ti–6Al–7Nb aimed at developing mixed oxide nanotubular arrays

PVD process as a thin film coating method is highly applicable for both metallic and ceramic materials, which is faced with the necessity of choosing the correct parameters to achieve optimal results. In the present study, a GEP-based model for the first time was proposed as a safe and accurate method to predict the adhesion strength and hardness of the Nb PVD coated aimed at growing the mixed oxide nanotubular arrays on Ti67. Here, the training and testing analysis were executed for both adhesion strength and hardness. The optimum parameter combination for the scratch adhesion strength and micro hardness was determined by the maximum mean S/N ratio, which was 350W, 20 sccm, and a DC bias of 90V. Results showed that the values calculated in the training and testing in GEP model were very close to the actual experiments designed by Taguchi. The as-sputtered Nb coating with highest adhesion strength and microhardness was electrochemically anodized at 20V for 4h. From the FESEM images and EDS results of the annealed sample, a thick layer of bone-like apatite was formed on the sample surface after soaking in SBF for 10 days, which can be connected to the development of a highly ordered nanotube arrays. This novel approach provides an outline for the future design of nanostructured coatings for a wide range of applications.

Effect of nitrogen pressure on mechanical properties of nc-TiAlN/a-Si3N4 nanocomposite coatings deposited by cathodic arc PVD process

The present work investigates effect of nitrogen pressure on composition and mechanical properties of superhard nc-TiAlN/a-Si3N4 nanocomposite coatings deposited by cathodic arc PVD process. As the nitrogen pressure increases, at.% ratio of (Al+Si)/Ti, initially, increases to a maximum and thereafter, it decreases while the nitrogen content follows the reverse trend. Hardness is influenced by chemical composition and crystallite size of TiAlN phase. Maximum average hardness of 37 GPa is achieved when at.% ratio of Al(+Si)/Ti or N/(Ti+Al+Si) approaches 1.0 and decrease in scratch adhesion strength is attributed to the defects caused by nitrogen deficiency.

Identification of critical load for scratch adhesion strength of nitride-based thin films using wavelet analysis and a proposed analytical model

The use of Acoustic Emission (AE) signal of scratch test to evaluate the thin films' adherence led to unavoidable large uncertainties due to the problematic determination of the frequency band and the improper installation of the acoustic sensor, especially for coatings thinner than 100μm. In this paper, thin film–substrate adherence in high-speed steel is evaluated by Wavelet Analysis (WA) of the force–displacement curve in micro-scratch tests performed on the samples. The measured load displacement signals of deposited thin films were used as inputs for the wavelet module. We propose an analytical model combined with wavelet analysis, which is based on experimental data. Scratch adhesion strength could be identified by applying wavelet technique to the measured force displacement data to detect the location of the critical load during micro-scratch testing for TiSiN coating on high-speed steel. An analytical model is also proposed to predict the adhesion stress and to support the wavelet analysis technique where the stress is difficult to be assessed. Thin films were studied by optical microscopy, micro scratch testing machine and X-ray diffraction. The WA results are compared with model predictions in order to establish indication of scratch adhesion strength aimed at improving the manufacturing process.

Improvement of adhesion strength and scratch resistance of fluorocarbon thin films by cryogenic treatment

Fluorocarbon thin films have been widely applied as protective coatings due to unique physical and chemical properties, but the scratch resistance and adhesion strength between the films and substrates are rather poor. Coating technologies for stronger scratch resistance and adhesion strength are definitely needed and have great significance in coatings applications of fluorocarbon thin films. In this work, the scratch resistance and adhesion strength between silicon substrates and fluorocarbon thin films deposited by radio frequency (R.F.) magnetron sputtering were improved via a remarkably simple, flexible and nondestructive cryogenic treatment method. The effect of the cryogenic treatment on the microstructure, hardness, adhesion strength and scratch resistance of fluorocarbon thin films were investigated. XPS results indicated that the content of fluorine decreased slightly and the amount of cross-linked units increased after cryogenic treatment. Furthermore, the hardness of fluorocarbon thin films slightly improved. Nano-scratch test revealed that fluorocarbon thin films after this treatment had excellent scratch resistance and good adhesion strength.

Toward hard yet tough CrAlSiN coatings via compositional grading

A set of CrAlSiN coatings was synthesized in homogenous and graded composition via magnetron sputtering in mixed Ar and N2 ambient. The microstructures are investigated using glancing angle X-ray diffractometry, field emission scanning electron microscopy and transmission electron microscopy. With compositional grading, CrAlSiN coatings exhibit much improved scratch adhesion strength and better crack propagation resistance at a little expense of hardness.

Scratch induced failure of plasma sprayed alumina based coatings

A set of plasma sprayed coatings were obtained from three alumina based top coat and two bond coat powders. Scratch test was undertaken on these coatings, under constant and linearly varying load. Test results include the lateral force data and scanning electron microscope (SEM) images. Failure occurred by large area spallation of the top coat and in most cases tensile cracks appeared on the exposed bond coat. The lateral force showed an increasing trend with an increase in normal load up to a certain point and beyond this, it assumed a steady average value. The locations of coating spallation and occurrence of maximum lateral force did not coincide. A bond coat did not show a significant role in determining the scratch adhesion strength.