Wear behavior of Ni–P and Ni–P–Al2O3 electroless coatings

In this research, hardness and wear resistance of two types of electroless coating have been investigated including Ni–P and Ni–P–Al₂O₃ coatings. These coatings were applied on AISI 1045 steel discs by electroless deposition process and then they were heat treated at 200, 400 and 600 °C for 1 h. Wear resistance of deposits was measured by the pin on disc method and wear surfaces and debris were studied by scanning electron microscopy (SEM). Also, microstructural changes were evaluated by X-ray diffraction (XRD) analysis.The results showed that the existence of alumina particles in Ni–P coating matrix led to an increase in the hardness and wear resistance of the deposits. It was also found that heat treated coatings at about 400 °C have the maximum hardness and wear resistance.     

Comparative tribological study of air plasma sprayed WC–12%Co coating versus conventional hard chromium electrodeposit

In this work, the properties of air plasma sprayed WC–12%Co coating before and after heat treatment were compared with the properties of the hard chromium electrodeposit. WC–12%Co coatings were heat treated at 650, 900 and 1150 °C for 1 h in an argon atmosphere. XRD patterns confirmed the formation of an amorphous phase in the as-sprayed coating. This amorphous phase gradually transformed to η-carbides in the course of heat treatment of the coating. This transformation was confirmed by the XRD analysis of the coatings heat treated above 900 °C. Pin-on-disc wear test results showed that WC–12%Co coatings had a significantly better tribological performance as compared with that of the hard chromium electrodeposits. The results also indicated that heat treatment of the WC–12%Co coatings at 900 °C gave the highest wear resistance among the coatings, which was due to the formation of hard η-carbides at this temperature.     

Novel investigation on tribological properties of Ni–P–Ag–Al2O3 hybrid nanocomposite coatings

In this research, silver and alumina particles were co-deposited within Ni–P matrix to obtain Ni–P–Ag–Al₂O₃ hybrid coating. The structure of coatings was analyzed by X-ray diffraction and the tribological properties of deposits were evaluated by pin on disc tribometer. 3D optical profiler and scanning electron microscopy were used to study wear rate and worn surfaces. The results showed that Ni–P–Ag and Ni–P–Ag–Al₂O₃ coatings have the self-lubrication property and maximum hardness (∼1310 HV) and wear resistance were obtained for Ni–P–Al₂O₃ coating. Also, Ni–P–Ag–Al₂O₃ hybrid nanocomposite coating had higher wear resistance than Ni–P and Ni–P–Ag coatings. Moreover, the best conditions was achieved for heat treated hybrid coating in the concentration of 30 mg/L silver and 150 mg/L alumina in the plating solution.     

Microstructure and wear properties of in situ TiC/FeCrBSi composite coating prepared by gas tungsten arc welding

Using a gas tungsten arc welding (GTAW) process, in situ synthesis TiC particles reinforced Fe-based alloy composite coating has been produced by preplaced FeCrBSi alloy, graphite and ferrotitanium powders. The microstructure and wear properties of the composite coatings were studied by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD) and wear test. The effects of thickness of the pre-placed powder layer on the microstructure, hardness and wear resistance of the composite coatings were also investigated. The results indicated that TiC particles were produced by direct metallurgical reaction between ferrotitanium and graphite during the GTAW process. TiC particles with sizes in the range of 3–5 μm were dispersed in the matrix. The volume fraction of TiC particles and microhardness gradually increased from the bottom to the top of the composite coatings. The TiC-reinforced composite coatings enhance the hardness and wear resistance. The highest wear resistance of the composite coating with a 1.2 mm layer was obtained.     

