Ball Counterface Research Articles

Duplex surface engineering of cold spray Ti coatings and physical vapor-deposited TiN and AlTiN thin films

The feasibility of a duplex coating based on cold spray technology and magnetron sputtering was evaluated for repair applications requiring a ‘thin-on-thick’ layered structure. Commercially pure angular-shaped Ti grade 4 particles are fed to a cold spray gun and accelerated toward a Ti alloy substrate to deposit thick coatings (∼4.5 mm). TiN and AlTiN thin films are deposited on polished cold spray coatings using a four-source closed-field unbalanced magnetron sputtering (CFUBMS) system. Microstructure was characterized using focused ion beam (FIB) lift-out, scanning electron microscopy (SEM), and electron channeling contrast imaging (ECCI). The nanoindentation technique was used to evaluate the mechanical properties of coatings. The H/E ratios and H3/E2 ratios for TiN films were found to be 0.098 and 0.26 GPa, respectively, while those for AlTiN films were measured at 0.066 and 0.052 GPa, respectively, suggesting higher capacity of TiN films to withstand both elastic and plastic deformation. Using scratch testing, the adhesion of TiN and AlTiN thin films to cold spray Ti was investigated, with TiN-Ti duplex coatings exhibiting better performance compared to AlTiN-Ti coatings. Tribological testing was performed on duplex coatings using a reciprocating tribometer equipped with an alumina ball counterface. The wear rate for AlTiN-Ti coatings after 2000 sliding cycles was found to be (1.0 × 10−3 ± 0.1 × 10−3 mm3/Nm), three orders of magnitudes higher than that for TiN-Ti (8 × 10−6 ± 2 × 10−6 mm3/Nm. SEM was used to reveal worn surface morphologies and cross-sectional analysis of the wear track. Subsurface microstructural changes due to wear were examined using focused ion beam cross-sectioning, revealing bending cracks and tribofilm formation.

Tribo-Mechanical Investigation of Glass Fiber Reinforced Polymer Composites under Dry Conditions.

Tribo-mechanical experiments were performed on Glass Fiber Reinforced Polymer (GRFP) composites against different engineering materials, and the tribological behavior of these materials under dry conditions was investigated. The novelty of this study consists of the investigation of the tribomechanical properties of a customized GFRP/epoxy composite, different from those identified in the literature. The investigated material in the work is composed of 270 g/m2 fiberglass twill fabric/epoxy matrix. It was manufactured by the vacuum bag method and autoclave curing procedure. The goal was to define the tribo-mechanical characteristics of a 68.5% weight fraction ratio (wf) of GFRP composites in relation to the different categories of plastic materials, alloyed steel, and technical ceramics. The properties of the material, including ultimate tensile strength, Young's modulus of elasticity, elastic strain, and impact strength of the GFPR, were determined through standard tests. The friction coefficients were obtained using a modified pin-on-disc tribometer using sliding speeds ranging from 0.1 to 0.36 m s-1, load 20 N, and different counter face balls from Polytetrafluoroethylene (PTFE), Polyamide (Torlon), 52,100 Chrome Alloy Steel, 440 Stainless Steel, and Ceramic Al2O3, with 12.7 mm in diameter, in dry conditions. These are commonly used as ball and roller bearings in industry and for a variety of automotive applications. To evaluate the wear mechanisms, the worm surfaces were examined and investigated by a Nano Focus-Optical 3D Microscopy, which uses cutting-edge μsurf technology to provide highly accurate 3D measurements of surfaces. The obtained results constitute an important database for the tribo-mechanical behavior of this engineering GFRP composite material.

Tribological Evaluation of Silica Nanoparticle Enhanced Bilayer Hydrogels as A Candidate for Cartilage Replacement.

