High Temperature Tribometer Research Articles

Tribological Investigations of TiC+a-C:H Coatings Manufactured on X38CrMoV5-1 Steel Using PVD Technology

X38CrMoV5-1 steel is a typical tool steel commonly used in forging and plastic moulding industry for production of ejectors, slides, dies, etc. In plastics moulding a lot of these parts sustain relative movement. Because of this, some seizing or micro-welding may appear, especially when lubrication is not used. For many years, the different types of protective coatings were developed to avoid such problems. Most of the obtained solutions relate to the manufacturing of low friction coatings obtained by different nitriding processes and by CVD or PVD methods. In this article, the friction coefficients and the wear resistances of TiC+a-C:H protective coatings manufactured on X38CrMoV5-1 steel samples by using PVD technology are studied. The investigations are based on tribometer tests in different temperature conditions. The process of deposition of PVD coatings was realized by using multisource, hybrid factory-scale equipment of type URM 079. This equipment allows for deposition of coatings by a physical method. The tribological tests were performed using a precision high temperature tribometer under ambient and high temperature conditions with a steel and corundum balls as a counter-samples. In this paper, the results of these tribological tests are presented. It is shown that the measured friction coefficient of steel samples with PVD coatings is significantly lower than the friction coefficient of uncoated steel. It is also shown that X38CrMoV5-1 steel samples with manufactured TiC+a-C:H coatings are characterized by a very low friction coefficient and high wear resistance.

Wear Resistance of Al<sub>2</sub>O<sub>3</sub>, Al<sub>2</sub>O<sub>3</sub>-40wt.%TiO<sub>2</sub> Coatings Prepared by Plasma Spraying on H13 Hot-Worked Die Steel

Al2O3 and Al2O3-40wt.%TiO2 ceramic coatings on H13 hot-worked die steel have been prepared by plasma spraying, and then the microstructure, micro-hardness as well as wear resistance of the prepared coatings have been investigated by means of x-ray diffraction (XRD), scanning electron microscope (SEM), Vickers hardness tester and ball-on-disk high temperature tribometer. The results showed that the plasma sprayed ceramic coatings are of higher hardness and wear resistance than H13 hot-worked die steel.

Tribological behavior of NiAl matrix composites with addition of oxides at high temperatures

NiAl, NiAl–Cr–Mo alloy and NiAl matrix composites with addition of oxides (ZnO/CuO) were fabricated by powder metallurgy route. It was found that some new phases (such as NiZn3, Cu0.81Ni0.19 and Al2O3) are formed during the fabrication process due to a high-temperature solid state reaction. Tribological behavior was studied from room temperature to 1000°C on an HT-1000 ball-on-disk high temperature tribometer. The results indicated that NiAl had high friction coefficient and wear rate at elevated temperatures, while incorporation of Cr(Mo) not only enhanced mechanical properties evidently but also improved high temperature tribological properties. Among the sintered materials, NiAl matrix composite with addition of ZnO showed the lowest wear rate at 1000°C, while CuO addition into NiAl matrix composite exhibited the self-lubricating performance and the best tribological properties at 800°C.

Friction and wear behaviors of WC/Co cemented carbide tool materials with different WC grain sizes at temperatures up to 600 °C

The friction and wear behaviors of WC/Co cemented carbide tool materials with average WC grain sizes ranging from 0.6 to 2.2μm were evaluated in ambient air at temperatures up to 600°C using a ball-on-disk high temperature tribometer. The friction coefficient and wear rate were measured. The microstructural changes and the wear surface features of the WC/Co cemented carbides were examined by scanning electron microscopy. Results showed that the friction coefficient of WC/Co cemented carbides decreased with the increase of test temperature. All the tested samples showed the highest friction coefficient when sliding at 200°C, and exhibited the lowest friction coefficient in the case of 600°C. The wear rate of WC/Co cemented carbides increased with the increase of test temperature. The cemented carbide with the smallest WC grain size showed improved wear resistance at temperature up to 600°C, which corresponds to its higher value of hardness. The difference of the worn surface features of the WC/Co cemented carbide after sliding at different temperature is related to the chemical transformation during sliding wear tests. Abrasion and grain cracking seemed to be the main wear types at temperature less than 200°C, the wear owing to binder removal by plastic deformation and grain pull out were suggested to be the main wear mechanism at intermediate temperature, while the mechanism of oxidative wear dominated at 600°C.