Microstructure and wear properties of in situ TiC/FeCrBSi composite coating prepared by gas tungsten arc welding

Using a gas tungsten arc welding (GTAW) process, in situ synthesis TiC particles reinforced Fe-based alloy composite coating has been produced by pre-coated FeCrBSi alloy, graphite and ferrotitanium powders on the substrate. The microstructure and wear properties of the composite coatings were studied by means of scanning electron microscopy (SEM), X-ray diffractometer (XRD) and wear test. The effects of thickness of the pre-coated powder layer on the microstructure, hardness and wear resistance of the composite coatings were also investigated. The results indicated that TiC particles were produced by direct metallurgical reaction between ferrotitanium and graphite during the GTAW process. TiC particles with sizes in the range of 3–5 μm were dispersed in the matrix. The volume fraction of TiC particles and microhardness gradually increased from the bottom to the top of the composite coatings. The TiC-reinforced composite coatings enhance the hardness and wear resistance. The highest wear resistance of the composite coating with a 1.2 mm layer was obtained.     

Effect of heat treatment on the structure,cavitation erosion and erosion–corrosion behavior of Fe-based amorphous coatings

In this study, high-velocity oxygen-fuel sprayed amorphous coatings have been heat treated at various temperatures to form microstructures with crystalline phases. The structure, micro-hardness, cavitation erosion resistance and erosion–corrosion resistance of these coatings are compared. Crystalline phases are discovered in the coatings after heat treatments at 650 °C and 750 °C. The coating heat treated at 750 °C exhibits the poorest cavitation erosion resistance in 3.5 wt% NaCl solution among all coatings due to the degraded corrosion resistance. However, the hardness of the crystallized coating can reach 1000 Hv and the erosion–corrosion resistance of the heat treated coating is better than the untreated one.     

Wear behavior of electroless Ni–P–B4C composite coatings

In this research, the wear of electroless Ni–P and Ni–P–B₄C composite coatings was reviewed. Auto catalytic reduction of Ni in nickel sulfate and sodium hypophosphate bath including suspended B₄C particles with different concentration was used to create composite coatings with 12, 18, 25 and 33 vol.% of B₄C particles. Coatings 35 μm thick were heat treated at 400 °C for one hour in an argon atmosphere and the wear resistance and friction coefficient of heat-treated samples were determined by block-on-ring tests. All wear tests were carried out at 24 °C, 35% moisture, 0.164 m/s sliding speed and about 1000 m sliding distance. Graphs show that an electroless Ni–P–B₄C composite coating with 25 vol.% of B₄C had the best wear resistance against a CK45 steel counterface.     

Two-body abrasive wear of electroless nickel composite coatings

The two-body abrasive wear of electroless nickel (EN), EN-silicon carbide, and EN-alumina composite coatings have been investigated using a scratch test with a diamond indenter. The coatings were heat treated at temperatures of 100–500° C. The hardness of the coatings increased with heat treatment temperature from 500 HV100 for the as-deposited condition to 1008 HV100 when fully hardened. Scratch testing showed that the as-deposited coating had scratch tracks with a high degree of plasticity, signs of microploughing and tensile cracking and was characterised as a ductile failure. On the other hand, the heat-treated coatings showed chipping and cracking on the edge of the scratch tracks, failing in a brittle manner. The heat-treated EN-silicon carbide coatings, however, exhibited no cracking nor chipping, believed to be due to its higher fracture toughness than the other heat-treated coatings, attributable to its lower phosphorus content. The volume of material removed from the silicon carbide scratch track was 1/3 of the volume removed from the steel substrate at a 20 N load, and showed the best wear/ scratch resistance of any of the coatings tested.     