Polymeric hydrogels can be used as artificial replacement for lesioned cartilage. However, modulating the hydrogel formulation that mimics articular cartilage tissue with respect to mechanical and tribological properties has remained a challenge. This study encompasses the tribological evaluation of a silica nanoparticle (SNP) loaded bilayer nanocomposite hydrogel (NCH), synthesized using acrylamide, acrylic acid, and alginate via modulated free-radical polymerization. Multi-factor pin-on-plate sliding wear experiments were carried out with a steel ball counterface using a linear reciprocating tribometer. Tribological properties of NCHs with 0.6 wt% SNPs showed a significant improvement in the wear resistance of the lubricious layer and a low coefficient of friction (CoF). CoF of both non-reinforced hydrogel (NRH) and NCH at maximum contact pressure ranged from 0.006 to 0.008, which is in the order of the CoF of healthy articular cartilage. Interfacial surface energy was analysed according to Johnson, Kendall, and Robert’s theory, and NCHs showed superior mechanical properties and surface energy compared to NRHs. Lubrication regimes’ models were drawn based on the Stribeck chart parameters, and CoF results were highlighted in the elastoviscous transition regime.

An investigation into the tribological behaviour of cutting fluid additives on Ti‐6Al‐4V alloy

AbstractThe performance of polymer‐based and phosphorus‐based cutting fluid additives have been shown to depend on the machining conditions employed. This study investigated the tribological behaviour behind the previously reported machining performance of polymer‐based and phosphorus‐based additives on Ti‐6Al‐4V using ball‐on‐disc tests. The coefficient of friction (COF) was evaluated using ball‐on‐disc tests, surface characterisation was performed on the Ti‐6Al‐4V and steel ball counterfaces to investigate the wear and friction reduction mechanisms. The tribological performance of the phosphorus‐based additive was observed to be influenced by the applied load and temperature. The activation of this additive resulted in a reduction in COF at elevated temperatures. However, the activation temperature was observed to be influenced by the applied load. The COF associated with the polymer‐based additive was noted to increase as the temperature increased, regardless of the applied load. The formation of tribolayers from the additives was related to the COF behaviour as well as the surface damage on Ti‐6Al‐4V and lower material transfer to the steel counterfaces.

Effect of minor La addition on wear behaviour of Mg-10Dy alloy

Magnesium alloys have attracted significant attention as a potential replacement material for aluminium alloys in the automobile industry due to their superior strength-to-weight ratio. The addition of rare earth elements to Mg alloys enhances its strength and tribological properties owing to the solid solution strengthening as well as increased melting temperatures of the second phase. The aim of the current study is to examine the effect of minor La addition on the wear behaviour of as-cast Mg-rare-earth alloy (Mg-10 wt%Dy) in dry sliding conditions at different loads. The addition of rare earth elements to the magnesium alloys improves the wear strength effectively at different loads. The experiments were performed using ball-on-disc tribometer with a steel ball counterface as a function of normal load and at a constant sliding velocity. The wear surfaces were analyzed using a 3D profilometer and a field emission scanning electron microscopy to investigate wear rate and wear mechanisms. It was observed that due to the formation of stable oxide surface layers and improved hardness of La containing alloy, the wear rate is significantly lower than the Mg-10Dy alloy at different applied normal loads. Abrasion, delamination, oxidation, and plastic deformation were established as the governing wear mechanisms.

Tribological assessments of bilayer titanium nanocomposite hydrogels for cartilage replacement in articular joints

Polymeric hydrogels are gaining recognition as cartilage implants for articular joints. Formulating and synthesizing hydrogels mimicking the native cartilage with respect to tribological properties have proven to be a challenging task. We hypothesized that a bilayer nanocomposite hydrogel (NCH) with an optimum amount of titania nanoparticles (NPs) could enhance tribological properties and be considered as a cartilage implant. In this work, a series of titania NPs loaded acrylamide-alginate bilayer hydrogels were synthesized via modulated polymerization process and tribological assessments of the hydrogels were conducted. Multi-factor sliding wear tests were conducted on hydrogel samples using a linear reciprocating tribometer, with a steel ball counterface. Tribological test results showed a low mean coefficient of friction values of 0.007 and 0.014 for non-reinforced hydrogels and NCHs, respectively, and wear resistance of NCHs improved significantly. SEM images showed that wear mechanisms are a combination of adhesive wear and fatigue wear.

