Scratch Adhesion Research Articles

The tribological properties of MoS 2/metal composite coatings deposited by closed field magnetron sputtering

MoS 2 coatings deposited by closed field magnetron sputtering are dense and adherent and have certain superior tribological properties compared to coatings deposited by other techniques. The properties can be further improved by the co-deposition of small amounts of metal with the MoS 2. The results of scratch adhesion, pin-on-disc and reciprocating wear tests are reported and compared to those from earlier coatings. A number of practical applications are given and, in particular, large improvements in the performance of cutting tools are reported.

Mechanical and optical properties of ITO films with anti-reflective and anti-wear coatings

In this study, radio frequency (rf) magnetron sputtered ITO films were coated with reactively sputtered SiO 2 films. The microhardness, pull-off strength, scratch adhesion strength, optical transmittance and reflectance of the SiO 2/ITO/substrate system are investigated. Coating of SiO 2 enhances both the hardness and pull-off strength and reduces the scratch critical load of the system. The optical transmittance in the visible range is also improved with the addition of SiO 2.

Reduction of stresses in thin films by high energy ion beams

A high degree of tensile stress tends to develop during the growth of refractory metal films. At increased values of film thickness the integrated stress becomes high enough to cause adhesion problems. When chromium films on the order of 1 μm were irradiated with Ni ions of energy 75 MeV, a reduction in strain as measured by X-ray diffraction was observed. Scratch Adhesion measurements demonstrated that this is accompanied by a large improvement in coating to substrate adherence. A new model is proposed to account for the observed effects and provides a basis on which to engineer stresses in thin films using ion beams. The model pictures mobile interstitials that escape from displacement cascades as nucleating into loops in preferred orientations. The preferential orientation is a result of the lattice strain. As these aligned loops grow, they introduce a strain of their own which cancels out the initial strain. A mathematical formulation enables prediction of strain with irradiation dose for a given initial stress.

Preparation and characterization of aluminum oxide films by plasma enhanced chemical vapor deposition

Aluminum oxide thin films were prepared on glass and silicon substrates by RF plasma enhanced chemical vapor deposition (PECVD) using AlCl 3, CO 2 and H 2 as gas sources. PECVD of aluminum oxide films has been formed by choosing appropriate substrate temperature, RF power and flow rate of reaction gas. The characteristics of films were investigated by X-ray diffraction, SEM, FTIR and electron probe microanalysis (EPMA). Scratch adhesion, surface hardness and residual stress were measured. The chlorine content in the amorphous as-deposited aluminum oxide film is influenced mainly by the substrate temperature for deposition. Adherent, hard and transparent films of refractive index 1.61–1.73 were obtained with a growth rate as high as 1.8 μm h −1 and the maximum surface hardness obtained is HV1200.

Architecture of multilayer nanocomposite coatings with super-hard diamond-like carbon layers for wear protection at high contact loads

Super-hard and low-friction diamond-like carbon (DLC) coatings deposited at low temperatures are currently of great interest for wear protection and friction reduction. However, their high hardness (50–80 GPa), intrinsic stresses, and poor adhesion limit their use to applications where contact pressures are below I GPa and the coating thickness is below 0.5 μm to prevent cracking and delamination. These negative effects are especially pronounced when the coatings are applied to relatively soft substrates, such as steels. The limitations were removed by a multilayer design, where metal and ceramic layers were used to increase the load support capability, improve the adhesion strength, and increase the thickness of DLC layers. Existing approaches to the design of tough multilayer coatings were considered critically and a coating architecture was suggested using the following concepts: (i) formation of a load support and adhesion promoting underlayer with mechanical characteristics varied gradually from the substrate to the DLC layer; (ii) separation of hard DLC layers with interlayers of softer material to reduce stresses and brake cracks; (iii) use of crystalline interlayers with thickness permitting operation of dislocation sources for stress relaxation and deflection of cross-sectional cracks. The development of these concepts is discussed sequentially from bilayer ceramic/DLC coatings to functionally gradient metal/carbide/DLC coatings, and finally to nanocomposite coatings consisting of stacks of Ti/DLC, TiC/DLC, and CN/DLC layers with individual thickness within 10–60 nm deposited onto a gradient TiTiC-DLC underlayer. The coatings were deposited onto stainless steel substrates by a hybrid of magnetron sputtering and pulsed laser deposition. They had a 1–2 μm total thickness of super-hard (60–70 GPa) DLC layers and resisted delamination to 50–80 N loads in scratch adhesion tests. In ball-on-disk sliding tests, these coatings supported Hertzian contact pressures above 2 GPa and had friction coefficients around 0.1. Their wear lives exceed 10 6 cycles under initial contact pressures of 1.4 GPa. The conceptual architecture of multilayer nanocomposite coatings presented extends the range of wear resistant applications for super-hard DLC materials.

