The development and application of nanolubricants has shown great potential to reduce friction and wear, especially in the automotive field for systems operating under boundary and mixed lubrication regimes. The search for additives that do not attack the environment has motivated the use of nanoparticles, especially metallic oxides, because of their characteristics such as low toxicity, high surface area, high wettability, and easy dispersion. The objective of this work was to evaluate the addition of iron oxide nanoparticles as additive to pure PAO 8 base oil. The nanoparticle action mechanisms, lubrication efficiency, friction, and wear rates were evaluated. The concentration of nanoparticles in the oil and the addition of oleic acid as a dispersing agent were varied. The synthesis of the nanoparticles was done by aqueous precipitation; characterization was performed by XRD, FTIR, Raman and SEM analyses. Tribological tests were performed in a reciprocating tribometer (Plint TE 67) using AISI 1020 prismatic samples and AISI 52100 chrome steel balls of 5 mm diameter. Test conditions resulted in boundary lubrication regime, for a starved contact with limited lubricant supply (0.5 µL). Concentrations of 0.4 and 1.6 wt% of nanoparticles were added to the base oil with and without the presence of oleic acid. Friction coefficient was not sensitive to the presence of nanoparticles, with statistically similar values for all the fluids tested. On the other hand, the presence of nanoparticles increased scuffing resistance and reduced wear rates. The lubricants with nanoparticles proved able to withstand relatively high loads, keeping the friction coefficient low for longer test durations due to the formation of protective tribolayers between the worn surfaces. The addition of nanoparticles reduced wear rates by around 27% when compared to tests using pure PAO 8. 

Scuffing resistance of polyalphaolefin (PAO)-based nanolubricants with oleic acid (OA) and iron oxide nanoparticles


 It has been five years since this review of elastic-plastic contact mechanics was published. The area still remains very active and many advancements have been made since then. This discussion summarizes these advances and points out what might be considered the most significant ones. In some cases experimental measurements have confirmed previous theoretical predictions. In most cases the models of contact mechanics have increased in complexity in order to improve predictions for real applications. As a fundamental area, contact mechanics will undoubtedly remain active as its implementation is often required for new applications of technology to succeed.

Discussion of “Ghaednia, H., Wang, X., Saha, S., Xu, Y., Sharma, A., & Jackson, R. L. (2017). A Review Of Elastic-Plastic Contact Mechanics. Applied Mechanics Reviews, 69(6).”

Decreasing harmful emissions of vehicle engines is becoming more and more challenging due to stricter standards. A possible solution is to improve the tribological attributes of lubricants, which can be achieved through the application of appropriate additives. According to preliminary studies conducted by the authors, ZrO2 (zirconium-dioxide) nano-sized ceramic particles as lubricant additives have overwhelmingly positive tribological attributes in the presence of non-metallic superficial materials. Additive concentration, as well as cross-effects with other additives were investigated in order to determine a formulation resulting in optimal tribological attributes. In this paper, the experimental investigation of ZrO2 nano-ceramic powder as a lubricant additive is presented. The tribological performance of individually samples were experimentally investigated on a ball-on-disc translational tribometer. The experiments revealed an optimal additive content of 0.3 wt%. Increasing the quantity of additives further ruined friction and wear properties of the examined tribological system.

/pdf/experimental-investigation-of-tribological-properties-of-two-13utbx0b.pdf

Experimental Investigation of Tribological Properties of Two Fully Formulated Engine Oils with Additional Nanoscale Spherical Zirconia Particles