Designing a Bioinspired Surface for Improved Wear Resistance and Friction Reduction

Abstract This study used 2-photon three-dimensional lithographic printing and replica molding to fabricate a micro-texture based on the Ocellated Skink. The fabricated surface texture was studied for friction and wear behavior using linear reciprocating tribological tests with a chrome steel ball counterface under various loading conditions and compared with samples fabricated with the same methods without a surface texture. The texture was found to decrease friction at low loads and provide steady friction under all loading conditions. The textured samples also decreased the average wear track width up to 61%. Wear was reduced on surfaces by the texture through the controlled formation of microcracking, which both reduced the amount of debris built up on samples and effectively reduced the worn area.

Effects of Nb Content and Heat Treatment on Fretting Wear Behavior of Ti-Nb Alloys

Ti-Nb alloys in deionized water and Hanks' balanced salt solution were investigated at 310K using a ball-on-disc type frictional test machine with a ZrO2 ball counterface. In this study, besides the fretting wear behavior of Ti-Nb alloys was investigated, the relationship between the microstructure and mechanical properties of the Nb-added Ti alloy was investigated, and the relationship between the composition and hardness on the fretting wear of the alloy will be clarified from the results of the wear volume and surface analysis of wear track. The results obtained from the frictional test indicate that the dynamic coefficient of friction converged to a constant value with time variation. Also, wear volume in HBSS was smaller than in water, and wear volume of heat-treated became smaller than As-Rolled. Microstructural observations suggest the scars of adhesive wear were observed. Comparing each morphology, the ratio of the peeling part was more significant in Ti-Nb alloys, which have α+β than in Ti-Nb alloys, which have only β. Moreover, the results of Open circuit potentiometry indicate that the corrosion potential difference increased with wear. This is most likely due to the passive film was damaged. Besides, the corrosion potential difference of β-Ti-Nb alloy heat-treated with HBSS is small. It is assumed that there is an influence of HBSS besides the fine structure.

Effect of counterface materials on friction and wear of graphene-coated steel under dry sliding contact

Graphene has drawn the attention of researchers across the globe due to its exceptional properties and has a great potential to reduce friction and wear in machine elements. The present investigation is aimed at exploring the effect of counterface ball materials (Si3N4, ZrO2, and steel) on friction and wear of a multi-layer graphene coating deposited on steel using chemical vapor deposition under reciprocating sliding. Results pointed out that the graphene coating on the steel surface reduces both friction and wear against each ball material in comparison to bare steel. Contact pressure played a vital role in determining tribological performance against different counterparts. Silicon nitride ball exhibited the highest friction and wear as surfaces were subjected to maximum contact stress. However, the minimum friction coefficient was observed for steel slid against multi-layer graphene-coated steel. The higher hardness of the zirconia ball in comparison to the steel ball helped in providing minimum wear.

Tribological Performance of Steel With Multi-Layer Graphene Grown by Low-Pressure Chemical Vapor Deposition

Abstract To explore the potential of directly grown multi-layer graphene as an agent in reducing friction and wear of steel on steel tribo-pair, multi-layer graphene films were synthesized on GCr15 steel in a low-pressure chemical vapor deposition (LPCVD) setup using a gaseous mixture of acetylene and hydrogen onto a bearing steel substrate. An interlayer of electroplated nickel was deposited on steel to assist and accelerate the graphene deposition. The tribological performance was evaluated using a ball-on-disc tribometer with an average Hertzian pressure of 0.2, 0.28, 0.34, and 0.42 GPa over a stroke length of 5 mm against GCr15 steel ball and compared with bare steel and nickel-plated steel. The results indicate that the friction coefficient is dependent on the applied load and decrease with increasing load, and the minimum friction coefficient of ∼0.13 was obtained for an applied normal load of 1 N; however, the coating failed after 250 cycles. The decrease in friction coefficient has been attributed to the homogenization of the deposited multi-layer graphene along the sliding direction and transfer of graphene to counter-face ball leading to inhibition of metal-metal contact. The investigation suggests that this kind of coating has the potential of improving the tribological performance of metal-metal tribo-pairs.