IMPROVED ADHESION OF TiN DEPOSITED ON PRENITRIDED STEELS

This study investigates the deposition of TiN coatings on two stainless steels that have been plasma nitrided before coating deposition. The steels were plasma nitrided under several conditions, producing compound layers and diffusion zones of varying thickness. Subsequently, TiN coatings were produced by electron beam P VD on the nitrided steel substrates. The hardness, microstructure, and phase distribution of the surface regions of the nitrided steels with TiN coatings were investigated by optical metallography, micro hardness measurements, scratch adhesion tests, Auger electron spectroscopy, and X -ray diffraction.

Mechanical properties of r.f. magnetron sputtered indium tin oxide films

In this study, the mechanical behavior of r.f. magnetron sputtered indium tin oxide (ITO) films with glass and polycarbonate as substrates was investigated. The microhardness, pull-off strength and scratch adhesion strength were measured to assess the film properties. The ITO coating improves the hardness of the polycarbonate substrate. Incorporation of oxygen in the sputtering ambient enhances the crystallization of the film; consequently, the film hardness of coated polycarbonate and the scratch adhesion strength of coated glass are improved. The thermal expansion mismatch between ITO and polycarbonate results in poor adhesion when polycarbonate is employed as the substrate.

密着性に優れたダイヤモンド被覆工具によるＡｌ‐１８ｍａｓｓ％Ｓｉ合金の切削特性

Coated cutting tools with CVD diamond film requires high adhesion strength between the diamond film and substrate. We studied the adhesion strength of diamond-coated WC-Co tools using Microwave Plasma CVD (MWPCVD) and an Al-18%Si alloy cutting test using diamond cutting tools.Diamond was coated onto tools using an MWPCVD apparatus. The reaction gas was a mixture of methane and hydrogen. Substrate temperature was varied from 673K to 1173K by controlling the microwave output power and growth pressure.SEM observation revealed that grain size grew with increasing substrate temperature. All deposits were clear diamond crystals. XRD showed that deposits were cubic diamond. Raman spectroscopy showed that deposits synthesized at a lower substrate temperature (673K) were of higher quality than those synthesized at a higher substrate temperature (1173K). A scratch adhesion strength test, from 673K to 873K showed that adhesion strength increased from 873K to 1173K, but it decreased with increasing substrate temperature. Deposition synthesized at 873K showed the best adhesion strength. In Al-18%Si alloy cutting test of using diamond-coated tools synthesized at 873K, diamond film did not peel after a 800m cutting test and the surface of Al-Si work pieces turned with diamond coating tools synthesized at 873K presented uniform roughness.The cutting performance of Al-18%Si alloys using diamond-coated WC-Co tools was related to adhesion strength.

Reactive magnetron sputter deposition of polycrystalline vanadium nitride films

Polycrystalline vanadium nitride films were deposited onto M2 steel substrates using a high-rate reactive dc magnetron sputtering system by sputtering vanadium metal in an Ar+N2 atmosphere under N2 partial pressure control. The crystal structure, surface morphology, and properties of the films were affected by several process parameters such as nitrogen partial pressure, target power, and negative substrate bias. Analytical techniques including x-ray diffraction and scanning electron microscopy were used to characterize the structure and morphology of the films, and the mechanical properties of the films were measured by a Vickers microhardness and a scratch adhesion testers. The nitrogen partial pressure was found to be the dominant deposition parameter for the formation of different phases which includes crystalline V metal, hexagonal β-V2Nx, and cubic δ-VNx, amorphous V–Nx solid solution, and their mixtures. The film hardness was affected by crystalline phase, and a maximum hardness of 3000 kgf/mm2 Hv0.05 was found at the β-V2Nx phase. The morphology of the films varied in a wide range from cauliflowerlike rough and porous surface to smooth and dense surface, and can be correlated to deposition parameters.

The effect of residual stress on the adhesion of PECVD-coated aluminum oxide film on glass

Transparent, amorphous and hard aluminum oxide films were deposited on glass at low temperatures (≤ 773 K) by r.f. plasma-enhanced chemical vapor deposition with AlCl 3, H 2 and CO 2 as the reactants. The adhesion of films, a predominant factor in determining the performance and reliability of a coating-substrate system, evaluated by the critical load in scratch testing strongly depends on the deposition conditions (substrate temperature and CO 2 flow rate) and compressive residual stress in the films measured by radii of curvature determinations. These films have shown a tensile cracking failure mode in scratch testing and as opposed to the prediction based on energy balance and the critical shear stress criteria, which indicates that the critical load will vary inversely with internal stress, the compressive residual stresses increase the adherence strength by increasing the resistance to the tensile cracking failure. Hence, it is important to characterize the failure modes associated with the scratch adhesion test to account for the dependence of critical load on internal stresses in the films.

