Increase In Wear Rate Research Articles

Influence of spheroidised eutectic silicon on tribo-mechanical behaviour of centrifugally cast functionally graded aluminium composite

ABSTRACT This study investigates the tribo-mechanical behaviour of centrifugally cast as-cast and T6 heat-treated A359/TiB2 functionally graded composite (FGC). Linear reciprocating wear tests were performed on both composites under varying sliding distances (500-1500 m) and loads (15-55 N). A gradient TiB2 particle distribution was observed from the outer to inner periphery (6, 2 and 1 wt % respectively) of the as-cast FGC, whereas the heat-treated FGC displayed spheroidised eutectic Si particles throughout the cross-section. This led to superior mechanical properties for the outer zone of heat-treated composite (188.7 HV, 286.1 MPa) when compared to the as-cast outer zone (147.5 HV, 243.4 MPa). The heat-treated composite had displayed enhanced tribological properties under reciprocating wear tests, and it was observed that both composites had exhibited a proportional increase in wear rate with increasing experimental parameters and with graded particle concentration, whereas the coefficient of friction (COF) was independent of the wear parameters and directly dependent on the TiB2 concentration. The wear mechanisms observed were adhesive and minor delamination under high and low load conditions. The mechanically mixed layer presence was confirmed through wear debris analysis, due to which the COF was observed to be constant after 1250 m of sliding distance.

The in vivo location of edge-wear in hip arthroplasties : combining pre-revision 3D CT imaging with retrieval analysis.

AimsAcetabular edge-loading was a cause of increased wear rates in metal-on-metal hip arthroplasties, ultimately contributing to their failure. Although such wear patterns have been regularly reported in retrieval analyses, this study aimed to determine their in vivo location and investigate their relationship with acetabular component positioning.Methods3D CT imaging was combined with a recently validated method of mapping bearing surface wear in retrieved hip implants. The asymmetrical stabilizing fins of Birmingham hip replacements (BHRs) allowed the co-registration of their acetabular wear maps and their computational models, segmented from CT scans. The in vivo location of edge-wear was measured within a standardized coordinate system, defined using the anterior pelvic plane.ResultsEdge-wear was found predominantly along the superior acetabular edge in all cases, while its median location was 8° (interquartile range (IQR) -59° to 25°) within the anterosuperior quadrant. The deepest point of these scars had a median location of 16° (IQR -58° to 26°), which was statistically comparable to their centres (p = 0.496). Edge-wear was in closer proximity to the superior apex of the cups with greater angles of acetabular inclination, while a greater degree of anteversion influenced a more anteriorly centred scar.ConclusionThe anterosuperior location of edge-wear was comparable to the degradation patterns observed in acetabular cartilage, supporting previous findings that hip joint forces are directed anteriorly during a greater portion of walking gait. The further application of this novel method could improve the current definition of optimal and safe acetabular component positioning.Cite this article: Bone Joint Res 2021;10(10):639–649.

Analysis of the hardness ratio effect on the tribological performance of NiCrBSi coating/debris particles using the Stribeck Curve

This work aims to propose an approach to estimate the final surface roughness as a function of the hardness ratio between coating and debris (Hpin/Hdebris = Hp/Hd) under lubricated conditions employing pin-on-disc configuration. Using this approach provides a better understanding and prediction of the lubrication regime (Stribeck Curve) compared with the traditional approach that uses the initial surface roughness. Our results demonstrate that a lower hardness ratio induces a higher friction coefficient and contributes to a marked increase in wear rate in lubricated conditions. To find an effective method for simulating the debris effect, four types of NiCrBSi powders were used as a source of debris: two metallic powders with a completely spherical morphology but different Cr concentrations and two other NiCrBSi (15.25%Cr) powders mixed with different concentrations 40 and 60% of ceramic, Zr + 7% Y2O3 (ZSP), composed of spherical particles morphology. Therefore, a set of four sources of debris material specimens were simulated by different types of particles with a similar size distribution but different average hardness. Each of these particles was dispersed in an oil lubricant. Observation of the worn surfaces using a rugosimeter and scanning electron microscope suggested that, together with the shape, size and number of debris, the hardness ratio must be considered when studying the tribological behavior of machine components. The proposed methodology may help to predict the variation in lubrication regime parameters (Stribeck curve) by controlling the hardness ratio.

