Lubricated Testing Conditions Research Articles

Tribological behavior of H-DLC and H-free DLC coatings on bearing materials under the influence of DC electric current discharges

In automotive industry, most of the moving components and lubricants are currently being reengineered in order to meet the much harsher operating conditions of electric vehicles (EVs). Diamond-like carbon (DLC) coatings have been widely used in automotive field mainly because of their lower friction and wear coefficients, high chemical inertness, corrosion resistance, and hardness. It is also possible that DLC coatings can afford very desirable tribological properties to the bearings and gears of electric vehicles. In addition, their superior dielectric properties could also be very ideal for such applications. In EVs, current leakages in the powertrain are very common and these can adversely impact the tribological behavior of bearings and/or other moving mechanical elements. Although DLC coatings provide superior tribological performance in IC engine applications, they have not yet been evaluated under electrified sliding conditions of EVs. In this work, two different types of DLC coatings (Hydrogenated DLC (H-DLC) and hydrogen-free DLC (H-free DLC) were produced on AISI 52100 steel substrates and tested using a ball-on-disc tribometer under non-electrified and electrified (DC, 3A) both dry and lubricated sliding conditions. Coefficient of friction (CoF), wear volumes, wear modes and mechanisms have been assessed and reported. The results showed that electrification can cause a decrease in CoF for baseline steel-on-steel contacts, but an increase for H-free DLC in lubricated condition. The change in CoF of H-DLC interface was negligible. However, electrification caused a significant increase in the wear volume of steel-on-steel and H-free DLC-coated surfaces, but little or no wear was observed for the H-DLC-coated cases in both dry and lubricated test conditions. Overall, the tribological behavior of H-DLC was almost unaffected by electrification, suggesting that one has to select the right kind of DLC for applications involving electrified contact conditions.

Effects of racetrack magnetic field strength on structure and properties of amorphous carbon coatings deposited by HiPIMS using deep oscillation pulses

In this study, non‑hydrogenated diamond like carbon (DLC) coatings were deposited by sputtering a graphite target in argon (Ar) by high power impulse magnetron sputtering (HiPIMS) using deep oscillation pulses. The effects of the magnetic field strength (B) tangential to surface of the target racetrack on the deposition parameters were studied. The structure, adhesion, and mechanical properties of DLC coatings deposited at different B were investigated by scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM), scratch test, and nanoindentation. The tribological properties of the DLC coatings were evaluated using ball on disk wear test under dry and lubricated test conditions. It was found that the peak target current and substrate current density increased as B increased due to the enhanced electron confinement which results in an increased ionization efficiency. The enhanced ion bombardment was beneficial for improving the structure and properties of DLC coatings. As B increased, the DLC coatings exhibited more compact structure, smaller carbon mounds, and higher sp3 bond fractions. The improvement of the microstructure of the DLC coatings contributed to improved hardness and wear resistance of the coatings in both dry and lubricated test conditions. However, the deposition rate decreased at higher B owing to the high probability of back-attraction of carbon ions. The results suggested that controlling B in the range of 600 G to 700 G is important for achieving fully dense structure, high sp3 bond fractions, and high hardness for the DLC coatings deposited using HiPIMS. A further increase in B to 850 G showed no significant changes in the magnetic field induced effects on the structure and properties of the coatings.

Pearlitic structure and wear properties of graphite cast iron reinforced with biphase TiC-TiB2 nanoparticles

The current research describes the preparation of nanoparticle-reinforced ductile iron specimens through an aluminum master alloy containing bi-phase TiC-TiB2 nanoparticles. The pearlitic structure, hardness and wear resistance were examined and compared for ductile iron specimens with and without nanoparticles. It was found that the presence of a small amount of TiC-TiB2 nanoparticles could refine the lamellar structure of pearlite, increase the hardness and lower the wear loss under dry and lubricated test conditions. Adhesion with plastic flow, material removal and material smearing were reduced on the wear track which was associated with the coupled effects of finer pearlite and higher hardness after engaging the TiC-TiB2 nanoparticles. In addition, it was found that the nanoparticles were distributed on the worn areas, which could withstand the normal load and minimize the contact between the ductile iron substrate and counterface during the wear tests.