Substrate surface finish effects in duplex coatings of PAPVD TiN and CrN with electroless nickel-phosphorus interlayers

The ability to deposit hard coating materials on to a wide range of substrate surface finishes and still maintain adequate structural and functional properties is a very desirable objective in the quest to optimise product economics. A better surface finish requires longer and more elaborate finishing processes which will result in substantial additional costs. In this investigation two different groups of substrate surface roughnesses were prepared for a number of appropriate testing procedures. The tests involved in this study were microhardness, surface profilometry, scratch adhesion and the wet sand rubber wheel abrasive test. Electrochemical corrosion testing was also carried out. The results reveal that the substrate roughness can be optimised to achieve the best compromise in terms of cost and performance. The addition of an electroless nickel-phosphorus (ENiP) interlayer, in particular, is beneficial in isolating the substrate from near-surface effects and in permitting the use of rougher surface finishes.

N + ion implantation effects on microhardness and adhesion in TiO 2 films

The epitaxial films of TiO 2 rutile (100) could be grown on sapphire (0001) substrates at 500°C by means of reactive ionized cluster beam (RICB) deposition. To achieve epitaxial growth at low substrate temperature, ionization of Ti vapor and O 2 gas was necessary. The difference of mechanical properties in epitaxial rutile films on sapphire and polycrystal rutile films on Si wafer has been studied by microhardness and scratch adhesion measurements. Epitaxial films are more hard about 1.9 times and adherent about 1.3 times than polycrystal films. High-energy (3 MeV) implantation has a stronger hardening and adhesion effects than low-energy (90 keV) implantation. In epitaxial films, the spread of interplanar spacing of rutile (200) planes occurred due to implantation-induced internal stress and strain. In polycrystal films, a phase transformation of crystalline rutile to anatase of TiO 2 occurred due to the relaxation of internal strain. The adhesion of TiO 2 films to the substrates could be increased about 27% in both epitaxial and polycrystal films by high energy (3 MeV and 400 keV respectively) implantation due to interface mixing and reaction between film and substrate.

Treatment of MoS 2 films by high-energy heavy ion beams

Very high energy (75 MeV) ion beam irradiation is used to modify the adhesion of thick MoS 2 films on stainless steel substrates. This new approach permits the treatment of thicker films of MoS 2 than was hitherto possible. Scratch adhesion tests were carried out to assess the adhesion of the coating to the substrate. In the unirradiated case the loss of coating occurs due to chipping outside the scratch. This loss of coating does not occur in the irradiated case. The spallation inside the scratch is delayed drastically to higher loads after the irradiation showing significant improvement in the adhesion of the MoS 2 coating to the stainless steel substrate. Irradiation does not change the friction significantly.

Effects of Surface Pretreatment of Ti-6AI-4V on the Adhesion and Wear Lifetimes of Sputtered MoS2Coatings

Improving the adhesion and wear endurance lifetimes of the solid lubricant molybdenum disulfide (MoS2) on titanium (Ti) alloys was studied in this experimental investigation. Ti-6Al-4V alloy specimens were implanted with gas ions or coated with ceramic layers prior to coating with sputtered MoS2 to investigate the adhesion and wear lifetimes of the MoS2 coatings. The greatest improvement in scratch adhesion (2.4 times Ti-6Al-4V coated directly with MoS2) was observed for an MoS2/diamond-like carbon/Si multilayer coating. Sliding wear tests revealed the greatest lifetime improvement (3.2 ×) was for an MoS2/TiC dual-layer coating. Increased MoS2 adhesion was observed for pretreated surfaces with a Vickers microhardness greater than 800 kgf/mm2. Increased adhesion of MoS2 for bond layers with lower elastic moduli (estimated) is suggested. Therefore the ratio hardness/elastic modulus may be a potential figure of merit for surface pretreatment selection. Presented at the 50th Annual Meeting in Chicago, Illinoi...

