Unlubricated Conditions Research Articles

Effect of regular surface textures generated by laser on tribological behavior of Si3N4/TiC ceramic

Two kinds of regular micro-grooved textures with different geometric characteristics were fabricated on the surfaces of Si3N4/TiC ceramics by Nd:YAG laser; friction and wear tests were carried out to investigate the tribological properties of these textured ceramics in unlubricated and MoS2 lubricated conditions. The wear surfaces of the textured ceramics and the balls were examined by SEM and the possible friction reduction and wear resistant mechanisms were discussed. The results show that the friction coefficient of the textured ceramics was reduced compared with the smooth ceramics among all the experiments, the wavy grooves are the most effective in the friction-reduction among the patterns investigated, and the wear life of textured ceramics can be increased in MoS2 lubricated condition. Furthermore, it is observed that the textured ceramics produce more abrasive wear on the ball specimens in unlubricated friction, while it reduces the wear of balls in MoS2 lubricated condition. The main effect mechanism of textures is to capture debris and reduces the contact area of couples in unlubricated condition, and increase lubricant supply by reservoir creation and form the continued lubricating film on the surfaces of spacing between the textures in MoS2 solid lubricated condition.

Effect of Reciprocating Sliding Speed on the Tribological Performance of Nano SiCp Reinforced Ni-Metal Matrix Composites Produced by Electrocodeposition

In the present work, Ni/SiC metal matrix composite (MMC) coatings were prepared from a modified Watt's type electrolyte containing nano-SiC particles by direct current (DC) plating method to increase wear resistance of the electro co-deposited Ni. SiC nano particles with average particle size of 0, 1-1 microm were co-deposited with nickel matrix on the steel substrates. For this purpose, several studies were carried out to optimize deposition parameters for specific applications. The depositions were controlled to obtain the specific thickness (between 175-200 microm) and particle volume fraction in the matrix (between 0.03 and 0.10). The hardness of the resultant coatings was measured and found to be 280-571 HV depending on the particle concentration in the electrolyte and therefore, particle volume in the Ni matrix. The tribological tests were performed by a reciprocating ball-on disk apparatus sliding against M50 steel ball (Ø10 mm). All the friction and wear tests were performed under the unlubricated conditions at room temperature and in the ambient air (relative humidity 55-65%). The wear tests were carried out at different sliding velocities of 50 mm/s, 100 mm/s and 150 mm/s by using a constant dead load of 1.0 N. It was detected that increasing sliding speed resulted to increase wear rate but decreasing friction coefficient due to change in wear mechanism. Increasing sliding speed showed formation of tribo induced oxides up to 20 g/l SiC(p) in the electrolyte and wear mechanism was controlled by temperature induced fatigue wear. Further increase in the SiC(p) in the electrolyte caused an abrasive type of the wear.

Wear behaviour of nanocrystallised Hadfield steel

A thick nanocrystalline surface layer with gradient nanostructure was produced on Hadfield steel through high-speed pounding (HSP) for 240min. The grain sizes in the surface layer decreased to about 25nm. To study the wear behaviour of the nanocrystallised Hadfield steel, three types of samples (a nanocrystallised sample (NS), an untreated sample (US) and a deformed sample (DS) had the same hardness as NS) were studied by using a pin-on-disc type tribometer under un-lubricated conditions at 25°C, 300°C, and 500°C. The experimental results show that the coefficient of friction and wear weight loss of the NS are lower than for the DS and the US and that the wear resistance is remarkably improved. Compared with the US, the enhanced wear properties of the NS must be attributed to the increased hardness, which improves the resistance to plastic deformation and wear removal. However, compared with the DS, after surface nanocrystallisation of the NS, a transition occurs in the dominant wear mechanism from adhesive wear to slight abrasive wear. Therefore, the advantages realised in the wear properties of the NS may be attributed to the enhancement of the surface activity by grain nanocrystallisation, which results in improvements in the formation of the oxide layer. The roughness of the worn surfaces shows that both the wear scar width and depth of the worn surface of the NS are much smaller than those found in the DS and the US. Finally, a wear model of nanocrystallised material was established.