Tribological Properties of Fe-Cu-MoS<sub>2</sub> and Self-Lubricating Behaviors

The Fe-Cu-MoS2composites with different adding amount of MoS2as lubricant were prepared by induction sintering method. Their mechanical and tribological properties from room temperature (RT) to 800°C were tested by universal testing machine and high temperature tribometer. The effects of amounts of MoS2, temperature, load and sliding distance on the friction and wear properties of composite were discussed. The structure of the composite was analyzed by XRD and worm surface morphologies were observed by SEM. It was found that MoS2was decomposed during the hot-press sintering process. Meanwhile, solid solution alloy of Mo and Fe, and sulfides were formed in composite, which were responsible for low-friction and high wear-resistance at elevated temperature, respectively. Hardness and anti-compress strength can be improved by adding 8 wt. % MoS2. The friction coefficients and wear rates of composites decrease with the increase of adding amount of MoS2until a critical value of 8 wt. %. The composite with 8 wt. % MoS2shows the optimum tribological properties over the temperature range of RT~800°C.

Friction and wear behavior of polycrystalline diamond at temperatures up to 700 °C

The friction and wear behavior of the polycrystalline diamond (PCD) were evaluated in ambient air at temperatures up to 700 °C using a ball-on-disk high temperature tribometer. The wear surface features of the PCD were examined by scanning electron microscopy. Energy dispersive X-ray analysis was used to investigate the chemical composition. XRD experiments were performed to study the crystal structure of the PCD specimens at different temperatures. Results showed that the friction coefficient of the PCD is different depending on the temperature, and decreases with the increase of temperature. The PCD exhibited the lowest friction coefficient of approximately 0.16 in the case of 700 °C sliding operation. The difference of the worn surface features of the PCD after sliding at different temperatures is related to the chemical transformation during sliding wear tests. The surface damage of the PCD appears to happen around 600 °C accompanied by extensive Co phase extrusion out of PCD. Numerous micro-cracks both at the grain boundaries and in the grains are observed with the increase of temperature to 700 °C. At this temperature, surface graphitization of diamond is to be expected, and the formation of graphite on the wear track is beneficial to the reduction of friction coefficient.

Structure and tribological properties of AlCrTiN coatings at elevated temperature

In this study, we analyzed the high temperature tribological behavior of AlCrTiN coatings deposited on WC substrates by low cathodic arc technique. The coatings chemical composition, Al 31at.%, Cr 16at.%, Ti 7at.% and N 46at.%, and the bonding state were evaluated by X-ray photoelectron spectroscopy. The mechanical properties of the coatings were studied by scratch-test and nanohardness depth sensing indentation. The morphology of the coatings surface, ball scars, wear tracks and wear debris as well as the oxidized samples was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The structure was analyzed using X-ray diffraction (XRD). Wear testing was carried out using a high temperature tribometer (pin-on-disc) with alumina balls as counterparts. The evaluation of the friction coefficient with the number of cycles (sliding distance) was assessed at different temperatures and the wear rates of the coatings and balls were determined; the maximum testing temperature was 800°C. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500°C and then decreased, whereas the wear rate was negligible up to 600°C and increased significantly at higher temperatures.

Effects of carbon content on the high temperature friction and wear of chromium carbonitride coatings

Chromium nitride-based coatings are often used in application at high temperature. They possess high wear and oxidation resistance; however, the friction coefficient is typically very high. Therefore, we doped CrN coatings by carbon with the aim to improve tribological properties at elevated temperature, particularly to lower the friction. CrCN coatings were prepared by cathode arc evaporation technology using constant N 2 flow and variable C 2H 2 flow. The coatings with a thickness of 3–4 μm were deposited on hardened steel substrates and high-temperature resistant alloy. The carbon content varied from 0 at.% (i.e. CrN) up to 31 at.%. The standard coating characterization included the nano-hardness, adhesion, chemical composition and structure (including hot X-ray diffraction). Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 700 °C. The coatings with carbon content 12–31 at.% showed almost identical tribological behaviour up to 700 °C.