Ultralow Wear Poly(tetrafluoroethylene): A Virtuous Cycle of Wear Reduction and Tribochemical Accumulation

Certain nanofillers have demonstrated a remarkable wear-reducing effect on poly(tetrafluoroethylene) (PTFE), a common solid lubricant polymer. In these unusual cases, ultralow wear rates are accompanied by tribochemical changes that stabilize surfaces by anchoring polymer chains to dispersed nanoparticles and the countersurface. The leading hypothesis is that nanofillers catalyze these favorable tribochemical processes, which ultimately causes ultralow wear rates. However, the extent to which reduced wear rates contribute to the accumulation of favorable tribochemistry remains untested. In this study, we used indexed reciprocation to eliminate the protective effects of transfer films, control the wear rate, and independently determine how wear rate and filler morphology affect these tribochemical outcomes. Despite large and important differences between the fillers tested (from nanoparticles to microparticles), we observed surprisingly little effect from the filler on tribochemistry when controlling the wear rate. By contrast, tribochemistry was extremely sensitive to the changes in wear rate regardless of the filler. Standard reciprocation, which promoted the development of protective transfer films, caused low wear rates and significant tribochemical accumulation for all three filler conditions. By removing the protective effects of transfer films, indexed reciprocation increased wear rates by 100-fold while effectively eliminating tribochemical accumulation and tribofilm formation on the polymer pin. In contrast to prior studies, which demonstrate that tribochemical accumulation enables ultralow wear rates, this study demonstrates that a pre-existing condition of low wear is needed to enable tribochemical accumulation. The results from this study and prior studies of PTFE wear appear to be most consistent with the hypothesis that protective transfer films initiate low wear rates, that low wear rates enable tribochemical accumulation, and that tribochemical accumulation reduces wear rates in a virtuous cycle.

Low energy proton irradiation tolerance of molybdenum disulfide lubricants

As the world’s space agencies look to long duration spaceflight beyond low earth orbit, engineering materials in deep space flight will endure galactic cosmic ray irradiation, of which 85% is protons. Characterization of proton irradiation damage near the threshold displacement energy is required to understand the mechanisms behind performance degradation and the fluence dependent effects of a thermalized spectrum on surface sensitive tribological characteristics. Here, tribological degradation of a space-grade molybdenum disulfide lubricant exposed to low energy (500 eV) protons is investigated as a function of fluence. A 21% increased coefficient of friction and 86% increase in wear rate is measured at 1020H/m2, and 170% increased CoF and 465% increased wear rate at 3·1023H/m2. Associated softening and decreased stiffness is measured by nanoindentation. X-ray photoelectron spectroscopy and Raman spectroscopy identify the mechanism of tribological degradation as being the preferential removal of sulfur leading to a disordered and reactive non-stoichiometric MoS2-x surface with compromised tribological properties. Missions beyond low-earth orbit will be required to withstand GCR radiation, and it is not suggested that the density of radiation damage sustained will be acutely detrimental to MoS2 lubricants. Still, research missions should plan to characterize the magnitude of radiation damage effects.

Wear resistance of nanostructured metal-polymer self-lubricating powder composites

Tribotechnical tests and microstructural studies were carried out. Wear mechanism of nanostructured metalpolymer self-lubricating composite materials has been established. This mechanism involves in the formation of separating polymer layers on the friction surface, which reduces the coefficient of friction and running-in period of parts of friction units. Carbon nanoparticles move along the friction surface, hinder the development of seizure processes during the interaction of microroughnesses of the contacting surfaces of the material and the counterbody during the destruction of the separating polymer layers. It was found that the polymer filler is displaced from the friction zone, carbon nanoparticles are pressed into the open areas of the surface of the copper matrix of the composite when the pressure in the tribocontact is higher than 1.5 MPa. The temperature in the tribocontact increases, the polymer filler degrades, the carbon nanoparticles are removed from the friction zone, the strength properties of the composite decrease, the friction coefficient and the wear rate increase at a sliding speed above 1.5 m/s. The obtained research results can be used in mechanical engineering, transportation industry and power engineering.