Tribological performance of PDA/PTFE + Graphite particle coatings on 60NiTi

60NiTi has unique combinations of high shock load and corrosion resistance, which is suitable for load-bearing applications exposed to chemically aggressive environments. However, it exhibits poor tribological properties in dry sliding contact conditions. Polydopamine (PDA)/polytetrafluoroethylene (PTFE) coatings are shown to reduce friction and wear of 60NiTi significantly. In this study, using Si3N4 balls as the counterface material, the effects of adding graphite particles (GrP) to the PTFE layers of the PDA/PTFE coatings on the sliding properties of 60NiTi were studied. The obtained results were compared to those of the PDA/PTFE coated and uncoated 60NiTi. The results showed that both types of coatings significantly decreased the coefficient of friction (COF) and wear of the 60NiTi substrates and the wear of the counterface balls. The PDA/PTFE + 0.25 wt% GrP coatings have less porosity and approximately 2.4 times durability when compared to the PDA/PTFE coatings. Scratch tests on the coated surfaces also revealed better adhesion strength, higher load-carrying capacity, and enhanced transfer films on the counterface balls for the PDA/PTFE + 0.25 wt% GrP coatings. The less porosity, the enhanced adhesion strength, and the transfer film contributed to the longer wear life of PDA/PTFE + 0.25 wt% GrP coatings on 60NiTi.

An Investigation of the Tribological Behavior of Hf-Based Bulk Metallic Glass and Crystalline Alloys

Abstract The use of bulk metallic glasses (BMGs) as advanced materials for many applications is attractive, due to their improved mechanical performance over their crystalline counterparts: typically providing higher strength and hardness. Hafnium-based alloys of two similar compositions were prepared by arc melting and suction casting to produce 6-mm-diameter cast rods of an amorphous alloy and a crystalline one. The selected compositions were Hf48Cu29Ni10Al13 (amorphous) and Hf58Cu20Ni16Ti6 (crystalline), as confirmed by X-ray diffraction. The hardness of the amorphous alloy was higher than that of the crystalline one. A detailed study of their tribological behavior was carried out, using a pin-on-disc wear tester, with tungsten carbide counterface balls. There were no statistically significant differences in friction coefficient or wear-rates between the two materials tested. Adherence of material from the tested alloy to the ball, and vice versa, were detected. No changes to the crystallinity of the bulk samples were induced by the wear process, as determined by X-ray diffraction. However, amorphous debris were obtained from both samples, indicating the possibility of local vitrification of particles detached from the crystalline alloy and confirming thermal stability of the amorphous alloy.

The effect of oxygen on the tribology of (PEI/GO)15 multilayer solid lubricant coatings on steel substrates

Multilayers of polyethyleneimine and graphene oxide, (PEI/GO)15, were coated onto steel substrates via electrostatic layer-by-layer (LbL) deposition, and their tribological properties were investigated as solid lubricants. The coefficient of friction (COF) and specific wear rate (SWR) were measured against a poly(methyl methacrylate) (PMMA) counterface ball, in various gas environments with different oxygen concentrations. The COF and SWR both significantly decreased with decreasing oxygen content. Detailed surface characterization of the contact area of the counterface ball revealed that continuous transfer films were formed in oxygen-free environments, but not in oxygen-rich environments. This is attributed to an increased proportion of sp3 bonding in the wear debris in the presence of oxygen (as confirmed by Raman spectroscopy), as well as possible suppression of wear debris adhesion on the counterface ball due to oxygen adsorption on the surface.

Covalently grafting of self-assembled functionalized graphene oxide multilayer films on Si substrate for solid film lubrication