Evaluation of PVD nitride coatings, using impact, scratch and Rockwell-C adhesion tests

In this work the scratch test, the impact test and the Rockwell-C adhesion test were compared by investigating the adhesion properties of three types of sputtered physical vapour deposition coatings: TiN, CrN and Cr 2N. Each coating type was deposited on polished SAE 52100 steel, with different thicknesses in the nominal range of 2–20 μm, to evaluate the thickness influence on the test results. All the tests showed a ductile behaviour for the TiN coating with small delaminations and a brittle behaviour for the CrN and Cr 2N coatings with relatively large delaminations. An increase of the dimensions of the delaminations with increased coating thickness was detected for all layer types. With the scratch test a significant increase in upper critical load with layer thickness was observed for all of the coatings. However, there was considerable variability especially for the Cr 2N coatings. The impact tests showed no coating failure for the TiN layer, and a decreasing impact crater volume with increasing layer thickness, whereas the CrN and Cr 2N layers failed after 10 3 impacts and showed an increasing impact crater volume with increasing layer thickness. The studies demonstrate the usefulness of using these test methods for differentiating between the behaviour of different coatings under various contact conditions.

Investigation of superlattice coatings deposited by a combined steered arc evaporation and unbalanced magnetron sputtering technique

In this paper we report on third-generation TiA1N-ZrN superlattice thin films deposited at industrial scale on high speed steel and stainless steel substrates by a combined steered arc evaporation and unbalanced magnetron sputtering technique. The superlattice period and hence the mechanical and physical properties of the film were varied by modification of the rotation velocity and type of rotation (one-fold and three-fold). Characterization of the films was undertaken by a range of bulk and surface analysis techniques including scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectrometry, hardness and adhesion measurement. Results show that a reproducible superlattice structure can be fabricated without a complex atmosphere separation and shuttering mechanism. Control of the planetary rotation velocity and type of rotation has led to variation in the superlattice period from 19 to 132 Å. Further analysis has shown that the TiA1N-ZrN superlattice system can exhibit hardness greater than 4000 HK, scratch adhesion values on high speed steel of above 50 N, <100> preferred orientation, average surface roughness less than 0.10 μm and a highly dense microstructure.

Investigation of superlattice coatings deposited by a combined steered are evaporation and unbalanced magnetron sputtering technique

In this paper we report on third-generation TiA1N-ZrN superlattice thin films deposited at industrial scale on high speed steel and stainless steel substrates by a combined steered arc evaporation and unbalanced magnetron sputtering technique. The superlattice period and hence the mechanical and physical properties of the film were varied by modification of the rotation velocity and type of rotation (one-fold and three-fold). Characterization of the films was undertaken by a range of bulk and surface analysis techniques including scanning electron microscopy, X-ray diffraction, glow discharge optical emission spectrometry, hardness and adhesion measurement. Results show that a reproducible superlattice structure can be fabricated without a complex atmosphere separation and shuttering mechanism. Control of the planetary rotation velocity and type of rotation has led to variation in the superlattice period from 19 to 132 Å. Further analysis has shown that the TiA1N-ZrN superlattice system can exhibit hardness greater than 4000 HK, scratch adhesion values on high speed steel of above 50 N, <100> preferred orientation, average surface roughness less than 0.10 μm and a highly dense microstructure.

Chemical vapour deposition of TiN on stainless steel

A study has been conducted regarding the deposition of titanium nitride on stainless steel for potential uses in surgical applications. Titanium nitride was deposited from a gaseous mixture of TiCl 4 , H 2 and N 2 using a CVD process at atmospheric pressure and a temperature of 1173 K employing a horizontal quartz reactor and linear flow velocities in the range 20 to 60 cm min −1 . Adhesion of the coatings was measured by using the scratch adhesion test and their thickness by using the ball cratering method. The results have shown that at low linear flow velocities the deposits obtained are thin, inhomogeneous and have a poor adhesion to the substrate. In contrast, at high velocities (50 cm min −1 ) the coatings had better properties and characteristics.

Chemical vapour deposition of TiN on stainless steel

A study has been conducted regarding the deposition of titanium nitride on stainless steel for potential uses in surgical applications. Titanium nitride was deposited from a gaseous mixture of TiCl 4, H 2 and N 2 using a CVD process at atmospheric pressure and a temperature of 1173 K employing a horizontal quartz reactor and linear flow velocities in the range 20 to 60 cm min −1. Adhesion of the coatings was measured by using the scratch adhesion test and their thickness by using the ball cratering method. The results have shown that at low linear flow velocities the deposits obtained are thin, inhomogeneous and have a poor adhesion to the substrate. In contrast, at high velocities (50 cm min −1) the coatings had better properties and characteristics.

Friction monitored scratch adhesion testing

During a scratch adhesion test, the plot of the frictional force against the normal applied load on the diamond can indicate different types of failure: small oscillations in the measured friction correspond to chipping, bigger variations show the presence of flaking. The first contact of the diamond with the substrate, total failure, is marked by an inflection point in the measured frictional force. A mathematical method is given to approximate the curve and determine the critical load where the derivative d(frictional force)/d(load) is maximum.