Design of low-friction and anti-corrosion a-C:H:SiOx films

Some properties of hydrogenated amorphous carbon (a-C:H) film are effectively improved via silicon (Si) and oxygen (O) incorporation, such as high friction coefficient (0.1–0.4) in the atmospheric environment and serious pitting corrosion caused by pores in the film. In this study, the Si and O incorporated a-C:H (a-C:H:SiOx) films were deposited by plasma-assisted chemical vapor deposition (PACVD) technology using acetylene (C2H2) and hexamethyldisiloxane (HMDSO) as precursors, and then studied their tribological and anti-corrosion properties in the atmospheric environment. The a-C:H:SiOx films exhibited impressive friction coefficient (0.05–0.07) and wear rate (1.8–5.6 × 10−7 mm3/Nm) owing to silicon oxide formed on surface of wear scar during friction process. Compared to pure a-C:H film, Si and O incorporated greatly increased the deposition rate of films. Therefore, a slightly increased wear rates of a-C:H:SiOx films are acceptable as long as the films are thick. In addition, the incorporation of Si and O makes the film have high resistance, thereby improving the corrosion resistance of the film. This excellent pitting corrosion resistance of the film can make up for the defects of the a-C:H film such as pinholes. The a-C:H:SiOx film with excellent tribological properties and corrosion resistance will have a good application prospect under the combined action of corrosion and mechanics.

On the origins of lubricity and surface cleanliness in ethanol-diesel fuel blends

Ethanol is the most used bio-derived fuel additive. However, adding ethanol in diesel fuel may negatively impact lubricity or surface cleanliness, which is critical for high-pressure fuel injection systems employed in compression ignition engines. This work investigates surfaces lubricated by ethanol–diesel blends. Adding 5 wt% ethanol in diesel showed negligible changes in fuel lubricity, while blending 10, 20, and 40 wt% ethanol increased wear rates by 46, 81, and 239% respectively. These increases in wear rates (with increases in ethanol by wt%) correlate with the evolution of electrical contact resistance (ECR) values over time. As more ethanol was added, the ECR values signaled thinner fuel films, more metal-to-metal contacts, and a delayed onset of frictional product growth. Raman spectra showed that forming frictional species produced by tribochemical reactions enhanced fuel lubricity. The absence of some frictional species in ethanol lubricated surfaces points to simultaneously improved surface cleanliness and reduced lubricity.

Effect of Martensite Volume Fraction on Oxidative and Adhesive Wear.

It is generally known that microstructure can considerably affect the tribological behavior of non-lubricated rubbing. However, there is still a lack of awareness about the effect of microstructure on oxidative wear. The present study focused on the effect of martensite volume fraction (MVF) on oxidative wear by using 25CD4 dual-phase steel. Dry friction tests were performed on a ball-on-flat tribometer with a normal load of 15 N and a mean sliding velocity of 0.013 m/s. Friction coefficient and wear rate increase with the increasing MVF. SEM observation and EDXS analyses of the wear scars showed that the oxidation increases with decreasing MVF. For lower MVF, the main wear mechanism is mild oxidative wear. For higher MVF, severe adhesion is predominant as a wear mechanism. The size of the debris decreases with decreasing MVF.

Dry sliding tribological properties of A356-SiCP aluminum matrix composites prepared by vacuum stir casting

PurposeThe purpose of this paper is to understand the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites manufactured using a newly developed vacuum stir casting technique.Design/methodology/approachA356 alloy reinforced with 10, 15 and 20 vol% SiC particles was prepared by vacuum stir casting. Tribological tests were carried out on block-on-ring tribometer under dry sliding conditions, room temperature. Wear mechanism was investigated by scanning electron microscope and energy dispersion spectrum.FindingsSiCP is homogeneously dispersed in the matrix. The increase in SiCP content decrease wear rate, but it leads to an increase in coefficient of friction. The wear rate increase and friction coefficient present different variation trends with increasing load. For A356-20%SiCP composite, when the load is less than 10 MPa, wear rate and friction coefficient under sliding speed of 400 rpm are lower than those of 200 rpm. Wear mechanism transition from abrasion, oxidation, delamination, adhesion to plastic flow as load and sliding speed increasing.Practical implicationsResults of this study will help guide the use of A356-SiCP in many automotive products such as brake rotors, brake pads, brake drums and pistons.Originality/valueThere are few paper studies the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites. Aluminum matrix composites with uniform distribution of reinforcing particles were successfully prepared by using the newly developed vacuum stir casting technique.