Anodic plasma electrolytic nitrocarburising of VT22 titanium alloy in carbamide and ammonium chloride electrolyte

The structure of alpha- and beta-titanium alloy VT22, its microhardness, surface roughness, wear and corrosion resistance after anodic plasma electrolytic nitrocarburising in an electrolyte containing carbamide and ammonium chloride were investigated. An X-ray diffractometer and a scanning electron microscope were used to characterize the phase composition and structure of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a ball-on-disc tribometer under lubricated testing conditions. The effect of processing temperature on corrosion resistance of the plasma electrolytic nitrocarburising samples was examined by means of potentiodynamic polarization in Ringer’s solution. It was shown that the anodic nitrocarburising provides saturation of the titanium alloy with oxygen, nitrogen and carbon and the formation of TiO2 with a rutile structure and a nitrogen/carbon solid solution in titanium. The anodic plasma electrolytic nitrocarburising at all treatment temperatures diminishes the wear rate of the titanium alloy samples and the surface roughness. Friction coefficient of treated samples can be reduced by 4.7 times. The anodic nitrocarburising results in an enhanced corrosion resistance since the corrosion potential increases by an order of magnitude.

IMPROVEMENT OF CORROSION AND WEAR RESISTANCE OF 45 STEEL WITH ANODE PLASMA ELECTROLYTE NITRIDING

For citation:Smirnov A.A., Silkin S.A., Belkin P.N., Dyakov I.G., Sevostyanova V.S., Kusmanov S.A. Improvement of corrosion and wear resistance of 45 steel with anode plasma electrolyte nitriding. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 1. P. 81-86.The wear and corrosion resistance was studied after anode plasma electrolytic nitriding (PEN) the carbon steel in electrolyte containing ammonium chloride and ammonia or ammonium nitrate. Tribological properties of nitrided samples were evaluated using a pin-on-disk and ball-on-disk tribometers under lubricated testing conditions and dry sliding. The effect of processing temperature on corrosion resistance of the PEN samples was examined by means of potentiodynamic polarization in a solution of sodium sulfate (0.1 N). The anode PEN at 750 °C during 5 min in electrolyte containing ammonium chloride (15%) and ammonium nitrate (5%) results in a decrease in a corrosion current density by a factor of 16. The anode PEN at 750 °C during 10 min in electrolyte containing ammonium chloride (10%) and ammonia (5%) results in the decrease in a corrosion current density by a factor of 6. Improving the corrosion resistance of steel takes place due to the formation of the surface oxide layer and the nitride-martensite zone. Results of wear tests under lubricated testing conditions with the speed of 0.49 m/s and load of 208.6 N against hardened steel (50 HRC) diskshow that friction coefficient of nitrided samples decreases at all PEN temperatures. The anode PEN at 750 °C during 10 min in electrolyte containing ammonium chloride and ammonia results in the decrease in wear rate more than 9 times and friction coefficient from 0.17 to 0.12. Nitriding in electrolyte with ammonium chloride and nitrate also results in minimum of the wear rate after the PEN at 750 °C during 10 min but it gives lesser result due to the lower hardness of the nitride-martensite sublayer. Wear tests during dry sliding with the speed of 0.2 m/s and load of 5 N against bearing steel ballshow that friction coefficient of nitrided samples decreases from 0.41 to 0.28. The increasing the load reduces the friction coefficient that means saving mode of elastic contact and a good running-in ability of oxide layer in the studied range. Linear wear decreases from 35 to 21 mm at load of 10 N and sliding speed of 0.4 m/s.