Effect of La2O3 on microstructure, mechanical and tribological properties of Ni-W coatings

In this paper, a Ni-W-La2O3 composite coating was prepared by the electrodeposition method. Microhardness tester and environmental scanning electron microscope equipped energy dispersive spectroscopy were employed to investigate the microhardness and the surface morphology of the composite coatings respectively, and the high temperature friction behavior and corrosion resistance of the coatings against molten glass were investigated by using a high temperature tribometer. The results show that La2O3 can refine the microstructure effectively, and make the element distribution uniform, which leads to the increase of average microhardness. La2O3 particulates can reduce the friction coefficient between the composite coating and glass during the sliding process at about 973 K largely, and the corrosion resistance of the La2O3 added Ni-W coatings is effectively improved compared with that of the non-added one, furthermore the mechanism of friction-reducing and anti-corrosion is also discussed.

High-temperature tribological behaviors of Ti 2AlNb-based alloys by plasma surface duplex treatment

Plasma tungstening followed by carburization (W-C duplex treatment) was performed on the Ti 2AlNb-based ( O phase) alloy by using the double glow plasma process to enhance its wear resistance. The microstructure and high-temperature tribological behaviors of the un-treated and W-C duplex-treated samples were investigated. The results show that the duplex-treated layer is mainly composed of W 2C or W 6C 2.54 phases and the contents of W and C elements in the alloyed layer change gradually along the depth by surface plasma duplex treatment. The diffusion depth of W is about 12 μm, while the carbon atoms most exist in the depth more than 12 μm. High temperature tribometer tests indicate that the friction coefficient of the W-C duplex-treated layer is approximately 1/6 that of substrate. The wear rate of the duplex-treated layer is about 28% that of the untreated one. So, plasma surface W-C duplex treatment can obviously improve the high-temperature tribological resistance of Ti 2AlNb-based alloy. The tribological mechanism of the duplex-treated layer is discussed by dividing the friction process of the duplex-treated layer into three fluctuate stages. The first stage is the formation of oxide film between W-C duplex-treated layer and counterface. The second stage is the detachment of oxide film, acting as “the third body”. The last stage is the period that the friction and wear occur between the compact particle layer and counterface.

Effect of nano-sized CeF 3 on microstructure, mechanical, high temperature friction and corrosion behavior of Ni–W composite coatings

Ni–W–CeF 3 composite coatings were prepared by electrodeposition in a Ni–W plating bath containing CeF 3 nano-particles. The shape and size of the CeF 3 nano-particles and the surface topography of the composite coatings were observed using an environmental scanning electron microscope, and the component and structure analysis was characterized by means of XRD. A microhardness tester was employed to investigate the microhardness of the coatings. The high temperature friction behavior and corrosion resistance of the coatings against molten glass were investigated by using a high temperature tribometer. It was found that the CeF 3 nano-particles appeared in the coatings as microspheres of a diameter less than 50 nm. The addition of CeF 3 nano-particles led to changes in morphologies of the composite coatings by refining the size of crystalline bulks. Therefore, the Ni–W–nanoCeF 3 composite coatings had more compact and fine granular morphologies. The co-deposited CeF 3 nano-particles were uniformly distributed in the Ni–W matrix and had contribution to greatly increasing the microhardness, high temperature tribological and anti-corrosion properties of the Ni–W alloy, furthermore the mechanism of anti-friction and anti-corrosion is discussed.

Tribological and anti-corrosion properties of Ni–W–CeO 2 coatings against molten glass

Composite plating was used to prepare Ni–W infused rare earth oxide CeO 2 composite coatings. The high temperature friction behavior and corrosion resistance of the coatings against molten glass were investigated by using a high temperature tribometer. A microhardness tester and an environmental scanning electron microscope equipped energy dispersive spectroscopy were employed to investigate the microhardness and the surface morphology of the composite coatings respectively. The results show that the brittle fracture, high temperature tribological properties and the corrosion resistance of Ni–W infused CeO 2 coatings are superior to those of a standard Ni–W coating. CeO 2 particles decrease the friction coefficient from nearly 0.5 to about 0.25 during the composite coatings sliding against the molten glass at about 973 K, and proper quantities of CeO 2 decrease the variation of the friction coefficient value. Furthermore, CeO 2 can improve the corrosion resistance of the Ni–W coatings at high temperature effectively.

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10 −6 mm 3/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS 2 composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS 2/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.

