Showing papers in "Surface Engineering in 2006"

Inorganic materials and coatings produced by EBPVD

Abstract: The present paper describes the process of high speed electron beam evaporation of inorganic substances under vacuum and process parameters controlling the deposition, structure and properties of thick condensates (films). Considered are examples of single phase and multiphase metal, metal–ceramic, cermet and ceramic condensates of the thickness from several micrometres to several millimetres with dispersed, multilayer, porous and graded structures in a broad range of structural element dimensions. Dimensional effects in the structure and mechanical properties of thick condensates are noted. Areas of practical application of inorganic materials deposited from the vapour phase are described.

Tribological properties of laser clad Stellite 6 coatings on steel substrates

Abstract: The laser cladding of diesel engine exhaust valves is an emerging technology that provides excellent results in terms of the wear and corrosion resistance of the repaired materials. This work focuses on the deposition by laser cladding of Stellite 6 alloy coatings on two different base materials: an AISI 1045 carbon steel and an AISI 304 stainless steel. Following a process optimisation criterion, several of the fundamental laser treatment parameters were varied in order to obtain defect-free coatings with good adherence and minimal dilution. The metallographic structure of the clad material, irrespective of the substrate used, consists of a typical dendritic microstructure in a solid solution of Co. The mechanical strength of the layers was analysed by measuring HV0·1 microhardness and sliding wear behaviour. Laser coatings achieved hardness greater than 500 HV0·1, and presented excellent dry sliding wear behaviour, with a dimensional wear coefficient k one and a half orders of magnitude lower th...

High temperature oxidation and erosion–oxidation behaviour of HVOF sprayed Ni–20Cr, WC–20Cr–7Ni and Cr3C2–Ni–20Cr coatings

Abstract: The oxidation and erosion–oxidation (E–O) behaviour of high velocity oxy fuel sprayed Ni–20Cr alloy as well as WC and Cr3C2 cermet coatings on a steel substrate were studied. The E–O tests were carried out in a rig with specimen assemblies that were rotated through a fluidized bed of erodent particles in the temperature range 500–850°C and with erodent impact velocities of 2·5– 19·5 m s−1. Alumina powder (∼200 μm) was used as the erodent. The oxidation behaviour of the coatings was determined gravimetrically. The Ni–20Cr and Cr3C2–25(Ni–20Cr) coatings showed significantly higher oxidation resistance than the WC–20Cr–7Ni coating, especially at temperatures above 800°C. The E–O resistance of the coatings was determined by wastage, as a function of temperature. The three coatings did not show any significant change in E–O at temperatures up to 500–600°C. At higher temperatures, wastage increased with temperature, reached a maximum at 700°C and then decreased with further increase in temperature. Diff...

Influence of bias and in situ cleaning on through cage (TC) or active screen plasma nitrided (ASPN) steels

Abstract: The effect of a substrate bias and prenitride plasma etching on the nitriding response of four steel substrates is investigated in a two factor two level full factorial experimental design. The steels investigated were P20 (M200, plastic mould steel), H13 (W302, hot work tool steel - as received), 4140 (preheat treated nitriding steel) and 1020 (CS1020, bright mild steel). The nitriding response was determined from surface and cross-sectional hardness measurements. Nitrogen depth profile measurements were obtained using glow discharge optical emission spectroscopy. Considering the main effects, the results show that without a worktable bias during the nitriding step there is effectively little or no nitriding response in most of the materials. The prenitride plasma etch did not produce a significant surface hardness response in all steels except H13, where a prior etch substantially increased surface hardness and influenced the hardness depth profile. The bias also significantly increased the nitrogen wt-%. The plasma etch also influenced the near surface nitrogen wt-% concentrations, however the practical implications of this require further investigation.

Status of pulsed laser deposition: challenges and opportunities

Abstract: Pulsed laser deposition (PLD) is a relatively new and unique method for producing multicomponent thin films. PLD films are used in diverse areas such as microelectronics, electro-optics, tribology and biomaterials. The success of this technique is due to its simplicity and the ease with which stoichiometric multicomponent films can be deposited. Among the physical vapour deposition (PVD) techniques, PLD is unique because of its ability to work in high pressures of reactive background gases.