Investigation of the Wear Behavior of Surface Welding AZ91 and AZ91+Gd Alloys under Variable Loading Conditions

Adding rare earth elements to magnesium alloys is an effective way to improve their wear resistance. However, the effect achieved is closely related to the friction condition. In this paper, two different types of welding wires, AZ91 magnesium alloy and AZ91 + gadolinium (Gd), were used for surface welding. Dry sliding friction and wear experiments were performed on the surfacing alloys using the pin-on-disc test. The effects of Gd addition on the wear resistance and wear mechanism of the alloy were systematically studied under low to high loads. The results show that as the load increases, the friction coefficient of the surfacing AZ91 alloy gradually decreases as the wear rate increases. A mild–severe wear transition occurred at 100 N. The addition of Gd only slightly increased the wear rate under a load of 15 N. The wear rate was significantly decreased with loads in the range of 30 to 100 N and mild–severe wear transition was avoided. The influence of both Gd addition and load on the wear mechanism were considered. The overall wear resistance of the surfacing magnesium alloy was determined.

Effect of cooling rate on C92900 bronze microstructure and properties

In the mechanical engineering, antifriction tin bronzes are used for the manufacture of friction parts. For example, the C92900 bronze has found use in aircraft braking system components. One of the ways to improve the properties of leaded tin bronzes is to increase the cooling rate during solidification. This paper studies the effect of the cooling rate and changes in the content of alloying elements within the limits established by the C92900 bronze industry standard OST 1 90054-72. In order to provide different cooling rates, the prepared alloys were casted into molds made of resin-bonded sand, steel and graphite with cooling rates 0.4, 5.0, and 14.6 °C/s, respectively. The influence of the cooling rate and the bronze composition on the freezing range, macrostructure, microstructure, thermal conductivity, mechanical, and tribological properties were investigated. Differential thermal analysis demonstrated that the upper-limit alloying of C92900 bronze leads to a decrease of the solidus temperature by 40 °C, which should be considered during deformation processing and heat treatment. An increase in the cooling rate during C92900 bronze ingot solidification provides a significant grain refinement and changes the amount, size and morphology of phases. For example, in case of metallic and graphite mold casting, the size of lead particles decreases, and its circularity increases. The change in the Sn content within the range established by the industrial standard has a significant effect on the γ-(Cu,Ni)3Sn intermetallic phase fraction. The increase in the cooling rate has no significant effect on the C92900 bronze thermal conductivity but increases hardness by 30 HB as well as cooling rate and yield strength and ultimate tensile strength. Wear tests carried out in accordance with the «shaft – partial insert» scheme in a kerosene medium using a steel counterbody showed that an increase in the cooling rate during solidification leads to an increase in the bronze wear rate from ~0.4·10–8 to ~1.2·10–8. The change in the bronze composition within the industrial standard range has practically no effect on the wear rate but leads to a slight increase of the coefficient of friction.

Experimental Investigation on Flank Wear of the Tool in Ultrasonic Vibration-Assisted Turning of Ti6Al4V Alloy

Abstract High cutting temperatures developed during machining of Ti6Al4V alloy diminish the tool life by rapid increase in rate of tool wear. The high cutting temperatures increase the chemical reactivity of the workpiece with tool material and form the localized temperature zones at the vicinity of cutting tool edge. Ultrasonic vibration-assisted turning (UVAT) is an effective cutting technique in which tangential vibrations are provided to the cutting tool. The reduced cutting force and temperature improve the tool life in the UVAT process. In the present study, flank wear of the uncoated carbide cutting tool has been studied in UVAT processes at various cutting speeds (90, 120, and 150 m/min) and ultrasonic powers (80, 90, and 100 %). The flank wear of the tool is measured with a scanning electron microscope, and it is observed that tool wear is low in UVAT compared with the conventional turning (CT) process. Fracture of the cutting edge of the tool is observed in CT because of high compressive stresses with the high cutting temperature, which did not occur in the UVAT process. The growth of average and maximum flank wear with cutting velocity is low in UVAT, whereas rapid growth is observed in the CT process. From the experimental results, tool life improvement is observed in UVAT compared with CT at an average flank wear of 300 µm; however, this improvement is decreased with an increase in cutting speed in the order of 62, 53.2, and 32 % for 90, 120, and 150 m/min, respectively, at 100 % ultrasonic power. Similarly, tool life is improved with an increase in ultrasonic power in the order of 18, 55, and 62 % for 80, 90, and 100 % ultrasonic power, respectively, at 90 m/min cutting speed.