Plasma electrolytic treatment of VT22 titanium alloy in electrolytes with carbon-containing compounds

The study investigates the influence of electrolyte compositions containing acetone, glycerol, sucrose, ethylene glycol and ammonium chloride on the properties of VT22 titanium alloy in the process of the anode plasma electrolytic treatment (PET). An X-ray diffractometer and a scanning electron microscopy (SEM) were used to characterize the phase composition and morphology of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a pin-on-disc tribometer under lubricated testing conditions. The effect of electrolyte compositions on the corrosion resistance of the PET samples was examined by means of potentiodynamic polarization in a solution of Na2SO4. It was assumed that the PET provides the saturation of titanium alloy with oxygen and carbon and formation TiO2 with a rutile structure and carbon solid solution in titanium. The anode PET in an electrolyte with glycerol results in an increase in microhardness to 540 HV and a decrease in the corrosion current density by 2.4 times. The friction coefficient of the treated samples in anelectrolyte with sucrose can be reduced 7.5 times. The anode PET in all electrolytes enables todiminish the wear rate of the titanium alloy samples by 3 orders of magnitude and the surface roughness, too, due to the anode dissolution of titanium.

Anode plasma electrolytic carburizing of commercial pure titanium

Abstract The study investigates the influence of electrolyte compositions with acetone, glycerol, sucrose, ethylene glycol and ammonium chloride on the properties and structure of commercial pure titanium (CP-Ti) in the process of anode plasma electrolytic carburizing (PEC). The wear of the samples was measured using pin-disk friction in lubricated testing conditions. The effects of electrolyte composition on corrosion resistance of the PEC samples were examined by means of potentiodynamic polarization in a solution of sodium sulfate. It is shown that anode PEC of CP-Ti samples leads to formation of solid solution of carbon in titanium and external oxide layer in all studied electrolytes. The mechanism of carbon transfer from electrolytes containing sucrose, ethylene glycol and acetone to treated CP-Ti is found. The anode PEC of CP-Ti samples at 850 °C during 5 min was established to result in decrease in their surface roughness Ra from 1.13 ± 0.01 μm to 0.04 ± 0.01 μm and friction coefficient from 0.29 ± 0.01 to 0.10 ± 0.01. The treatment in the aqueous solution of ammonium chloride (10 wt.%) and sucrose (10 wt.%) resulted in the decrease in the wear rate by 3–3 orders. The base-sucrose electrolyte conditioned a decrease in the corrosion current density by a factor 18 due to passivating effect of the oxide layer.

Anode plasma electrolytic boronitrocarburising of low-carbon steel

Multicomponent saturation of low-carbon steel with carbon, nitrogen, and boron was investigated under the anode plasma electrolytic treatment. Optical and scanning electron microscopes with an energy dispersive attachment were used to characterize the composition of the modified layer and its surface morphology. Surface roughness and microhardness were studied with a profilometer–profilograph and a microhardness tester; tribological properties were evaluated using a pin-on-disc tribometer at lubricated testing conditions. It has been established that the thickness of the oxide layer slowed down the diffusion of carbon, nitrogen, and boron as determined by the anode dissolution and high temperature oxidation, which are dependent on the processing temperature. Dissolution prevails over oxidation up to 850°C that results in the sample weight loss. At 900°C, the sample weight increases owing to oxidation which prevails over dissolution. The maximal boronitrocarburising layer thickness (0.11 mm) is observed at 850°C. The maximal microhardness of this layer is 880 HV after saturation at 850°C for 5 min. The friction coefficient and the wear rate of the samples treated at 850°C decrease by a factor of 2 in comparison with those of an untreated sample.

Mechanical characterization of brain tissue in compression at dynamic strain rates

Traumatic brain injury (TBI) occurs when local mechanical load exceeds certain tolerance levels for brain tissue. Extensive research has been done previously for brain matter experiencing compression at quasistatic loading; however, limited data is available to model TBI under dynamic impact conditions. In this research, an experimental setup was developed to perform unconfined compression tests and stress relaxation tests at strain rates ≤90/s. The brain tissue showed a stiffer response with increasing strain rates, showing that hyperelastic models are not adequate. Specifically, the compressive nominal stress at 30% strain was 8.83 ± 1.94, 12.8 ± 3.10 and 16.0 ± 1.41 kPa (mean ± SD) at strain rates of 30, 60 and 90/s, respectively. Relaxation tests were also conducted at 10%–50% strain with the average rise time of 10 ms, which can be used to derive time dependent parameters. Numerical simulations were performed using one-term Ogden model with initial shear modulus μo=6.06±1.44, 9.44 ± 2.427 and 12.64 ± 1.227 kPa (mean ± SD) at strain rates of 30, 60 and 90/s, respectively. A separate set of bonded and lubricated tests were also performed under the same test conditions to estimate the friction coefficient μ, by adopting combined experimental–computational approach. The values of μ were 0.1 ± 0.03 and 0.15 ± 0.07 (mean ± SD) at 30 and 90/s strain rates, respectively, indicating that pure slip conditions cannot be achieved in unconfined compression tests even under fully lubricated test conditions. The material parameters obtained in this study will help to develop biofidelic human brain finite element models, which can subsequently be used to predict brain injuries under impact conditions.