The manufacturing process defines not only the component’s geometry, but also how its surface senses and interacts with the outside world via its topography. Every manufactured surface is rough, but the component can benefit from the roughness control. Topography in functional surfaces is optimized either by controlling the manufacturing parameters or by post-manufacturing surface patterning technologies. However, how are topographic features measured and characterized? How do rough surfaces contact each other? What happens if fluid is present at the contact interface? And what are the mechanisms that correlate surface topography and its functionalities? This article will cover the engineering of surface topography in manufacturing by addressing empirical advancements and scientific understanding in the field. The functionalities covered are adhesion, friction, and convective heat transfer. Relatively large surface structures used for heat transfer mainly take advantage of recent advances in additive manufacturing, while conventional manufacturing processes and deterministic surface patterning techniques are discussed for the control of adhesion and friction. Graphical abstract

Optimizing the surface of manufactured components for friction, adhesion, and convective heat transfer

This paper aims to obtain a fine wear-resistance cladding that can be applied in guide shoe of shearer. The performance of two cladding claddings fabricated by additive manufacturing technology, no chromium-high carbon (NCrHiC) claddings and high chrome-high carbon (HiCrHiC) claddings, was analyzed through a series of characterization experiments (optical microscope, hardness, coefficient of friction, wear rate, and surface morphology). The experimental results show that the NCrHiC cladding has obvious cracks and cracks are not observed on the surface of HiCrHiC cladding. However, the hardness and wear resistance of NCrHiC cladding is better than that of HiCrHiC cladding. The microstructure of NCrHiC cladding is composed of carbides, pearlite and ledeburite, and the one of HiCrHiC cladding is M(Fe, Cr)7C3 carbides and martensite. The worn width of HiCrHiC cladding is higher than that of NCrHiC cladding. Wear mechanism of NCrHiC cladding is abrasive wear while the one of HiCrHiC cladding is adhere wear.

Study on Wear Behavior of Coatings Fabricated by Additive Manufacturing Technology on the Surface of Guide Shoe of Shearer

Surface texturing can improve lubrication and entrap wear debris but increases the effective roughness of the surfaces, which can induce higher contact pressures. On the one hand, this can be detrimental, but on the other hand, the increase in contact pressure could be used to activate the formation of a ZDDP tribofilm from fully-formulated lubricants. This work investigates the synergistic effect between surface texturing via Maskless Electrochemical Texturing (MECT) and ZDDP additive. The surface texture consisted of an array of annular pockets manufactured on a gray cast iron cylinder liner. These textured surfaces were evaluated by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDX). The results indicated that surface texturing via MECT changes the chemical composition of the surfaces, by inducing a preferential dissolution of the metal matrix. Consequently, it exposed the carbon present in the material. The tribological performance was evaluated by a ring-on-cylinder-liner tribometer in reciprocating sliding under boundary lubrication conditions using both a base oil and a commercial formulated oil containing ZDDP additive. For comparison, a commercially honed liner was also tested. After the tribological tests, the surfaces were evaluated by white light interferometry and SEM/EDX. Although the textured surfaces showed higher friction, they induced more ZDDP-tribofilm formation than conventional cylinder liner finish.

https://www.mdpi.com/2075-4442/10/6/118/pdf?version=1654604812

ZDDP Tribofilm Formation from a Formulated Oil on Textured Cylinder Liners

Hardness is a powerful property to evaluate the deformation behavior of materials. It serves as confident quality control for several processes, especially in the heat treatment of metals. With the advent of depth-sensing indentation, this technique embraces the determination of other mechanical properties. As proof, recognized standards are available to guide the evaluation of Young’s modulus using instrumented indentation. However, there are continuous efforts to describe the strength using hardness apparatus. This critical review aims to compile all ways of correlation between hardness and uniaxial strength. This relationship is usually addressed by a single value, called constraint factor, vastly recognized in metals as approximately 3. From a theoretical point of view, this value works well for materials with rigid-plastic behavior, where hardening effects can be discharged. Divergent variations presented herein show difficulties in incorporating the effect of plastic properties on the constraint factor determination. In the same way, the empirical determinations did not consider the differences in hardening exponents, putting in the same statistical analysis diverse microstructures. A specific section discusses the constraint factor for nonmetallic materials. There are critical doubts for determining strength from hardness values in this case. The existence of several approaches to estimate the constraint factor in brittle materials did not assure yet a unique value for the same material, which put in evidence the lack of a robust physical basis to understand the plastic deformation under indentation. Future trends are indicated along with these observations to become practical the recent developments that have allied hardness and strength. The most important aspect is to combine adequately the experimental and simulation approaches, which can be supported by an analysis of residual imprints of hardness and finite element model. 