Surface modification of martensitic stainless steels by laser marking and its consequences regarding corrosion resistance

Abstract: Marking is of prime importance in the field of biomaterials to allow the identification of surgical tools or implants. Markings are obtained under industrial conditions with a pulsed Nd:YAG laser on a X30C13 martensitic stainless steel. Depending on laser parameters, two modes of marking are considered: a surface oxidisation mode and a matter photoablation mode. Electrochemical behaviour, i.e. passive state, corrosion rate, resistance to pitting, is evaluated in Ringer’s saline solution. Results are then explained on the basis of metallurgical modifications regarding the phases composition and the distribution of alloying elements. In oxidative regime, laser treatment drastically affects both microstructure and chemical composition. Specially, chromium depletion is measured in subsurface, leading to a loss of passive ability. In ablative mode the surface is transformed into a thin favourable layer of austenite. Moreover, the overall chromium distribution is little modified. Therefore, the passive character is maintained, but with nevertheless a shorter passive domain than base material one.

Novel hydroxyapatite/niobium surface coating for endodontic dental implant

Abstract: Endodontic dental implants have been used for many years. Many materials have been advocated for use as endodontic implants but a few of them have shown biocompatibility and have been acceptable. The aim of this study was to design and produce a novel biomaterial by producing a new surface coating on metallic substrate in order to achieve two goals, namely, an improvement in the corrosion behaviour of metallic endodontic dental implant and the bone osteointegration simultaneously. Stainless steel (SS) 316L was used as the metallic substrate and a novel double layer hydroxyapatite/niobium (HA/Nb) composite coating was prepared on it. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were utilised to characterise the coating. Electrochemical tests were performed in physiological solutions in order to determine the corrosion behaviour of the coated and uncoated specimens. Two types of endodontic implants were used, including SS with and without novel HA/Nb coating, which were prepared and subsequently implanted in the mandibular canine of 22 cats after completion of root canal treatment and osseous preparation. After a healing period of 4 months, osteointegration evaluation and histopathological interpretation were carried out using SEM and optical microscopy. In vitro tests indicated that the novel HA/Nb composite coating could improve the corrosion resistance and therefore the biocompatibility of SS endodontic dental implant. The clinical evaluation results showed that the average bone osteointegration of coated implants was more than for uncoated implants. The histopathological results and bone tissue response to the coated endodontic dental implants were acceptable. It can be concluded that HA/Nb composite coated SS could be used as an endodontic dental implant material.

Plasma surface engineering of precipitation hardening stainless steels

Abstract: Low temperature plasma nitriding of 17-4 PH martensitic and A286 austenitic precipitation hardening stainless steels has been investigated over a wide range of treatment temperatures and times. Experimental results have shown that the microstructural characteristics and properties are highly process condition dependent and there exits the possibility to provide considerable improvement in wear resistance without compromising corrosion resistance properties.

Formation of surface layers on Ti–6Al–4V titanium alloy by laser alloying

Abstract: This paper presents the results of the laser surface treatment of Ti–6Al–4V two phase titanium alloy. It was carried out in order to modify the microstructure and properties of the alloyed zone. Laser treatment was performed on samples coated by graphite and BN powders in stream of nitrogen in order to form martensitic phase, titanium nitrides, titanium carbides and borides as a consequence of the laser irradiation. The laser melted zone was examined and its microstructure and phase composition were determined. Microstructural analysis was carried out using Epiphot 300 optical microscope and Novascan 30 scanning electron microscope equipped with an EDS X-ray detector for compositional analysis. The phases were identified by X-ray diffractometry (Philips) with CuKα radiation. The Vickers microhardness under the load of 1.96 N and thermoelectric power were measured on the surface of cross-sections. The high hardness level (920–570 HV1.96) can be attributed to the formation of TiN, TiC and TiB phases...

Improvement in galling performance through surface engineering

Abstract: The aim of the present work was to investigate and compare different surface engineering techniques in terms of galling properties of forming tool steel when sliding against different work materials. The surface engineering techniques included were different grades of polishing, plasma nitriding and different hard coatings, all applied to cold work tool steel respectively. Investigation results indicate that the galling tendency can be greatly reduced by proper polishing of the tool surface. If polished after treatment, plasma nitrided surface will provide further improvement in friction and wear properties of the tool steel and especially for aluminium and titanium alloys reduce the galling tendency. On the other hand, coating selection for improved galling performance of coated forming tool steel greatly depends on the type of work material. In the case of stainless steel, carbon based coatings provide the best protection against the work material transfer, while forming of aluminium and titanium based alloys, requires nitride type coatings.