Finite element analysis and experimental confirmation of warm hydroforming process for aluminum alloy

Abstract The hydroformability of an extruded aluminum alloy at elevated temperatures was investigated in this study. To properly analyze the process, it is necessary to account for the variation in the mechanical properties of the aluminum that depend on the forming temperature and the heat conduction during warm hydroforming. Simulations coupling the plastic deformation and temperature distribution in the warm hydroforming process were performed and compared with experimental data. The multi-purpose finite element code DEFORM-2D can handle the calculations, but requires significant computation time if contact heat transfer between the die, the tube, and the pressure medium occurs. Experiments were conducted with a high temperature tribometer (pin-on-disk) allowing the measurement of the friction coefficient for the aluminum alloys at several temperatures. These friction results are applied to the coupled simulation. From the simulations, the optimal process parameters, such as internal pressure and preset temperature on hydroformability, can be found. The comparison of the finite element analysis with the experimental results shows that the hydroformability trends (given by bulge height) and the temperature distribution of the tube specimen agree well with one another. The finite element results also showed that the temperature distribution did not strongly affect the hydroformability of the aluminum tubes.

Friction and wear behaviour of CrN coating at temperatures up to 500 °C

CrN coatings prepared by low arc deposition technology on hardened steel substrates were studied in this paper. Wear testing was done using a high temperature tribometer (pin-on-disc); the maximum testing temperature was 500 °C in order to prevent significant softening of substrate. Evaluation of friction coefficient with the number of cycles was measured at different temperatures and the wear rates of coatings and balls were determined. Three different materials were used as counter-parts: 100Cr6 bearing steel, Si 3N 4 and Al 2O 3 balls with a diameter of 6 mm. The coating microstructure was studied by X-ray diffraction (XRD) measured in situ up to 600 °C; the chemical composition was obtained by energy dispersive X-ray analysis (EDX). Mechanical properties of these coatings were studied by scratch and microhardness testing. Morphology of coating surface, ball scars, wear tracks and wear debris were examined by scanning electron microscopy (SEM). The experiments have shown strong dependency of tribological parameters on temperature. Wear of CrN coating sliding against the 100Cr6 ball was not measurable. Generally, the wear rate of coating increases with temperature when sliding with ceramic balls. The wear debris analysis has shown that the tribochemical wear is dominant at high temperature (Si 3N 4 balls), while the sliding process with the Al 2O 3 balls can be described as a three-body wear with the wear particles consisting mainly of chromium oxides conglomerated into relatively homogenous layer protecting coating from rapid wear. The average dimension of wear particles decreases with temperature, while the protecting layer thickness increases.

The Influence of Chemical Alloying on the High Temperature Wear Resistance of H-Free DLC Coatings

A commercial RF-sputtering deposition rig was employed to deposit H-free diamond-like carbon (DLC) coatings. The influence of alloying elements such as Ti and Si on the structure, mechanical and tribological properties of the coatings was investigated. The coating was observed in cross section and in plan view with SEM, TEM and AFM. Because of the highly-ionized plasma generated by the RF-powered glow discharge, ion bombardment suppresses the formation of a columnar structure regardless of the composition of the coatings. The method produces featureless microstructures and smooth surfaces. TEM investigations confirm that no crystalline phases form in the coatings regardless of the presence of considerable concentrations of Ti and Si. Tribological tests were performed with a high-temperature tribometer in a ball-on-disk configuration, using coated disks and different materials for the ball countepart. At ambient T the sliding friction coefficient decreases as the concentration of alloying elements increases. Nevertheless, high-T tribotests with a constant thermal load showed that the presence of alloying elements decreases the thermal stability of the coatings. For each coating a temperature exists above which a sudden increase of friction coefficient is observed, with subsequent detachment and failure of the coatings. The mechanism of disruption of the self-lubrication effects is identified and the influence of the alloying elements on the thermal degradation of tribological performance of the coatings is discussed.

Influence of oxides on friction in hot rolling: Experimental investigations and tribological modelling

In a hot strip mill, the contact established between the hot strip and the work rolls in the first times of running has to be oxide on oxide to allow the strip to be pulled in the roll bite. The oxide scale formed on the roll is submitted to thermo-mechanical stresses and grows up. From a critical thickness, the scale spalls and causes some superficial damage to the rolls and to the strip. For the roll manufacturers as well as for the steel makers, it is essential to understand the influence of the creation and the growth of such a scale on friction in order to control the antagonist superficial damage and consequently to reduce the running cost of the mill. The present work aims to study the interaction between the oxides formed on a work roll grade and the coefficient of friction established with a strip steel usually rolled by this roll grade. A high temperature tribometer was set up in a pin-on-disc configuration. A previous part of study showed that friction was dependent on the nature of antagonist materials and the thermal transfer. We observed the establishment of a running-in period in the case of a metal-on-oxide initial contact between the pin and the disc which corresponds to the creation of an oxide layer on the pin. The mechanisms that allowed the formation of this scale were determined. SEM observations in conjunction with EDS analysis, both inside and outside the contact area on both antagonists, led to the development of a phenomenological model explaining the creation and the movement of oxide debris in the contact.