Hardness as an indicator of material strength: a critical review

Wear Regimes of Fe–Cr–C Hardfacing Alloys in Microscale Abrasion Tests

The study evaluates the mechanical and wear properties of LM26 alloy and its hybrid composites with silicon carbide (SiC) and nickel-coated graphite (Ni-Gr). LM26 aluminum alloy is generally known for its high strength, wear, and corrosion resistance compared to similar materials such as zinc and magnesium. The effect of Ni-Gr was studied, with 2 wt.% was found to provide the best mechanical properties. LM26 composites reinforced with varying percentages of SiC (0 to 30 wt.%) showed the best properties at 20 wt.% reinforcement after fabrication using a bottom pouring type stir casting setup (Two step feeding method). Evaluation of five hybrid LM26 composites through tensile strength, elongation, hardness, impact, porosity, and thermal studies showed that the LM26/2 wt.% Ni-Gr/20 wt.% SiC configuration showed the best filler composition for improved strength. Sliding wear evaluation using experimental and Taguchi analysis was performed at different configurations to identify the best wear resistance. Microstructure studies showed the presence of Ni-Gr particles forming coatings and temperature playing a significant role in the progression of the wear rate. Furthermore, the hybrid composite with 20% SiC and 2% Ni-Gr reinforcement showed the best wear resistance.

/pdf/mechanical-and-tribological-behavior-of-lm26-sic-ni-gr-3uh0r4xx.pdf

Mechanical and Tribological Behavior of LM26/SiC/Ni-Gr Hybrid Composites

Gas-Shielded Tungsten Arc Welding (GTAW) was modified to a Flux-Cored-Double-Wire GTAW (FCDW-GTAW); in this technique, wires of different compositions are used simultaneously to obtain different microstructures. In the modified GTAW, automatic flux-cored double-wire was used with a combination of four different wires deposited in AISI1020 steel, allowing different microstructures. Pin-on-disk wear tests described by ASTM G99 was used to evaluate the wear coefficients of four hardfacing materials combining Fe–Cr–C, Fe-Cr-C-Nb, Fe-Cr-C-Mo-Nb, and Fe-Cr-C-Mo-Ti alloys. The combination of these wires resulted in a hypoeutectic microstructure with niobium and titanium carbides, with an average hardness of 650 HV0.3, and hypereutectic microstructures formed by different niobium contents, with a microhardness range from 820 to 1020 HV0.3. The wear tests were performed without lubrication at room temperature, using a 6.0 mm diameter polished alumina sphere as a counter-body. The total distance covered was 1000 m with a speed of 0.1 m/s, a track radius of 6.0 cm, and an applied load of 10 N. Hardness, microstructure, wear coefficient, and wear mechanisms were compared. The results showed that wear resistance could be differentiated by the predominant wear mechanism: polishing for the hypoeutectic hardfacing and cracking for the hypereutectic ones. 

/pdf/dry-sliding-wear-resistance-of-fe-cr-c-hardfacing-deposited-34i15snn.pdf

Giuseppe Pintaúde

Papers

ZDDP Tribofilm Formation from a Formulated Oil on Textured Cylinder Liners

Hardness as an indicator of material strength: a critical review

Wear Regimes of Fe–Cr–C Hardfacing Alloys in Microscale Abrasion Tests

Mechanical and Tribological Behavior of LM26/SiC/Ni-Gr Hybrid Composites

Dry Sliding Wear Resistance of Fe-Cr-C hardfacing Deposited by Flux-Core-Double-Wire GTAW