Cladding with Stellite 6 + WC using a YAG laser robot system

Abstract: A Nd:YAG laser robot cladding system, which combines a 6-axis robot, powder supply equipment and special powder delivery nozzle has been used for a powder cladding process. The Stellite 6 + WC mixed powder were clad on to mild carbon steel plate (SM400B). The depth of penetration, cracking behaviour, microstructure, Vickers hardness and wear resistance were investigated. Vickers hardness and wear resistance were found to increase with WC volume fraction in the range of 0–90%. The microstructures of clad layer can be divided into hypoeutectic (0–40%WC) and hypereutectic (50–100%WC) regions.

Influence of shot peening on tension-tension fatigue property of two high strength Ti alloys

Abstract: Surface roughness, residual compressive stress caused by shot peening and the effect of shot peening on fatigue property of Ti–5Al–5Mo–5V–1Cr–1Fe (TC18) and Ti–10V–2Fe–3Al (TB6) titanium alloys were investigated. The results show that fatigue limit for 1 × 107 cycles can be increased by 27 and 29% for TC18 and TB6 titanium alloys respectively. By comparing fatigue life under the same stress for different shot peening regimes treated specimens, the optimum shot peening process was determined. For a given material, there is an optimal shot peening intensity, and insufficient shot peening and over shot peening will not result in good fatigue performance. However, double shot peening, a shot peening process by which parts are peened initially with cast iron shot to induce a deep residual compressive stress field, followed by shot peening with glass shot to decrease the surface roughness and to remove the contaminants caused by the cast iron shot, can significantly improve fatigue performance.

Properties of surface layer generated by new combined process of burnishing and nitriding

Abstract: The results of a metal surface layer (MSL) investigation are presented in the present article. The surface layer was created using a new technological process. This process is the result of a combination of mechanical treatment (i.e. burnishing) and thermochemical treatment (i.e. nitriding). As a result of increasing the dislocation density during a burnishing treatment, which is followed by a nitriding treatment, the diffusion process in MSL is intensified. In the present article, specimens made of Armco iron (as a model material) were investigated. Four different stages of the surface layer development were investigated, i.e. initial material (after annealing), material after burnishing, material after nitriding and material treated by the combined technology. The main goal of the investigations carried out was a comparison of the changes in properties of the surface layers as a result of the different technologies. Investigations were performed on the metallography of different MSL structures, nitrogen concentration and hardness together with stress measurements.

Evaluation of electrochemical and surface characteristics of conversion coatings on ZM21 magnesium alloy

Abstract: Surface of a metal or material is important and suitable modification of the surface can provide enhanced properties for different applications. Magnesium is the lightest of all structural metals. Its low density (1·8 g cc−1 in alloy form) coupled with favourable casting properties, makes magnesium the material of choice for light weight components. But the metal is chemically highly reactive and prone to corrosion. Hence modification of the surface is important. The magnesium alloy under consideration is Mg–Zn–Mn, (ZM21) alloy system, and the composition is 2·03Zn–0·81Mn over which phosphate–permanganate, chromate conversion coatings were applied. The samples were subjected to surface roughness measurements, salt spray exposure tests, electrochemical potentiostatic polarisation studies in corrosive environment such as NaCl, NaOH, Na2SO4, NaHCO3 and NH4NO3. Microstructural examination, SEM analysis (for surface morphology), Fourier transform infrared (FTIR) spectral investigation (for determining...

Effect of alloying additions and preoxidation on high temperature sulphidation resistance of iron–chromium alloys

Abstract: High temperature corrosion of structural alloys in sulphur bearing environments is many orders of magnitude higher than in oxidising environments. Efforts to increase sulphidation resistance of these alloys include addition of alloying elements. This paper reports the effect of yttrium, aluminium and yttrium plus aluminium addition on the sulphidation behaviour of an Fe–20Cr alloy in H2–2%H2S at 700 and 800°C. The effect of preoxidation of these alloys on sulphidation behaviour was also investigated. The initial stages of sulphidation of these alloys were observed and overall sulphidation kinetics was determined. In the presence of yttrium, the sulphidation rate of the alloy decreased by an order of magnitude, and the sulphide layer on the FeCrY alloy was significantly thinner than that formed on the FeCr alloy. Aluminium addition increased sulphidation resistance even more. The FeCrAl and FeCrAlY alloys exhibited parabolic sulphidation kinetics at the two temperatures. On both alloys, initial chr...