Graphene-based polymer brush containing multilayer film has been fabricated on silicon wafer (SW) via self-assembled multistep approach based on covalent insertion of 3-aminopropyltrimethoxysilane as a chemical linker on graphene oxide (GO) followed by covalently anchored with polyethyleneimine (PEI). A multilayer polymer brush film was then constructed by electrostatic layer-by-layer (LBL) self-assembly technique between positively charged outer layer PEI grafted GO and anionic polyelectrolyte, poly (sodium 4-styrenesulfonate) (PSS). The LBL formation and microstructure of as prepared films were characterized by Raman spectroscopy, atomic force microscopy, field emission scanning electron microscopy and elemental electron dispersive spectroscopy analysis. The changes in wettability of films during grafting of chemical components on silicon substrate were determined by water contact angle measurement. Microtribological performances of the films were investigated using ball-on-disc contact geometry in ambient condition. The influence of contact pressure and sliding velocity were also studied under reciprocating tribo contact to evaluate the load bearing ability of the films. The multilayer films exhibited low (~0.15–0.17) and steady coefficient of friction (COF) at 1 N load (contact pressure ~ 0.54 GPa) compared to bare SW (~0.6) with remarkable wear-resistivity. With increasing contact pressure (4 N, ~0.86 GPa), the multilayer films provided minimal COF and low wear depth with improved sliding durability among the films. The improved friction and wear resistivity of the multi-layer films are attributed to densely packed polymeric graphene lamella contributing low-resistance to shear during sliding and the presence of sulphur on PSS might assists in superior adhesion of delaminated film to steel counterface ball during shearing, which was investigated by microscopic and Raman spectral analysis.

Residual stresses and wear properties of induction-hardened medium carbon steel

A systematic experimental investigation was performed to study the residual stress, microstructure and work hardening on the wear properties of induction-hardened medium carbon steel. The dry sliding wear tests were performed using a reciprocating ball-on-flat apparatus under normal loads of 20, 50, and 100 N against ceramic ball counterface, respectively. The wear mechanism was mainly abrasive wear at low load (20 N) and delamination wear at higher load (100 N) as evidenced by the worn surface topography and wear debris. The deformation layer generated by friction work hardening reduced the friction coefficient, exhibited better antifriction. Typically, the high compressive residual stress could improve the wear resistance by delaying the propagation of microcrack and inhibiting the delamination.

Dry sliding tribological behaviour of bilayer Cr/Cr coatings obtained in sulphate Cr(III) baths

ABSTRACTThis study was intended to investigate the properties of Cr/Cr bilayer coatings. These coatings were deposited on a copper substrate by the DC electrodeposition method from Cr(III) sulphate baths with additions of formate-urea or glycine as complexing agents. Examination of the surface morphology of Cr coatings with SEM has shown that both single and bilayer Cr coatings obtained in the Cr(III) bath with formate-urea, and those obtained in the Cr(III) bath with glycine are cracked. It has been determined that the surface microhardness (HV) of bilayer Cr coatings obtained in the Cr(III) bath with glycine is higher compared with that of single-layer Cr coatings. Wear testing of the coatings was undertaken against an Al2O3 ball counterface (6 mm diameter) at 1N load. The results indicate that the friction coefficients (COF) of bilayer Cr/Cr coatings obtained in the Cr(III) bath with formate-urea increased from 0.2 to 0.5 compared with that of single-layer Cr coatings, while their wear resistance deteriorated. However, bilayer Cr/Cr coatings obtained in the Cr(III) bath with glycine exhibit wear resistance close to that of single coatings with COF equal to 0.05.

Relationship Between the Integrity of Lubricating Film and the Tribological Behavior on TiAl-Ag Self-Lubricating Composites

To explore the relationship between the integrity of the lubricating film and the tribological behavior of a metal matrix self-lubricating composite, the friction and wear experiments of TiAl-Ag self-lubricating composites were carried out with a ball-on-disk configuration. Besides, an approximate model was developed for analyzing the relationship based on Blau’s theory. The research results suggest that the friction and wear behavior of the TiAl-Ag self-lubricating composites changes in accordance with the formation conditions of the Ag-rich lubricating film. Specifically, the friction coefficients and wear rates of the TiAl-Ag self-lubricating composites decreased from high levels at full composite–counterface ball contact to low levels at full-film lubrication. Hence, the integrity of the lubricating film is a possible criterion for the self-lubricating property of the self-lubricating composites.