Tribological properties of the uncoated and aluminized Ti–48Al–2Cr–2Nb TiAl alloy at high temperatures

Al-rich phases are often recommended as potential coating candidates for TiAl alloys and their application as a turbine blade material in aero engines. As high wear resistance is also required for this application, the tribological properties of Al-rich phases need to be investigated with a focus on the influence of temperature. Therefore, a comparative investigation of the dry sliding wear behavior of the uncoated and aluminized Ti–48Al–2Cr–2Nb TiAl alloy was conducted between room temperature and 600 °C in air. While the uncoated TiAl alloy suffers from successively increasing wear rates with increasing temperature, the aluminized alloy shows lower wear rates up to 400 °C. However, barely any positive influence on the required wear protection can be observed at 600 °C due to partial failure of the coating. Wear mechanisms of both the uncoated and aluminized samples are characterized by high material transfer to the counterpart material, the Ni-based alloy IN718. This phenomenon is caused by the tendency for strong adhesive bonding between the two metallic counterparts and becomes even more pronounced with increasing temperature.

Tribotechnical properties of sintered friction material based on copper with the additives of the ultrafine powder of aluminide of Ti–46Al–8Cr system

The article presents the results of study of the effect of additives of an ultrafine powder of the Ti–46Al–8Cr system obtained by MASHS on the tribotechnical properties of a friction material based on BrO6 bronze. It is shown that in the range of powder additive concentrations 0.5–1.5 wt. %, the dynamic coefficient of friction increases from 0.04 to 0.055, in the range of 1.5–2.5 % – to 0.055–0.058. The introduction of the 0.5–1.0 % Ti–46Al–8Cr powder permitted to reduce the wear rate of the friction material from 4.0 to 3.7 μm/km. An increase in the additive to 2.5 % led to an increase in the material wear rate up to 6 μm/km.

An Influence of Oxygen Flow Rate on Structural, Optical and Tribological Properties of Molybdenum Oxide Thin Films

The influence of oxygen flow rate is examined on structural, optical and tribological properties of molybdenum oxide films deposited by reactive magnetron sputtering. The films were characterized by X-ray diffraction, scanning electron microscope (SEM), and contact angle measurement system. The optical properties of the films were measured by UV-Vis-NIR spectrophotometer and transmittance of ∼73% in the visible region of the spectrum was achieved. The band gap increases with increases in oxygen gas flow rate. AFM figure illustrates that the roughness of surface increases as oxygen flow rate increases. As oxygen increases wear rate and COF decreases while at the 18 sccm the lowest wear rate found.

Microstructural characterisation of subsurface deformation and the degradation of Stellite 6 induced by self-mated sliding contact in a simulated PWR environment

Stellite 6 (Co-29.5%Cr-5%W-1.2%C in wt%) is traditionally used as a hardfacing material in the primary circuit of pressurised water reactors (PWRs) due to its good corrosion and wear resistance in water at up to 300 °C. In this study, pin-on-disc type sliding contact tribocorrosion testing was conducted on HIPed Stellite 6 at 20 °C and 250 °C using a bespoke tribometer to simulate a primary circuit environment. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize, for the first time, the material affected by tribocorrosion. Whilst the material loss increases by 16–39 times when the test temperature is increased from 20 °C to 250 °C, the mechanisms of degradation and deformation remain largely unchanged. Furthest from the sliding contact, strain is principally accommodated by the deformation-induced transformation of the γ Co-based matrix to ε-martensite. Closer to the sliding contact, the ε-martensite phase accommodates further strain via twinning and dislocation slip. At the sliding contact the intense deformation generates a nanocrystalline structure. The tribologically affected material is resistant to plastic strain localisation; this confines wear to the nanoscale where the synergistic effects of chemical degradation and mechanical deformation permit the removal of nanoscale particulates (corrosion enhanced nanowear (tribocorrosion)). The increased wear rate at 250 °C is attributed to a temperature dependent increase in corrosion enhanced nanowear. The degradation mechanisms revealed are important for the design of future hardfacings.