Plasma nitriding design for aluminium and aluminium alloys

Abstract: Plasma nitriding for aluminium and aluminium alloys is a promising processing to improve the wear resistance for automotive parts. Normal plasma nitriding is characterised by three processes: presputtering, aluminium nitride nucleation and nitrided layer growth processes. N2+ presputtering is used to effectively eliminate the preexisting oxide films of Al2O3, covering the surface of aluminium matrix. Relatively long incubation time is required for nucleation process to form AlN islands or nodules on its surface. In addition, formation rate becomes very slow owing to low nitrogen diffusion coefficient in the nitrided layer. Physical and chemical modification methods to this normal nitriding processing are proposed to accelerate the formation rate of nitrided layer. Refinement of grain size in the aluminium matrix increases the formation rate by enlarging grain boundary area as a diffusion path. Crystallographic coherency between TiN and AlN reflects on enhancement of nucleation process by coformati...

High deposition rate magnetrons: key elements and advantages

Abstract: An innovative coating technology based on ion plasma magnetron sputtering physical vacuum deposition (IMPS-PVD) method has been developed to produce new complex coatings to meet the constantly growing demand of advanced industries, with a view to replacing chemical coating methods owing to their ecology danger and to complement/replace high temperature PVD methods. The high deposition rate magnetron (HDRM) technology has initiated a rebirth of mosaic targets as the key component leading to a big increase in the design accuracy of both targets and coatings to be deposited.

Effect of some thermal treatments on interface adhesion toughness of various thick thermal spray coatings

Abstract: Interfacial indentation is used to create and propagate a crack in the interface plane between a coating and its substrate. It has been shown earlier that this methodology allows the measurement of an apparent interface toughness, which can represent the adhesion of the coating to its substrate. In service thermal spray coatings are subjected to various external influences, which could be detrimental to their adhesion, e.g. thermal shock, fatigue, wear, corrosion and combinations of these. The objective of the present work is to study some of these effects and their influence on the interface adhesion toughness of various substrate/coating systems based on new phenomenological approaches to the residual stress state existing in the coating: (a) annealing treatment – for as sprayed specimen, it was first shown that the interface toughness is directly proportional to the reciprocal of the squared coating thickness. Extrapolated to an infinite thickness, the toughness could be assumed then to repres...

Advances in cold spraying

Abstract: Developments for different thermal processes or cold spraying commonly aim to minimise coating defects as porosity, disturbing oxides or undesired phase transformations as side effects. Whatever spray process is considered, a certain amount of energy is requested for building up coatings. Comparing thermal spray techniques in Fig. 1, ranging from arc spraying (AS), plasma spraying (PS) and conventional flame spraying (FS) to high velocity oxyfuel flame (HVOF) spraying, a trend to reduced particle temperatures and increased particle velocities is observed with respect to attaining optimum coating properties. The balance of requested energy for successful coating formation by thermal heat or kinetic impact energy is highly dependent on the type of coating material. For cermets and metallic spray materials, new developments in HVOF spraying already shifted the balance towards higher kinetic energy. All that has to be tuned to the wide variety of different feedstock types, which are available for one spray material. In that comparison, cold spraying represents the far edge, operating at temperatures far below the melting temperatures of metallic materials and at very high particle impact velocities, ranging more than 1000 m s 21 with respect to different process conditions. The major benefits of cold spraying are given by negligible amounts of side reactions during deposition. Therefore, microstructures and properties of feedstock materials can be retained in the coatings. 1 As compared with thermal spraying, also the particle beam with typical diameters from 6 to 8 mm is much smaller, reducing overspray and therefore costs as well as efforts for masking. In addition, the localised deposition allows to build up solid structures which is interesting for rapid prototyping or repair work. Cold spraying was developed around 20 years ago by a group of scientists at the Institute of Theoretical and Applied Mechanics, Novosibirsk, Russia. 2,3 Already these early work reported conditions for building up coatings of different spray materials. Moreover, they postulated a so called critical velocity for successful bonding in cold spraying. In the western world, cold spraying attracted rapidly increasing interests in the late 1990s, as demonstrated by the number of contributions to the annual meetings of the Thermal Spray Society. To facilitate applications, spray systems were developed which meet industrial standards. So far, about 20 to 30 units of such commercial spray systems are operated worldwide. About two-thirds of them are used by research centres or universities. 4 Companies operate the other third for various, mainly high tech, applications. As compared with the units of commercial equipment, a probably similar number of own design ‘home made’ cold spray units are operated at universities or research centres.