High temperature wear resistance of (TiAl)N PVD coating on untreated and gas nitrided AISI H13 steel with different heat treatments

The wear resistance of a PVD (Ti_0.7Al_0.3)N coating deposited on an as-received and gas nitrided AISI H13 has been examined by using ball-on-disc tests at room temperature and at 600 °C. In order to determine the influence of a previous heat treatment on this type of steel on the wear resistance of the (Ti_0.7Al_0.3)N coating, two commercial heat treatments were employed which gave rise to the same substrate hardness. Surface microhardness measurements have been carried out to determine the load-carrying capacity of the coated systems. In general, the wear behavior was found to be independent of the nature of the heat treatment applied to the substrate prior to the nitriding process but strongly dependent on the testing temperature. At room temperature, there were small variations between the different systems tested, whereas at high temperatures, clear differences were found between them. At 600 °C, a typical temperature that could be achieved during the aluminum extrusion processes, the nitrided H13 steel/(Ti_0.7Al_0.3)N PVD duplex coating shows a satisfactory wear resistance compared to both the nitrided steel and the steel substrate only coated with (Ti_0.6Al_0.4)N, which exhibited the worst performance. The satisfactory wear resistance observed for the duplex coating system at high temperature is mainly a consequence of two different aspects. Firstly, its higher load-carrying capacity due to the existence of a hard nitrided layer, as well as its high H/E ratio. Both parameters allow the presence of higher elastic strains without the failure of the ceramic layer, which would normally occur in the case of TiAlN PVD coatings deposited directly on the AISI H13 steel. Secondly, the intrinsic characteristics of the coating, i.e. its chemical constitution, which allows the formation of a dense oxide mixture inside the wear track that impedes both its further oxidation and the deterioration of the mechanical properties as consequence of nitrogen diffusion.     

Microstructure and Wear Resistance of Fe-Cr-C Hardfacing Alloy Reinforced by Titanium Carbonitride

In order to improve the wear resistance of Fe-Cr-C hardfacing alloy, titanium carbonitride was introduced in situ and a TiC-Ti_x(C,N)_y coating was deposited on the surface of ASTM G3101 steel by a gas metal arc welding process. The microstructure and wear resistance of the hardfacing layer were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDS), macroscopic hardness meter, spectrometry, and transmission electron microscopy (TEM). The results show that the hardfacing layers mainly consist of (Cr,Fe)₇C₃, TiC carbides, Ti_x(C,N)_y carbonitrides, and α-Fe (C_0.14Fe_1.86 and C_0.12Fe_1.88 martensite) (BCT) in addition to a low content of retained CFe_15.1 austenite (FCC). The titanium carbonitride–reinforced coating has high hardness and excellent wear resistance under dry sliding wear test conditions.     

Sliding wear behaviour of ZrN and (Zr, 12 wt% Hf)N coatings

In the present study, the sliding wear resistances of ZrN and (Zr, 12 wt% Hf)N coatings deposited on a hardened AISI D2 tool steel by arc-physical vapor deposition (PVD) technique were examined by a ball-on-disc wear tester. Alloying of ZrN coating with 12 wt% Hf did not change the hardness significantly, but achieved an improvement on adhesion strength and dry sliding wear resistance against steel (AISI 52100-55HRC) and Al₂O₃ balls.     

Effect of heat treatment on wear behavior of HVOF thermally sprayed WC-Co coatings

A WC-17Co coating was deposited onto ST37 mild steel substrate using HVOF spray technique and then heat treated at different temperatures in a vacuum chamber. The coatings were then evaluated in the as sprayed and heat treated conditions. Inspections by SEM and phase analysis by XRD indicated that some brittle eta (η) phases were produced at high temperature heat treatments. Generation of these phases increased the coating's hardness and decreased fracture toughness of the coating. Tribological properties were studied under dry condition by using pin on disc machine and diamond metal matrix composite disc as counterface. Wear test results showed that as sprayed deposit had the best wear resistance and its wear mechanism was sharp cutting abrasion. The weight loss in heat treated samples increased by increasing heat treatment temperature and the wear mechanisms gradually changed from cutting to gouging abrasion.     