Wear behaviours of PVD-TiN coating onTi-6Al-4V alloy processed by laser powder bed fusion or conventionally processed

Ti-6Al-4V alloy is the most preferred alloy used in laser powder bed fusion (LPBF) and physical vapour deposition (PVD) coating may often be needed. However, whether the wear performance of the coating on the high hardness LPBF Ti-6Al-4V substrate may perform differently to that on the conventionally processed (CP) and significantly lower hardness alloy substrate has not been clear. In this study, dry sliding wear tests have been conducted on PVD TiN-coated Ti-6Al-4V samples processed either by LPBF or by CP, using WC-Co as counter material. It has been found that local fracturing of coating after being thinned to 0.4–0.5μm in both coated LPBF and CP samples is similar. The major wear mechanism leading to a gradually rapid increase in wear rate of the coated samples will be demonstrated and explained through a wear process described as thickness reduction and local fracturing of the coating before the widening of the wear track. It will be shown that the local fracturing of coating was accompanied by the local deformation in CP substrate due to its low hardness. For the LBPF substrate, the deformation was not readily observed. That the higher amount of deformation underneath the coating for the case of CP substrate has affected little the overall wear rate will be illustrated.

Characterization and Property Analysis of Heat-treated Functionally Graded Al8Si3Cu Alloy and TiC reinforced Composite

Functionally graded (FG) Al8Si3Cu alloy and 8 wt% titanium carbide (TiC) reinforced composite (∅out100 × ∅56in × 100 mm) was fabricated through horizontal centrifugal casting, followed by T6 heat treatment. Metallographic analysis confirmed fine grain structure at FG alloy outer layers, whereas heat-treated alloy displayed spheroidised eutectic silicon. Gradient microstructure was observed for FG composite. Enhanced hardness for outer layer (10.31%) and tensile strength for outer zone (58.71%) were observed for heat-treated Al8Si3Cu/TiC composite owing to the high concentration of spheroidised eutectic Si and TiC particles, compared to as-cast composite. Linear reciprocating wear analysis performed on as-cast, heat-treated alloy and composite, respectively, at varying load (10–40 N) and sliding distance (500–2000 m) confirmed increasing wear rate, with heat-treated composite having superior wear resistance. Delamination wear was the predominant wear mechanism influencing wear behaviour of heat-treated composite. The alloy and composite were characterized using X-ray diffraction (XRD), energy dispersive spectrometry (EDS), optical microscopy (OM) and scanning electron microscopy (SEM).

THREE-DIMENSIONAL SETUP OF COMPOSITE MATERIALS AS A WAY TO ACHIEVE HIGH MECHANICAL PROPERTIES

Polymer resins are popular dry lubricants and protective coatings for metal products. However, their friction coefficient is high, which leads to increased wear rates and limited service life. Reinforcement with nanoscale fillers, due to their large surface area and their uniform distribution within the polymer matrix volume, can help reduce friction and wear. This paper aimed to study the effect of three-dimensional organization of silicon dioxide nanoparticles with a concentration of 1, 3, and 5% on the mechanical properties of an epoxy resin. The dispersion of nanoparticles was carried out using ultrasonic field technology. The friction coefficient was measured using a pendulum tribometer. Empirical results have shown that reduction in the concentration of nanoparticles from 5% to 1% resulted in a two-fold decrease in the values of the friction coefficient. Also, it was found that prolongation of test time in experiments with a nanoparticle concentration of 3 and 1% had practically no effect on the friction coefficient values. This behavior is associated with the polymer interface mobility regulation due to the low concentration of nano inclusions and uniform three-dimensional organization in the polymer matrix by the ultrasonic field, which contributed to a uniform redistribution of applied loads. The developed technique can be used to other types of polymer nanocomposites to study the effect of the three-dimensional organization of nanoscale fillers on wear resistance, bending strength, and impact resistance.