Tribological behavior of SiC coating on C/C composites against SiC and WC under unlubricated sliding

In this work, SiC coatings were prepared by chemical vapor deposition on carbon/carbon (C/C) composites. The microstructure and mechanical characteristics of the as-prepared SiC coatings were investigated by scanning electron microscopy, X-ray diffraction and nano-indention. The tribological behavior of SiC coating was evaluated by a tribometer with a ball-on-disk configuration, applying SiC and WC balls as counterparts with normal contact loads of 2N, 10N and 20N under unlubricated condition. The results of tribological tests show that the friction coefficient of the SiC coating against the SiC ball (SiC/SiC coupling) is lower than that of the SiC coating against the WC ball (SiC/WC coupling) at all tested loads, and the wear volume of SiC coating for the SiC/SiC coupling is lower than that for the SiC/WC coupling by an order of magnitude. A silica film was formed between the contact surfaces for SiC/SiC coupling at 10 and 20N, which could act as lubrication layer. However, the dominant wear mechanisms of SiC/WC coupling were a mixture of abrasive and fatigue wear.

Lubricity of environmentally friendly HFO-1234yf refrigerant

Global warming concerns have triggered the interest in alternative refrigerants for air-conditioning and refrigeration compressors. Newly developed refrigerant HFO-1234yf is an attractive and environmentally friendly candidate to replace existing hydrofluorocarbon refrigerants, such as R-134a. Herein, the tribological compatibility of gray cast iron material with this new refrigerant was investigated under aggressive unlubricated conditions. HFO-1234yf exhibits excellent performance compared to R-134a due to the formation of a fluorine-containing protective tribolayer on the topmost surface as X-ray photoelectron spectroscopy (XPS) analysis, inside and outside the wear tracks, revealed. The morphology of the layer was also studied using scanning electron microscopy (SEM) studies.

Scratch resistance and tribological properties of DLC coatings under dry and lubrication conditions

Scratch resistance and tribological properties of hydrogenated and hydrogen free diamond like carbon (DLC) coatings were investigated in ambient atmosphere under unlubricated and lubricated conditions using layers of oleic (C18H34O2) and linoleic acid (C18H32O2). Scratch resistance property improved in hydrogenated DLC while using linoelic and oleic acids compared to unlubricated condition. Coefficient of friction (CoF) was found to decrease under ambient dry conditions, while under lubrication condition, it was found to increase with normal load. At low load of 1N, hydrogenated and hydrogen-free coatings show a super low CoF of 0.001 and high wear resistance with oleic acid.

Friction and wear behavior of nanosilica-filled epoxy resin composite coatings

Hydrophilic silica nanoparticles (abridged as nano-SiO2) surface-capped with epoxide were dispersed in the solution of epoxy resin (abridged as EP) in tetrahydrofuran under magnetic stirring. Resultant suspension of nano-SiO2 in EP was then coated onto the surface of glass slides and dried at 80°C in a vacuum oven for 2h, generating epoxy resin-nanosilica composite coatings (coded as EP/nano-SiO2). EP coating without nano-SiO2 was also prepared as a reference in the same manner. A water contact angle meter and a surface profiler were separately performed to measure the water contact angles and surface roughness of as-prepared EP/nano-SiO2 composite coatings. The friction and wear behavior of as-prepared EP/nano-SiO2 composite coatings sliding against steel in a ball-on-plate contact configuration under unlubricated condition was evaluated. Particularly, the effect of coating composition on the friction and wear behavior of the composite coatings was highlighted in relation to their microstructure and worn surface morphology examined by means of scanning electron microscopy. Results indicate that EP/nano-SiO2 composite coatings have a higher surface roughness and water contact angle than EP coating. The EP-SiO2 coatings doped with a proper amount of hydrophilic SiO2 nanoparticles show lower friction coefficient than EP coating. However, the introduction of surface-capped nanosilica as the filler results in inconsistent change in the friction coefficient and wear rate of the filled EP-matrix composites; and it needs further study to achieve well balanced friction-reducing and antiwear abilities of the composite coatings for tribological applications.