Development of a Sliding-Rolling Contact Fatigue Tester

Abstract Contact fatigue failure is a common problem experienced in many applications such as bearings, gears, and railway tracks. In recent years, research companies have developed finishing processes that aim to improve components’ contact fatigue life. Preliminary rolling contact fatigue tests have shown that superfinishing processes could potentially improve a component’s contact fatigue life by 300 %. However, before these technologies can move from the laboratories to industrial platforms, more tests are needed to verify the claim. The objective of the work herein is to discuss the completion and verification of a sliding-rolling contact fatigue (S-RCF) test rig. This project is funded by the U.S. Army to assess the real benefit of superfinishing on the contact fatigue life of gears used in helicopter transmission boxes. The proposed tester design uses three rollers around a specimen, a hydraulic loading mechanism, and two servo motors. This configuration of the S-RCF tester allows for shorter testing time, more flexible testing parameters such as any combination of slide-roll ratio between the surfaces, any operating speed, and dry or lubricated testing conditions. Failure is detected with a state-of-the-art eddy current crack detection system, which can also be used to monitor and investigate crack growth for different materials, levels of superfinish, and operating conditions. Preliminary tests on a common gear material (AISI 8620 steel) were performed to assess the mechanical limits as well as the control software performance. This paper presents the detailed development and validation of the tester. It discusses issues involved with servo controllers, electronic gear ratio, and their ability to provide precise speed and slip ratios.

Sliding wear behaviour of electrolytic plasma nitrided cast iron and steel

A new nitriding method, called electrolytic plasma nitriding (EPN), was used for surface modification of a cast iron G3500 and cast steel S0050A. The phase structure of the treated samples was determined by X-ray diffraction (XRD). Hardness of the treated and untreated cast iron and steel was measured using a microhardness tester, and their tribological properties were evaluated using a pin-on-disc tribometer at dry and lubricated testing conditions. Scanning electron microscopy and surface profilometry were also employed to study their wear behaviours. It was found that the EPN treatment could significantly increase hardness and wear resistance of the cast iron and cast steel.

Selective transfer phenomenon in lubricated sliding surfaces with copper and its alloy coatings made by electro-pulse spraying

The decrease of the coefficient of friction and wear are characteristics of the selective transfer phenomenon caused by the self-formation of a non-oxidising metal film in the friction zone. In this paper, the possibility of providing the selective transfer phenomenon by electro-pulse spraying (EPS) will be discussed. The analysed copper and brass coatings were manufactured by an electric pulse at 5 kV and an energy density of about 4.7–5 MJ/kg. EPS manufactured coatings have a fine-grained, multi-layer structure with a small share of voids and non-metal inclusions. The analysis (tribological test, microscopy) of such conditioned friction pairings has shown that a protecting metal film will be formed by itself, even at marginal lubricated test conditions. As a consequence, a low coefficient of friction ( f = 0.003–0.004) occurs in the contact zone, which is similar to those, which indicate viscous friction.