A study on the wear resistance characteristics of pulse electroforming Ni–P alloy coatings as plated

In this study, attempt has been initiated to investigate the wear resistance of Ni–P alloy coatings manufactured by pulse current (PC) electroforming technology. The wear tests of such plated coatings were carried out at ambient temperature and without lubricants. The parameters of the electroforming experiments include peak current density, duty cycle and pulse frequency. The results of this investigation showed that the internal stress of the PC-deposited Ni–P coating is much lower than that of direct current (DC) deposited Ni–P coating. The analytical results indicate that increasing of the phosphorus content in the layer reduces the hardness of the Ni–P electroformed coatings, and it gradually leads to transformation of the coatings structure from micro-crystalline to nano-crystalline/X-ray amorphous. Wear trace morphology shows that the wear mechanism of Ni–P coatings herein is related to hardness. As the hardness increases, the worn morphology of the coatings changes from with scratches and abrasions to that with the steel debris adhered on the coatings. The wear resistance of Ni–P alloy electroformed layers increases with the hardness of the coatings. The hardness primarily affects the wear resistance of the Ni–P as plated coatings, and the optimum wear resistance of Ni–P coatings can reach 11 times that of Ni coatings.     

Mechanical and unlubricated tribological properties of titanium-containing diamond-like carbon coatings

Titanium-containing diamond-like carbon (Ti-DLC) coatings were deposited on steel with a close-field unbalanced magnetron sputtering in a mixed argon/acetylene atmosphere. The morphology and structure of Ti-DLC coatings were investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy. Nanoindentation, nanoscratch and unlubricated wear tests were carried out to evaluate the hardness, adhesive and tribological properties of Ti-DLC coatings. Electron microscopic observations demonstrated the presence of titanium-rich nanoscale regions surrounded by amorphous carbon structures in Ti-DLC coating. The Ti-DLC coatings exhibit friction coefficients of 0.12–0.25 and wear rates of 1.82 × 10^?9 to 4.29 × 10^?8 mm³/Nm, depending on the counterfaces, sliding speed and temperature. The Ti-DLC/alumina tribo-pair shows a lower friction coefficient than the Ti-DLC/steel tribo-pair under the identical wear conditions. Increasing the test temperature from room temperature to 200 °C reduces the coefficient of friction and, however, clearly increases the wear rate of Ti-DLC coatings. Different wear mechanisms, such as surface polishing, delamination and tribo-chemical reactions, were found in the tribo-contact areas, depending on different wear conditions.     

The influence of heat treatment on the sliding wear behavior of a ZA-27 alloy

The effects of heat treatment, involving solutionizing at temperature of 370 °C for a relatively short period of time (3 or 5 h), followed by quenching in water, on tribological behavior of ZA-27 alloys were examined.Dry sliding wear tests were conducted on as-cast and heat-treated ZA-27 samples using block-on-disk machine over a wide range of applied loads. To determine the wear mechanisms, the worn surfaces of the samples were examined by scanning electron microscopy (SEM). The tribological results were related to the microstructure and mechanical properties.The heat treatment resulted in reduction in the hardness and tensile strength but increase in elongation. The heat-treated alloy samples attained improved tribological behavior over the as-cast ones, both from the aspects of friction and wear. The improved tribological behavior of the heat-treated alloys, in spite of reduced hardness, could be the result of breaking the dendrite structure, when the fraction of interdendrite regions was considerably decreased and a very fine α and η mixture was formed at the same time. The wear response of the samples has been corroborated through characteristics of worn surfaces and dominant wear mechanisms.     

Abrasive wear behavior of sprayed hydroxyapitite coatings by gas tunnel type plasma spraying

Hydroxyapatite (HA) coatings were sprayed using gas tunnel type plasma spraying at different arc currents. Abrasive wear test was carried out for the coatings sprayed at different arc currents under unlubricated conditions in air atmosphere. The abrasive wear rate was measured at different coatings thickness to study the effect of coating thickness on the anti-abrasion resistance of HA coatings. The results showed that the abrasive wear resistance of HA coatings increases as the operating arc current of the plasma torch increases. On the other hand, the abrasive wear rate reaches a minimum value near the substrate with coating thickness less than 50 μm. The results showed that the coating hardness increases in the region near the substrate and increases as the arc current increases. The experimental results indicated that there is a relation between the abrasion resistance and hardness properties of HA coatings.     