High temperature tribological behavior of nanostructured and conventional plasma sprayed alumina-titania coatings

Alumina-titania coatings are used where a high wear and oxidation resistances are required. These coatings are usually deposited by thermal spraying. The use of nanoparticles as feeding powders can lead to improved properties if some technological problems are solved. The small size of the nanoparticles makes necessary to prepare agglomerates able to be sprayed by conventional equipments. The plasma spray parameters should be chosen to maintain the starting nanostructure in the final coating. This can be achieved if the coating contains partially melted particles. In this work the mechanical and high temperature wear behaviour of Al2O3-13%TiO2 nanostructured coatings was compared to that of the conventional ones. Microstructural characterization was performed using scanning and transmission electron microscopy and X-rays diffraction techniques. Mechanical properties such as Young's modulus, hardness and fracture toughness were determined by depth sensing indentation. Wear rates and friction coefficients were measured by means of a Pin on disc machine in which both counterparts were made of Al2O3-13%TiO2. Experiments at different loads under unlubricated conditions, without elimination of the wear debris were carried out. Although the mechanical properties are slightly higher in the nanostructured coatings, they exhibit a much better wear behaviour under all the testing conditions.

Understanding the dry sliding wear behaviour of atmospheric plasma-sprayed rare earth oxide coatings

In this paper, the friction and wear behaviours of Yttria Stabilized Zirconia (YSZ) coatings; Lanthanum Zirconate (LZ) coatings and Inconel 738 base material (BM) sliding against a sintered tungsten carbide surface were studied and compared under unlubricated conditions. Sliding experiments were performed in a pin-on-disc configuration. Further, relationships among porosity, normal load and disc speeds with respect to wear loss were derived by using the response surface methodology, and the wear mechanisms were discussed adequately. It was found that the wear resistance of the ceramic coatings gets deteriorated with the increase in the percentage volume of porosity.

Sliding wear behavior of gas tunnel type plasma sprayed Ni-based metallic glass composite coatings

Ni60Nb20Zr20 glass composite coatings were successfully produced in a single step using gas tunnel type plasma spraying torch. The resultant phases and structures obtained were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques, respectively. The sliding wear behavior of the developed metallic glass composite coatings was evaluated under unlubricated condition using Ball-on-Disk (BOD) tribometer. The results showed that minimum amount of metal oxides and intermetallic phases can be obtained in the coatings at intermediate plasma current only. It is evident that the sliding wear rate of the metallic glass composite coating varied with the loading conditions and its amorphous-crystalline composition. The coating produced at a plasma current of 300 A gives the minimum wear rate and friction coefficient during sliding.

Adhesion at oxide layer/substrate interface during sliding wear

Protective oxide film plays an indispensable role in reducing wear during metal-metal sliding contact, and its adherence to the substrate and stability is a major issue. This review examines some prevalent views proposed in literature on the adhesion between protective oxide layer formed during sliding wear and the steels and cast irons substrate under unlubricated condition. Attempt has been made to correlate some of them to be more connected and take them into account in a broader sliding condition in some sections in this review. Although this review is more relevant to the steels and cast irons as the tested materials during unlubricated unidirectional sliding, other alloys such as aluminium and Ni-based alloys would be hopefully to some extent associated.

마그네슘 압출용 금형의 내마모성 향상을 위한 CrN, TiN 코팅

The friction and wear characteristics of CrN and TiN coatings on SKD61 which is mold material using for extrusion of AZ80 magnesium alloy were investigated. The coatings were deposited by the arc ion-plating method, and the thickness were about <TEX>$3.59{\mu}m$</TEX> and <TEX>$3.28{\mu}m$</TEX>, respectively. Reciprocating friction wear tests were conducted by varying pin load and temperature of counter substrate at un-lubricated condition. The pin loads were 11, 15 and 19 kgf, and the substrate temperatures were room temperature and <TEX>$120^{\circ}C$</TEX>. CrN coating which has a lower friction coefficient and a smaller adhesive wear with AZ80 magnesium alloy showed better wear resistance than TiN coating.