Effect of gas tungsten arc welding process variables on dilution and bead geometry of Stellite 6 hardfaced valve seat rings

Abstract: Hardfacing is one of the surfacing methods most widely employed in valve manufacturing industries to deposit Stellite 6, a cobalt based alloy, on low carbon steel valve seat rings to enhance specific properties such as wear and corrosion resistance. Gas tungsten arc welding (GTAW) process is used for hardfacing smaller size valves. The quality of the hardfaced deposits depends on the degree of dilution. The control of dilution will result in better metallurgical and mechanical properties of hardfaced deposits. Mathematical models have been developed in this paper to study the effects of GTAW process parameters on dilution and other important hardfacing parameters, namely, penetration, reinforcement and bead width. Models have been tested for their adequacy by regression methods. The direct and interaction effects are presented in graphical form which can be used not only for the prediction of geometry but also for controlling weld bead quality.

Ion nitrided AISI H13 tool steel Part I - Microstructural aspects

Abstract: In the present paper, five different operating conditions of a plasma nitriding process on annealed AISI H13 were investigated. A systematic variation of processing parameters such as gas mixture, time of processing and current density has been carried out in order to study their effect on microstructure. X-ray diffraction, microhardness testing and scanning electron microscopy techniques coupled with semiquantitative energy dispersive X-ray analysis were used to characterise the nitrided samples. The results revealed that the current density during plasma processing has a considerable influence on both the compound layer formation and depth of the diffusion zone. Also, it has been shown that the geometrical configuration of the workload may affect the uniformity of the diffusion zone, giving rise to the presence of heterogeneous nitrogen distribution zones along it.

Evaluation of corrosion behaviour of organic coatings with electrochemical noise and electrochemical impedance spectroscopy

Abstract: Electrochemical noise (EN) and electrochemical impedance spectroscopy (EIS) measurements were used to evaluate protective properties and corrosion behaviour of two different organic coating systems. The coatings of commercial grade (zinc rich ethyl silicate) were applied to steel substrates and immersed for up to 3 months in 0·5M NaCl at 25°C. An analysis of the EN data was performed during this time, including the measurements of the mean potential Emean, the mean current Imean and the noise resistance Rn. The time series noise patterns were transformed into frequency domain by fast Fourier transformation. The power spectral densities (PSDs) of the potential and of the current and roll off slope coatings were then compared with each other. These coated plates were assessed by EIS. Electrolytic penetration through the coating, changes in the dynamic characteristics of the conduction and resistance of the coating film of the protected system as a function of time. Equivalent circuits were used to i...

Preparation and characterisation of nanostructured tin oxide (SnO2) films by sol–gel spin coating technique

Abstract: Highly transparent tin oxide thin films (SnO2) have been prepared using the sol–gel spin coating technique, optimising process parameters such as the solute concentration, spin rate and time of the turn table, film thickness (number of coatings) and heat treatment temperature. The X-ray diffraction (XRD) studies point to the polycrystalline structure of the developed films. The films deposited under optimum conditions are highly transparent in the visible region with a transmittance of 94% at 550 nm and have a resistivity of 3 × 10−2 Ωcm. The films have been obtained at a relatively low process temperature of 400°C.

Effect of aeration on superficial residual stress level of carburised and quenched gears treated by water cavitation peening

Abstract: Cavitation impacts, which are generally considered as the dominant factor affecting cavitation erosion of hydraulic machinery, can also be applied to introduce compressive residual stress in the surface layer of mechanical components in a similar way to traditional shot peening. By using a high speed submerged water jet instrument, in which high pressure water is passed through a jet nozzle to the specimen, a uniform cloud of large bubbles can be generated. Bubble collapse on the surface of the specimen will produce an impact effect very similar to shot peening. Therefore, the design of the jet nozzle is very important to obtain the optimum pressure of bubble collapse. In the present study, a new nozzle design with air addition was used, the effect of the air addition flux on the impulse pressure of bubble collapse was investigated, and a comparative study of the residual stress in a carburising quenched gear treated by water cavitation peening with and without air addition was carried out. The re...