Tribological Properties of Arc-Evaporated NbAlN Hard Coatings

Nb_1−x Al _x N hard coatings were synthesised by cathodic arc-evaporation with different Al contents to study its influence on the tribological properties. Ball-on-disc tests at temperatures up to 700 °C were performed and the recorded coefficient of friction was generally in the range from 0.8 to 1.0. Subsequent analysis of the coating wear track and the counterpart wear scar by optical profilometry and Raman spectroscopy revealed details on the wear behaviour of the tested coatings. The best wear performance for the Nb-rich coatings was in the temperature range of 300–500 °C, whereas at the maximum testing temperature the higher oxidation resistance with increasing Al content was beneficial in terms of wear resistance.     

Tribological characterization of tungsten nitride coatings deposited by reactive magnetron sputtering

The structure, hardness, friction and wear of tungsten nitrides prepared by d.c. reactive magnetron sputtering were investigated. The coatings were deposited with different nitrogen to argon ratios; the total pressure was kept constant. The tribological tests were performed on a pin-on-disc tribometer in terrestrial atmosphere with 100Cr6 steel, Al₂O₃ and Si₃N₄ balls as sliding counter-bodies. The wear tracks, the ball-wear scars and the wear debris were analysed by scanning electron microscopy in order to characterize the dominant wear mechanisms.The coatings exhibited different phases as a function of the nitrogen content: films with low N content exhibited the α-W phase; β-W phase was dominant for nitrogen contents from 12 to 15 at.% and β-W₂N was observed for nitrogen content higher that 30 at.%. The mechanical and tribological properties of the tungsten nitride coatings were strongly influenced by the structure. The hardness and the Young's modulus values were in the ranges (29–39 GPa) and (300–390 GPa), respectively; the lowest values correspond to the coatings with the highest nitrogen content. Generally, the friction and wear rate of tungsten nitride coatings sliding against ceramic balls increased with nitrogen content reaching a maximum at 12 at.%; further increase of the nitrogen content led to a decrease of the friction and wear. The sliding with the steel balls did not wear the coatings under the selected testing conditions.     

Influence of aging treatment on microstructure, wear and corrosion behavior of a nickel base hardfaced coating

In this work nickel based hardfacing alloy (Colmonoy 5) was deposited on 316 L (N) stainless steel substrate to study the effects of aging treatment on coating microstructure, wear and corrosion properties. Coatings, deposited through plasma transferred arc (PTA) welding process, were aged at 923 K for 5000 h. Microstructural characterization studies carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the coarsening of dendrites and precipitation of Cr₂₃C₆ particles in the aged coating. The wear behavior of the as deposited and aged coatings was compared in room temperature (RT) and high temperature (823 K) under dry sliding wear condition (pin-on-disc configuration). At RT, aged coating experienced more wear loss when compared to as-deposited. At high temperature, the wear loss was almost same with similar operating wear mechanisms (tribo-oxidation) for both as-deposited and aged coating. From pitting corrosion studies, it was found that aged coatings are more prone to pitting when compared to the as-deposited coatings.     

Development of a new wear resistant coating by arc spraying of a steel-based cored wire

In the present study, a cored wire of 304 L stainless steel as sheath material and NiB and WC-12Co as filler materials was designed and deposited to produce a new wear resistant coating containing amorphous phase by arc spraying. The microstructure of the coating was investigated. The porosity and hardness of the coating were determined. The wear performance of the coating was evaluated. The XRD and TEM analyses showed that there are high volume of amorphous phase and very fine crystalline grains in the coating. DTA measurements revealed that the crystallization of the amorphous phase occurred at 579.2°C. Because metallurgical processes for single droplets were non-homogenous during spraying, the lamellae in the coating have different hardness values, which lie between about 700 and 1250 HV_{100 g}. The abrasive wear test showed that the new Fe-based coating was very wear resistant.