Elevated temperature tribological behavior of non-hydrogenated diamond-like carbon coatings against 319 aluminum alloy

Diamond-like carbon (DLC) coatings are promising candidates for dry machining of aluminum alloys since in ambient conditions aluminum has much less tendency to adhere to the DLC coating surfaces compared to other hard coatings such as TiN, TiAlN and CrN. In an attempt to better understand the tribological properties of the DLC coatings for cutting tool coating applications, non-hydrogenated DLC coatings were produced by magnetron sputtering and their elevated temperature friction and wear behavior were studied. DLC coated M2 tool steel discs were tested against 319 Al pins using a high-temperature tribometer. Counterface materials of tungsten carbide (WC) and sapphire (Al 2O 3) balls were also tested for comparison. Tests were done at 25, 120, 300 and 400 °C in air. The wear resistance of the DLC coating has been found to be poor at elevated temperatures. The mechanisms that provide the high wear resistance of the coating in ambient temperature cease to operate at temperatures as low as 120 °C. Annealing at elevated temperatures in air causes oxidation of the coating. Although much softer than WC and sapphire, the 319 Al alloy causes the most severe wear to the DLC coating. A two- and three-body abrasive wear model is proposed to explain this surprising observation.

The tribological characteristics of TiCN coating at elevated temperatures

The tribological behaviour of TiCN coating prepared by unbalanced magnetron sputtering is studied in this work. The substrates made from austenitic steel were coated by TiCN coatings during one deposition. The measurements were provided by high temperature tribometer (pin-on-disc, CSM Instruments) allowing measuring the dependency of friction coefficient on cycles (sliding distance) up to 500 °C. The evolution of the friction coefficient with the cycles was measured under different conditions, such as temperature or sliding speed and the wear rate of the ball and coating were evaluated. The 100Cr6 balls and the Si 3N 4 ceramic balls were used as counter-parts. The former were used at temperatures up to 200 °C, the latter up to 500 °C. The wear tracks were examined by optical methods and SEM. The surface oxidation at elevated temperatures and profile elements composition of the wear track were also measured. The experiments have shown considerable dependency of TiCN tribological parameters on temperature. Rise in temperature increased both friction coefficient and the wear rate of the coating in case of 100Cr6 balls. The main wear mechanism was a mild wear at temperatures up to 200 °C; fracture and delamination were dominating wear mechanisms at temperatures from 300 to 500 °C.

High-temperature tribological characterization of zirconium nitride coatings

Zirconium nitride coatings were deposited onto medium carbon steel (AISI 1045) substrates. The coatings were produced commercially by a closed field unbalanced magnetron-sputtering ion-plating deposition process. The unlubricated friction and wear behavior of coatings were evaluated at room temperature and during exposure at temperatures of 400 and 700 °C, respectively. Adhesion, composite microhardness, and other fundamental coating characteristics, such as thickness, surface morphology, microstructure, and chemical composition were determined before and after exposure to the test temperature. Methods such as ball cratering, surface profilometry, and scanning electron microscopy (SEM) were also used. For evaluation purposes, the wear behavior was studied under a load of 2 N, using a ball-on-disc high-temperature tribometer and Al 2O 3 balls (6-mm diameter) as counterpart. The results indicated that the test temperature affected considerably the wear performance of ZrN coatings. The exposure of these coatings at high temperature caused an increase in the friction coefficient, and this increase in temperature was accompanied by a noticeable decrease in the composite hardness of the system coating–substrate. After the coating exposure at 700 °C, delamination of the coatings occurred mainly due to the volume change, which took place as result of an intensive oxidation process of the unreactive zirconium microdroplet particles, previously found in various parts of their surface. The SEM observations showed the coating fracture and the loss of adhesion between the coating and the substrate. The best tribological performance was obtained for the coating tested at room temperature, which had the maximum composite Vickers hardness and presented the lowest friction and the highest critical load ( L c) values. Results of the friction coefficients values, the wear volumes, debris composition of the heat-exposed and -unexposed samples are compared. The mechanisms of the wear process and adhesion failure at various test temperatures are explained.