Characterisation of chromium nitride physical vapour deposition coating on diesel engine pistons

Abstract: The development of PVD coatings on pistons for internal combustion engines is described. The aim is to achieve better control of friction, wear, oxidation and corrosion in critical engine components such as pistons and cylinders in order to achieve higher energy efficiency, prolonged life and improved power output. The aim of the study was to find an optimum substrate–coating combination for aluminium piston applications. PVD CrN arc deposited coatings have been found to offer excellent properties for this application, showing improved friction and wear properties and good adhesion as measured in the scratch test. The coating process has been shown not to affect the hardness or microstructure of the LM-13 piston alloy.

Preliminary study on plasma surface modification of medical grade 316LVM and high nitrogen austenitic stainless steels

Abstract: Specimens of 316LVM (F138) and high N (F1586) medical grade austenitic stainless steels (ASS) have been low temperature plasma surface alloyed with nitrogen and carbon, at temperatures between 370–550°C, to enhance their tribological properties and corrosion resistance. Systematic materials characterisation was conducted to investigate the microstructure, phase constituents, composition and surface mechanical properties of the plasma alloyed layers. The tribological and corrosion properties of the surface engineered materials have been evaluated by pin on disc tribometer and electrochemical corrosion tests. Experimental results showed that the surface hardness of both materials was significantly improved by all plasma treatments. Wear resistance was increased by up to 109 times, and wear volumes differed only slightly between treatments. Wear modes were altered from severe abrasive wear to mild oxidative wear. Anodic polarisation test results revealed that when nitrided at ≤400°C and carburised at...

Age hardening of Ni–P–Mo electroless deposit

Abstract: A Ni–P–Mo autocatalytic coating was developed in order to study the structural changes according with the molybdenum codeposition and the effects of aging treatment. Results show that heat treatment induces structural changes that allow for total crystallisation of amorphous regions and the reordering of crystalline phases, to produce a Ni–Mo solid solution with precipitation of Ni3P and MoNi4 particles. Hardness of the as plated condition is similar to high phosphorous Ni–P deposits as mentioned in the literature, however the present work revealed that subsequent heat treatment was beneficial in enhancing the hardness of the metallic coating with a maximum of 1450 HV(100 g) being measured for coatings treated at 500°C for 2 h. This hardening can be interpreted as a consequence of amorphous to crystalline phase transformation and the aging processes of Ni–P–Mo ternary alloy. This enhancement is further reinforced by the precipitation of MoNi4 intermetallic particles.

Modelling of kinetics of nitriding titanium alloys

Abstract: Models for simulation and monitoring of the evolution of surface layers during gas nitriding of titanium alloys were developed using own experimental results. They are based on analytical and numerical solutions of the diffusion equation and model the nitrogen distribution, the thickness of the nitrided layers and the incubation time for the formation of layers on the surface of titanium alloys.

Surface changes of plasma sprayed hydroxyapatite coatings before and after heat treatment

Abstract: Plasma sprayed and heat treated hydroxyapatite (HA) coatings, produced from fine HA powder (38–75 μm) under a spraying power of 45 kW (in short FCs) and coarse HA powder (75–106 μm) under a spraying power of 35 kW, (in short CCs) have been investigated, especially in terms of their surface characteristics. The X-ray diffraction results show that most of amorphous and decomposed phases transform into crystalline HA and the crystallinities of coatings are improved. The surface morphology of the coatings has been examined by electron probe microanalyser and field emission scanning electron microscope. At high magnifications the as sprayed FCs, with new nanosize particles and a netlike aggregated lamellar texture are observed on the surface. After heat treatment at 650°C, the nanograde particles of FCs have a tendency to grow and increase in quantity. While the netlike aggregation disperses into a uniform petal-like texture similar to a porous structure with a high surface roughness. Energy dispersive...

Evaluation of toughness of hard coatings

Abstract: Repeated impact has been introduced to evaluate different properties of hard coatings, such as impact wear resistance, bonding strength, fatigue, etc. The load and impact number relationships are similar to that of fatigue curves, and close to some real applications of coated parts. Cr–Cu–N coatings were performed on a hardened steel substrate and the repeated impact tests were conducted on the coating substrate system. At a low impact load, the intrinsic strength of the coating layer and the bonding strength between the coating and substrate are in competition. Coating layer cracking or delamination might occur and the strength plays an important role like that of high cycle fatigue. When the load is increased and towards the low cycle fatigue regime, toughness of the coating layer turns out to be predominant. The cohesive failure in high load regime preferentially depends on the toughness of the coating layer, and the failure cycles can be employed as a toughness criterion.