Microstructure and friction performance of copper film fabricated by ion implantation assisted electroless plating on PTFE

The polytetrafluoroethylene (PTFE), which was implanted with Ni ion to different energy and doses, fabricated metallic structures by selective electroless copper plating. The characteristic and microstructure of the copper film were studied using SEM and X-ray diffraction. Friction performance of the interface between copper film and basal body of PTFE was tested with a CETR UMT-2 (CETR Co., Campbell, CA, USA) multifunction micromechanics instrument. The test loads were 10, 20 and 40 N, while the line velocity was 8 mm s−1, and the frequency of data acquisition was 1 Hz. The Ni ion implantation replaces the complicated electroless plating surface pretreatment, and it is an assisted technique of electroless plating of copper on the surface of PTFE and plate Cu directly on its surface. Continuous, prepressing and uniformity plating was obtained with proper technique parameters and the dosage of Ni+. The frictional performance comprehensive property of copper film was remarkably influenced by different plating methods, annealing treatment and testing loads under unlubricated condition. The friction coefficients and wear rates changed with the varied load. Annealing treatment improves the tightness and uniformity of the copper film, while it decreases its cavity. Friction performance of copper film was thus increased. The mechanisms of friction and wear of copper film under different test conditions are also discussed.

Comparison of high temperature wear behaviour of plasma sprayed WC–Co coated and hard chromium plated AISI 304 austenitic stainless steel

The wear behaviour of plasma sprayed coating and hard chrome plating on AISI 304 austenitic stainless steel substrate is experimentally investigated in unlubricated conditions. Experiments were conducted at different temperatures (room temp, 100°C, 200°C and 300°C) with 50N load and 1m/s sliding velocity. Wear tests were carried out by dry sliding contact of EN-24 medium carbon steel pin as counterpart on a pin-on-disc wear testing machine. In both coatings, specimens were characterised by hardness, microstructure, coating density and sliding wear resistance. Wear studies showed that the hard chromium coating exhibited improved tribological performance than that of the plasma sprayed WC–Co coating. X-ray diffraction analysis (XRD) of the coatings showed that the better wear resistance at high temperature has been attributed to the formation of a protective oxide layer at the surface during sliding. The wear mechanisms were investigated through scanning electron microscopy (SEM) and XRD. It was observed that the chromium coating provided higher hardness, good adhesion with the substrate and nearly five times the wear resistance than that obtained by uncoated AISI 304 austenitic stainless steel.

Need for optimization of graphite particle reinforcement in ZA-27 alloy composites for tribological applications

Abstract The objective of present work is to investigate the effect of macroscopic graphite particles on mechanical, wear and thermal behavior of ZA-27 alloy composites. Compo casting technique was used to prepare the composites in which the graphite particles were used to reinforce ZA-27 alloy. Wear tests were conducted using pin on disc apparatus under unlubricated conditions at various load and speeds. Damping capacity, stress–strain and amplitude behaviors were studied using dynamic mechanical analyzer at various temperatures from ambient to 300 °C. Thermal conductivity and diffusivity were found using laser flash apparatus and specific heat values were found using simultaneous thermal analyzer. It was observed that the tribological property improves with the addition of graphite particle. However with observations of other parameter, it is clear that reinforcement percentage need to be optimized based on application requirement in order to have better performance and the composites can be used as structural material in various applications like bearings and thermal control functions.

Coining Test for Evaluation of Tool Performance

The performance of M2 tool steel without any special coating on a set of cold formable steels is evaluated in this work using the coining technique. Cylindrical specimens were prepared from spheroidize annealed SAE 1012, 1020, 5120 and 1050 steels (representatively covering the whole gamut of cold workable steels) with an aspect ratio of do/ho = 1.5 (Where do being the original diameter and ho being the original height). These annealed materials were measured for their initial roughness as well flatness values. They are compressed to true strains of 0.1, 0.2, 0.3 and 0.4 under unlubricated and phosphated conditions of the chosen work materials. For each of the specimen tested, the results of this study are presented and discussed. The surface roughness, crown height and barreled volume were evaluated. The study shows that the lubricated work pieces were found to have lower crown heights, smaller barreled volumes, lesser surface roughness compared to unlubricated samples.