Ultra-low friction between polymers and graphene oxide multilayers in nitrogen atmosphere, mediated by stable transfer film formation

The efficiency and lifetime of mechanical devices is significantly decreased by friction and wear, significantly contributing to global energy consumption. We previously showed that multilayer polyethyleneimine/graphene oxide thin films, (PEI/GO)15, on steel display superlubricity against a steel counterface ball. Here, the coefficient of friction (COF) and wear of (PEI/GO)15 with six different counterface polymer balls is investigated in air and in nitrogen, with particular focus on the formation of tribological transfer films. The polymers polyoxymethylene (POM), polyetheretherketone (PEEK), polyethylene (PE), poly(methyl methacrylate) (PMMA), polycarbonate (PC), and polytetrafluoroethylene (PTFE) are utilized. The COF of (PEI/GO)15 vs steel is 0.35 in both air and nitrogen. In air, the COF ranges from 0.06 to 0.17 for all polymers. Significantly, in nitrogen, four polymers (POM, PEEK, PMMA and PC) display ultra-low friction (COF ∼0.02) whilst two do not (PTFE and PE). The wear tracks and transfer films are investigated using e.g. optical microscopy, electron microscopy, and Raman mapping, and the tribological behavior is correlated to the hydrophilicity and relative hardness of the polymer balls compared to GO.

Tribological behavior of N-doped ZnO thin films by metal organic chemical vapor deposition under lubricated contacts

N-doped ZnO thin films were deposited on 304L stainless steel through the pyrolysis of zinc acetate and ammonium acetate in different ratios at a temperature of 420 °C using metal organic chemical vapor deposition. Compositional and structural analyzes of the films were performed by using Rutherford backscattering spectroscopy and X-ray diffraction. The frictional behavior of the thin films and 304L stainless steel substrate was evaluated using a ball-on-flat configuration with reciprocating sliding under marginally lubricated and fully flooded conditions. Al alloy (2017) was used as ball counterface, while basestock synthetic polyalfaolefin oil (PAO10) without additives was used as lubricant. The flat and ball counterface surfaces were examined to assess the wear dimension and failure mechanism. Under marginally lubricated condition, N-doped ZnO thin films provided significant reduction in friction, whereas the films have minimal or no effect in friction under fully flooded condition. N-doped ZnO thin films showed a significant effect in protecting the ball counterface as wear volume was reduced compared with that of the substrate under the marginally lubricated condition. Under the fully flooded condition, with the exception of one of the films, the wear volume of the N-doped ZnO thin films ball reduced compared with that of the substrate. In all the ball counterfaces for N-doped ZnO thin films under both conditions, wear occurred through abrasive mechanism of various degrees or mild polishing. Thus, superfluous lubrication of N-doped ZnO thin films is not necessary to reduce friction and wear.

Effect of copper molybdate on the lubricating properties of NiCrAlY laser clad coating at elevated temperatures

The goal of the current work was to prepare a self-lubricating composite coating NiCrAlY/Cr3C2(NiCr)/Cu/MoO3 on GH4169 alloy substrate by laser cladding with hard phase Cr3C2(NiCr) as the reinforcing agent and Cu-MoO3 as the primary fillers. The composition and microstructure of the feedstock powders and corresponding composite coating were examined by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and X-ray diffraction. The tribological behavior of the composite coating from 25°C to 800°C was performed in air with a ball-on-disk tribometer against Si3N4 ball counterfaces and a dual-mode three-dimensional surface profiler. It has been found that the composite coating shows the most serious abrasion at 200°C, the friction coefficient was 0.7 and the wear rate was 7.7×10−5mm3/N·m. Better tribological properties could be found when the temperature higher than 200°C, and the composite coating got the best wear resistance with the friction coefficient 0.34 and the wear rate was 1.0×10−5mm3/N·m at 800°C. The morphology and compositions of the worn surfaces were analyzed by SEM-EDS and Raman spectroscopy. Findings indicate that copper molybdate (CuMoO4) is converted by in situ reaction between Cu and MoO3 during friction at elevated temperatures. The synergetic lubricating effect between CuMoO4 and oxide lubrication (such as MoO3, Cr2O3, CuO, and NiO) is the principal reason for the anti-wear and self-lubricate of the composite coatings. Particularly, composite coating containing CuMoO4 and Cr2O3 exhibits the lowest friction coefficient and smallest wear rate when the temperature above 600°C. Abrasive wear, plastic deformation, delamination as well as adhesive wear was main wear mechanism of the composite coating during friction at different temperature.