An evaluation of surface properties and frictional forces generated from Al–Mo–Ni coating on piston ring

Surface properties of the Al–Mo–Ni coating plasma sprayed on the piston ring material and the frictional forces obtained by testing carried out under different loads, temperatures and frictional conditions were evaluated. Al–Mo–Ni composite material was deposited on the AISI 440C test steel using plasma spraying method. The coated and uncoated samples were tested by being exposed to frictional testing under dry and lubricated conditions. Test temperatures of 25, 100, 200, and 300 °C and loads of 83, 100, 200, and 300 N were applied during the tests in order to obtain the frictional response of the coating under conditions similar to real piston ring/cylinder friction conditions. Gray cast iron was used as a counterface material. All the tests were carried out with a constant sliding speed of 1 m/s. The properties of the coating were determined by using EDX and SEM analyses. Hardness distribution on the cross-section of the coating was also determined. In addition, the variations of the surface roughness after testing with test temperatures and loads under dry and lubricated conditions were recorded versus sliding distance. It was determined that the surface roughness increased with increasing loads. It increased with temperature up to 200 °C and then decreased at 300 °C under dry test conditions. Under lubricated conditions, the roughness decreased under the loads of 100 N and then increased. The roughness decreased at 200 °C but below and above this point it increased with the test temperature. Frictional forces observed under dry and lubricated test conditions increased with load at running-in period of the sliding. The steady-state period was then established with the sliding distance as a normal situation. However, the frictional forces were generally lower at a higher test temperature than those at a lower test temperature. Surprisingly, the test temperature of 200 °C was a critical point for frictional forces and surface roughness.

Tribological study of lubricious DLC biocompatible coatings.

DLC (diamond-like carbon) coatings have remarkable tribological properties due mainly to their good frictional behavior. These coatings can be applied in many industrial and biomedical applications, where sliding can generate wear and frictional forces on the components, such as orthopaedic metal implants. This work reports on the development and tribological characterization of functionally gradient titanium alloyed DLC coatings. A PVD-magnetron sputtering technique has been used as the deposition method. The aim of this work was to study the tribological performance of the DLC coating when metal to metal contact (cobalt chromium or titanium alloys) takes place under dry and lubricated test conditions. Prior work by the authors demonstrates that the DLC coating reduced considerably the wear of the ultra-high-molecular-weight polyethylene (UHMWPE). The DLC coating during mechanical testing exhibited a high elastic recovery (65%) compared to the values obtained from Co-Cr-Mo (15%) and Ti-6Al-4V (23%). The coating exhibited an excellent tribo-performance against the Ti-6Al-4V and Co-Cr-Mo alloys, especially under dry conditions presenting a friction value of 0.12 and almost negligible wear. This coating has passed biocompatibility tests for implant devices on tissue/bone contact according to international standards (ISO 10993).

Influence of ion implantation and overlay coatings on various physico-mechanical and wear properties of stainless steel, titanium and aluminium

Abstract This work represents the data on the wear behaviour of 304 stainless steel, commercial grade titanium and commercial grade aluminium without and with different surface treatments, namely ion implantation of boron and nitrogen and overlay coatings of titanium carbide and nitride. The surface treatments were characterized by phase identification, hardness, bend strength, as well as adhesion of overlay coatings. Wear properties were evaluated in adhesive, erosive and abrasive modes of wear. The experimental results showed that surface treatments produced measurable changes in hardness and strength. The results of adhesive wear tests indicated that the wear resistance of all the substrate materials can be considerably improved by overlay coating with superhard materials in dry as well as lubricated test conditions. Ion implantation resulted in improvement of wear properties for only a limited regime of adhesive wear under lubricated conditions and for the abrasive mode of wear. Overlay coatings produced a marked improvement in abrasive wear tests under lubricated conditions on all substrate materials.

Silicon nitride as a rolling bearing material—A preliminary assessment

Using a simple, accelerated service simulation test silicon nitride has been compared in a preliminary manner with En31 ball bearing steel, high speed tool steels and tungsten carbide under conditions of heavily loaded, lubricated, unlubricated and elevated temperature rolling contact. Low density, porous, heterogeneous reaction bonded silicon nitride does not appear to be a suitable rolling bearing material. Under lubricated test conditions hot-pressed silicon nitride was not as effective a material as En31 and high speed tool steels. Under unlubricated conditions it was inferior to tungsten carbide. Further work to allow a fuller assessment is suggested.