Influence of small amount of sintering additives on unlubricated sliding wear properties of SiC ceramics

Fully densified SiC ceramics were developed from commercially available β-SiC powders using small amount (3 wt%) of AlN–Sc 2O 3 or AlN–Y 2O 3 additives by hot pressing at 2050 °C for 6 h in nitrogen atmosphere, and their wear properties were investigated by subjecting to self-mated sliding at different loads (1, 6 and 13 N) under unlubricated conditions. SiC ceramics prepared with 3 wt% AlN–Y 2O 3 additives consisted of mostly large equi-axed grains with amorphous grain boundary phase of ∼1.2 nm thickness, whereas SiC ceramics sintered with 3 wt% AlN–Sc 2O 3 additives showed duplex microstructure of elongated and fine equi-axed grains with clean grain boundary. As the load was increased, the steady state coefficient of friction reduced from ∼0.6 to ∼0.2, and wear rate increased from 10 −6 to 10 −5 mm 3/N·m. It was observed that the friction did not depend on the additive composition, while less wear was observed for the SiC ceramics sintered with 3 wt% AlN–Sc 2O 3 additives consisting of clean grain boundary. The material loss was increased with the increased amount of sintering additive to 10 wt%. The worn surface morphology revealed that the material was primarily removed via surface grooving and microcracking at 1 N load, while tribochemical wear dominated at 6 and 13 N loads.

Effect of Atmospheric Plasma Spraying Power on Microstructure and Properties of WC-(W,Cr)2C-Ni Coatings

WC-(W,Cr)2C-Ni coatings were prepared by atmospheric plasma spraying (APS) with different spraying powers. The effect of spraying power on microstructure, phase composition, hardness, fracture toughness, and oscillating dry friction and wear behaviors of the coatings were studied. Simultaneously, the microstructure and properties of the as-sprayed coatings were compared with those of WC-17Co coating prepared under the optimal spraying power. It was found that spraying power had significant effect on the molten degree of feedstock powder and phase composition as well as microstructure and properties of WC-(W,Cr)2C-Ni coatings. WC-(W,Cr)2C-Ni coating deposited at a moderate spraying power of 22.5 kW had the highest fracture toughness and the best wear resistance. WC-17Co coating obtained under the moderate spraying power had poor fracture toughness and wear resistance. Moreover, the four kinds of coatings were all dominated by subsurface cracking and removal of materials when sliding against Si3N4 ball under unlubricated conditions.

Influence of SiC addition on tribological properties of SiAlON

The tribological properties of gas pressure sintered SiAlON and its composite with 18 wt% silicon carbide (SiC) against two different mating materials, i.e., alumina and SiAlON are evaluated. SiAlON and SiAlON–18%SiC composite ceramics were prepared by pressure less sintering and gas pressure sintering. Fretting wear tests were carried out under dry unlubricated ambient conditions (room temperature 23–25 °C; relative humidity 50–55%) with a load of 8 N for 45,000 cycles. Friction and wear properties of SiAlON–SiC proved better than the monolithic SiAlON. The formation of silica roll like structure on the composite worn surface was observed.

The structure and properties of VN-VCN-VC coatings deposited by a high energy ion assisted magnetron sputtering method

In the last years the scientific interest for transition metal compounds, used for protective and functional coatings, was extended and included, besides Ti, other elements such as Zr, V, and Hf as potential candidates. Due to their promising mechanical properties, and resistance to high temperature, V compounds received an increasing attention from scientists and end-users.The present work is dedicated to the study of the characteristics and the properties of the vanadium based multilayer hard coatings deposited by a magnetron sputtering process, assisted by a high voltage pulse discharge. Different multilayer coatings (VC/VN, VN/VC, VN/VCN/VC) were obtained and comparatively analyzed relative to vanadium nitride and vanadium carbide monolayers. Coatings with microhardness up to 3700HV 0.05 and thickness up to 20μm have been produced.Elemental and phase composition, as well as tribological characteristics (wear factor and friction coefficient) of the coatings were investigated. The chemical and structural investigations were performed by GDOES (Glow Discharge Optical Emission Spectrometry), EDX (Energy Dispersive X-ray analysis), XRD (X-ray Diffraction) and SEM (Scanning Electron Microscopy), while microhardness measurements and wear test were used to assess the coatings characteristics. The friction coefficient and the wear resistance of the coatings were evaluated by using pin on disc tests in unlubricated conditions.